OCTOBER 2015

SPRINTING EDITIONBy Chris Beardsley

WelcomeWelcome to the Sprinting Edition! In this edition, wehave a number of great new papers all about sprintrunning. Since two of these articles are about sledtowing, in this editorial I discuss whether sled towingalters sprint running biomechanics from normal sprintrunning, when measured acutely or chronically.

Does sled towing alter movement patterns during sprint running?

IntroductionWhen sled towing was first developed for improvingsprint running performance, some coaches suggestedthat it would likely not improve sprint running abilitybecause it would adversely affect sprint techniqueacutely, which might have two consequences: one, itmight lead to muscular adaptations that were specificto sled towing and would therefore not contributepositively to sprint running without a sled; and two, itmight ingrain habits that were suitable for sled towingbut might then be detrimental in performing normalsprint running. To test whether these coaches werecorrect, two lines of research were pursued. Firstly,researchers set out to see whether sled towing canimprove sprint running ability when included in a long-term training program. Secondly, researchers set outto investigate whether sled towing alters movementpatterns compared to normal sprint running, eitheracutely or in the long-term. We can subdivide analysisof movement patterns into two categories, with thefirst being the main determinants of sprint runningability (i.e. stride length and stride frequency), andthe second being the finer points of technique (i.e.joint angle movements).

Long-term effects on sprint running abilityIn the time since sled towing was originally conceived,several studies have been performed in highly-trainedadult athletes that have explored whether sled towingdoes improve sprint running ability: Spinks et al.(2007), Harrison and Bourke (2009), Clark et al.(2010), Upton (2011), Alcaraz et al. (2012), West etal. (2013), Lutberget et al. (2015). The majority ofthese studies reported that resisted sprint runningusing sled towing improves sprint running ability ofhighly-trained athletes over short distances.

Acute effects on stride length and frequencyIn general, it seems that sled towing with almost anyload reduces stride length and potentially also stridefrequency, acutely. Such reductions seem to increasewith increasing level of resistance (usually by addingmore weight to the sled load). In an early study,Letzelter et al. (1995) tested the effects of sled towingin trained female sprinters with a range of loads. Allloads caused a reduction in stride length and stridefrequency acutely. Moreover, the magnitude of thesereductions increased with increasing load. Several

years later, Lockie et al. (2003) tested the effects ofsled towing with loads equal to 12.6% and 32.2% ofbodyweight in male field sports athletes. They foundsimilar results to the previous researchers but theirresults differed insofar as while both light and heavyloads led to reductions in both stride length and stridefrequency, only stride length reduced to a greaterextent with a greater load. Cronin et al. (2008) foundidentical results, with all loads producing reductions inboth stride length and stride frequency, but only stridelength reduced to a greater extent with the heavierload (20% of bodyweight) than with the lighter load(15% of bodyweight). Similarly, Alcarez et al. (2008)found reductions in both stride length and stridefrequency when using either a sled, a parachute, or aweight belt. Despite these studies all being in closeagreement with one another, Murray et al. (2005) andMaulder et al. (2008) both found that sled towing ledto reductions in stride length but no changes in stridefrequency. Consequently, the acute effects of sledtowing on stride length are relatively clear: sledtowing leads to acute reductions in stride length. Incontrast, the acute effects of sled towing on stridefrequency are less clear. Small decreases probably dooccur in at least some individuals. However, it hasbeen suggested by some sprint researchers that someathletes may attempt to compensate for reductions instride length during sled towing by increasing stridefrequency. If this is the case, then this would naturallylead to smaller reductions in stride frequency than instride length.

Long-term effects on stride length and frequencyTraditionally, it has been suggested that only heavysled loads might alter stride length or stride frequencyover a long-term training program. However, theliterature is conflicting. Spinks et al. (2007) and Clarket al. (2010) both explored the effects of a single(light) sled load during sled towing training. Bothfound no differences in the long-term effects on eitherstride length or stride frequency of sled towingsprinting compared to a normal sprint running group.However, Alcaraz et al. (2012) found that stride lengthincreased in a sled towing group but not in a normalsprint running group in the maximal velocity phase ofsprinting but not in the acceleration phase. Thus, theunique effects of sled towing on stride length andstride frequency are unclear.

Acute effects on joint angle movementsTraditionally, it was suggested that only heavy sledloads altered joint angle movements acutely. Letzelteret al. (1995) tested the acute effects of sled towing onmovements patterns in trained female sprinters withloads of 2.5, 5.0 and 10.0kg. Only the heavy loadincreased ground contact time, forward trunk lean,and hip joint angle at ground contact. Thus, it wasdeduced that lighter loads would not alter sprintrunning technique acutely.

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Does sled towing alter movement patternsduring sprint running? Continued...

Acute effects on joint angle movements continued...Lockie et al. (2003) later tested the effects of sledloads equal to 12.6% and 32.2% of bodyweight inmale field sports athletes. In this case, both the lightand heavy loads caused an increase in ground contacttime and an increase in forward trunk lean, althoughonly ground contact time lengthened more with theheavier load while forward trunk lean did not changewith heavier load. Cronin et al. (2008) tested theeffects of sled loads equal to 15 and 20% ofbodyweight and similarly found that ground contacttime and forward trunk lean were larger during sledtowing compared to normal sprint running. They alsofound that ground contact time lengthened more withthe heavier load but that forward trunk lean did notalter with increasing load. Alcarez et al. (2008)similarly found an increase in forward trunk lean andBentley (2015) reported an increase in ground contacttime and an increase in the hip flexion angle at footstrike during sled towing. Although Maulder et al.(2008) explored a sled load of 20% of bodyweight,they found no alterations in ground contact time.Nevertheless, there seems to be a trend such that allsled loads cause acute increases in trunk lean andground contact time and that heavier loads causegreater changes in ground contact time.

Long-term effects on joint angle movementsTraditionally, it has been suggested that only theheavy sled loads might alter joint angle movementpatterns over a long-term training program. Spinks etal. (2007) explored the effects of a single (light) sledload during sled towing training. They found thatground contact time decreased in the sled towinggroup by more than the normal sprint running groupwhile forward trunk lean increased by more in the sledtowing group than in the normal sprint running group.In partial agreement, Alcaraz et al. (2012) found thatforward trunk lean increased by more in the sledtowing group than in the normal sprint running group,albeit only in the acceleration phase. In contrast, theyfound that ground contact time decreased by more inthe normal sprint running group than in the sledtowing group. The discrepancy in effects on groundcontact time are found across many studies and Clarket al. (2010) found no changes in ground contact timein a sled towing group compared to a normal sprintinggroup.

ConclusionsIn summary, the following conclusions can be drawn:(1) The majority of long-term studies assessing theeffects of resisted sprint running using sled towing inhighly-trained athletes have found that it improvessprint running ability over short distances. (2) Acutely,sled towing with almost any load reduces stride lengthand potentially may also reduce stride frequency. Thesmaller reduction in stride frequency may be causedby some athletes compensating for the reductions instride length during sled towing by increasing stridefrequency.

(3) Acutely, all sled loads cause increases in trunk leanand increases in ground contact time. It seems likelythat heavier loads cause greater increases in groundcontact time than lighter loads. (4) How the long-termeffects of sled towing training on stride length andfrequency differ from those of normal sprint running isunclear. (5) The long-term effects of sled towingtraining on other movement parameters seem toinclude a larger increase in forward trunk lean (likelyonly in the acceleration phase) than that observedafter normal sprint running training. Whether suchchanges are associated with superior improvementsfollowing training or inferior changes is unclear.

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Strength coach notes

The effect of training volume and intensity onimprovements in muscular strength and size in resistance‐trained men

The researchers concluded that training with high relative loads, long rests and low volumes may be superior for upper body hypertrophy than training with lowrelative loads, short rests and high volumes. However, which training variable was responsible for the difference is unclear.

Unilateral eccentric resistance training – a direct comparison between isokinetic and dynamic constant external resistance modalities

The researchers concluded that except in respect of eccentric isokinetic torque, the changes in strength and muscle architecture resulting from a program of either variable or constant load eccentric resistance training are very similar. The difference in strength gains appears to be only somewhat external-load specific, with the only superior improvement in strength by the variable group being the same measurement as was used during training (eccentric isokinetic).

Are the responses to resistance training different between the preferred and non-preferred limbs?

The researchers concluded that a unilateral, isokinetic, eccentric resistance training program reduced the strength asymmetry between legs within 12 weeks without altering muscle size. This may support the use of unilateral resistance training for reducing between-limb strength deficits.

Neuromuscular adaptations to unilateral vs. bilateral strength training in women

The researchers found that the unilateral training group improved unilateral 1RM knee extension to a greater extent than the bilateral training group. However, both groups improved bilateral 1RM knee extension and quadriceps muscle thickness similarly. This difference may be caused by neural adaptations, as the unilateral training group increased muscle activity during unilateral 1RM testing but the bilateral training group did not.

The response to, and recovery from maximum strength and power training in elite track and field athletes

The researchers observed a reduction in maximum isometric force immediately after and at 24-hours following a typical strength workout in elite track and fieldathletes. However, there was no similar reduction in maximum isometric force after a similar power workout using similar exercises but lower loads and faster bar speeds.

Modulation of work and power by the human lower-limb joints with increasing steady-state locomotion speed

Faster running is not achieved by simply increasing the work and power at eachjoint proportionally but in fact involves a shift in the relative contributions of each joint. Specifically, the relative contribution of the hip joint increases with increasing running speed in both the stance and swing phases.

Acute response of well-trained sprinters to a 100-m race – higher sprinting velocity achieved with increasedstep rate compared to speed training

The researchers concluded that sprint athletes run faster in competition than in training and that the increase in speed appears to be caused by a faster stride frequency and not by a longer stride length. Why these higher stride frequencies are possible in competition is unclear but it may relate to elevated arousal levels.

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Sports medicine notes

A step towards understanding the mechanisms of running-related injuries

The researchers concluded that the exact relationships between weekly running time and running injury and between session frequency and running injury are very unclear. The data in the current study suggest thepresence of counterintuitive relationships, such that fewer running sessions and short running times are associated with greater risk of injury. Such results may be a feature of experience and/or training consistency.

Effects of two different injury prevention resistance exerciseprotocols on the hamstring torque-angle relationship – a randomized controlled trial

The researchers concluded that the eccentric training protocol increased knee flexion torques at the two most open knee flexion angles (35 and 45 degrees) where the hamstrings are lengthened while unstable protocolimproved at more closed knee angles (60, 80, and 90 degrees) where thehamstrings are less lengthened. This suggests that exercises that display peak torque at long muscle lengths tend to increase strength most at long muscle lengths while exercises that display peak torque at short muscle lengths tend to increase strength most at short muscle lengths.

Is there evidence to support the use of the angle of peak torque as a marker of hamstring injury and re-injuryrisk?

The researchers concluded that evidence for the use of the angle of peak knee flexion torque as a predictor for hamstring strain injury risk remainsweak.

MRI does not add value over and above patient history and clinical examination in predicting time to return to sport after acute hamstring injuries: a prospective cohort of 180 male athletes

The researchers concluded that certain variables recorded during taking patient history and performing clinical examination at baseline can explain 29% of the variance in time to return to sport following an acute hamstring strain in male athletes. However, adding MRI has limited further benefit.

An evidence-based review of hip-focused neuro-muscular exercise interventions to address dynamic lower extremity valgus

The researchers concluded that hip-focused exercises appear to help reduce knee valgus during a range of dynamic movements, as indicated by the evidence from a small body of long-term trials.

The effectiveness of non-operative rehabilitation programs for athletes diagnosed with osteitis pubis

The researchers concluded that there is currently no better evidence beyond case studies to support the use of non-operative rehabilitation programs in the treatment of osteitis pubis in athletes. Future research isrequired of a higher quality, including retrospective cohort trials, prospective cohort trials, and randomized controlled trials.

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Strength and Conditioning Research

CONTENTS

SPRINTING EDITION...........................................................................................................................................................2

CONTENTS.........................................................................................................................................................................5

1. STRENGTH & CONDITIONING, POWER AND HYPERTROPHY........................................................................................... 8

1. The effect of training volume and intensity on improvements in muscular strength and size in resistance‐trained men, by Mangine, Hoffman, Gonzalez, Townsend, Wells, Jajtner, and Stout, in Physiological reports (2015) ............................................................................9

2. Effects of resistance training with moderate vs. heavy loads on muscle mass and strength in the elderly – a meta‐analysis, by Csapo and Alegre, in Scandinavian Journal of Medicine & Science in Sports (2015) ............................................................................................. 10

3. Does training frequency and supervision affect compliance, performance and muscular health? A cluster randomized controlled trial, by Dalager, Bredahl, Pedersen, Boyle, Andersen, and Sjøgaard, in Manual Therapy (2015) ...................................................................... 11

4. Unilateral eccentric resistance training – a direct comparison between isokinetic and dynamic constant external resistance modalities, by Coratella, Milanese, and Schena, in European Journal of Sport Science (2015) ..................................................................................... 12

5. Modified daily undulating periodization model produces greater performance than a traditional configuration in powerlifters, by Zourdos, Khamoui, Lee, Park, Ormsbee and Kim, in Journal of Strength & Conditioning Research (2015) .................................................13

6. Effect of different inter‐set rest intervals on performance of single and multi‐joint exercises with near maximal loads, by Senna, Willardson, Scudese, Simão, Queiroz, Avelar, and Dantas, in Journal of Strength & Conditioning Research (2015) .................................. 14

7. Effects of exercise intensity and occlusion pressure after 12 weeks of resistance training with blood‐flow restriction, by Lixandrão, Ugrinowitsch, Laurentino, Libardi, Aihara, Cardoso, and Roschel, in European Journal of Applied Physiology (2015) ..............................15

8. The response to, and recovery from maximum strength and power training in elite track and field athletes, by Howatson, Brandon, andHunter, in International Journal of Sports Physiology and Performance (2015)..........................................................................................16

9. Strength and power development in professional rugby union players over a training and playing season, by Gannon, Stokes, and Trewartha, in International Journal of Sports Physiology and Performance (2015) ....................................................................................17

10. Sprinting activities and distance covered by top level Europa League soccer players, by Andrzejewski, Chmura, Pluta, and Konarski, in International Journal of Sports Science and Coaching (2015)..................................................................................................................... 18

11. Reliability of pull up and dip maximal strength tests, by Coyne, Tai, Tran, Secomb, Lundgren, Farley, Newton, and Sheppard, in Journal of Australian Strength and Conditioning (2015).......................................................................................................................................... 19

12. Effects of a low‐load gluteal warm‐up on explosive jump performance, by Comyns, Kenny, and Scales, in Journal of Human Kinetics (2015)........................................................................................................................................................................................................... 20

13. Performance and endocrine responses to differing ratios of concurrent strength and endurance training, by Jones, Howatson, Russell and French, in Journal of Strength & Conditioning Research (2015)........................................................................................................... 21

14. Are the responses to resistance training different between the preferred and non‐preferred limbs? By Baroni, De Azevedo Franke, Rodrigues, Geremia, Schimidt, and Carpes, in Journal of Strength & Conditioning Research (2015) ......................................................... 22

15. Neuromuscular adaptations to unilateral vs. bilateral strength training in women, by Botton, Radaelli, Wilhelm, Rech, Brown, Pinto, and Botânico, in Journal of Strength & Conditioning Research (2015)........................................................................................................23

2. BIOMECHANICS AND MOTOR CONTROL.......................................................................................................................24

16. Comparison of kinematics and muscle activation in free weights back squat with and without elastic bands, by Saeterbakken, Andersen, and Van den Tillaar, in Journal of Strength & Conditioning Research (2015) .............................................................................25

17. The influence of footwear type on barbell back squat using 50, 70 and 90% of 1RM: a biomechanical analysis, by Whitting, Meir, Crowley‐McHattan, and Ryan Holding, in Journal of Strength & Conditioning Research (2015) ................................................................ 26

18. Neuromuscular fatigue and physiological responses after five dynamic squat exercise protocols, by Raeder, Wiewelhove, Westphal‐Martinez, Fernandez‐Fernandez, Alvaro de Paula Simola, Kellmann, Meyer, Pfeiffer, and Ferrauti, in Journal of Strength & Conditioning Research (2015)............................................................................................................................................................................................27

19. Effects of sled towing on peak force, the rate of force development and sprint performance during the acceleration phase, by Martínez‐Valencia, Romero‐Arenas, Elvira, González‐Ravé, Navarro‐Valdivielso, and Alcaraz, in Journal of Human Kinetics (2015) .......................28

20. Impact of harness attachment point on kinetics and kinematics during sled towing, by Bentley, Atkins, Edmundson, Metcalfe, and Sinclair, in Journal of Strength & Conditioning Research (2015)..................................................................................................................29

21. Modulation of work and power by the human lower‐limb joints with increasing steady‐state locomotion speed, by Schache, Brown, andPandy, in The Journal of Experimental Biology (2015).................................................................................................................................30

22. Acute response of well‐trained sprinters to a 100‐m race – higher sprinting velocity achieved with increased step rate compared to speed training, by Otsuka, Kawahara, and Isaka, in The Journal of Strength & Conditioning Research (2015) ......................................... 31

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23. Sprint running research speeds up – A first look at the mechanics of elite acceleration, by Clark and Weyand, in Scandinavian Journal ofMedicine and Science in Sports (2015)........................................................................................................................................................ 32

24. The effects of eccentric conditioning stimuli on subsequent counter‐movement jump performance, by Ong, Lim, Chong, and Tan, in Journal of Strength & Conditioning Research (2015)...................................................................................................................................33

25. Lunging exercise potentiates a transient improvement in neuromuscular performance in young adults, by Horan, Watson, Lambert, andWeeks, in Journal of Strength & Conditioning Research (2015).................................................................................................................. 34

26. The effect of the number of sets on power output for different loads, by Morales‐Artacho, Padial, García‐Ramos, and Feriche, in Journalof Human Kinetics (2015).............................................................................................................................................................................35

27. Peak power output in the bench pull is maximized after 4 weeks of specific power training, by Jolley, Goodwin, and Cleather, in Journal of Strength & Conditioning Research (2015)............................................................................................................................................... 36

28. The relationship between clinically measured hip rotational motion and shoulder biomechanics during the pitching motion, by Laudner,Wong, Onuki, Lynall, and Meister, in Journal of Science and Medicine in Sport (2014) .............................................................................. 37

29. The role of muscle morphology on jumping, sprinting and throwing performance in participants with different power‐training duration experience, by Methenitis, Zaras, Spengos, Stasinaki, Karampatsos, Georgiadis, and Terzis, in Journal of Strength & Conditioning Research (2015)............................................................................................................................................................................................38

3. ANATOMY, PHYSIOLOGY, AND NUTRITION................................................................................................................... 39

30. Calorie for calorie, dietary fat restriction results in more body fat loss than carbohydrate restriction in people with obesity, by Hall, Bemis, Brychta, Chen, Courville, Crayner, and Yannai, in Cell Metabolism (2015)...................................................................................... 40

31. Fat‐free mass changes during ketogenic diets and the potential role of resistance training, by Tinsley and Willoughby, in International Journal of Sport Nutrition and Exercise Metabolism (2015)........................................................................................................................ 41

32. Myostatin as a mediator of sarcopenia versus homeostatic regulator of muscle mass – insights using a new mass spectrometry‐based assay, by Bergen, Farr, Vanderboom, Atkinson, White, Singh, and LeBrasseur, in Skeletal Muscle (2015) ................................................. 42

33. Myostatin dysfunction is associated with reduction in overload induced hypertrophy of soleus muscle in mice, by Minderis, Kilikevicius, Baltusnikas, Alhindi, Venckunas, Bunger, and Ratkevicius, in Scandinavian Journal of Medicine & Science in Sports (2015) ....................43

34. Early resistance training‐induced increases in muscle cross‐sectional area are concomitant with edema‐induced muscle swelling, by Damas, Phillips, Lixandrão, Vechin, Libardi, Roschel, and Ugrinowitsch, in European Journal of Applied Physiology (2015) ....................44

35. The metabolic and temporal basis of muscle hypertrophy in response to resistance exercise, by Brook, Wilkinson, Smith, and Atherton, in European Journal of Sport Science (2015)................................................................................................................................................45

36. Influence of combined resistance training and healthy diet on muscle mass in healthy elderly women: a randomized controlled trial, by Strandberg, Edholm, Ponsot, Wåhlin‐Larsson, Hellmén, Nilsson, and Kadi, in Journal of Applied Physiology (2015) ................................46

37. Nutritional interventions to augment resistance training‐induced skeletal muscle hypertrophy, by Morton, McGlory, and Phillips, in Frontiers in Physiology (2015)......................................................................................................................................................................47

38. Caffeine and diuresis during rest and exercise: a meta‐analysis, by Zhang, Coca, Casa, Antonio, Green, and Bishop, in Journal of Science and Medicine in Sport (2014).......................................................................................................................................................................48

4. PHYSICAL THERAPY AND REHABILITATION................................................................................................................... 49

39. A step towards understanding the mechanisms of running‐related injuries, by Malisoux, Nielsen, Urhausen, and Theisen, in Journal of Science and Medicine in Sport (2015).......................................................................................................................................................... 50

40. Scapula kinematics of pull‐up techniques: avoiding impingement risk with training changes, by Prinold and Bull, in Journal of Science and Medicine in Sport (2015).......................................................................................................................................................................51

41. Effects of two different injury prevention resistance exercise protocols on the hamstring torque‐angle relationship – a randomized controlled trial, by Naclerio, Larumbe‐Zabala, Monajati, and Goss‐Sampson, in Research in Sports Medicine (2015) .............................52

42. Is there evidence to support the use of the angle of peak torque as a marker of hamstring injury and re‐injury risk? By Timmins, Shield, Williams, and Opar, in Sports Medicine (2015)............................................................................................................................................53

43. MRI does not add value over and above patient history and clinical examination in predicting time to return to sport after acute hamstring injuries: a prospective cohort of 180 male athletes, by Wangensteen, Almusa, Boukarroum, Farooq, Hamilton, Whiteley, and Tol, in British Journal of Sports Medicine (2015)..........................................................................................................................................54

44. Onset and maximum values of electromyographic amplitude during prone hip extension after neurodynamic technique in patients with lumbosciatic pain: a pilot study by Horment‐Lara, Cruz‐Montecinos, Nuñez‐Cortes, Letelier‐Horta, and Henriquez‐Fuentes in Journal of Bodywork and Movement Therapies (2015)................................................................................................................................................55

45. Blood flow restriction exercise – a progressive injury rehabilitation model, by Staunton, in Journal of Australian Strength and Conditioning (2015)......................................................................................................................................................................................56

46. Cold vs. heat after exercise – is there a clear winner for muscle soreness, by Petrofsky, Khowailed, Lee, Berk, Bains, Akerkar, and Laymon, in Journal of Strength & Conditioning Research (2015)................................................................................................................ 57

47. An evidence‐based review of hip‐focused neuro‐muscular exercise interventions to address dynamic lower extremity valgus, by Ford, Nguyen, Dischiavi, Hegedus, Zuk, and Taylor, in Open Access Journal of Sports Medicine (2015) ..............................................................58

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48. Differences and correlations in knee and hip mechanics during single‐leg landing, single‐leg squat, double‐leg landing, and double‐leg squat tasks, by Donohue, Ellis, Heinbaugh, Stephenson, Zhu, and Dai, in Research in Sports Medicine (2015) .........................................59

49. Management of chronic recurrent osteitis pubis/pubic bone stress in a premier league footballer: evaluating the evidence base and application of a nine‐point management strategy, by McAleer, Gille, Bark, and Riepenhof, in Physical Therapy in Sport (2015) .............60

50. The effectiveness of non‐operative rehabilitation programs for athletes diagnosed with osteitis pubis, by Cheatham, Kolber, and Kumagai, in Journal of Sport Rehabilitation (2015)..................................................................................................................................... 61

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Strength and Conditioning Research

1. STRENGTH & CONDITIONING, POWER AND HYPERTROPHY

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Strength and Conditioning Research

The effect of training volume and intensity onimprovements in muscular strength and size inresistance‐trained men, by Mangine, Hoffman,Gonzalez, Townsend, Wells, Jajtner, and Stout, inPhysiological reports (2015)

Background

IntroductionThe optimal structure of a resistance training programis unclear. Many variables can be altered, includingrelative load, volume, frequency, proximity tomuscular failure, rest period duration, muscle actionand repetition speed. Researchers have studied theeffect of volume on gains in strength and size morethan any other single training variable.

Effect of volume on strength gains (read more)A number of long-term trials have assessed the effectsof different volumes on strength gains in variouspopulations. At our last count, at least 22 studies havecompared the effects of high and low volumes onstrength gains over long-term interventions inuntrained subjects (where low is usually a single setand high is usually multiple sets, most commonly 3sets). This research is relatively clear that highvolumes are superior to low volumes for strengthgains, as 13 of these 22 trials found that high volumesled to significantly greater strength gains than lowvolumes and many of the remaining studies reportednon-significant trends in the same direction. Fortrained subjects, there is much less research available.At our last count, at least 6 studies had beenperformed, of which 3 found a significant benefit ofusing higher volumes. In addition, several meta-analyses have been performed of the underlying data,across both trained and untrained subjects. Thus, itseems completely appropriate that current guidelinesrecommend progressive, higher volume resistancetraining in order to achieve optimal strength gains.

Effect of volume on hypertrophy (read more)A number of long-term trials have assessed the effectsof different volumes on size gains in variouspopulations. At our last count, at least 14 studies havecompared the effects of high and low volumes on sizegains over long-term interventions in untrainedsubjects (where low is usually a single set and high isusually multiple sets, most commonly 3 sets). Thisresearch is relatively clear that high volumes aresuperior to low volumes for size gains, as 6 of these14 trials found that high volumes led to significantlygreater size gains than low volumes and many of theremaining studies reported non-significant trends inthe same direction. For trained subjects, there is muchless research available. At our last count, only 2studies had been performed and neither found asignificant benefit of using higher volumes. However,meta-analyses of the underlying data, across bothtrained and untrained subjects, indicate that highervolumes are superior. Thus, it seems appropriate thatcurrent guidelines recommend progressive, highervolume resistance training in order to achieve optimalhypertrophy.

OBJECTIVE: To compare the effects of high-volume-low-relative-load-short-rest resistance training withthe effects of high-relative-load-low-volume-long-restresistance training on changes in body composition,lean total body mass, and lean mass of the limbs(measured by dual energy x-ray absorptiometry[DEXA]), muscle cross-sectional area (measured byultrasound in the vastus lateralis, rectus femoris,pectoralis major and triceps brachii), muscle strength(measured by 1RM in the back squat and bench pressexercises), and hormone levels (using blood samplesto measure testosterone, growth hormone, insulin-likegrowth factor-1 (IGF1), cortisol, and insulin).

POPULATION: 33 resistance-trained males, aged24.0 ± 3.0 years.

INTERVENTION: All subjects performed a resistancetraining program for 8 weeks, training 4 days perweek, using the following exercises: back squatsdeadlifts, leg press, lat pull downs, barbell bent-overrows, barbell biceps curls, bench press, incline benchpress dumbbell flys, seated shoulder press, lateraldumbbell raise, triceps extension. All of the subjectswere randomly allocated to either a high-volume-low-relative-load-short-rest group (VOL) who performed 4sets of 10 – 12 repetitions with ~70% of 1RM with 1minute inter-set rest periods or a high-relative-load-low-volume-long-rest group (REL) who performed 4sets of 3 – 5 repetitions with ~90% of 1RM with 3minute inter-set rest periods.

What happened?

Muscular size and strengthActual increases in muscular mass or size were notreported. However, the researchers found significantincreases in lean arm mass in both groups that weregreater (5.2 ± 2.9% vs. 2.2 ± 5.6%) in REL comparedto VOL. The researchers observed that both groupsdisplayed significant increases in both 1RM back squatand 1RM bench press. There were no differencesbetween groups in the 1RM back squat change.However, there were greater increases in 1RM benchpress (14.8 ± 9.7% vs. 6.9 ± 9.0%) in REL comparedto VOL.

Hormone levelsThe researchers noted that while cortisol responseswere greater post-VOL on each acute measure, theVOL group displayed a significant reduction in acutecortisol response from pre- to post-training.

What did the researchers conclude?The researchers concluded that training with highrelative loads, long rests and low volumes may besuperior for upper body hypertrophy than training withlow relative loads, short rests and high volumes.However, which training variable was responsible forthe difference is unclear.

LimitationsThe study was limited by the substantial number ofvariables that differed between groups and by theapparent small overall changes in muscle size.

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Effects of resistance training with moderate vs. heavyloads on muscle mass and strength in the elderly – ameta-analysis, by Csapo and Alegre, in ScandinavianJournal of Medicine & Science in Sports (2015)

Background

IntroductionThe optimal structure of a resistance training programis unclear. Many variables can be altered, includingrelative load, volume, frequency, proximity tomuscular failure, rest period duration, muscle actionand repetition speed. Researchers have studied theeffect of relative load on gains in strength and sizemore than almost any other single training variable.

Effect of relative load on strength gains (read more)At our last count, at least 18 studies have comparedthe effects of heavy and light loads on strength gainsover long-term interventions (where light is defined as<60% of 1RM or <15RM). This research is fairly clearthat heavy relative loads are superior to light relativeloads for strength gains, as 13 of these 18 trials foundthat heavy loads led to significantly greater strengthgains than light loads and 3 further studies reportednon-significant trends in the same direction. Only oneprevious trial has found that light loads producedsuperior increases in strength to heavy loads. Thus, itis completely appropriate that current exerciseguidelines recommend progressive, heavy relative-load resistance training in order to achieve optimalstrength gains. Unlike comparing heavy and lightloads, the literature is more conflicting in respect ofthe difference in strength gains between heavy andmoderate loads. Thus, it is difficult to conclude onwhether heavy loads are definitively better thanmoderate loads for increasing strength. Individualslooking to improve strength may wish to make use ofmoderate (i.e. 5 – 15RM) loads rather than heavy(<5RM) loads if safety is a concern, or if greatervolume is considered desirable.

Effect of relative load on size gains (read more)At the last count, at least 10 trials have beenperformed comparing the effects of heavy versus lightrelative loads on hypertrophy. Of these 10 trials, only3 found a significantly superior effect of heavy loads,while 3 further trials reported a non-significant trendin the same direction. The remaining 4 trials reportedno differences whatsoever between heavy and lightloads in terms of increases in muscular size.Therefore, whether heavy loads (>65% of 1RM) arebetter for hypertrophy than lighter loads (<65% of1RM) in untrained individuals is hard to say. Onbalance, while there is evidence that lighter loads areable to produce some hypertrophy, it is likely that thisdegree of hypertrophy is less than that achievablewith heavier loads. Therefore, when working withuntrained beginners, personal trainers may be able toproduce hypertrophy using lighter loads. There is noevidence currently available for trained individuals andit seems probable that there is a larger difference inrespect of relative loads in these populations, althoughthis remains to be confirmed.

OBJECTIVE: To carry out a meta-analysis (using arandom effects model) comparing the efficacy of highload (around 80% of 1RM) resistance training withlight-to-moderate load (about 45% of 1RM) resistancetraining on changes in muscle strength and size inelderly people.

STUDY SELECTION: Studies were included thatcompared multiple training protocols in both work-matched (i.e. similar volume) and non-work-matchedprotocols (i.e. different volume).

What happened?

Study selectionThe researchers identified 15 studies that measured atleast changes in muscle strength, which included 448subjects (202 females and 246 males) with a meanage of 67.8 years. Of these 15 studies, 11 used work-matched programs and 4 used programs that were notwork-matched. In the 11 work-matched programs, thelight-to-moderate load group performed significantlymore repetitions than the high load group but in theremaining 4 studies, there was no such significantdifference. In addition, the researchers found 7studies that measured changes in muscle size, ofwhich 5 were work-matched.

Muscular strengthAcross all 15 studies, the effect of high loads wasfound to be substantially greater than the effect oflow-to-moderate loads (μ = 0.43) but this effect didnot reach significance because of large confidenceintervals. In the 11 work-matched studies, both highand low-to-moderate groups produced substantialgains in muscle strength and the effect of high loadswas larger than the effect of low-to-moderate loads (μ= 0.30) and even though this effect was smaller thanthe overall effect, it did reach significance because ofthe smaller variability.

Muscle sizeAcross all 7 studies, the effect of high loads was foundto be greater than the effect of low-to-moderate loads(μ = 0.14) and this effect reached significance.However, in the 5 work-matched studies, the effect ofhigh loads was not greater than low-to-moderateloads (μ = 0.06).

What did the researchers conclude?The researchers concluded that both high loads andlow-to-moderate loads can produce gains in musclestrength and size in elderly people. They concludedthat high loads appear to be superior to low-to-moderate loads for strength gains but this superioritycan be partly compensated for by matching workloads(i.e. using higher numbers of repetitions with lighterloads). They concluded that there is no differencebetween high and low-to-moderate loads for changesin muscle size, when workloads are matched.

LimitationsThis meta-analysis was limited as it was performed inelderly subjects and different results might be found inother groups.

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Does training frequency and supervision affectcompliance, performance and muscular health? Acluster randomized controlled trial, by Dalager,Bredahl, Pedersen, Boyle, Andersen, and Sjøgaard, inManual Therapy (2015)

Background

IntroductionThe optimal structure of a resistance training programis unclear. Many variables can be altered, includingrelative load, volume, frequency, proximity tomuscular failure, rest period duration, muscle actionand repetition speed. Frequency is discussed in twocontexts. Firstly, in relation to the number of times perweek that a single body part can be trained effectively.Secondly, whether training should be performed astotal body, split, or individual body part routines.There are two underlying principles in each case:recovery and volume. For recovery, the question ishow long it takes (for either the individual or themuscle) to recover before training can be performedagain. Optimal frequency would be expected toproduce superior results. For volume, the question iswhether increasing frequency in order to increasevolume leads to superior results. Greater volumemight be expected to lead to increased gains.

Effect of frequency on strength gains (read more)Currently, the evidence indicates that training withdifferent volume-matched frequencies over the courseof a week has little effect on strength gains inuntrained individuals. This is on the basis of 6 long-term trials comparing >2 training groups, of which allbut one reported no differences between groups. Onthe other hand, the evidence indicates that trainingwith a higher volume-matched frequency mightpossibly be superior to training with a lower volume-matched frequency for increasing strength in trainedindividuals. However, this is on the basis of 3 long-term trials comparing >2 training groups, of which 1reported a benefit in favor of training with a higherfrequency for at least one of the outcome measuresfor strength while the other 2 trials reported nodifferences between groups.

Effect of frequency on size gains (read more)Currently, the evidence indicates that training withdifferent volume-matched frequencies over the courseof a week has little effect on gains in muscular size inuntrained individuals. This is on the basis of 4 long-term trials comparing >2 training groups, of which allbut one reported no differences between groups. Onthe other hand, the evidence indicates that trainingwith a higher volume-matched frequency mightpossibly be superior to training with a lower volume-matched frequency for increasing muscular size intrained individuals. However, this is on the basis of 3long-term trials comparing >2 training groups, ofwhich 1 reported a benefit in favor of training with ahigher frequency for at least one of the outcomemeasures of muscular size while the other 2 trialsreported no differences between groups.

OBJECTIVE: To compare the effects of frequency andlevels of supervision on compliance (as measured byself-report on a 6-point scale and by training diaryrecords), self-rated health (as measured by a 5-pointscale), self-efficacy for exercise (as measured using a6-point questionnaire), maximal muscle strength (asmeasured by 1RM bilateral lateral raise) and repetitionmuscle strength (as measured by maximal number ofbilateral lateral raise repetitions with a sub-maximalload).

POPULATION: 573 office workers (351 females and222 males).

INTERVENTION: All subjects in training groupsperformed resistance training of 1 hour per week for20 weeks. The 1 hour was apportioned over differentnumbers of sessions. Additionally, some groups weresupervised and some were not. The 1 hour of trainingcomprised 9 exercises for >7 minutes each, including5 specific exercises using dumbbells for the shouldersand arms, including the front raise, lateral raise,reverse flies, shrugs, and wrist extensions. There were4 groups: 1S = one 60-minute training session perweek with supervision; 3S = three 20-minute trainingsessions per week with supervision; 9S = nine 7-minute training sessions per week with supervision;and 3U = three 30-minute training sessions per weekwithout supervision except in the first 2 weeks inwhich instructions were given.

What happened?

Self-reported health and self-reported efficacyThe researchers found that none of the groupsincreased in either self-reported health or exerciseself-efficacy and they found no effect of trainingfrequency or supervision level on either of thesevariables. Why there was no change in these variablesis unclear.

ComplianceThe researchers found no effect of training frequencyor supervision level on the degree of compliance,either as measured by training diary records or byself-report on a 6-point scale. They found that the twomeasures were closely associated (r = 0.72).

Muscle strengthThe researchers found no effect of training frequencyor supervision level on the changes in maximal musclestrength or repetition muscle strength.

What did the researchers conclude?The researchers concluded that training frequency andsupervision level do not have any effect on exercisecompliance and do not lead to differences in changesin self-reported health, exercise self-efficacy, or eithermaximal or repetition muscle strength.

LimitationsThe study was limited in that the exercises performedwere limited to the upper body and different resultsmight be observed if full-body compound exercisessuch as squats and deadlifts had been programmed.

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Unilateral eccentric resistance training – a directcomparison between isokinetic and dynamic constantexternal resistance modalities, by Coratella, Milanese,and Schena, in European Journal of Sport Science(2015)

Background

IntroductionThe optimal structure of a resistance training programis unclear. Many variables can be altered, includingrelative load, volume, frequency, the proximity tomuscular failure, rest period duration, muscle actionand repetition speed. During resistance training, thetype of external load can be changed but this has onlyrarely been explored. In general, the type of externalload can be divided into types where the load remainsthe same throughout the movement (isoinertial) andtypes where the load varies during the movement(variable). Variable types of resistance can be furthersubdivided into types were the load changes in orderto maintain a constant velocity during the exercise(isokinetic) and those in which the load is altered tofollow the force-angle curve more generally (strictlyvariable, but sometimes also called accommodatingresistance).

Effects of variable resistance on strength gainsVarious researchers have investigated the differencesin effects on strength gains during long-term periodsof resistance training using either constant load orvariable load resistance types, while training withbarbells. In such cases, the variable loads are createdby the use of either bands or chains. To date, at least5 studies have been performed in resistance-trainedsubjects. However, among these studies, only 1 hasreported a superior benefit on strength gains of usingvariable resistance types compared to using constantload resistance. The use of variable resistance orconstant loads may therefore make little difference tostrength gains in trained subjects. Similarly, to date,only 1 study has been carried out assessing thedifference in the effect on strength gains betweenconstant load or variable load resistance types, whiletraining with barbells in untrained subjects. In thisstudy, there was no difference between the variableand the constant load resistance type. Therefore,despite the huge popularity of variable resistance, theaddition of bands and chains may not be superior toconstant loads for resistance trained and untrainedpopulations. Whether benefits might be observed inelite powerlifters, however, is unclear.

OBJECTIVE: To compare the effects of variable loads(constant velocity) and constant loads (variablevelocity) during unilateral eccentric-only training onchanges in muscle strength (as measured by 1RMknee extension, isometric knee extension torque,eccentric knee extension torque, and concentric kneeextension torque using a dynamometer), changes invastus lateralis muscle architecture (as measured byultrasound), and changes in quadriceps lean mass (asmeasured by a dual-energy X-ray absorptiometry[DEXA] scan).

POPULATION: 47 recreational athletes who were notresistance trained, aged 20.5 ± 2.3 years, randomlyallocated into either variable load (VAR), constant load(CONS) or control (CONT) groups.

INTERVENTION: The subjects in the training groupsperformed only single-leg knee extension resistancetraining 2 days per week, for 6 weeks. Each workoutcomprised 5 sets of 8 eccentric-only repetitionsthrough a fixed range of motion from 90 to 5 degrees(0 = full extension). The VAR group used isokineticresistance as an external load and the CONS groupused a constant load as an external load.

What happened?

Muscle strengthThe researchers found that both groups displayedsignificant increases in all strength measures overtime. The groups displayed similar strength increasesexcept in respect of eccentric knee extension torque,where VAR increased significantly more than CONS(84.2 vs. 38.2%).

Muscle architectureThe researchers found that neither group changedvastus lateralis pennation angle or quadriceps leanmass. However, both groups increased fascicle lengthand muscle thickness. Nevertheless, there were nodifferences between groups in respect of any of thechanges in muscle architecture.

What did the researchers conclude?The researchers concluded that except in respect ofeccentric isokinetic torque, the changes in strengthand muscle architecture resulting from a program ofeither VAR or CONS eccentric resistance training arevery similar. The difference in strength gains appearsto be only somewhat external-load specific, with theonly superior improvement in strength by the VARgroup being the same measurement as was usedduring training (eccentric isokinetic).

LimitationsThe study was limited in that it did not involveresistance-trained subjects. Different results might beobserved in other populations.

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Modified daily undulating periodization modelproduces greater performance than a traditionalconfiguration in powerlifters, by Zourdos, Khamoui,Lee, Park, Ormsbee and Kim, in Journal of Strength &Conditioning Research (2015)

BackgroundPeriodization has been proposed to lead to superiorgains in muscular strength and size when applied toresistance-training programs. Periodization methodsfall into three main categories: linear, non-linear, andblock. Linear (and reverse linear) periodizationinvolves sequential alteration of key training variablesover time. Non-linear periodization involves alteringtraining variables from day-to-day or from week-to-week such that all training variables are used similarlywithin short periods of time. Block periodizationinvolves training for a specific goal in successive,additive cycles. These blocks are designed to achievespecific training goals and are often referred to bytheir names, such as strength, hypertrophy, andpower. Although linear and block periodization havedistinctly different origins and were designedseparately, they are often confused in both theliterature and by coaches. Similarly, the modern non-linear model can be subdivided into either weeklyundulating periodization, which involves changesbetween high-volume low-relative load training andlow-volume high-relative load training on a week-by-week basis within a single month, and daily undulatingperiodization, which involves changes between high-volume low-relative load training and low-volumehigh-relative load training on a day-by-day basiswithin a single week. Daily undulating periodization ismuch more commonly used and studied than weeklyundulating periodization. Despite the common use bycoaches of most if not all of these periodizationmethods, they have rarely been compared forenhancing gains in strength and size duringresistance-training and where they have beencompared they are rarely compared against a non-periodized control group. Thus, it is difficult to beconfident about the abi l i ty of the differentperiodization methods for improving gains in muscularstrength and size. Overall, it seems that there is someevidence that periodization may be superior to noperiodization for increasing strength gains. However,the effect on hypertrophy is still unclear.

OBJECTIVE: To compare the effects of two non-linear(daily undulating periodization) weekly training orderson strength gains (as measured by 1RM squat, benchpress, deadlift, and powerlifting total), total volumeload (sets x repetitions x weight lifted), and changesin hormone levels (testosterone and cortisol).

POPULATION: 18 male powerlifters, aged 21.1 ± 1.9years, allocated into traditional (TRAD) or modified(MOD) daily undulating periodization program groups.

INTERVENTION: All powerlifters trained using a dailyundulating periodization program involving the squat,bench press and deadlift exercises for 6 weeks,training on 3 non-consecutive days per week. Thesquat and bench press were performed in all 3workouts but the deadlift was only performed in 1workout (the strength workout). TRAD trained using ahypertrophy, strength, and power training order andMOD trained using a hypertrophy, power, and strengthtraining order. Hypertrophy training often comprisedworkouts such as 5 sets of 8 repetitions at 75% of1RM; power training typically comprised workoutssuch as 5 sets of 1 repetition at 80% of 1RM; strengthtraining typically comprised of 3 sets of maximalrepetitions at 85% of 1RM.

What happened?

Training volumeThe researchers found that MOD displayed greatercombined, squat and bench press training volume loadthan TRAD. However, there was no difference betweengroups for the deadlift. Combined training volume loadwas moderate-to-strongly correlated (r = 0.68) withchange in powerlifting total. Squat training volumeload was moderate-to-strongly correlated (r = 0.69)with change in squat 1RM. Bench press trainingvolume load was strongly correlated with change inthe bench press 1RM (r = 0.89). Deadlift trainingvolume load was moderately correlated with increasein deadlift 1RM (r = 0.48).

Muscle strengthThe researchers found that there was no difference instrength changes for the powerlifting total, 1RM squator 1RM deadlift between TRAD and MOD but MODdisplayed greater gains in bench press 1RM.

Hormone responsesThe researchers found no significant changes over thetraining program in either group or between groups inrelation to either testosterone or cortisol levels.

What did the researchers conclude?The researchers found that a modified daily undulatingperiodization order (hypertrophy – power – strength)led to greater strength increases in 1RM bench pressthan a traditional order. The superiority of this orderappeared to be driven by greater training volumes,which were closely correlated with changes in 1RM.

LimitationsThe study was limited as it involved powerlifters anddifferent results might be observed in other groups.

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Effect of different inter-set rest intervals onperformance of single and multi-joint exercises withnear maximal loads, by Senna, Willardson, Scudese,Simão, Queiroz, Avelar, and Dantas, in Journal ofStrength & Conditioning Research (2015)

Background

IntroductionThe optimal structure of a resistance training programis unclear. Many variables can be altered, includingrelative load, volume, frequency, the proximity tomuscular failure, rest period duration, muscle actionand repetition speed. Traditionally, short rest perioddurations have been programmed for bodybuildersand other individuals seeking increases in musclemass and long rest period durations have beenprogrammed for powerlifters and individuals who areprioritizing strength gains.

Effects of rest period on hypertrophy (read more)Based on a review of the mechanisms thought to leadto hypertrophy, it was once proposed that shorter restperiods would lead to increased muscle mass byincreasing the metabolic stress experienced. However,the long-term trials have not yet provided support forthis hypothesis. In trained subjects, only 1 study hasbeen performed comparing long and short rest periodsand it found no differences between groups. Inuntrained subjects, only 2 studies have similarly beenperformed comparing long and short rest periods and1 reported a superior effect of longer rest perioddurations and 1 reported a superior effect of short restperiod durations. Training with a shorter rest periodduration is therefore unlikely to be superior forhypertrophy in either trained or untrained populations.

Effects of rest period on strength gains (read more)Based on the assumption that greater rest perioddurations would allow a heavier load to be lifted andthereby challenge the neuromuscular system to agreater extent, it has been suggested that longer restperiods would lead to increased strength gains. Onbalance, this appears to be the case. In trainedsubjects, 4 studies have been performed comparinglong and short rest periods. Of these 4 studies, 2 ofthem reported superior benefits of a long rest periodduration while the remainder reported no differences.Increasing rest period duration may therefore have abeneficial effect on strength gains in this population.In untrained subjects, 6 studies have been performedcomparing long and short rest periods. Of these 6studies, 3 reported significant benefits of a long restperiod duration, 1 reported a benefit of short restperiod duration, and the remainder reported nodifferences. Increasing rest period duration maytherefore similarly have a beneficial effect on strengthgains in this population.

OBJECTIVE: To compare the acute effects of alteringinter-set rest periods on repetition performance (reps)of single and multi-joint exercises with heavy loads.

POPULATION: 15 resistance-trained males, aged26.40 ± 4.94 years.

INTERVENTION: All subjects performed 5 sets eachof a single-joint (machine chest fly) and a multi-joint(barbell bench press) exercise with a 3RM load ondifferent occasions, using either 1, 2, 3 or 5 minutesof inter-set rest.

What happened?

Repetition performance – single-jointThe researchers observed that significantly more repswere completed for the 2 minute (12.6 ± 2.4 reps), 3minute (13.7 ± 1.8 reps) and 5 minute (12.9 ± 2.3reps) conditions compared to the 1 minute (10.3 ±2.6 reps) condition when using the machine chest fly.

Repetition performance – multi-jointThe researchers observed that significantly more repswere completed for the 3 minute (11.7 ± 2.8 reps)and the 5 minute (12.9 ± 2.3 reps) conditionscompared to the 1 minute (7.6 ± 3.5 reps) conditionwhen using the bench press. They also noted thatsignificantly more reps were completed for the 5minute (12.93 ± 2.25 reps) than the 2 minute (9.5 ±3.1 reps) condition.

What did the researchers conclude?The researchers concluded that in order to maintainmaximal numbers of repetitions per set, rest periodsmust be longer for multi-joint exercises than forsingle-joint exercises. Specifically, inter-set restperiods of 2 minutes are enough for the machine chestfly but 3 – 5 minutes may be required for the benchpress.

LimitationsThe study was limited in that only upper bodyexercises were tested and the results may differ forthe lower body.

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Effects of exercise intensity and occlusion pressureafter 12 weeks of resistance training with blood-flowrestriction, by Lixandrão, Ugrinowitsch, Laurentino,Libardi, Aihara, Cardoso, and Roschel, in EuropeanJournal of Applied Physiology (2015)

BackgroundBlood flow restriction (BFR) training is used toincrease gains in muscular size. BFR training istypically prescribed as low-relative-load resistance-training (20 – 30% of 1RM) combined with blood flowrestriction applied in the form of either carefullycalibrated pressure cuffs or simple elastic wrappings.Previous studies have found that the use of BFRtraining can increase strength and muscle mass invarious populations, ranging from the elderly totrained athletes. Several theories have been putforward regarding mechanisms to explain thebeneficial effects observed following BFR training. It isthought that the mechanisms by which such increasesoccur might include increased fast-twitch fiberrecruitment, metabolic and hormonal alterations,intramuscular signaling, and cellular swelling.However, there is no current strong consensus arounda single, dominant mechanism by which BFR trainingexerts its effects. While there are currently noguidelines available for describing the use of BFRtraining in different populations, it is noted that it maybe possible to achieve gains in muscular size in manyindividuals with lower loads than are typicallyrecommended for resistance-training. The AmericanCollege of Sports Medicine (ACSM) recommends using>60% of 1RM as the desired relative load forincreasing muscular strength and size. However,research indicates that loads of 20 – 50% may beappropriate in combination with BFR. Thus, BFR incombination with resistance-training may be mostuseful for populations who cannot tolerate the largemechanica l loads that are assoc iated withconventional, heavy resistance-training, such as theelderly or infirm.

OBJECTIVE: To compare the effects of different BFRocclusion pressures and different relative loads duringresistance training on gains in muscle strength (asmeasured by 1RM knee extension) and muscle cross-sectional area of the quadriceps (as measured bymagnetic resonance imaging [MRI] scans).

POPULATION: 26 untrained males, with mean age of26 – 30 years in each group.

INTERVENTION: All subjects performed unilateralresistance training comprising 2 – 3 sets of 10 – 15repetitions for 12 weeks with both legs, with each legallocated to 2 of 5 protocols, including 4 BFR trainingprotocols and 1 conventional protocol (CONV). The 4BFR training protocols were performed with either20% or 40% of 1RM and with either 40% or 80%occlusion pressure. The 4 BFR possibilities werelabelled as: BFR-20-40, BFR-20-80, BFR-40-40 andBFR-40-80.

What happened?

Muscular strengthThe researchers reported that 1RM knee extensionstrength increases in all BFR groups similarly andthere was no effect of manipulating either occlusionpressure or relative load. However, there were strongindications that all BFR groups displayed inferiorincreases in strength to the CONV group.

Muscle sizeThe researchers reported that muscle cross-sectionalarea increased in all groups except BFR-20-40, whichinvolved the lower relative load and the lowerocclusion pressure. However, the difference betweengroups training with different occlusion pressures wasonly significant between the two groups training withthe lower relative load. On the other hand, both higherrelative load groups achieved greater increases inmuscle size than their comparison groups with lowerrelative loads.

What did the researchers conclude?The researchers concluded that during BFR training,greater occlusion pressure leads to greater increasesin muscle size when training at lower relative loads(20% of 1RM); that higher relative loads lead togreater increases in muscle size than lower relativeloads (40% vs. 20% of 1RM); that neither occlusionpressure nor relative load affect the magnitude ofstrength gains during BFR training; and that CONVtraining leads to superior muscle strength but not sizegains compared to BFR training.

LimitationsThe study was limited in that it was performed inuntrained subjects and different results might beobserved in resistance trained individuals.

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The response to, and recovery from maximumstrength and power training in elite track and fieldathletes, by Howatson, Brandon, and Hunter, inInternational Journal of Sports Physiology andPerformance (2015)

BackgroundTrack and field is a collection of competitive physicalevents that fits within a larger body of events calledathletics. Track and field is contested both outdoor andindoor and the events incorporated under its umbrellacomprise those that require skill in running, jumpingand throwing. Track events are those that involverunning while field events are those that involve eitherjumping or throwing. The running events comprise thesprint, middle and long distances and range from 60mto 10,000m. Sprint distances are those ranging from60m to 400m. Middle distances are those rangingfrom 800m to 1500m (or perhaps also the 3,000m)and long distance are those ranging from 3,000m to10,000m. Running events can be contested either withor without hurdles but the distances differ dependingon whether hurdles are present. Running events canalso be contested in teams of athletes, as relays.Jumping events include bilateral and unilateral jumpsin horizontal and vertical directions both with andwithout implements and are contested as the longjump, triple jump, high jump and pole vault. Throwingevents differ predominantly depending on the weightof the implement being thrown but also on thethrowing technique and are contested as the shot put,javelin, discus and hammer. Combinations of theseevents are organized into separate competitions forathletes who excel as all-rounders, which include thedecathlon, heptathlon and pentathlon. The decathloncomprises the 100m sprint, the long jump, the shotput, the high jump, the 400m sprint on a single day ofcompetition, followed by the 110m hurdles, thediscus, the pole vault, the javelin, and the 1500m runon a second day. The heptathlon comprises the 100mhurdles, the high jump, the shot put, the 200m sprinton a single day of competition, followed by the longjump, the javelin, and the 800m run on a second day.The pentathlon is contested on a single day andcomprises the 100m high hurdles, long jump, shotput, high jump, and 800m run. In general, except forthe middle and long distance running events, mosttrack and field events require a considerable amountof strength and power in order to excel at a high leveland therefore most training programs for the trackand field events will include resistance training,ballistic resistance training, and/or plyometrics inorder to develop athletes to their full potential. Inaddition, many athletes will continue to perform agreat deal of skill practice and drills intended toimprove the efficiency of movements.

OBJECTIVE: To compare the acute and 24 hourneuromuscular responses to strength and powerexercise in elite athletes, by reference to maximalvoluntary contraction (MVIC) knee extension force (asmeasured using an isokinetic dynamometer), counter-movement jump (CMJ) height, voluntary activation (asmeasured by the central activation ratio [CAR] usingpercutaneous stimulation), the rating of perceivedexertion (RPE), and blood lactate.

POPULATION: 10 elite track and field athletes(sprinters or long jumpers).

INTERVENTION: All subjects performed 2 differentworkouts (strength or power) comprising 4 sets of 5repetitions of the back squat (or back squat jump),split squat (or split squat jump), and press (or pushpress) exercise. The strength workout was performedwith >80% of 1RM and the power workout was carriedout using just 30% of the load used for the strengthworkout.

What happened?

Blood lactate and RPEThe researchers found that blood lactate post-exerciseincreased significantly compared to pre-exercise in thestrength workout but not in the power workout. Also,they found that the post-exercise RPE was greaterdirectly after the strength workout than directly afterthe power workout.

MVIC The researchers found that MVIC reduced significantlycompared to pre-exercise in the strength workout butnot after the power workout. Additionally, they foundthat MVIC was still reduced significantly compared topre-exercise at 24-hours after the strength workout.The researchers noted that there was a significantrelationship (R-squared = 0.71) between relative backsquat strength and relative reduction in MVIC, withstronger athletes displaying larger reductions in MVIC.

Voluntary activationThe researchers found that CAR was not significantlydifferent from pre-exercise either immediately post-exercise or after 24 hours.

Jump heightThe researchers found that jump height was notsignificantly different from pre-exercise either directlypost-exercise or after 24 hours.

What did the researchers conclude?The researchers observed a reduction in MVIC forceimmediately after and at 24-hours following a typicalstrength workout in elite track and field athletes.However, there was no similar reduction in MVIC forceafter a similar power workout using similar exercisesbut lower loads and faster bar speeds.

LimitationsThe study was limited as it did not record testosteroneor cortisol levels, nor did it record resting heart rate orheart rate variability changes.

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Strength and power development in professionalrugby union players over a training and playingseason, by Gannon, Stokes, and Trewartha, inInternational Journal of Sports Physiology andPerformance (2015)

BackgroundRugby union is one major type of rugby (rugby leaguebeing the other) and is a contact team sport belongingto the football codes, which include Australian Rulesfootball, American football and Gaelic football. Like allof the football codes, rugby union is a game of twohalves involving intermittent activity for the players, inwhich periods of slow walking, jogging or standing areinterspersed with periods of high-speed running,sprinting. Rugby union is a very similar game to rugbyleague and is played in two halves of 40 minutes.However, the line-up of players differs from rugbyleague in that there are 15 players, comprising 8forwards and 7 backs. The forwards comprise 2 props,1 hooker, 2 second-row forwards (confusingly calledlocks), and 3 back-row forwards (blind-side and open-side flankers on either side and the number 8 in themiddle). The backs comprise the scrum-half, fly-half,inside centre, outside centre, right wing, left wing andfull back. The scoring system differs slightly fromrugby league in that a try is worth 5 points (1 morethan in rugby league), a conversion is worth 2 points(the same as in rugby league), a penalty kick is worth3 points (1 more than in rugby league) and a dropgoal is also worth 3 points (2 more than in rugbyleague). Previous analysis of athletes in many of thefootball codes using video analysis and GlobalPositioning System (GPS) tracking of playermovements has revealed that the majority of sprintsperformed are of very short durations, indicating thegreat importance of sprint running acceleration forthese players.

OBJECTIVE: To investigate changes in strength (asmeasured by isometric squat peak force, force at50ms and force at 100ms), and power output (asmeasured by explosive machine hack squat using aplate-loaded sled) in elite rugby players throughoutthe different phases (pre-season [PRE], post pre-season [POST-PRE], mid-way through the competitiveseason [MID], and at the end of the competitiveseason [END]) of a professional playing season.

POPULATION: 16 professional rugby union athletesfrom an English premiership team, aged 23 ± 4 years.

What happened?

Changes from PRE to PRE-POSTFrom PRE to PRE-POST, the researchers found verylikely beneficial increases in force at 50ms (+16%,effect size = 0.75 ± 0.40) and in force at 100 ms(+14%, effect size = 0.63 ± 0.40) but the change inpeak force was unclear (+2.7%, effect size = 0.21 ±0.30) and the change in power was trivial (+0.2%,effect size = 0.02 ± 0.20).

Changes from PRE-POST to MIDFrom PRE-POST to MID, the researchers found a likelybeneficial increase in power (+4%, effect size = 0.31± 0.2) but the changes in peak force, force at 50msand force at 100ms were all unclear.

Changes from MID to ENDFrom PRE-POST to MID, the researchers found a likelyharmful decrease in force at 50ms (-6%, effect size =-0.39 ± 0.3) and in force at 100ms (-9%, effect size =-0.52 ± 0.4) but the change in peak force was trivial(-0.6%, effect size = -0.07 ± 0.50) and the change inpower was also trivial (-0.8%, effect size = -0.08 ±0.50).

What did the researchers conclude?The researchers concluded that improvements in earlyforce production (but not peak force or power)occurred in the pre-season training period; increasesin power occurred through to the mid-point of theseason (but no changes occurred in early force orpeak force); and early force production reducedtowards the end of the season, while peak force andpower were maintained.

LimitationsThe study was limited in that it was observational andit is unclear what factors led to the changes observed.

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Sprinting activities and distance covered by top levelEuropa League soccer players, by Andrzejewski,Chmura, Pluta, and Konarski, in International Journalof Sports Science and Coaching (2015)

BackgroundSoccer or Association Football is the world's mostpopular team sport and is played by more than 250million people in over 200 separate countries. Throughthis incredible popularity, it is known simply as“football” in most parts of the world, despite theexistence of many other football codes, includingAmerican Football, Australian Rules Football, GaelicFootball, and Rugby. Soccer is played in teams of 11players in two halves of 45 minutes in length with a15-minute break between the two halves. Play runscontinuously within halves, such that the clock is notstopped while the ball is out of play. There is usually a15-minute half-time break between halves. Every fouryears, the World Cup is held, in which around 200national teams compete in qualifying tournaments inthe hope of becoming one of the 32 national teamsthat compete in the 4-week competition. The mostrecent World Cup was held in Brazil and was thetwentieth such competition. Germany beat Argentina1–0 in the final to take their fourth title. Training forsoccer requires a focus on many different aspects,including physical qualities, technical skills, andtactical abilities. There are many different physicalqualities that are important for soccer, includingaerobic endurance, anaerobic endurance, strength,power and flexibility. Traditionally, soccer teams placedthe most emphasis on aerobic endurance, noting thatplayers needed to be able to run long distances duringgames. Indeed, there is a basic agreement that soccerplayers travel around 9 – 14km in a single 90-minutematch, although the exact distance depends on theposition played. Training methods for improvingaerobic capacity include interval training, small-sidedgames, game simulations, soccer-specific circuits,repeated sprints, and agility drills. More recently,soccer teams have begun to focus more on sprintrunning ability, which appears to be crucial in allowingsoccer athletes to dominate situations during play.This change in focus came out of the realization thatthe nature of the activity performed by soccer playersduring a game comprises long periods of low-intensitywalking or jogging, interspersed by short periods ofmaximal or near-maximal effort, including acceleratingsprints. Some studies have found that players performmany such accelerating sprints per match, for a totaldistance of around 200m. Sprint running ability can beimproved by various training methods, includingsprinting, heavy load resistance-training, ballisticresistance-training, plyometrics, and assisted andresisted sprinting. There is currently no strongconsensus around which type of training is best,although a recent meta-analysis concluded that noviceathletes benefit most from sprint running practice andmore advanced athletes benefit more from a variedprogram.

OBJECTIVE: To examine the sprint running activities(as measured by reference to the mean sprintingdistance covered, duration of rest between sprintingactivities and maximal running speed), and distancecovered by professional soccer players in two separateseasons of the Europa League competition, recordedby a computerized player tracking system using 8fixed cameras around the stadium. Sprint runningevents were defined as any movement ≥24km/hcarried out over a ≥1.0 second time period.

POPULATION: 147 soccer players participating in 10matches played at one ground in the 2008-2009 and2010-2011 Europa League seasons, divided into 5categories of positions, being: central defenders,external defenders, central midfield players, externalmidfield players, and forwards.

What happened?

Distance coveredThe researchers reported that the mean overalldistance covered by all players during the match was11,114 ± 885m. They noted that the centralmidfielders covered the greatest distances (11,760 ±797m), while the central defenders covered thesmallest distances (10,336 ± 471m).

Sprint running distance coveredThe researchers found that the mean total distancecovered in sprint running actions in each game was237 ± 123m, while the mean distance per sprint was21 ± 3m. The longest mean total distance covered insprint running actions in each game was seen in theforwards (345 ± 29m) while the shortest was seen inthe central midfielders (167 ± 87 m).

Rest periods between sprintsThe researchers found that the mean rest period takenbetween sprint running activities was 472 ± 230s. Theforwards took the shortest rest periods (311 ± 72s)and the central midfielders took the longest restperiods (567 ± 275s).

Maximal sprint running speedsThe researchers found that the mean maximal sprintrunning speed for all players was 31.9 ± 2.0km/h(8.86 ± 0.56m/s). The highest mean maximal sprintrunning speed was attained by the forwards (33.1 ±1.9km/h or 9.19 ± 0.53m/s) and the lowest maximalsprint running speed was attained by the centralmidfielders (31.0 ± 1.7km/h or 8.61 ± 0.47m/s).

What did the researchers conclude?The researchers concluded that the mean distancecovered by soccer players in each sprint was around20m, that mean rest period durations between sprintswere quite long (>7.5 minutes), and that maximalsprint running speeds reached were extremely high(>9m/s).

LimitationsThe study was limited in that it reflects data from asingle stadium in just two seasons of the EuropaLeague.

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Reliability of pull up and dip maximal strength tests,by Coyne, Tai, Tran, Secomb, Lundgren, Farley,Newton, and Sheppard, in Journal of AustralianStrength and Conditioning (2015)

BackgroundWhen using tests or screens, it is important to becertain that they are both reliable and valid. Reliablemeans that the test routinely produces the sameresult (output) for the same performance (input).Valid means that the test actually measures what it issupposed to measure. Tests can display very goodreliability and poor validity and vice versa. Reliability ismuch easier to measure than validity for tests andscreens and therefore there are usually more studiesfor any given test or screen for reliability than validity.Reliability can be measured in at least two, if not threeways: inter-rater reliability, intra-rater reliability, andtest-re-test reliability. Each of these contribute to ouroverall assessment of the reliability of a test. Inter-rater reliability describes whether a test can beperformed by different people at the same time andyet still produce the same (or at least a very similar)result. If two people score a subject or an outcomevery differently while watching them perform the testat the same time, this would mean that the test hadpoor inter-rater reliability and this would challenge theoverall assessment of the reliability of a test. Similarly,intra-rater reliability describes whether a test can beperformed by the same person on two differentoccasions and yet still produce the same result. If thesame person scores a subject or an outcome verydifferently on two different occasions, this would meanthat the test had poor intra-rater reliability and thiswould challenge the overall assessment of thereliability of a test. Sometimes, true intra-rater can bedifferentiated from test-re-test reliability andsometimes it cannot. True intra-rater reliability can betested when we are certain that the underlyingoutcome is truly identical in both cases. For example,when the Functional Movement Screen (FMS) is testedby a rater watching the same video of a screeningperformance on two separate occasions, this is trueintra-rater reliability. Test-re-test reliability differsfrom true intra-rater reliability, as it involves theoutcome being measured again shortly after the initialtest. For example, when the FMS is tested by raterswatching a person perform the screen on two separate(live) occasions, this is test re-test reliability. Itincludes variability inherent in the individualperformance as well as in the rater assessment.Consequently, test-re-test reliability is normally worsethan true intra-rater reliability.

OBJECTIVE: To investigate the test-re-test reliability(as measured by the intra-class correlation coefficient[ICC], standard error of measurement [SEM], andsmallest worthwhile change [SWC]), of the weightedpull up and dip maximal strength tests (1RM).

POPULATION: 15 male athletes (either swimmers orsurfers of varied ability levels), aged 27.8 ± 6.5 years,with bodyweight of 73.9 ± 9.8kg.

INTERVENTION: All subjects performed two 1RMmaximum pull up and dips tests on two separateoccasions separated by 7 days.

What happened?

Pull upsThe mean pull up 1RM (including bodyweight) was 106± 18kg. This was found to have a near perfect test-re-test reliability (ICC = 0.99). The SEM was 2.1kg andthe SWC was 3.5kg. Therefore, a difference of 2.1kgwould be necessary to establish that one athlete wasbetter at 1RM pull ups than another, while a differenceof 3.5kg would be required to be certain that oneathlete had improved their 1RM pull up. The relative1RM was 1.43 ± 0.15 times and this was slightly lessreliable (ICC = 0.96).

DipsThe mean dip 1RM (including bodyweight) was 117 ±24kg. This was found to have a near perfect test-re-test reliability (ICC = 0.99). The SEM was 2.7kg andthe SWC was 4.8kg. Therefore, a difference of 2.7kgwould be necessary to establish that one athlete wasbetter at 1RM dips than another, while a difference of4.8kg would be required to be certain that one athletehad improved their 1RM dip. The relative 1RM was1.58 ± 0.22 times and this was slightly less reliable(ICC = 0.97).

What did the researchers conclude?The researchers concluded that 1RM pull ups and 1RMdips are highly reliable in a population of swimmingathletes with varying ability levels.

LimitationsThe study was limited in that the test-re-test reliabilitywas calculated based on a broad population and worsereliability measures would typically be expected if thetests had been performed in a group with more similarability levels.

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Effects of a low-load gluteal warm-up on explosivejump performance, by Comyns, Kenny, and Scales, inJournal of Human Kinetics (2015)

BackgroundIt is generally accepted that warm-ups improvesubsequent athletic performances. There are severalmechanisms by which warm-ups might be effective.Most of these mechanisms are physiological, and mostphysiological mechanisms are thought to arise fromtemperature-related factors. Firstly, it is thought thatwarm-ups lead to decreased viscous resistance of themuscles: increasing muscle temperature may reducethe passive resistance or stiffness of muscle tissue,making the fibers more elastic, which is likely toimprove both absolute force and rate of forcedevelopment. Secondly, it is thought that warm-upslead to increased oxygen delivery to the muscles:increasing muscle temperature may improve oxygendelivery to the muscles as a result of a rightward shiftin the oxy-haemoglobin dissociation curve (this shiftmakes it easier for hemoglobin to release the oxygenthat is bound to it and therefore increases delivery ofoxygen to the muscles) as well as by greatervasodilation. This is likely to improve mainly longerduration anaerobic and aerobic performances. Thirdly,warm-ups are thought to allow increased anaerobicmetabolism: increased muscle temperature appears tocause an elevation in muscle glycogen breakdown,which may then improve subsequent short-termanaerobic performance. Fourthly, warm-ups arethought to lead to increased nerve conduction rate:increased muscle temperature increases thetransmission speed of nervous impulses, which islikely to increase both reaction times and rate of forcedevelopment. Fifthly, warm-ups are believed to lead tometabolic effects that might improve oxygen delivery:the metabolic byproducts of exercise might lead toincreased oxygen delivery to the muscles as a resultof a rightward shift in the oxy-haemoglobindissociation curve and increased vasodilation, just asincreased muscle temperature does. Sixthly, warm-ups may lead to elevation of baseline oxygenconsumption: where tasks can be started with anelevated level of oxygen consumption, the initial partof the task will not be performed anaerobically,thereby placing a reduced strain on the athlete at thebeginning of the workout or competition. Seventhly,warm-ups have been proposed to lead to changes incontractile apparatus: during periods of inactivity, thenumber of bonds between actin and myosin filamentsbonds increases and this elevates the stiffness of amuscle. Physical activity breaks these bonds, reducingmuscle stiffness. An active warm-up involving largemuscular excursions to lengthen muscles may breakactin-myosin bonds and reduce the passive stiffness ofmuscle, thereby increasing subsequent rate of forcedevelopment. Finally, it is well-known that prioractivity can cause a post-activation potentiation (PAP)effect in subsequent activities.

OBJECTIVE: To investigate the effects of a low-loadwarm-up focusing on the gluteus maximus muscle onboth squat (SQ) and counter-movement (CMJ) jumpheight, peak ground reaction force and rate of forcedevelopment (RFD) (measured by a force platform).

POPULATION: 11 track and field athletes (6 malesand 5 females), aged 20.9 ± 2.6 years.

INTERVENTION: All subjects completed jumpsbefore and after a low-load, 7 minute, warm-up thatfocussed on the gluteus maximus muscle. The warm-up comprised 7 exercises for 1 set of 10 repetitionseach. The exercises were a two-leg glute bridge,quadruped hip extension, quadruped hip abduction,side lying clams in 60 degrees of hip flexion, side lyinghip abduction, prone single-leg hip extension, andstability ball wall squats.

What happened?

Jump heightThe researchers observed that both the SQ and CMJjump heights reduced at 30s, 2 minutes, 4 minutes,and 6 minutes of rest, likely as a result of fatigue.

Peak ground reaction forceThe researchers observed that there was a non-significant decrease in CMJ peak ground reaction forceat 30s and non-significant increases at 2, 4 and 6minutes, and then a second non-significant decreaseat 8 minutes. In contrast, there were non-significantincreases in SQ peak ground reaction force at all timeintervals.

Peak RFDThe researchers observed a significant increase inpeak RFD during the SQ at 2 minutes and they alsoobserved non-significant increases at the other timepoints.

What did the researchers conclude?The researchers concluded that the low-load warm-upfocussing on the gluteus maximus musculature wasable to potentiate peak RFD but not force or jumpheight.

LimitationsThe study was limited in that it is unclear why RFDwas improved but jump height was not enhanced.

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Performance and endocrine responses to differingratios of concurrent strength and endurance training,by Jones, Howatson, Russell and French, in Journal ofStrength & Conditioning Research (2015)

BackgroundAlthough several previous studies have found thatconcurrent training can lead to inferior gains inmuscular strength, size and power in comparison withresistance-training alone (which is called the“interference effect”), it is unclear exactly why thishappens. Reviews have concluded that the inferiorgains differ between qualities, with gains in muscularpower being most markedly reduced by concurrenttraining, but gains in muscular size being affected verylittle. Such reviews have found that the extent towhich concurrent training leads to inferior adaptationsmay also be mode- and intensity-dependent. A greaterinterference effect has been observed between aerobicexercise and resistance-training where the mode ofaerobic exercise is long-distance running, while long-distance cycling appears to have very minor adverseeffects and may even have beneficial effects onquadriceps muscular size. Thus, attempts to discern amolecular pathway for the interference effect thatignores these apparent differences between aerobicexercise modes may be flawed. Similarly, greaterinterference effects have been observed where aerobicexercise is performed for longer periods with lowerlevels of intensity, while less substantial effects havebeen observed where the aerobic exercise is of shorterduration and higher intensity. It is possible that onefactor involved in the interference effects observedduring concurrent training may arise from functionalor non-functional overreaching, which may lead toaccumulated fatigue such that performance in tests ofmuscular strength and power is impaired. This mightexplain why gains in muscular size are least affectedby concurrent training and why power is most stronglyaffected.

OBJECTIVE: To explore the effects of adding differentquantities of endurance training to a resistancetraining program on gains in lower body strength (asmeasured by the sum of back squat 1RM and deadlift1RM), upper body strength (as measured by the sumof bench press 1RM, bent over row 1RM, and overheadpress 1RM), maximal aerobic capacity (as measuredby an incremental treadmill running test to ascertainVO2-max), countermovement jump height, changes inhormone levels (as measured by blood levels ofcortisol and testosterone), and any changes in bodycomposition (as measured by BodPod air displacementplethysmography).

POPULATION: 30 resistance-trained males, aged 24± 3 years.

INTERVENTION: All subjects completed 6 weeks ofan intervention. One group performed only strengthtraining, 3 days per week (ST), a second groupperformed concurrent strength and endurance trainingin the ratio 3:1 (CT3), a third group performedconcurrent strength and endurance training in a ratio1:1 (CT1) and a final control group performed notraining (CON). In each case, the strength trainingcomprised compound exercises (e.g. back squat,bench press, bent over row, deadlift, and overheadpress) and the endurance training involved treadmillrunning.

What happened?

Changes in strength and jump heightThe researchers found that all of the training groupsincreased lower body strength from pre- to post-training. ST improved lower body strength comparedto CT1 only. They found that all training groupsincreased upper body strength from pre- to post-training. The researchers found that all of the traininggroups increased jump height from pre- to post-training. ST improved jump height more than bothCT1 and CT3.

Hormone levelsTestosterone response to training increased in both STand CT3 from pre- to post-training. Cortisol responsedid not change over time but was elevated in allgroups as a result of each training session in which itwas measured.

What did the researchers conclude?The researchers concluded that high volumes ofendurance running training appear to reduce thedevelopment of lower body strength but low volumesdo not. In contrast, they concluded that both high andlow volumes of endurance running training reduce theability to improve jumping performance.

LimitationsThe study was limited in that it remains unclear whymeasures of high-velocity force production (such asjumping) are much more affected by concurrentendurance training than measures of low-velocityforce production (such as 1RM back squat).

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Are the responses to resistance training differentbetween the preferred and non-preferred limbs? ByBaroni, De Azevedo Franke, Rodrigues, Geremia,Schimidt, and Carpes, in Journal of Strength &Conditioning Research (2015)

BackgroundThe bilateral force deficit is a phenomenon based uponthe observation that the maximal voluntary forceproduced by an ipsilateral limb is less when it exertsforce at the same time as the contralateral limb thanwhen it exerts force alone. It has been suggested thatthe bilateral force deficit during resistance trainingmay imply that single-limb exercises such as the splitsquat could lead to greater strength gains comparedto two-limb exercises such as the traditional backsquat, as greater loads can be used. Similarly, giventhat the greater loads may lead to greater volumes, itmay be the case that two-limb exercises could lead tosuperior hypertrophy. However, this has not previouslybeen widely explored. The bilateral force deficit can beobserved during isometric and during dynamic muscleactions and should properly be distinguished from thebilateral deficit in jumping, which is the observationthat individuals do not jump twice as high when usingtwo legs compared to when they use one leg. Thebilateral deficit in jumping occurs because jump heightis primarily a function of work done and not of force.Work done is the area under the power-time curveand is dependent on both force and velocity, as power= force x velocity. In a two-leg jump, since theimpulse is greater, the muscles contract more quicklyand therefore the muscles reach faster shorteningvelocities. This moves them up the force-velocitycurve. The force-velocity curve is a key biomechanicalrelationship, which states that as force productionincreases, the muscle contraction velocity decreasesexponentially and vice versa. Since velocity is a keydeterminant of work done, this means that two-legjumps cannot involve twice as much work done asone-leg jumps. And since work done is the keydeterminant of jumping height, this explains why two-leg jumps are not twice as high as one-leg jumps.However, although the bilateral deficit in jumping isnow relatively comprehensively explained, the reasonsfor the bilateral force deficit are much less clear.

OBJECTIVE: To assess the differences in gains instrength gains (as measured by concentric, isometricand eccentric knee extensor torque using an isokineticdynamometer) and size gains (as measured by thequadriceps muscle thickness with ultrasound) betweenthe preferred (dominant) and non-preferred (non-dominant) legs following a long-term program ofisokinetic, eccentric unilateral resistance training.

POPULATION: 12 healthy, physically active males,aged 24.9 ± 4.3 years.

INTERVENTION: All subjects completed a 4-weekcontrol period followed by a 12-week resistancetraining program, comprising 2 workouts per week inwhich 3 – 5 sets of 10 maximal isokinetic (at 60degrees/s), eccentric unilateral knee extensionexercises through a controlled range of motion ofbetween 90 and 30 degrees (0 = full extension) foreach leg were performed.

What happened?

Pre-training strength asymmetryPre-training, the researchers found that concentrictorque was similar between limbs but isometric andeccentric torques were significantly smaller in the non-preferred limb (by 4.9% and 5.8%, respectively).

Post-training strength asymmetryPost-training, the researchers found that concentric,isometric and eccentric torque for the non-preferredand preferred limbs were all similar, with differences ofjust 0.73%, -0.62% and -1.93%, respectively.

Muscle thicknessThe researchers found that there were no changes inmuscle thickness during the study and that there werelittle or no differences between legs.

What did the researchers conclude?The researchers concluded that a unilateral, isokinetic,eccentric resistance training program reduced thestrength asymmetry between legs within 12 weekswithout altering muscle size. This may support the useof unilateral resistance training for reducing between-limb strength deficits.

LimitationsThe study was limited in that it did not use anecologically valid resistance training program for thelower body, such as a rear-foot elevated split squat.

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Neuromuscular adaptations to unilateral vs. bilateralstrength training in women, by Botton, Radaelli,Wilhelm, Rech, Brown, Pinto, and Botânico, in Journalof Strength & Conditioning Research (2015)

BackgroundThe bilateral force deficit is a phenomenon based uponthe observation that the maximal voluntary forceproduced by an ipsilateral limb is less when it exertsforce at the same time as the contralateral limb thanwhen it exerts force alone. It has been suggested thatthe bilateral force deficit during resistance trainingmay imply that single-limb exercises such as the splitsquat could lead to greater strength gains comparedto two-limb exercises such as the traditional backsquat, as greater loads can be used. For a detailedintroduction to the bilateral force deficit, see theprevious study review.

OBJECTIVE: To compare strength gains (as measuredby 1RM bilateral and unilateral knee extension testsand maximum voluntary isometric contraction [MVIC]knee extension force), rectus femoris and vastuslateralis muscle activity (as measured by surfaceelectromyography [EMG]), and quadriceps musclethickness (as measured by ultrasound) betweenunilateral and bilateral resistance training.

POPULATION: 43 recreationally active females, aged24 ± 4 years, allocated to a control group (CON) whodid not perform any resistance training, a unilateralgroup (UG) who trained using only single-leg training,and a bilateral group (BG) who trained only using bothlegs at the same time.

INTERVENTION: Subjects in the training groupsperformed 2 resistance training sessions per week for12 weeks. Each training session comprised eitherunilateral (UG) or bilateral (BG) knee extensionexercise and also bilateral knee flexion, bench press,lat pull-down, hip abduction, hip adduction, crunch,biceps flexion and triceps extension.

What happened?

Changes in unilateral strengthThe researchers reported that the UG and BG groupssignificantly increased unilateral knee extension 1RM(by 33.3 ± 14.3% and 24.6 ± 11.9%, respectively).However, the increase in unilateral knee extension1RM displayed by the UG was significantly greaterthan the increase displayed by the BG.

Changes in bilateral strengthThe researchers reported that both the UG and BGgroups increased bilateral 1RM (by 20.3 ± 6.8% and28.5 ± 12.3%, respectively) and bilateral isometricMVIC force (by 14.7 ± 11.3% and 13.1 ± 12.5%,respectively).

Changes in muscle thickness and muscle activityThe researchers observed that quadriceps musclethickness increased similarly in both UG and BGtraining groups. In contrast, they found that muscleactivity only increased in the UG group and onlyduring the unilateral test (by 39.9 ± 18.3% in UG vs.12.0 ± 21.7% in BG). There was no increase inmuscle activity in the bilateral test in either group.

What did the researchers conclude?The researchers found that UG improved unilateral1RM knee extension to a greater extent than BG.However, UG and BG improved bilateral 1RM kneeextension and quadriceps muscle thickness similarly.This difference may be caused by neural adaptations,as UG increased muscle activity during unilateral 1RMtesting but BG did not.

LimitationsThe study was limited in that it did not use anecologically valid resistance training program for thelower body, such as a rear-foot elevated split squat.

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Strength and Conditioning Research

2. BIOMECHANICS AND MOTOR CONTROL

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Strength and Conditioning Research

Comparison of kinematics and muscle activation infree weights back squat with and without elasticbands, by Saeterbakken, Andersen, and Van denTillaar, in Journal of Strength & Conditioning Research(2015)

BackgroundThe squat is a key exercise in training programs andcan be classified in different ways (including barbellplacement, technique, stance width or foot placement,and fixed or free weight). Test-re-test reliability ofback squat 1RM testing is nearly perfect, although afamiliarization effect has been observed. Prime moversin the back squat are the quadriceps, gluteusmaximus and erector spinae. The hamstrings areantagonist co-contractors. The roles of the adductors,calves and abdominals are unclear. In the back squat,using a wider stance and knee wraps increase gluteusmaximus muscle activity, while using running shoesrather than no footwear increases quadriceps muscleactivity. Most squat variations appear to lead to similarquadriceps, gluteus maximus and erector spinaemuscle activity, but the back squat displays greaterquadriceps muscle activity than the split squat andoverhead squat. No other exercise has been found toinvolve greater quadriceps muscle activity than theback squat but the barbell hip thrust involves greatergluteus maximus activity and the deadlift involvesgreater erector spinae muscle activity. Heavier loadsare lifted during partial rather than parallel squats byindividuals with greater levels of resistance trainingexperience, and by athletes using a powerlifting-styleof squat compared to an Olympic weightlifting-style ofsquat. Ground reaction forces are primarily a functionof the absolute loads used. The optimal load for powerduring back squats is unclear. Supportive equipment(knee wraps and weightlifting belts) increases poweroutput, most likely by increasing velocity as a result ofstored elastic energy in the lowering phase. Greatertrunk angles in the back squat are observed insubjects wearing no footwear rather than runningshoes and when using cues to restrict the movementof the knees over the toes. The effect of cues toprevent knee movement over the toes on peak hipangle is unclear but cues to look downwards ratherthan upwards lead to more acute peak hip angles,while increasing fatigue leads to less acute peak hipangles. Increasing load and wearing running shoesrather than no footwear lead to more acute peak kneeangles, while using cues to prevent forward kneemovement over the toes and fatigue lead to less acutepeak knee angles. Weightlifting shoes and runningshoes both lead to more acute peak ankle angles thanusing no footwear, while cues to prevent the kneefrom moving forward over the toes lead to less acutepeak ankle angles. Hip extensor moments in the backsquat increase with increasing relative load, squatdepth, trunk lean and with cues to prevent forwardmovement of the knees over the toes. They aregreater using a powerlifting-style squat than astandard squat. In the Smith machine, hip extensormoments are greater with a foot position that is moreforward of the barbell or with a backward inclination.

OBJECTIVE: To compare the muscle activity (asmeasured using surface electromyography [EMG]) ofthe biceps femoris, vastus medialis, and vastuslateralis muscles between 6RM back squats usingconstant resistance (free weights) and using variableresistance (free weights plus elastic bands). Muscleactivity was measured in different regions in themovement: (1) in the region before the sticking region(PRE); (2) in the sticking region (STICKING); and (3)in the region after the sticking region (POST). Thesticking region is the point between the first barbellpeak velocity and the minimum barbell velocity.Reaching the point of first peak barbell velocity is anindicator that upward acceleration has ceased.

POPULATION: 20 recreationally trained females,aged 23.3 ± 2.6 years, with 4.6 ± 2.1 years ofresistance training.

INTERVENTION: All subjects completed two trials of6RM back squats, one with free weights only, and theother with free weights plus elastic bands. The elasticbands provided approximately 33% of total externalresistance in the variable load condition.

What happened?

Effect of external resistanceThe researchers found that there was no differencebetween the constant load or variable resistance typesin any of the three regions (PRE, STICKING, POST).

Effect of regionThe researchers found that there was a difference inmuscle activity between regions. They found that forthe biceps femoris, muscle activity increased from thePRE to the STICKING phase (by 50 – 70%) but therewas no change from the STICKING to the POST phase.In the vastus medialis and vastus lateralis, muscleactivity decreased from the STICKING to the POSTphase (by 8 – 12% and by 10 – 13%, respectively).There were no other significant changes.

What did the researchers conclude?The researchers concluded that the muscle activity ofthe biceps femoris, vastus medialis, and vastuslateralis muscles does not differ between 6RM backsquats performed with free weights and performedwith free weights plus elastic bands. However, theyfound that muscle activity varies between regionswithin the squat movement (from before to after thesticking region).

LimitationsThe study was limited in that the researchers did notmeasure the gluteus maximus muscle. Additionally, itwas limited in that the measurements were takenduring the final repetition of the 6RM set when themuscles were very fatigued. The fatigue may have ledto differences in the EMG activity recorded.

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The influence of footwear type on barbell back squatusing 50, 70 and 90% of 1RM: a biomechanicalanalysis, by Whitting, Meir, Crowley-McHattan, andRyan Holding, in Journal of Strength & ConditioningResearch (2015)

BackgroundThe barbell squat is a fundamental exercise in trainingprograms and can be classified in different ways(including barbell placement, technique, stance widthor foot placement, and fixed or free weight). For adetailed review of the barbell squat, see the previousstudy review.

OBJECTIVE: To compare the joint angle movements(using 3D motion analysis) and the center of pressuredeviation (using a force plate) during back squatswearing either standard athletic training shoes orOlympic weightlifting shoes at three different loads(50%, 70% and 90% of 1RM).

POPULATION: Nine males, aged 26.4 ± 5.4 years.

INTERVENTION: All subjects completed two batchesof trials of sub-maximal back squats (1 rep with 90%of 1RM, 3 reps with 70% of 1RM, and 5 reps with 50%of 1RM). One batch of trials was performed whilewearing standard athletic training shoes (STANDARD)and the other batch of trials was performed whilewearing Olympic weightlifting shoes (OLY).

What happened?

Effect of footwear on joint anglesThe researchers found that STANDARD displayed agreater degree of peak ankle dorsiflexion compared toOLY. However, there were no differences in peak kneeflexion, peak hip flexion or trunk angles betweenSTANDARD and OLY.

Effect of load on joint anglesThe researchers found that peak ankle dorsiflexionincreased with increasing load (from 50% up to 90%of 1RM). They noted that there was no effect of loadon peak knee flexion angle. They found that peak hipflexion angle increased with increasing load (from50% up to 90% of 1RM) but these findings were onlysignificant for the left side and not for the right side.Trunk lean increased with increasing load (from 50%up to 90% of 1RM).

Effect of footwear on center of pressure deviationSurprisingly, the researchers found that the center ofpressure deviation (anterior-posterior direction) wasgreater in OLY than in the STANDARD footwearcondition. There was no difference in the center ofpressure deviation (medial-lateral direction).

Effect of load on center of pressure deviationThe researchers found that the center of pressuredeviation (anterior-posterior direction) reduced withincreasing load. There was no difference in the centerof pressure deviation (medial-lateral direction).

What did the researchers conclude?The researchers concluded that although OLY footwearled to reduced peak ankle dorsiflexion, no otherdifferences in joint angles were observed. Theyconcluded that load altered several joint angles,including increasing peak dorsiflexion angle, peak hipflexion angle, and peak trunk lean angle. Theyconcluded that center of pressure deviation appearedto be greater when wearing OLY footwear, althoughthe implications of this finding are unclear.

LimitationsThe study was limited in that the findings regardingthe center of pressure deviation between footweartypes are unclear.

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Neuromuscular fatigue and physiological responsesafter five dynamic squat exercise protocols, byRaeder, Wiewelhove, Westphal-Martinez, Fernandez-Fernandez, Alvaro de Paula Simola, Kellmann, Meyer,Pfeiffer, and Ferrauti, in Journal of Strength &Conditioning Research (2015)

BackgroundThe barbell squat is a fundamental exercise in trainingprograms and can be classified in different ways(including barbell placement, technique, stance widthor foot placement, and fixed or free weight). For adetailed review of the barbell squat, see the previousbut one study review.

OBJECTIVE: To compare variously the neuromuscular,metabolic and perceptual fatigue induced by 5different types of squat exercise: (1) straight sets, (2)drop sets, (3) eccentric overload, (4), flywheel, and(5) plyometric jumps. In each case, metabolic fatiguewas measured by reference to blood lactate andserum creatine kinase levels. Perceptual fatigue wasmeasured by delayed onset muscle soreness (DOMS)and rating of perceived exertion (RPE). Neuro-muscular fatigue was measured by countermovementjump (CMJ) height, multiple rebound jump (MRJ)performance, and maximum voluntary isometriccontraction (MVIC) force.

POPULATION: 15 male resistance-trained athletes,aged 23.1 ± 1.9 years.

INTERVENTION: All subjects performed workoutsinvolving the 5 types of squat exercise: (1) straightsets, (2) drop sets, (3) eccentric overload, (4),flywheel, and (5) plyometric jumps. Straight setscomprised 4 sets of 6 repetitions with 85% of 1RM.Drop sets comprised 1 set of 6 repetitions with 85% of1RM followed immediately by 3 further sets of 6 dropsets. Eccentric overload comprised 4 sets of 6repetitions using 70% of 1RM in the concentric phaseand 100% of 1RM in the eccentric phase. The flywheelcondition used the YoYoTM flywheel for 4 sets of 6maximal repetitions. The plyometric jumps exercisecomprised 4 sets of 15 maximal jumps.

What happened?

Neuromuscular fatigueThe researchers identified no differences in respect ofany of the three neuromuscular fatigue measures(CMJ, MRJ and MVIC) between the 5 different squatprotocols.

Metabolic fatigueThe researchers found that blood lactate was higherimmediately post-exercise in the flywheel protocolthan in any other protocol and lower in the plyometricjumps protocol than in any other protocol. There wasno difference between groups in respect of serumcreatine kinase levels.

Perceptual fatigueThe researchers found that RPE was higherimmediately post-exercise in the flywheel protocolthan in several other protocols and lower in theplyometric jumps protocol than in any other protocol.There was no difference between groups in respect ofDOMS.

What did the researchers conclude?The researchers concluded that the flywheel exerciseprotocol led to the greatest metabolic and perceptualdemands and the plyometric jumps led to the leastmetabolic and perceptual demands.

LimitationsThe study was limited insofar as it is unclear howthese acute measures relate to long-term adaptations.

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Effects of sled towing on peak force, the rate of forcedevelopment and sprint performance during theacceleration phase, by Martínez-Valencia, Romero-Arenas, Elvira, González-Ravé, Navarro-Valdivielso,and Alcaraz, in Journal of Human Kinetics (2015)

BackgroundSprint running is a key athletic quality that iscontested in its own right in track and field, as well asbeing critical for success in many team sports, such assoccer, rugby, and both Australian Rules and AmericanFootball. Consequently, many researchers haveperformed extensive work into sprint running, bothoverall and in respect of certain specific aspects,including kinematics (joint angles) kinetics (forces andmoments), stiffness, electromyographic (EMG)activity, and the transfer of training to sprint running.As a result, there is a large body of knowledge inrespect of the features that are characteristic of elitesprinters and also of the training methods that maylead to best results. Sprint running performance isdetermined by the combination of stride length andstride frequency. Observational research indicates thatsome athletes rely on stride length for increasedspeed while others rely more on stride frequency forincreased speed. Analysis of biomechanics suggeststhat for improving stride length, hopping, boundingand stepping drills may be able to develop differentaspects of force production during the sprint runninggait cycle. Analysis of experimental trials suggeststhat sprint training, resistance training, plyometricsand resisted sprint training all produce significantimprovements in stride length. The effectiveness ofplyometrics may be related to observations that thestorage of elastic energy is important for sprintrunning performance. Indeed, researchers have foundthat this elastic energy storage becomes moreimportant with increasing sprinting speed. Thisindicates that drop jumps and other verticalplyometric exercises might be among the mosteffective training tools. Indeed, since biomechanicalanalysis suggests that the main role of the kneeextensors is one of shock absorption and increasedjoint stiffness upon ground contact, this furthersupports a role for reactive plyometric training thatstresses this muscle group, such as drop jumps.Related to this idea are the results of musculoskeletalmodeling research, which has reported that thelimiting factor for sprint running performance ismuscle contraction velocity. This suggests that trainingrate of force development for the key running musclesmay be the single most important factor in developingsprint running performance. This probably requires amix of training involving low loads with high velocities(which can be achieved using plyometrics) and highloads with low velocities. For improving stridefrequency, both experimental trials and biomechanicalanalysis indicate that combined heavy and explosivetraining along with overspeed running, using either adownhill slope or towing are all effective.

OBJECTIVE: To assess the effects of load (10%, 15%and 20% of body mass) during sled towing on sprinttimes (as measured by 20m and 30m sprint timesrecorded using photocells) and both the peak forceand the peak rate of force development (RFD) duringthe first step of the sprint (as measured using a loadcell).

POPULATION: 17 males (aged 17.9 ± 3.3 years) and6 females (aged 17.2 ± 1.7 years).

INTERVENTION: All subjects completed 30m sprintswhile towing a sled using 3 different weights of sled(10%, 15% and 20% of body mass).

What happened?

Effect of load on sprint timesThe researchers found that increasing load led tosignificantly increased sprint times, as expected.Sprint times (both 20m and 30m) increased byapproximately 5% from unweighted sprints with 10%of body mass, and by approximately 10% with 20% ofbody mass.

Effect of load on peak force and peak RFDThe researchers also found that the increasing sledload caused significant increases in peak RFD butalthough there were increases in peak force withincreasing sled load, these were not significant. Thismay imply that greater sled loads are superior fordeveloping peak RFD during sprint running.

What did the researchers conclude?The researchers concluded that sprint times areincreased by around 5% compared to unweightedsprints when using a sled load of 10% of body massand by around 10% when using a sled load of 20% ofbody mass. They concluded that peak RFD is greatestwhen using the heaviest sled loads. Therefore, whereincreasing RFD is desirable, heavier sled loads shouldbe used.

LimitationsThe study was limited in that no heavier sled loadswere used and therefore it is unclear at what load thepeak RFD is greatest.

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Impact of harness attachment point on kinetics andkinematics during sled towing, by Bentley, Atkins,Edmundson, Metcalfe, and Sinclair, in Journal ofStrength & Conditioning Research (2015)

BackgroundSprint running is a key athletic quality that iscontested in its own right in track and field, as well asbeing critical for success in many team sports, such assoccer, rugby, and both Australian Rules and AmericanFootball. For a detailed introduction to sprint running,see the previous study review.

OBJECTIVE: To compare the effects of attaching thesled at the shoulder or at the waist during sled towingsprints, on joint angle movements (as measured usingmotion analysis) and on ground reaction forces andother force-related variables (as measured using aforce plate during the third foot strike).

POPULATION: 14 resistance-trained males, aged26.7 ± 3.5 years.

INTERVENTION: All subjects performed sled towingsprints with a load such that velocity over 6m wasreduced by 10%. Sprints were performed at maximalvelocity with a shoulder harness attachment and witha waist harness attachment.

What happened?

Joint angle movementsThe researchers found that there were severalsignificant differences between the normal and thesled towing trials in terms of joint angle movements.They noted that peak hip flexion, knee flexion at foot-strike, knee flexion at toe-off, dorsiflexion at foot-strike, and peak ankle dorsiflexion were all greater inthe sled towing conditions compared to the normalrunning condition. However, they also found that therewere no differences between harness attachmentpoints.

Ground reaction forces and related variablesThe researchers found that the sled towing trialsinvolved significantly greater net horizontal meanforce, net horizontal impulses, propulsive horizontalmean force and propulsive horizontal impulse than thenormal conditions. In addition, they found that thewaist harness led to greater net horizontal impulsecompared to the shoulder harness. This fits well withprevious findings in sled towing walks, which havereported greater hip extensor moments and lowerknee extensor moments than shoulder attachments(the hip extensors are believed to be more importantfor horizontal force production).

What did the researchers conclude?The researchers concluded that sled towing with aload that reduces sprint times by 10% does lead toalterations in joint angle movements during shortsprints. However, they found that the attachmentpoint (waist or shoulder) does not affect the size ofsuch changes. They also concluded that sled towinginvolves significantly greater net horizontal meanforce, net horizontal impulses, propulsive horizontalmean force and propulsive horizontal impulse thannormal sprint running and that the waist harness leadsto greater net horizontal impulse compared to theshoulder harness.

LimitationsThe study was limited in that it was an acute trial andthe long-term implications of sled towing with either awaist or shoulder harness are unclear.

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Modulation of work and power by the human lower-limb joints with increasing steady-state locomotionspeed, by Schache, Brown, and Pandy, in The Journalof Experimental Biology (2015)

BackgroundSprint running is a key athletic quality that iscontested in its own right in track and field, as well asbeing critical for success in many team sports, such assoccer, rugby, and both Australian Rules and AmericanFootball. For a detailed introduction to sprint running,see the previous but one study review.

OBJECTIVE: To investigate changes in joint work andcontribution to overall power between different speedsof steady-state walking and running on level ground,using inverse dynamics calculations based on analysisof joint angle movements (as measured with motionanalysis) and ground reaction forces (as measuredusing a force plate).

POPULATION: 7 experienced sprinting athletes (5males and 2 females), aged 26.6 ± 8.3 years.

INTERVENTION: All subjects performed a range ofsteady-state walking and running, from (walking at1.59 ± 0.09m/s to sprint running at 8.95 ± 0.70m/s.

What happened?

Hip, knee and ankle work doneThe researchers found that ankle positive workincreased with increasing speeds until a running speedof 5.01 ± 0.11m/s, where it plateaued. However, hippositive work during stance and swing and kneenegative work during swing increased above runningspeeds of 5.01 ± 0.11m/s.

Hip, knee and ankle contribution to average powerThe researchers found that when running speedincreased from 2.08 ± 0.13m/s to 8.95 ± 0.70m/s,the relative contribution of the hip joint to averagepower generated by the lower limb during the stancephase increased from 5.5 ± 4.6% to 22.1 ± 5.3%, therelative contribution of the hip joint to average powerabsorbed by the lower limb during the stance phaseincreased from 20.1 ± 5.3% to 46.9 ± 6.7%, and therelative contribution of the hip joint to average powergenerated by the lower limb during the swing phaseincreased from 88.2 ± 2.8% to 92.8 ± 2.6%. Incontrast, the relative contribution of the knee joint toaverage power absorbed by the lower limb during thestance phase decreased dramatically from 50.5 ±12.6% to 16.8 ± 9.0%.

What did the researchers conclude?Faster running is not achieved by simply increasingthe work and power at each joint proportionally but infact involves a shift in the relative contributions ofeach joint. Specifically, the relative contribution of thehip joint increases with increasing running speed inboth the stance and swing phases.

LimitationsThe study was limited in that only steady staterunning was assessed and it is unclear how the lowerlimb joints inter-relate during periods of acceleration.

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Acute response of well-trained sprinters to a 100-mrace – higher sprinting velocity achieved withincreased step rate compared to speed training, byOtsuka, Kawahara, and Isaka, in The Journal ofStrength & Conditioning Research (2015)

BackgroundSprint running is a key athletic quality that iscontested in its own right in track and field, as well asbeing critical for success in many team sports, such assoccer, rugby, and both Australian Rules and AmericanFootball. For a detailed introduction to sprint running,see the earlier study review.

OBJECTIVE: To compare the difference in sprintrunning performance (as measured by split times to50m as recorded using a high-speed camera), stridefrequency, stride length, ground contact time andflight time (all measured using a high-speed camera)between training and competition sprints.

POPULATION: 19 well-trained male and femalesprinters, with ≥6 years of sprint training experience,and an average personal best 100m time of 11.36 ±0.80 seconds.

INTERVENTION: All subjects completed sprints of<100m in both training and competition.

What happened?

Sprint timesThe researchers reported that the sprint velocityachieved in competition was significantly greater thanthe sprint velocity achieved in training (8.26 ± 0.22vs. 8.00 ± 0.70m/s).

Stride frequencyThe researchers reported that the stride frequencyachieved in competition was significantly greater thanthe stride frequency achieved in training (4.56 ± 0.17vs. 4.46 ± 0.13Hz). In addition, the researchersobserved a significant correlation between 50m sprinttime and stride frequency differences (r = 0.570),which suggests that stride frequency explains a largeproportion of the difference in sprint times betweentraining and competition.

Stride lengthThe researchers reported that the stride lengthachieved in competition was not significantly greaterthan the stride length achieved in training (1.81 ±0.09 vs. 1.80 ± 0.09m).

Ground contact and flight timesThe researchers reported that ground contact time incompetition was significantly shorter than in training(0.113 ± 0.008 vs. 0.116 ± 0.008s) but there was nodifference between flight times in competition and intraining (0.103 ± 0.010 vs. 0.107 ± 0.010s).

What did the researchers conclude?The researchers concluded that sprint athletes runfaster in competition than in training and that theincrease in speed appears to be caused by a fasterstride frequency and not by a longer stride length.Why these higher stride frequencies are possible incompetition is unclear but it may relate to elevatedarousal levels.

LimitationsThe study was limited in that the researchers did notalso take measurements of autonomic nervous systemactivity in order to ascertain whether changes inarousal levels could explain the variance betweentraining and competition performances.

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Sprint running research speeds up – A first look at themechanics of elite acceleration, by Clark and Weyand,in Scandinavian Journal of Medicine and Science inSports (2015)

BackgroundOne of the most fierce debates in all of strength andconditioning rages between those coaches andresearchers who believe in the importance of verticalground reaction forces (GRFs) and those who believein the importance of horizontal GRFs for sprint runningspeed. GRFs are usually measured using force plates.The force plate records the force exerted by theground back onto the athlete’s foot as they step ontoit, hence: GRF. In accordance with Newton’s ThirdLaw, this force must be equal and opposite to theforce exerted by the athlete in each direction. Sinceduring running the athlete is moving upward andforward, the GRFs will be both vertical and horizontal.During vertical jumping, on the other hand, horizontalGRF is minimal. In line with basic physical principles, itis generally accepted that both stride length and stridefrequency during running are increased as a result ofgreater GRFs. However, as noted above, there isdisagreement regarding whether it is vertical GRFs orhorizontal GRFs that are more important for increasingrunning speeds. Care is needed here to understandwhat is being said – this debate does not refer toaccelerating to faster running speeds but to constantrunning speeds following a period of acceleration. Inbrief, the researchers who support the view thatvertical GRFs are more important for faster runningspeeds have suggested this is because the verticalGRFs are much larger than the horizontal GRFs. Theynote there is little horizontal resistance to overcome.They suggest that the requirement for horizontalpropulsive GRFs at constant speeds need only besufficient to counteract the braking GRFs. Therefore,they propose that vertical GRFs are more important.Based on this conclusion, they believe that exercisesthat stress the musculature in an axial direction (e.g.squats) are more important than exercises that stressthe musculature in an anteroposterior direction (e.g.hip thrusts). On the other hand, researchers whosupport the opposing view have suggested thathorizontal GRFs are more important than vertical GRFsbecause research clearly shows that the extent towhich horizontal GRFs increase with increasingrunning speed is far greater than the extent to whichvertical GRFs increase. Based on this conclusion, theybelieve that exercises that stress the muscles in ananteroposterior direction are more important thanexercises that stress the musculature in an axialdirection. Until long-term trials are carried out tocompare the effects of exercises in each category,however, it is unlikely that there will be a resolution tothe debate.

OBJECTIVE: To provide an editorial discussing therecent study by Rabita et al. (2015).

STUDY SUMMARY: Rabita et al. (2015) comparedthe differences in direction of force applicationbetween track sprinters of differing abilities (4 elitetrack sprinters with 100m personal best time of 9.95 –10.29 seconds and 5 sub-elite track sprinters withpersonal best time of 10.40 – 10.60 seconds). Allsubjects performed 7 sets of 40m sprints with 5minutes of rest between each, while vertical andhorizontal GRFs were recorded with a 7m-long forceplate. The elite group displayed smaller values thanthe sub-elite group for vertical GRFs relative tobodyweight but greater values than the sub-elitegroup for horizontal GRFs relative to bodyweight.Therefore the ratio of horizontal to vertical GRF wasgreater in the elite than in the sub-elite sprinters(20.3 ± 0.7% vs. 18.3 ± 1.0%). Elite sprinters wereable to produce a greater proportion of the total GRFin the horizontal direction compared to the sub-elitesprinters. Horizontal GRF was strongly correlated withmaximal sprint running speed and performance over40m (r = 0.904 and r = 0.816). The ratio of horizontalto vertical GRF was strongly associated with maximalsprint running speed and performance over 40m (r =0.899 and r = 0.933). Rabita et al. (2015) thereforeconcluded that horizontal GRF is closely linked tosprinting performance but total force is not.

What did the editorial propose?

MethodologyThe researchers note that the recent study by Rabitaet al. (2015) was a substantial step forwards for thestudy of sprint running biomechanics, as it involvedelite track sprinters and also collected data about GRFfrom multiple steps in sequence over a short (40m)sprint. In this way, the study overcomes many of theprevious criticisms in this area.

Constant speed and accelerating sprint runningThe researchers noted that in maximal, constantvelocity sprint running, the vertical GRFs are typicallytwice bodyweight while horizontal GRF is around onethird. They propose that this implies that the mostimportant function of the leg musculature duringmaximal, constant speed sprint running is to provideenough vertical GRF to counteract gravity. How thispoint relates to between-subject differences was notclarified. During accelerating sprinting, the researchersnoted that the largest between-subject differenceswere found at the starting block, where elite sprintersapplied forces relative to bodyweight that were nearly20% greater than the sub-elite sprinters.

LimitationsThe editorial was limited as it did not discuss the mainstudy findings: vertical GRFs are larger than horizontalGRFs (which is because gravity accelerates mass morethan sprinters can accelerate) and differences invertical and total GRF do not explain between-subjectdifferences in maximal sprint running performance orspeed, but differences in horizontal GRF do.

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The effects of eccentric conditioning stimuli onsubsequent counter-movement jump performance, byOng, Lim, Chong, and Tan, in Journal of Strength &Conditioning Research (2015)

BackgroundThe post-activation potentiation (PAP) effect is thewell-known phenomenon in which performance in agiven muscle action is increased when it is carried outafter another muscle act ion, known as theconditioning contraction. Many studies have beenperformed exploring the PAP effect. Above all, a largeamount of inter-individual variability has beenreported, with great differences being observed fromone person to the next in respect of their responses toany given PAP. Additionally, there is some evidencethat trained individuals display greater PAP effectsthan untrained people. The PAP effect is mostnormally studied using heavy resistance exercises butmany studies have found that performance can alsobe enhanced following plyometrics, ballistic exercisesand isometric contractions. Indeed, most early studiestended to use maximum voluntary isometriccontractions (MVICs) in combination with single-jointexercises, most often the dynamic knee extension,because it is easier to standardize more variableswhen using this modality. However, later research hastended to move towards using heavy resistanceexercise protocols, as they appeared most effective. Ingeneral, it has been found that the PAP effect can bemaximized by using multiple sets at moderate relativeloads (60 – 84% of 1RM) with moderate rest periodlengths (7 – 10 minutes), using both isometric anddynamic protocols as conditioning contractions.However, these are only general outlines and specificcircumstances often lead to substantial variation in theoutcomes. Moreover, the exact mechanism by whichthe PAP effect occurs is unclear. Researchers haveproposed various mechanisms by which PAP mightwork. Three such mechanisms that have beenproposed are as follows: (1) increased regulatory lightchain phosphorylation as a result of an elevation inCa2+ release from the sarcoplasmic reticulum, whichincreases the sensitivity of the actin-myosininteraction, altering the structure of the myosin headand resulting in a higher force-generation state of thecross-bridges; (2) increased recruitment of motorunits because of an increased excitation potentialfollowing the previous muscular contractions; and (3)favorable alterations in muscle fiber pennation angle.It seems that most researchers tend to lean towards aneurological explanation, such as enhanced motor unitactivation. Indeed, recent research found no changesin muscle architecture following a PAP protocol.

OBJECTIVE: To assess the PAP effects of two differenteccentric loads (105% of 1RM and 125% of 1RM) onsubsequent counter-movement jump peak power (asmeasured using a force plate) and height (measuredusing a linear transducer).

POPULATION: 14 males, aged 28.5 ± 5.0 years.

INTERVENTION: All subjects performed counter-movement jump trials before and at 3, 6, 9 and 12minutes after 2 sets of conditioning contractions usingan eccentric 45-degree leg press, with loads of either105% of 1RM or 125% of 1RM. Each set of theconditioning contractions comprised 6 repetitions for 5seconds each.

What happened?

Effect of timeThe researchers observed significantly higher counter-movement jump peak power and jump height at the3-minute and 6-minute time points only.

Effect of loadThe researchers observed that there was no differencebetween the 105% and 125% of 1RM loads in respectof their effects on subsequent counter-movementjump peak power or height.

What did the researchers conclude?The researchers concluded that a supra-maximal, low-volume (6 repetitions for 5 seconds) eccentric legpress exercise produced a PAP effect on both peakpower and height during counter-movement jumps at3 and 6 minutes.

LimitationsThe study was limited in that it is unclear whetherdifferent volumes of exercise would lead to differentPAP effects, either in respect of the time course or inrespect of the magnitude of the effect.

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Lunging exercise potentiates a transient improvementin neuromuscular performance in young adults, byHoran, Watson, Lambert, and Weeks, in Journal ofStrength & Conditioning Research (2015)

BackgroundThe post-activation potentiation (PAP) effect is thewell-known phenomenon in which performance in agiven muscle action is increased when it is carried outafter another muscle act ion, known as theconditioning contraction. For a detailed introduction tothe PAP effect, see the previous study review.

OBJECTIVE: To assess whether repeated bouts ofalternating lunges can produce a PAP effect oncounter-movement vertical jump performance, byreference to jump height, peak vertical groundreaction force, impulse, and flight time (all measuredusing a force plate).

POPULATION: 43 healthy adults (24 females and 19males), aged 26 ± 4 years.

INTERVENTION: All subjects performed counter-movement jumps before and 30 seconds after 6 boutsof 20 unweighted, alternating lunges performed at arate of 0.5Hz.

What happened?

Jump heightThe researchers found that alternating lunges causedan increase in jump height after the first 4 bouts butreturned to baseline for the fifth and sixth bouts.

Other variablesThe researchers identified no differences from baselinefor the ground reaction force or impulse recorded aftereach of the bouts of alternating lunges. They identifiedconflicting data with respect to flight time, with somebouts leading to shorter flight times and othersleading to no differences. These data are thereforedifficult to interpret.

What did the researchers conclude?The researchers concluded that sequential bouts ofunweighted, alternating lunges lead to a transientincrease in counter-movement vertical jump height forthe first 4 of 6 trials before performance returned tobaseline. This finding is valuable as it indicates thatheavy loads and complex set-ups are not required toproduce PAP effects. However, these improvementswere not mirrored by a similar change in force-relatedvariables (ground reaction force and impulse), whichmay indicate that movement patterns were affected toa greater extent than force production.

LimitationsThe study was limited as it was not performed in anathletic population and different results may be foundin track and field athletes who are trained at jumpingactivities.

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The effect of the number of sets on power output fordifferent loads, by Morales-Artacho, Padial, García-Ramos, and Feriche, in Journal of Human Kinetics(2015)

Background

IntroductionThe best way to train for maximal power is currentlyunclear. The evidence from long-term trials does notallow us to determine the best methods or trainingvariables to use in order to develop athletes optimally.Few coherent hypotheses have been put forward fortesting and currently the only theory of power trainingthat is considered as having any validity is the optimalload for power model. In this model, it is proposedthat training at the load that maximizes the poweroutput during acute trials is the best way to developpower across all loads in long-term training programs.This is based upon the simple assumption that higherpower outputs produced in training will cause largerlong-term adaptations. It is important to note that thelong-term trials do not provide good support for thistheory, as power can evidently be developed by arange of loads and there is no evidence that using theoptimal load is superior to using any other load.

Load-specificityLoad-specificity makes it very hard to properly test thelong-term effects of training on maximal poweroutput. Long-term trials typically compare the trainingeffects of two different groups (experimental vs.control). An example study might compare anexperimental group training at the optimal load forpower with a control group training at a lower orhigher load. However, it is difficult to assess whichgroup has increased power to a greater extent, as theexperimental group will experience high load-specificity of training at the optimal load for powerwhile the control group will experience high load-specificity of training at the higher or lower load.Often, the same test of power is used for both groups,which is “maximal power at the load that producesmaximal power” which then gives the advantage tothe experimental group. Since sports are played with arange of loads, this is arbitrary.

Differences between internal and external powersThe difference between the external power output andthe individual joint powers (and muscle powers) mayhave important implications for determining theoptimal parameters for training. Some musculoskeletalmodeling studies of lower body movements havereported that while external power output peaks whenexternal force is around 50% of maximum, musclepower output peaks when external force was just 15%of maximum. This implies that if maximizing poweroutput of individual muscles is central to developingthe ability of a muscle to produce power over a long-term training intervention, then optimizing poweroutputs by reference to the system output would notbe the best way to achieve this aim.

OBJECTIVE: To investigate the effect of set numberon mean power output (as measured using a lineartransducer attached to the barbell) for a given loadduring bench presses.

POPULATION: 14 resistance-trained males, aged22.73 ± 3.97 years, who had >3 years of resistancetraining experience.

INTERVENTION: All subjects performed 3 sets of 3bench press repetitions with each of the followingloads: 30, 40 and 50kg. Rest periods of 3 – 5 minuteswere taken between sets.

What happened?

Effect of set numberThe researchers observed an overall increase in meanpower from the first to the third set across all loads.However, the driver of this overall increase appearedto be the increase in power with the 30kg load, whichchanged substantially from 6.01 ± 0.75 to 6.35 ±0.85W/kg.

Effect of loadThe researchers found that mean power was lowerwith 50kg compared to both the 30 and 40kg loadsbut there were no differences between 30 and 40kg.

What did the researchers conclude?The researchers concluded that the number of setsperformed at a given load affects the maximal poweroutput, particularly at lower loads.

LimitationsThe study was limited in that the researchers did notascertain the 1RM for each subjects and did notidentify the optimum load for power as a percentageof 1RM depending on the set number.

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Peak power output in the bench pull is maximizedafter 4 weeks of specific power training, by Jolley,Goodwin, and Cleather, in Journal of Strength &Conditioning Research (2015)

BackgroundThe best way to train for maximal power is currentlyunclear. The evidence from long-term trials does notallow us to determine the best methods or trainingvariables to use in order to develop athletes optimally.For a detailed introduction to the optimal load forpower, see the previous study review.

OBJECTIVE: To compare the effects of training withthe optimal load for power or a lighter load on gains inpeak power output (as measured using a TENDOlinear force transducer) in the bench pull exercise.

POPULATION: 21 male athletes, with >1 year ofresistance training experience, randomly allocated to agroup that trained with their optimal load (OPT) into agroup that trained with a load that was 10% of their1RM below the optimal load (OPT-10),

INTERVENTION: Subjects in both groups completed2 training sessions per week comprising 5 sets of 3repetitions for 4 weeks, after which optimal load forpower was reassessed. Subjects then trained for anadditional 3 weeks with a new load per the setguidelines (i.e. either optimal load for power oroptimal load for power less 10% of 1RM).

What happened? The researchers reported that the overall cohort ofsubjects (across both groups) improved peak poweroutput by 4.6% after 4 weeks of training. However,there was no increase after the second 3-week blockof training. The researchers found that there were nosignificant differences in the improvements in peakpower between the OPT and OPT-10 groups, whichfails to provide support for the optimal load for powerhypothesis.

What did the researchers conclude?The researchers concluded that their study indicatesthat similar gains in peak power can be achieved bytraining with the optimal load for power or loads thatare slightly lighter. They also concluded that gains inpower are realized quickly when training with thesame load and that alterations in load may benecessary in order to continue to improve.

LimitationsThe study was limited in that only two loads weretested and only a short time period was assessed.Different results might be observed if a range of loadswas investigated over a much longer period of time.

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The relationship between clinically measured hiprotational motion and shoulder biomechanics duringthe pitching motion, by Laudner, Wong, Onuki, Lynall,and Meister, in Journal of Science and Medicine inSport (2014)

BackgroundThrowing is a key feature of human behavior andappears to be one of the factors differentiating usfrom other primates. Evidence for hominids takingpart in throwing activities stretches back before theexistence of homo sapiens and these facts suggestthat throwing may have played some role in theevolution of modern humans, potentially through itsbenefit for hunting and the consequent provision offood or in defense against predators. In modern times,throwing is now a key action in many sports, includingAmerican Football, rugby, baseball, basketball andcricket. Athletes who compete in these sports oftendevote considerable effort to being able to throw withgreater force and accuracy. From the layman'sperspective, throwing is an activity that almostexclusively involves the arm and shoulder. However,researchers investigating the biomechanics of suchmovements have uncovered that the act of throwinginvolves the whole body in a sequential kinetic chain.This phenomenon is where joint angular motionsfollow a distinctive proximal-to-distal pattern ofactivity. Movements are initiated by larger, centralbody segments and then proceed outward to thesmaller, more distal segments, such as the arms andhands. Where optimal proximal-to-distal kinematicsequences occur in throwing motions, the pelvis is firstrotated as a result of force produced by the leg andhip muscles. The pelvis therefore initially acceleratesbut then quickly decelerates as it transfers this kineticenergy to the torso. The same pattern is repeatedwith the torso and the arm, and then the arm and thehand, ultimately resulting in the object being thrown.The exact factors that are associated with optimalthrowing ability are unclear but may include theprecise co-ordination of the sequential kinetic chain,the strength of the key muscles involved, the ability tostore elastic energy in the shoulder joint during recoil,and also the maximum and actual ranges of motion(ROM) of each of the joint angles involved.

OBJECTIVE: To investigate the relationships betweenhip rotation range of motion (ROM) of each leg (asmeasured using a digital inclinometer to record peakhip external and internal rotation angles duringstandard clinical tests) and both shoulder externalrotation torque of the throwing arm and maximumshoulder horizontal adduction ROM during pitching (asrecorded by 8 synchronized digital cameras to trackthe positions of reflective markers placed upon thethrowing arm and on the head of each subject).

POPULATION: 34 collegiate baseball pitchers, aged20.0 ± 1.3 years.

What happened?

Shoulder external rotation torqueThe researchers found that total hip rotational ROM ofthe lead leg displayed a significant and moderate-to-strong relationship with shoulder external rotationtorque during the throwing motion (r = 0.56).

Shoulder horizontal adduction ROMThe researchers found that total rotational ROM of thetrail leg displayed a significant, moderate relationshipwith shoulder horizontal adduction ROM (r = 0.43).

What did the researchers conclude?The researchers concluded that that baseball pitcherswho display greater lead leg hip rotation ROM alsodisplay increased shoulder external rotation torqueduring the throwing motion. In addition, they foundthat increased hip rotation ROM of the trail leg wasassociated with increased horizontal adduction ROM ofthe throwing arm during this motion. These findingsindicate that passive ROM at the hip affects themovement patterns and forces acting at the shoulderduring throwing, with greater ROM at the hip beingassociated with greater ROM and greater torque at theshoulder.

LimitationsThe study was limited in that the researchers did notalso report the correlations between these variablesand pitching velocity, so it is unclear how these factorsaffect performance-related variables.

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The role of muscle morphology on jumping, sprintingand throwing performance in participants withdifferent power-training duration experience, byMethenitis, Zaras, Spengos, Stasinaki, Karampatsos,Georgiadis, and Terzis, in Journal of Strength &Conditioning Research (2015)

BackgroundThrowing is a key feature of human behavior andappears to be one of the factors differentiating usfrom other primates. For a detailed introduction tothrowing, see the previous study review.

OBJECTIVE: To investigate the correlations betweenmuscle mass (as measured by dual energy x-rayabsorptiometry [DEXA]), thigh muscle muscle crosssectional area (estimated by using anthropometry andskinfold measurements), muscle architecture (asmeasured by ultrasound), muscle fiber type (asmeasured by biopsies analyzed using histochemistry),and jumping (as measured by both countermovementand squat jump heights and power outputs), sprintrunning (as measured by 10m and 60m outdoor sprinttime using photocells), and throwing (as measured byshot put distance with a 6kg shot) abilities.

POPULATION: 36 young male athletes (track andfield, basketball, volleyball, and Olympic weightlifting)allocated into three groups according to the length oftheir power-related training experience, being low (<1year) (LOW), moderate (1-3 years) (MOD), and high(4-7 years) (HIGH). Power-related training comprisedboth heavy resistance training with upper and lowerbody multi-joint exercises and also plyometrics orballistic resistance training exercises.

What happened? The researchers found that countermovement jumpheight was only significantly correlated with vastuslateralis fascicle length (r = 0.27). They also foundthat squat jump height was significantly correlatedwith lower body lean mass (r = 0.32) and type IIXproportion (r = 0.32). However, these correlationswere weak. In contrast, both squat and counter-movement jump power outputs were found to bestrongly and significantly correlated with both total (r= 0.79; r = 0.60) and lower body (r = 0.81; r = 0.87)lean mass as well as most of the measures of musclearchitecture and thigh cross-sectional area (r = 0.32 –0.52). The researchers found that 10m sprint timewas not significantly correlated with any morphologymeasure but 60m sprint time was significantly butweak-to-moderately correlated with thigh cross-sectional area (r = 0.40), vastus lateralis musclethickness (r = 0.42) and pennation angle (r = 0.32).Finally, shot throwing performances were significantlycorrelated with both total (r = 0.46 – 0.48) and lowerbody lean mass (r = 0.50 – 0.51) and type IIA (r =0.39 – 0.44) and type IIX (r = 0.32 – 0.36) musclefiber proportions. The researchers noted that lowerbody lean mass was the largest contributor forperformance in LOW, while muscle architectureproperties and type II fiber proportion were thelargest contributors in MOD. In HIGH, fascicle lengthand type II muscle fiber proportion were the largestcontributors to performance.

What did the researchers conclude?The researchers concluded that muscle size andquality only partly explain jumping, sprint running andthrowing abilities in power-trained male athletes.

LimitationsThe study was limited as it was cross-sectional andaltering muscle size or quality may or may not affectjumping, sprinting and throwing abilities differently.

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Strength and Conditioning Research

3. ANATOMY, PHYSIOLOGY, AND NUTRITION

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Calorie for calorie, dietary fat restriction results inmore body fat loss than carbohydrate restriction inpeople with obesity, by Hall, Bemis, Brychta, Chen,Courville, Crayner, and Yannai, in Cell Metabolism(2015)

BackgroundObesity and overweight are rapidly rising phenomenaworldwide and are both important contributors tomortality and ill health. Weight loss is the primarytechnique for addressing both of these conditions.Weight loss is essentially achieved by means ofaltering the balance between the amount of caloriesconsumed and expended. At its most basic, therefore,weight loss can be achieved either by reducingcalories consumed, increasing calories expended, or acombination of both. However, there are many ways inwhich calorie intake can be increased and in whichcalorie expenditure can be increased. Calorie intakecan be reduced directly by conscious dietarymodifications or indirectly by bariatric surgery,pharmacology, and even psychological protocols.Conscious dietary modifications can themselves befurther subdivided into either (1) a reduction in foodvolume without changes in macronutrient ratios orfood choices or (2) a change in dietary patterns toalter either macronutrient ratios or food choices.Calorie expenditure can be increased either byphysical activity or by specific exercise protocols. Themajority of individuals in the general populationappear to instinctively identify diet as the primary wayto lose weight although many also include exercise asan adjunct. However, there are widely varyingopinions regarding the optimal ways to lose weightand experts have made recommendations regardingthe optimal macronutrient ratios, food choices,exercise protocols (i.e. aerobic steady state vs.anaerobic intervals vs. resistance training, etc.) andtarget rate of weight loss to achieve over a set periodof time. The extent to which these recommendationshave been supported by long-term trials, however, isunclear. In addition, the extent to which differenttypes of weight loss intervention lead to differentresults in males and females is also currentlyunknown.

OBJECTIVE: To compare the very short-term (6-day)effects of reduced carbohydrate and reduced fatisocaloric diets on body composition changes (asmeasured by cumulative net fat balance as estimatedby indirect calorimetry and as measured directly bydual-energy X-ray absorptiometry [DEXA]) and on fatoxidation (also measured by indirect calorimetry).

POPULATION: 19 obese adults (10 males and 9females) with a body mass index (BMI) of 35.9 ± 1.1kg/m2, aged 35.4 ± 1.74 years, randomly allocated toeither a reduced fat or a reduced carbohydrate group.

INTERVENTION: Prior to commencing the 6-dayintervention, all subjects were fed an energy-balanceddiet comprising 50% carbohydrate, 35% fat, 15%protein) for a 5-day period. After this period, allsubjects received a calorically restricted diet by 30%of total calories. The reduced carbohydrate groupdecreased carbohydrates by 60% and the reduced fatgroup decreased fat by 85%. All subjects performed60 minutes of treadmill walking at a fixed but self-selected pace and incline. The whole experimentalperiod took place in a metabolic ward.

What happened?

Body compositionUsing indirect calorimetry, the researchers found thatthe reduced fat diet resulted in 463 ± 37g of lost bodyfat while the reduced carbohydrate diet resulted in245 ± 21g of lost body fat. The difference betweengroups was significant. The DEXA measurement wasnot sufficiently sensitive to detect the changes.

Fat oxidationThe researchers found that the reduced carbohydrategroup displayed increased net fat oxidation by 463 ±63 kcal/day and decreased net carbohydrate oxidationby 595 ± 57 kcal/day by the end of the intervention.There was no similar change in the reduced fat group.

What did the researchers conclude?The researchers concluded that a tightly-controlled butvery short-term period of caloric restriction showedthat reduced fat diets lead to greater weight loss thanreduced carbohydrate diets. However, only reducedcarbohydrate diets lead to increased fat oxidation.

LimitationsThe study was limited in several key ways. Firstly, thetype of macronutrient and the total calories consumedwere both completely controlled. This approacheliminated any mechanism by which macronutrientproportion might affect caloric intake by means ofchanges in appetite. Secondly, it was limited in thatthe trial only lasted for 6 days and since it is relativelycommonly-accepted that reduced carbohydrate dietsrequire an adaptation phase of around 2 weeks, thismay have affected the results. Thirdly, the method formeasuring body composition used as the primaryoutcome measure (indirect calorimetry) was not adirect measure of body fat but is a proxy. For furtherreading on this topic, see Rosado et al. (2013).

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Fat-free mass changes during ketogenic diets and thepotential role of resistance training, by Tinsley andWilloughby, in International Journal of Sport Nutritionand Exercise Metabolism (2015)

BackgroundWeight loss is essentially achieved by means ofaltering the balance between the amount of caloriesconsumed and expended. At its most basic, therefore,weight loss can be achieved either by reducingcalories consumed, increasing calories expended, or acombination of both. For a detailed introduction toweight loss, see the previous study review.

OBJECTIVE: To carry out a systematic review in orderto examine the relationship between ketogenic dietsand body composition changes, particularly lean bodymass.

STUDY SELECTION: Studies were included that useddiets that contained ≤50g of carbohydrate per day (or≤10% of total daily energy from carbohydrates), thatmeasured lean body mass before and after a long-term intervention that lasted ≥4 weeks and whichincluded ≥8 adult subjects in each group. Only studiesthat were published in the last 15 years were included.

What happened?

Study selectionThe researchers identified a total of 13 studies thatmet the inclusion criteria. Of these 13 studies, 10 useddual-energy X-ray absorptiometry (DEXA) to measurelean body mass, 2 used bio-electrical impedance, and1 used skinfolds and anthropometry to estimate bodycomposition. Many but not all of the studies imposedcaloric restriction and where this was performed, thelevel was around 25 – 30% of total calories. Eleven ofthe 13 studies were performed in overweight or obeseindividuals, 1 study was performed in normal weightmales and 1 study was performed in male athletes.

Effects of ketogenic diets on body compositionThe researchers reported that the majority of the 13included studies reported weight loss of between 5 –13kg and fat mass loss of 3.5 – 11kg. Lean massgains were reported in 1 study of 1.1kg while theremaining trials reported lean mass losses of between1 – 3.5kg. In general, although a formal meta-analysiswas not performed, the researchers suggested thatthe percentage of lean mass lost is similar during aketogenic diet (or perhaps higher) than a diet with ahigher proportion of carbohydrates.

Effects of resistance training during ketogenic dietsThe researchers only identified 2 studies that includedresistance training interventions in conjunction withketogenic diets. These studies produced conflictingresults with 1 study demonstrating that while carryingout resistance training, a ketogenic diet led to no lossin lean body mass. The other study reported somelosses in lean body mass but these were similar tothose reported in a higher carbohydrate diet.

What did the researchers conclude?The researchers concluded that reductions in leanbody mass appear to occur following adherence to aketogenic diet that may be similar or perhaps greaterthan those occurring when following a diet that ishigher in carbohydrates. However, the impact ofresistance training on this comparison remains unclearas this typically helps retain lean mass during dieting.

LimitationsThe review was limited in that there was very littleavailable literature exploring the interactions betweenthe diets and the impact of resistance training.

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Myostatin as a mediator of sarcopenia versushomeostatic regulator of muscle mass – insights usinga new mass spectrometry-based assay, by Bergen,Farr, Vanderboom, Atkinson, White, Singh, andLeBrasseur, in Skeletal Muscle (2015)

BackgroundMyostatin, also known as growth and differentiationfactor 8 (GDF-8), is a chalone protein that regulatesmuscle mass, affecting both the proliferation anddifferentiation of myoblasts. Chalone proteins arehormones that are secreted by organs and that inhibitthe growth of those organs by temporarily preventingcellular mitosis. Myostatin causes hypertrophy whenits expression is reduced and atrophy when itsexpression is increased. There are some earlyindications that natural levels of myostatin expressionmay be related to the phenomenon of sarcopenia, theage-related loss of muscle mass, or cachexia, thedisease-related loss of muscle mass. Case-controlstudies comparing normal and atrophied muscles havefound elevated levels of myostatin where muscle losshas occurred either as a result of age, disuse ordisease but whether such muscle loss is mediated bythe change in myostatin levels or causes the reductionin myostatin levels is unclear. When mutations leadingto failure of myostatin genes occur, this can cause amassively muscled physique in mammals even at avery young age. This unusual phenomenon has beenobserved in a range of different species, includingdogs, cows and even humans. Interestingly, thisphenotype also appears to cause a reduction inadipose tissue but whether this decrease occursdirectly as a result of the action of myostatin orindirectly as a result of the increased muscle mass isunclear. Intriguingly, there are indications from mousemodels that increasing muscle mass by blockingmyostatin from inhibiting hypertrophy may impairmuscular function by reducing specific force, or theforce production per unit cross-sectional area. Thus,where therapeutic myostatin inhibitors are developed,this may not actually improve functional outcomes.The reduction of specific force production whileincreasing muscle mass when manipulating myostatinhas been ascribed to the failure to maintain a constantmyonuclear domain. In myostatin-deficient mousemodels, researchers have reported that the size ofindividual myonuclear domains in the hypertrophiedmuscle fibers of the myostatin-deficient mice issignificantly correlated with the specific force. Thissuggests that myostatin deficiency alone increases thesize of the myofiber without concomitantly increasingthe number of myonuclei and that it is able to increasethe myonuclear domain past the point where it canfunction efficiently. Interestingly, although myostatinwas once believed to interact with satellite cells, thisnow does not appear to be the case. Rather, myostatinappears to act directly on the muscle fiber to producehypertrophy. This failure to activate satellite cells whilestill producing marked hypertrophy may be whymyostatin inhibition fails to maintain a constantmyonuclear domain and thereby also specific force.

OBJECTIVE: To compare concentrations of myostatinand two of its key inhibitors, follistatin-related gene(FLRG) protein and growth and serum protein-1(GASP-1) between young, old, and sarcopenic malesand females, using a novel measurement methodinvolving liquid chromatography with tandem massspectrometry.

POPULATION: 40 younger females, aged 32.3 ± 5.5years; 40 older females, aged 76.0 ± 8.6 years; and40 sarcopenic females, aged 78.4 ± 8.2 years; 40younger males, aged 33.0 ± 3.8 years; 40 oldermales, aged 74.8 ± 7.3 years; and 40 sarcopenicmales, aged 78.9 ± 6.8 years.

What happened?

Circulating myostatin in femalesThe researchers reported that the older females hadsignificantly higher total circulating myostatin levelsthan younger females whereas sarcopenic females hadcomparable levels. However, controlling for total leanbody mass, both older females and sarcopenic olderwomen had 40% and 23% higher total myostatinlevels than younger females, respectively

Circulating myostatin in malesThe researchers reported that younger males hadsignificantly higher total circulating myostatin levelsthan older males and males with sarcopenia. Thisdifference was maintained when controlling for leanbody mass, as younger males displayed >25% highertotal myostatin levels than older males and males withsarcopenia.

Circulating myostatin inhibitorsIn both males and females, the researchers found thatthe sarcopenic older subjects displayed the highestlevels of FLRG. Similar findings were reported inrespect of GASP-1 although these differences onlyreached significance in females.

What did the researchers conclude?The researchers concluded that older females appearto display higher circulating myostatin levels thanyounger females, while the reverse is the case formales. The reasons underlying this discrepancy arecurrently unclear.

LimitationsThe study was limited in that it was a cross-sectionalanalysis and it is unclear whether altering musclemass levels in the younger or older males or femaleswould alter the myostatin levels observed.

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Myostatin dysfunction is associated with reduction inoverload induced hypertrophy of soleus muscle inmice, by Minderis, Kilikevicius, Baltusnikas, Alhindi,Venckunas, Bunger, and Ratkevicius, in ScandinavianJournal of Medicine & Science in Sports (2015)

BackgroundMyostatin, also known as growth and differentiationfactor 8 (GDF-8), is a chalone protein that regulatesmuscle mass, affecting both the proliferation anddifferentiation of myoblasts. For a more detailedintroduction to myostatin, see the previous studyreview.

OBJECTIVE: To investigate if myostatin dysfunctionleads to increases in both muscle mass (as measuredby weight) and muscle strength (as measured by peakisometric force and specific tension of muscle fiberstaken from the soleus muscle) of mice after functionaloverloading caused by ablation of the gastrocnemiusmuscle.

POPULATION: 15 male Berlin high (BEH) mice withmyostatin dysfunction and 17 wild-type (WILD) micewithout myostatin dysfunction.

INTERVENTION: Both the BEH and WILD mice weresubjected to functional overloading of the soleusmuscle by ablation of the gastrocnemius muscle for 28days at the age of 14 weeks.

What happened?

Effects on muscle massThe researchers reported that the soleus muscle ofWILD mice was heavier than that of the BEH micefollowing the functional overloading intervention (13.5± 1.5 vs. 21.4 ± 1.8mg). This difference in musclemass change between WILD and BEH was significant(34.9 ± 11.5 vs. 17.7 ± 11.9%).

Effects on muscle strengthThe researchers reported that peak isometric forcereduced in BEH but remained similar in WILD followingthe intervention. Consequently. specific tension alsoreduced in BEH and this was significant compared toWILD (8.4 ± 1.4 vs. 10.8 ± 1.3N/g).

What did the researchers conclude?The researchers concluded that BEH mice showedsmaller gains in muscle mass compared with WILDmice and also displayed a reduction in both peakisometric force and specific tension after functionaloverloading of the soleus muscle by ablation of thegastrocnemius muscle. They suggested that thisimplies that myostatin dysfunction may impair muscleadaptations, at least in certain muscles in a mousemodel.

LimitationsThe study was limited in that it was performed in miceand different results might be observed in othermammals, including humans.

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Early resistance training-induced increases in musclecross-sectional area are concomitant with edema-induced muscle swelling, by Damas, Phillips,Lixandrão, Vechin, Libardi, Roschel, and Ugrinowitsch,in European Journal of Applied Physiology (2015)

BackgroundMuscle hypertrophy occurs in response to resistance-training (and consumption of protein post-workout). Itis thought that this process occurs by way of analteration in the balance between muscle proteinsynthesis and muscle protein breakdown over asustained period of time. In support of this, previousstudies have found that muscle protein synthesis iselevated post-workout. It is thought that suchincreases are important contributors to long-termgains in muscle mass, although investigations havefound no association between acute increases in levelsof muscle protein synthesis and hypertrophy over along-term period. Nevertheless, assuming that there isa connection between elevations in muscle proteinsynthesis post-workout, the activity in variousmolecular signaling pathways has been suggested toexplain how the acute rise in muscle protein synthesismight be triggered by a resistance-training workout.Indeed, it is well-known that the primary regulator ofmuscle protein synthesis is the mammalian-target ofrapamycin (mTOR) pathway. mTOR phosphorylates itstargets, the downstream effectors 4E binding protein 1(4EBP1) and the 70-kDa ribosomal protein S6 kinase(p70S6K). Importantly, unlike muscle proteinsynthesis itself, the phosphorylation of these two keyeffectors in human muscle is significantly associatedwith long-term gains in muscle mass duringresistance-training. The mitogen-activated proteinkinase (MAPK) pathway may be another, differentsignaling pathway that may also have an importantrole in regulating muscle protein synthesis. Thereappears to be cross-talk between these pathways,however, with components of the MAPK pathway beingable to phosphorylate signaling proteins bothupstream and downstream of mTOR itself.

OBJECTIVE: To identify whether early increases invastus lateralis cross-sectional area (measured usingultrasound) during long-term resistance training wereassociated with muscle swelling (as measured usingB-mode ultrasound echo intensity).

POPULATION: 10 untrained males, aged 27 ± 3years.

INTERVENTION: All subjects performed 3 sets of 45-degree leg press followed by 3 sets of knee extensionsfor 9 – 12 repetitions to muscular failure, with 90seconds inter-set rest, 2 times per week for 10 weeksof resistance training. Each subject consumed 25g ofisolated whey protein immediately after each trainingsession.

What happened?

Muscle size gainsThe researchers reported that vastus lateralis cross-sectional area increased significantly after 2 weeks ofresistance training (by around 2.7%) and after 10weeks of resistance training (by around 10.4%)compared to baseline.

Muscle swelling changesThe researchers reported that vastus lateralis echointensity also increased significantly after 2 weeks ofresistance training (by around 17.2%) and after 10weeks of resistance training (by around 13.7%). Whenvastus lateralis echo intensity was normalized to therespective vastus lateralis cross-sectional area as amarker of cell swelling, the researchers found that itwas greater after 2 weeks compared to either baselineand also to the post-intervention measure after 10weeks.

What did the researchers conclude?The researchers concluded that a marker of cellswelling increased after 2 weeks of resistance trainingand potentially contributed to apparent increases inmuscle size.

LimitationsThe study was limited in that it remains unclear howmuch of the increase in muscle size following the earlyphases of resistance training can be attributed tochanges in muscle size and how much must beattributed to cellular swelling.

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The metabolic and temporal basis of musclehypertrophy in response to resistance exercise, byBrook, Wilkinson, Smith, and Atherton, in EuropeanJournal of Sport Science (2015)

BackgroundMuscle hypertrophy occurs in response to resistance-training (and consumption of protein post-workout). Itis thought that this process occurs by way of analteration in the balance between muscle proteinsynthesis (MPS) and muscle protein breakdown (MPB)over a sustained period of time. It is thought that thelarge acute changes that occur in MPS following eitherresistance training or feeding (particularly of protein)are primarily responsible for the long-term changes inmuscle hypertrophy over time, while MPB is thought toplay a much smaller role. For a detailed introduction tomuscle hypertrophy, see the previous study review.

OBJECTIVE: To provide a narrative review of themeasurement methods for MPS (in acute studies) andmuscle hypertrophy (in long-term studies).

What happened?

MPS rates and responses to food consumptionThe researchers explain that at rest and in isolationfrom the influence of either resistance training or food,MPS rates are around 0.03 – 0.07% per hour. Thisrate increases to around 0.06 – 0.1% for around 2 – 3hours following the consumption of food containingessential amino acids (AAs), particularly leucine. Theyexplain that maximal MPS stimulation occurs with just20g of suitable protein and that further consumptiondoes not increase MPS to a greater degree.

MPS measurementThe researchers explain that the main methods usedto measure MPS comprise isotopically-labelled tracertechniques in which a labelled AA is introduced intothe system and later muscle biopsies are taken toidentify the rate at which the AA is incorporated. Theprocess of labeling involves replacing one of theelements within the AA (e.g. carbon, hydrogen ornitrogen) with a heavier isotope (e.g. 13C for 12C).The presence of the heavier isotope can then beidentified using mass spectrometry. By first takingmeasurements without food or resistance traininginterventions, a baseline can be established and thenchanges against this baseline can be observed. One ofthe main limitations of this approach is that it can onlyascertain acute changes. The researchers note that amore recent trend has been towards the developmentof methods using deuterium (heavy water), which canbe provided over longer term periods and allow theassessment of long-term MPS and its association withmuscle hypertrophy.

Hypertrophy measurementThe researchers explain that when measuring single,whole muscles, magnetic resonance imaging (MRI)and computed tomography (CT) scans are the goldstandard. However, these methods are costly andprovide radiation exposure, which is undesirable.While dual-energy X-ray absorptiometry (DEXA) ismuch lower cost and causes less radiation exposure, itmay overestimate muscle mass. Many new studies aremaking use of ultrasound, as this method is cheap andrelative non-invasive and can allow the measurementof additional muscle architectural variables, such aspennation angle and fascicle length.

What did the researchers conclude?The researchers concluded that the measurementmethods for both acute MPS and long-term musclehypertrophy are difficult and complex and requiresubstantial investment. Meanwhile, the process bywhich MPS contributes to muscle hypertrophy remainsunclear.

LimitationsThe study was limited as it was a narrative review.

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Influence of combined resistance training and healthydiet on muscle mass in healthy elderly women: arandomized controlled trial, by Strandberg, Edholm,Ponsot, Wåhlin-Larsson, Hellmén, Nilsson, and Kadi,in Journal of Applied Physiology (2015)

BackgroundThe global consumer market for dietary supplementsin 2011 was estimated at ~$30 billion. Proteinsupplements are among the most popular itemspurchased. Protein supplements are available in bothliquid and solid forms, although the liquid form is themost common. Additionally, while various types ofprotein are available, whey is the most commonlyused in commercially-available supplement formulas.Protein supplements are primarily intended to increasemuscular strength and size when consumed incombination with periods of resistance-training,largely by increasing total daily protein intake.Research indicates that consuming a proteinsupplement may increase total protein intake butother dietary factors may be modifying factors,including whether individuals are engaged in caloricrestriction or not. Nevertheless, a substantial body ofacute research has found that dietary proteinconsumption immediately post-resistance-trainingexercise leads to an increase in muscle proteinsynthesis and a reduction in muscle proteinbreakdown. Increases or decreases in muscular size(hypertrophy or atrophy) are thought to occur througha sustained imbalance between muscle proteinsynthesis and muscle protein breakdown. Sinceincreases in muscle protein synthesis are believed tobe important contributors to long-term gains in musclemass, this is often taken as evidence that proteinsupplementation can be used to enhance gains inmuscular strength and size. However, not all long-term trials have supported this claim and we shouldbe cautious about drawing strong inferences abouthypertrophy from the behavior of muscle proteinsynthesis and the balance between muscle proteinsynthesis and muscle protein breakdown in acutetrials, as some studies have found no correlationbetween these acute responses and long-term gains inmuscle mass. It is fortunate that meta-analyses oftrials of resistance-training programs of >6 weekshave reported that protein supplementation does leadto superior gains in strength and size in both youngand old adult subjects. Protein supplementation maybe provided from several different sources and someresearchers have suggested that the use of eitherwhey, casein or essential amino acids may lead todifferent effects, most likely by altering the rate ofmuscle protein synthesis or muscle protein breakdownpost-exercise. Indeed, essential amino acids such asthe branched-chain amino acids (BCAA) can increasemuscle protein synthesis and reduce muscle proteinbreakdown. Additionally, the essential amino acidleucine could be an important modulator insofar as itseems to lead to an increase in the activity ofimportant signaling proteins.

OBJECTIVE: To compare the effects of 24 weeksresistance training, with resistance training plus ahealthy diet on muscle strength (measured by 1RM inexercises used plus maximum voluntary isometriccontraction (MVIC) knee extension force), muscle size(measured by dual X-ray absorptiometry [DEXA]) andinflammatory markers (measured by blood samples ofC-reactive protein and IL-6).

POPULATION: 203 healthy and physically activeelderly females, randomly allocated to a control group(CON, aged 68 ± 1 years), a resistance-training group(RESIST, aged 68 ± 2 years), and a resistance-training plus healthy diet group (RESIST-DIET, aged67 ± 1 years).

INTERVENTION: Subjects in the RESIST and in theRESIST-DIET groups performed supervised resistancetraining, 2 times per week for 24 weeks, comprising 3sets per exercise with 75 – 85% of 1RM for 8 – 12reps per set) using the squat, leg-extension, leg-press, seated row and lat pull-down exercises. TheRESIST-DIET group also consumed a diet in line withthe following guidelines: carbohydrate energy intake =44% of total calories, protein energy intake = 20% oftotal calories, fat intake = 36% of total calories, fiber>25g per day, unsaturated fat ≥2/3 of total fat, and n-6-to-n-3 ratio <2.

What happened?

Muscular strength and sizeThe researchers observed that 1RM knee extensionsignificantly increased in RESIST (+20.4%) andRESIST-DIET (+20.8%) but not in CON. Leg lean masssignificantly increased only in RESIST-DIET (+1.8%).

Effects of dietThe researchers observed that the n-6-to-n-3 ratiodietary intake significantly decreased only in RESIST-DIET by 42% (from 3.1 ± 1.3 to 1.8 ± 0.6 times),which was as planned. This was supported by asignificant increase in n-3 DHA serum levels (+ 8.3 %)in RESIST-DIET also.

Inflammatory markersThe researchers found no changes in serum C-reactiveprotein or in IL-6 levels in any of the groups. However,they did note a significant decrease in serum levels ofarachidonic acid (-5.3 ± 9.4%) in RESIST-DIET, whichis thought to be a pro-inflammatory precursor.

What did the researchers conclude?The researchers concluded that a supervised programof whole body resistance training leads to increasedmuscle strength in healthy, recreationally activeelderly females. They also concluded that gains inmuscle mass occurred only when resistance trainingwas accompanied with a healthy diet.

LimitationsThe study was limited in that the diets were preparedby the subjects following guidance from a nutritionistand full compliance may not have occurred.

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Nutritional interventions to augment resistancetraining-induced skeletal muscle hypertrophy, byMorton, McGlory, and Phillips, in Frontiers inPhysiology (2015)

BackgroundProtein supplements are primarily intended to increasemuscular strength and size when consumed incombination with periods of resistance-training,largely by increasing total daily protein intake. For adetailed introduction to protein supplementation, seethe previous study review.

OBJECTIVE: To review the effects of protein dosage,timing, quality and co-ingestion with carbohydrates onacute muscle protein synthesis (MPS) rates.

What happened?

Protein dosageThe researchers note that just 20g of protein seems tobe almost identically effective at elevating MPS as 40gof protein in both untrained and trained individuals.The researchers explain that protein additional to thisamount is oxidized more quickly and turned into urea.

Protein timingThe researchers explain that there are indications thatto support the use of a moderately frequent timingpattern of whey protein ingestion in which 20g ofprotein is consumed 4 times over a 12-hour period,with each dose consumed every 3 hours. This hasbeen found to elevate MPS more than a less frequenttiming pattern (40g of protein consumed 2 times,every 6 hours) or a highly frequency (10g of proteinconsumed 8 times, every 1.5 hours). They note that itis remarkable that the ideal dosage of 20g fits withthe amount of protein that can be processed at onetime (see dosage section above).

Protein qualityThe researchers explain that three types of protein areconsumed regularly by individuals undergoing regularresistance training soy, casein, and whey. They notethat whey and soy are digested more rapidly thancasein and this leads to a shorter but larger rise inMPS. But the reduction in muscle protein breakdown(MPB) seems to be greater with casein. Finally, theynote that the size of the rise in MPS is greater withwhey than with soy. They suggest that this may bebecause of differences in leucine levels, as when soy,whey and casein blends are matched for leucinelevels, there are no differences in the resulting MPS.

Co-ingestion with carbohydrates (CHO)It has been suggested that raising insulin levels mayenhance increases in MPS when consumed togetherwith protein, as infusing insulin at rest in isolationdoes increase MPS. Indeed, the researchers note thatwhen combined with amino acids, infusion of insulindoes elevate MPS above levels observed followingadministration of amino acids alone and also reducesMPB. When considering consumption of CHO (ratherthan administration of insulin), the researchers notethat, when consumed in isolation, CHO does not affectMPS but does reduce the negative effects on MPB.When consumed together with amino acids, CHOsimilarly does not have any additive effect on MPS andalso fails to have any additional benefit on MPB, solong as protein is sufficient (>25g).

What did the researchers conclude?The researchers conclude that MPS is affected byprotein dosage, timing, and quality but is not affectedby whether it is co-ingested with CHO.

LimitationsThis study was limited as it was a narrative review.

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Caffeine and diuresis during rest and exercise: ameta-analysis, by Zhang, Coca, Casa, Antonio, Green,and Bishop, in Journal of Science and Medicine inSport (2014)

BackgroundCaffeine has been widely studied by researchers as anergogenic supplement in endurance sports. However,while it is also very popular among strength andpower athletes, less work has been done in that area.Caffeine is essentially a central nervous systemstimulant with a historic legacy of being consumed bya large majority of the Western population. Thus, itremains entirely unregulated. Caffeine is most oftenconsumed in coffee, tea, cola, or in infusions such asyerba maté. As a stimulant, it reduces drowsiness andincreases alertness. In high doses (e.g. >10g) caffeineis toxic, but in lower quantities, it appears to haveeffects that are both variable on an individual leveland that are dose-responsive. The exact mechanismsby which caffeine might exert its effects are likelymultifactorial. There is evidence both for effects on thecentral nervous system and also at the peripheral levelthrough alterations to the excitation-contractioncoupling of skeletal muscle. Reviewers have generallyconcluded that the central effects of caffeine are mostlikely related to adjustments occurring in the effortperception threshold, while peripheral effects onexcitation-contraction coupling probably involve thepotentiation of calcium release from the ryanodinereceptor. Prior to 2004, caffeine was classified as acontrolled substance according to the World Anti-Doping Association (WADA) regulations. In 2004, itwas removed from the list. When controlled, the limitfor caffeine was <12ug/ml of urine, which the ACSMsuggests would be equivalent to consuming 5-6 cupsof filter coffee. Studies performed since that date havefound that while most athletes (around 75%) nowconsume caffeine, very few (0.6%) typically exceedthe limit that was in place pre-2004. Caffeine is widelyutilized by strength and power athletes and theresearch generally supports this use. Indeed, itappears that maximal strength, repetition strength,and isokinetic strength in resistance-training might allbe improved by caffeine supplementation to somedegree, depending on dosage. More importantly,however, there are stronger indications that bar speedand/or power output during isoinertial resistance-training are enhanced by the use of caffeine.Additionally, it seems that supplemental caffeine ismost effective in improving performance in themorning and that larger doses are required for heavierloads (or slower speeds).

OBJECTIVE: To perform a meta-analysis assessingthe effects of caffeine on diuresis in adults during restand exercise, using the standardized mean differenceas an effect size.

STUDY SELECTION: Studies were selected involvinghealthy adults irrespective of their level of physicalactivity, that used changes in urine volume as theprimary outcome to assess diuresis following caffeineingestion from any source, including pills, tea, coffee,and caffeinated soft beverages.

What happened?

Study selectionThe researchers found a total of 16 studies including28 trials, including 379 predominantly young subjects(246 males and 133 females) and using a mediancaffeine dosage of 300mg, which is comparable to thelevels normally used for enhancing performance.PEDro quality scores ranged between 7 and 11, whichis relatively high. However, inter-study variability(heterogeneity) of the studies included within themeta-analysis was high (I-squared = 50%) but meta-regression did not identify any predictive effect ofeither caffeine dosage or the duration of the periodover which diuresis was measured. Other factors musttherefore be responsible for the differences in effectsobserved between studies.

Effects of caffeine on diuresisThe researchers found a wide range of results, in linewith the high degree of heterogeneity. Of the 28 trials,6 effect sizes were negative, 4 were trivial, 10 weresmall (0.2 – 0.49), 3 were moderate (0.50 – 0.79),and 5 were large (≥0.80). The basic meta-analysisdemonstrated a small but significant overall effect sizefor the effect of caffeine on diuresis (0.29, whichcorresponded to an increase in urine volume of 109 ±195mL or 16.0 ± 19.2% compared to no caffeine).Following sub-group analysis, it was clear that theeffects were greater when at rest (0.54) than whenexercising (0.10).

What did the researchers conclude?The researchers concluded that although caffeine doesinduce diuresis, the mean effect size is small (0.29)and is greatly minimized during exercise (0.10).However, they also noted that neither the caffeinedosage nor the measurement duration affected theextent of the diuresis.

LimitationsThe meta-analysis was limited in that it only measureddiuresis and did not assess the physiological impact ofthe diuresis on healthy individuals, either at rest orduring exercise.

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4. PHYSICAL THERAPY AND REHABILITATION

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A step towards understanding the mechanisms ofrunning-related injuries, by Malisoux, Nielsen,Urhausen, and Theisen, in Journal of Science andMedicine in Sport (2015)

BackgroundAll physical activity involves a certain risk of injury,whether acute (traumatic) or chronic (overuse). Forelite amateur and professional athletes, these risksare accepted in return for the ultimate reward thatcomes from successful participation at the highestlevels. On the other hand, for non-elite amateurathletes and individuals who make use of participativesport for the purposes of exercise, injury risk (as wellas enjoyment) should be an important factor indeciding which type of sport to take part in. Some ofthe most popular amateur exercise pastimes are long-distance running, cycling and triathlon. However, theinjury risk associated with long-distance running ishigh. Injury risk in sports is typically assessed byreference to prevalence, incidence or rate. Injury ratesprovide the best metric for understanding injury risk,as they correct for the number of hours typically spentin performing the activity. Injury rates in long-distancerunning reported in the literature range from 2.5 –12.1 injuries per 1,000 hours training. Injury rates intriathlon are typically around half as high, from 1.4 –5.5 injuries per 1,000 hours training, which may implythat not focusing solely on one activity is less injuriousfrom an overuse perspective, or it may imply thatswimming and cycling are fundamentally lessdamaging than running. The injury incidence in longdistance running is also very high, with between 27 –79% of recreational and competitive runnerssustaining overuse injuries over the course of a singleyear. Injury during long-distance running is thought toarise from repetitive stress, which causes cumulativem i c ro - t rauma , l e ad i ng t o ove ru se i n j u ry.Consequently, a great deal of time and effort has beendevoted to finding different strategies that mightreduce loading and prevent overload. Proposals forhelpful strategies include: varying the type of loadingby performing a greater amount of cross-trainingrather than running, switching from rear-foot to mid-foot or forefoot striking patterns in order to reduce theground impact forces, varying shoe types in order toalter the loading patterns, and strengthening lowerbody muscles in order to improve their ability toperform a shock-absorbing role during ground contact.

OBJECTIVE: To investigate the influence of runningtime (in hours per week) and frequency (number ofsessions per week) on the incidence of running injuryin recreational runners. The definition of runninginjury was taken as “any physical pain located at thelower limbs or lower back region, sustained during oras a result of running practice and impeding plannedrunning activity for >1 day”.

POPULATION: 517 recreational runners (running >1time per week), aged 42.2 ± 9.9 years.

What happened?

Running time, frequency, distance and speedThe researchers found that their subjects ran for anaverage of 2.1 ± 1.1 sessions per week for a totalrunning time of 2.3 ± 1.6 hours per week. The meanrunning distance was 22.1 ± 16.2 km per week andthe average running speed was 9.6 ± 1.6km/h.

Running injury rateThe researchers found that 167 of the 517 subjects(32.3%) sustained a running injury during the periodin review. Using the running time data provided, thiscorresponded to 6.7 injuries per 1,000 hours ofrunning. Of these injuries, 32.9% were recurrent andthe remainder were novel. Unsurprisingly, the mostcommon injury locations were the lower leg (22.7%),knee (22.2%) and thigh (20.9%).

Factors influencing injury risk Counterintuitively, the researchers found that weeklytime <2h was associated with a 3.3 times greater riskof running injury than >2h and that <2 sessions perweek was associated with a 2.4 times greater risk ofrunning injury than >2 times per week.

What did the researchers conclude?The researchers concluded that the exact relationshipsbetween weekly running time and running injury andbetween session frequency and running injury arevery unclear. The data in the current study suggestthe presence of counterintuitive relationships, suchthat fewer running sessions and short running timesare associated with greater risk of injury. Such resultsmay be a feature of experience and/or trainingconsistency.

LimitationsThe study was limited in that there was no measure ofrunning consistency assessed in the model.

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Scapula kinematics of pull-up techniques: avoidingimpingement risk with training changes, by Prinoldand Bull, in Journal of Science and Medicine in Sport(2015)

BackgroundShoulder impingement syndrome (SIS) is oftendiagnosed by clinicians when an individual presentswith pain (which is usually worse when the arm ispositioned overhead), shoulder weakness, and a lossof shoulder range of motion (ROM). Sometimes,individuals also complain of popping sensations duringsome shoulder movements. SIS is also referred to assubacromial impingement syndrome, and eitherswimmer's or thrower's shoulder. The underlyingcause of shoulder impingement is believed to becompression of the rotator cuff tendons inside thesubacromial space, which is the area beneath theacromion of the scapula. Researchers and cliniciansgenerally differentiate between two types of SIS:primary and secondary. It is thought that primary SISis caused by compression of the rotator cuff tendonsbetween the humeral head and the overlying anteriorthird of the acromion, coracoacromial ligament,coracoid or acromioclavicular joint, most likelyfollowing on from degenerative changes and spurringin the joint area. On the other hand, it has beensuggested that secondary SIS can also lead to similarcompressive symptoms following underlying instabilityof the glenohumeral joint or following scapulardysfunction. Instability of the glenohumeral jointmight feasibly arise where the shoulder is placedunder excessive strain from powerful or repetitiveoverhead movements, such as are performed byswimmers and throwers, which might then lead toincreased humeral head translation within the jointand consequently an impinged biceps tendon androtator cuff. Scapular dysfunction has been linked to anumber of different shoulder disorders, and maycause secondary SIS by increasing the contactbetween the greater tuberosity and posterior-superiorglenoid and thereby impinging the posterior rotatorcuff tendons and labrum. Some researchers who haveperformed long-term trials of rehabilitation for SIShave provided details of their intervention programs.Others have made recommendations for exercisesbased on the results of acute investigations of muscleactivity in individuals with and without SIS. Commonexercise guidance for the treatment of SIS includesstrengthening of the middle trapezius, lower trapezius,serratus anterior and rotator cuff and stretches for theupper trapezius and pectoralis minor, levator scapulae,latissimus dorsi and rhomboids. However, the exactexercise program that is optimal for SIS rehabilitationremains unclear.

OBJECTIVE: To compare scapular kinematics (using aScapular Tracker and a 9 camera motion analysissystem tracking the position of 21 retro-reflectivemarkers placed upon the upper body) and externalforces (using a force plate upon which the pull upframe was positioned) during three different pull-uptechniques (pronated grip, supinated grip, pronatedwide grip) performed for three repetitions per set.

POPULATION: 11 subjects, aged 26.8 ± 2.4 yearswho regularly performed pull ups.

What happened?

Scapula protraction-retraction ROMThe researchers observed significant differences inrespect of scapula protraction-retraction between thethree types of pull ups. They found that the pronated,wide grip, and supinated pull ups displayed differentprotraction-retraction ROMs of 22, 10 and 17 degrees,respectively. Thus, the wide grip pull up displayed farless protraction-retraction ROM than the other twovariations.

What did the researchers conclude?The researchers concluded that the wide grip pull updisplays far less protraction-retraction ROM than thestandard shoulder width pull up variations (eitherpronated or supinated grips). They suggested that thewide grip pull up may therefore place individuals atgreater risk of subacromial impingement.

LimitationsThe study was limited in that it was an analysis ofscapular biomechanics, which does not allow us toinfer injury risk directly.

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Effects of two different injury prevention resistanceexercise protocols on the hamstring torque-anglerelationship – a randomized controlled trial, byNaclerio, Larumbe-Zabala, Monajati, and Goss-Sampson, in Research in Sports Medicine (2015)

BackgroundHamstring strains are a common injury in manypopular team sports and they lead to the loss of manyhours of training and competition, as well as a veryhigh re-injury rate. Hamstring strains account for 12 –16% of all injuries in athletes across a range ofpopular team sports, including rugby, soccer, AmericanFootball, and Australian Rules Football. The re-injuryrate for hamstring strains ranges from 16 – 34%,depending upon the sport. Running activities accountfor most hamstring strains, with 57 – 68% of strainsoccurring during running. The traditional model forhamstring strain injury is that there are variousfactors that could cause an injury to occur, including:flexibility, strength, fatigue, core stability, musclearchitecture, and damage resulting from previousinjury. A modern, more sophisticated approach hassuggested that while these factors could individuallylead to an injury, it is more likely that they interactwith each other in order to create multi-factorialscenarios that raise injury risk. Some researchershave suggested that there are at least two differenttypes of hamstring strain injury: those caused bystretching activities and those caused by high-speedrunning movements. The hamstring strain injurycaused by high-speed running is thought to occurmost normally in the long head of biceps femoris,typically involves the proximal muscle-tendonjunction, displays a greater reduction in strengthfollowing injury than those following stretchingmovements, and leads to a relatively long recoverytime to reach pre-injury levels of performance (e.g.around 50 weeks). The biceps femoris (long head) isgenerally thought to be the most commonly-injuredhamstring muscle, although some researchers havesuggested that this perception might be incorrectbecause of inherent errors in common diagnosticapproaches. Biomechanically, however, there are goodreasons for assuming that the biceps femoris might bemost at risk. Firstly, this muscle increases in length bymore than the other hamstring muscles duringsprinting. Secondly, the moment arm lengths of thebiceps femoris in the sagittal plane increase in the lateswing position compared to the anatomical position.Previous research has identified that hamstring strainsoccur most frequently either in the late swing or earlystance phases of gait. Late swing involves the greateststrain in the muscle, while early stance involves thelargest joint moments. There is good evidence tosuggest that hamstring strain injuries can be reducedby eccentric hamstring training but not by flexibilitytraining alone. This has encouraged many strengthcoaches to incorporate the Nordic hamstring curl intohamstring strain prevention programs. However, thereis only limited evidence to suggest that hamstringweakness predicts strain injury risk.

OBJECTIVE: To compare the effects of two different6-week lower body injury prevention programs on theknee flexion torque–angle relationship (by measuringmaximal voluntary isometric contraction (MVIC) kneeflexion torque at 35, 45, 60, 80, 90, and 100 degrees)before and after the intervention.

POPULATION: 32 recreationally-trained male soccerplayers, aged 22.2 ± 2.6 years, randomly allocated to3 groups: hamstring eccentric (ECC), unstable squat(UNS), and control (CON).

INTERVENTION: The two training groups trainedtwice per week for 6 weeks using 3 individualhamstring eccentric (ECC) or unstable squat (UNS)exercises, respectively. ECC performed the coach- andband-assisted assisted Nordic hamstring curl, theeccentric single-leg stiff-legged deadlift, and theeccentric two-leg stiff-legged deadlift. UNS performedthe single-leg squat, the single-leg squat on a BOSUball, and forward lunges on a BOSU ball.

What happened?

Knee flexion torque-angle relationshipAt baseline, the researchers reported that all 3 groupsdisplayed peak torque at between 45 and 80 degreesof knee flexion angle and there were no differencesbetween groups.

Changes in knee flexion torque-angle relationshipThe researchers reported that MVIC knee flexiontorque increased at 35 and 45 degrees in ECC and at60, 80 and 90 degrees in UNS.

What did the researchers conclude?The researchers concluded that ECC increased kneeflexion torques at the two most open knee flexionangles (35 and 45 degrees) where the hamstrings arelengthened while UNS improved at more closed kneeangles (60, 80, and 90 degrees) where the hamstringsare less lengthened. This suggests that exercises thatdisplay peak torque at long muscle lengths tend toincrease strength most at long muscle lengths whileexercises that display peak torque at short musclelengths tend to increase strength most at short musclelengths.

LimitationsThe study was limited in that it is unclear whether theunstable surface was necessary for the UNS condition.It is possible that a simple single-leg squat programwould have produced similar results without the needfor the instability condition.

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Is there evidence to support the use of the angle ofpeak torque as a marker of hamstring injury and re-injury risk? By Timmins, Shield, Williams, and Opar, inSports Medicine (2015)

BackgroundThe length-tension relationship is a very importantconcept in biomechanics. It is based upon theobservation that the tensile force exerted by a muscleisometrically is dependent upon its length whentested. It is thought that this relationship can beexplained by reference to two underlying mechanisms:the active and passive length-tension relationships.The active length-tension relationship is thought tooccur as a result of the degree of overlap between theactin and myosin filaments within an individualsarcomere. Too much or too little overlap leads to sub-optimal tension being developed but where theoverlap is “just right” the maximal tension isdeveloped. The passive length-tension relationship isthought to occur much more simply as a result of theelastic elements within a sarcomere, within a musclefiber and within the muscle itself. Thus, the passivelength-tension relationship is largely unnoticed atsmall muscle fiber lengths but becomes veryimportant very quickly once the muscle is stretchedbeyond a certain length. The combination of the activeand passive length-tension relationships explains theoverall length-tension relationship. Overall, where theactive length-tension relation predominates (i.e. atshort lengths), the curve rises, plateaus and then fallsback down. The rising part of this section is known asthe “ascending limb” and the falling part is known asthe “descending limb”.

OBJECTIVE: To provide a narrative review of the useof the angle of peak torque as a marker of hamstringinjury and re-injury risk.

What happened?

Potential mechanismsThe angle of peak torque is a proxy measure for themuscle fascicle length, because of the length-tensionrelationship. Moving the angle of peak torque to amore lengthened muscle position (a larger joint angle)implies that fascicles have become longer. This isthought to have implications for muscle strain, aslonger muscle fascicles by necessity have a greaternumber of in-series sarcomeres. A larger number ofsarcomeres in a muscle fascicle may indicate thateach individual sarcomere spends less time on thedescending limb of the length-tension relationship,where passive structures provide the greatest part ofthe contribution to overall muscle tension.

Limitations with angle of peak torqueThe researchers explain that there are several keyvalidity concerns when measuring the angle of peakknee flexion torque using dynamometry as a measureof sports injury risk, as is currently performed. First,there are multiple hamstring muscles that contributeto the knee flexion joint action but typically the bicepsfemoris (long head) is most commonly subject tostrain injury. Second, the gastrocnemius muscle alsocontributes to the knee flexion joint action. Third, themuscle action during sport that typically leads toinjury is eccentric but tests usually use isometric orconcentric muscle actions. Fourth, the velocity of themovement in sport is usually very high but velocity insport is typically low or even static. Fifth, it seemslikely that muscle length during the terminal swing orearly stance phases of sprint running is much shorterthan that assessed during current dynamometry tests.Sixth, reliability studies have demonstrated only poor-to-moderate reliability, as measured by the intra-classcorrelation coefficient (ICC), with values rangingbetween 0.5 – 0.7.

Longitudinal cohort trials of hamstring strain injuryThe researchers explain that only 1 prospective cohorttrial has investigated the relationship between theangle of peak knee flexion torque and hamstring straininjury risk and this found no association. However,retrospective trials have reported some associations,although these may have arisen because of the injury.

What did the researchers conclude?The researchers concluded that evidence for the use ofthe angle of peak knee flexion torque as a predictorfor hamstring strain injury risk remains weak.

LimitationsThe article was a narrative review and therefore maynot reflect the views of other researchers in the field.

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MRI does not add value over and above patient historyand clinical examination in predicting time to return tosport after acute hamstring injuries: a prospectivecohort of 180 male athletes, by Wangensteen, Almusa,Boukarroum, Farooq, Hamilton, Whiteley, and Tol, inBritish Journal of Sports Medicine (2015)

BackgroundHamstring strains are a common injury in manypopular team sports and they lead to the loss of manyhours of training and competition, as well as a veryhigh re-injury rate. For a detailed introduction tohamstring strains, see the previous but one studyreview.

OBJECTIVE: To carry out a prospective observationaltrial to compare the predictive values of patienthistory and clinical examination vs. patient history,clinical examination plus magnetic resonance imaging(MRI) scans on determining the time to return to sport(as measured by number of days).

POPULATION: 180 male athletes with a clinicaldiagnosis of acute hamstring injury, of whom 177were professional athletes and 3 were competitiveamateur athletes.

What happened?

Descriptive statisticsThe researchers observed that 141 (78%) of theathletes displayed a positive MRI result while 39(22%) displayed a negative MRI result. They notedthat in 112 cases (79%) the primary injury occurredto the biceps femoris (long head). They found that thetime to return to sport varied very widely from 1 – 72days but the average was 21 ± 12 days.

Return to sport: without MRIExcluding the MRI information, the researchers built amultiple regression model including only the variablesfrom patient history and clinical examination. Theyfound that two patient history variables (maximumrecalled pain as registered on a visual analogue scale(VAS) and whether they were forced to stop sportwithin 5 minutes of the injury) were independentlyassociated with return to sport time. However, thepresence of previous injury was not associated withreturn to sport time. They also found that two clinicalvariables (length of hamstring tenderness along themuscle and presence of pain during resisted kneeflexion at 90 degrees of hip and knee angle) were alsoindependently associated with return to sport time.The total variance in return to sport time explained bythese patient history and clinical examination was29% (R-squared).

Return to sport: with MRIIncluding the MRI information, the researchers built asecond multiple regression model that included thevariables from patient history, clinical examination andMRI. The total variance in return to sport timeexplained by these patient history, clinical examinationand MRI variables was 32% (R-squared). Therefore,adding in the MRI variables explained just 3% of thevariance in return to sport time.

What did the researchers conclude?The researchers concluded that certain variablesrecorded during taking patient history and performingclinical examination at baseline can explain 29% ofthe variance in time to return to sport following anacute hamstring strain in male athletes. However,adding MRI has limited further benefit.

LimitationsThe study was limited as females were not included inthe analysis. Different results might be observed infemale athletes.

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Onset and maximum values of electromyographicamplitude during prone hip extension afterneurodynamic technique in patients with lumbosciaticpain: a pilot study by Horment-Lara, Cruz-Montecinos,Nuñez-Cortes, Letelier-Horta, and Henriquez-Fuentesin Journal of Bodywork and Movement Therapies(2015)

BackgroundThe gluteus maximus originates on the posteriorquarter of the iliac crest, the posterior surface of thesacrum and coccyx and the fascia of the lumbar spine.It inserts on the oblique ridge on the lateral surface ofthe greater trochanter of the femur and the iliotibialband of the fascia latae. In humans, the gluteusmaximus is much larger than in other apes,particularly in respect of the upper region.Additionally, it is attached to the iliac crest as well asthe ischium, which is not the case in other apes. Also,in other apes, the gluteus maximus is subdivided intotwo separate muscles whereas in humans it is a singlemuscle, albeit with multiple subdivisions. Indeed, thegluteus maximus contains 3 divisions from top tobottom (superior, middle, inferior) and two halvesfrom side to side (medial and lateral) that can beshown to perform distinctly different functions in 6regions, as can be shown by both muscle architectureand electromyography (EMG) activity. The gluteusmaximus can also be subdivided into superficial, deepsacral and deep iliac layers. The gluteus maximus isan extremely important muscle and is the largest andheaviest of all the muscles in the body. It comprisesaround 13 – 15% of total leg muscle mass by weight(around 600g in elderly males). It has a physiologicalcross-sectional area of ~34cm2 and an anatomicalcross-sectional area of ~ 48.4cm2. The musclearchitecture of the gluteus maximus is extraordinaryin that it has both a long fascicle length and a largecross-sectional area. It is also strongly pennate, asmight be expected from its large cross-sectional area.The gluteus maximus is 52 – 68% percent type Ifibers, making it an evenly mixed slow and fast twitchmuscle. It has its most significant moment arm in thesagittal plane for hip extension but also has a largemoment arm in the transverse plane for externalrotation. It also has a very small adduction momentarm in the frontal plane. Our current understandingbased on anatomy, muscle architecture and EMGstudies indicates that the gluteus maximus performs anumber of different hip actions from extension, toexternal rotation and abduction/adduction. It alsoraises the trunk when the femur is fixed in position,and posteriorly tilts the pelvis. The gluteus maximustherefore requires a range of different movementsperformed with these actions in mind in order totarget it fully. Various pathologies have beenassociated with gluteus maximus weakness. A weakgluteus maximus has been associated with anincreased risk of lower back pain, excessive anteriorpelvic tilt, sacroiliac joint pain, piriformis syndrome,anterior femoral hip glide, knee valgus and increasedACL injury risk and hip internal rotation andconsequent foot pronation.

OBJECTIVE: To explore the acute effects of aneurodynamic sliding technique on the muscle activity(as measured by electromyography [EMG]) of thegluteus maximus, semitendinosus and both ipsilateraland contralateral erector spinae muscles during pronehip extension in patients with sciatic pain.

POPULATION: 12 patients with sciatic pain (8females, aged 51.1 ± 9.1 years; 4 males, aged 44.5 ±16.4 years), allocated into a treatment group and acontrol group.

INTERVENTION: The subjects in the treatment groupperformed a neurodynamic sliding technique while thecontrol subjects received a placebo. Neurodynamicsliding comprised two phases: in the first phase, thesubject sits in a slump position and performs neckextension, knee extension, and dorsiflexion; in thesecond phase, the subject performs neck flexion, kneeflexion, and plantar-flexion. This sequence of phases isrepeated 5 times for 60 seconds.

What happened?

Changes in placebo groupThe researchers observed that EMG magnitudeincreased in the placebo group in the contralateralerector spinae (from 53.34 ± 18.81 to 63.34 ± 17.67208 μV) but did not increase significantly in any othermuscle.

Changes in the neurodynamic sliding groupThe researchers observed that EMG magnitudedecreased in the neurodynamic sliding group in thecontralateral erector spinae (from 80.59 ± 10.01 to57.70 ± 17.85 μV) and ipsilateral erector spinae (from71.48 ± 17.58 to 53.3 ± 13.3 μV). Trends wereobserved for increasing gluteus maximus and semi-tendinosus muscle activity but these did not reachsignificance.

What did the researchers conclude?The researchers concluded that the neurodynamicsliding technique leads to reduced erector spinaemuscle activity during prone hip extension.

LimitationsThe study was limited in that it did not elucidate whythese changes might have occurred in muscle activityfollowing the neurodynamic sliding technique.

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Blood flow restriction exercise – a progressive injuryrehabilitation model, by Staunton, in Journal ofAustralian Strength and Conditioning (2015)

BackgroundBlood flow restriction (BFR) training is used toincrease gains in muscular size. BFR training istypically prescribed as low-relative-load resistance-training (20 – 30% of 1RM) combined with blood flowrestriction applied in the form of either carefullycalibrated pressure cuffs or simple elastic wrappings.Previous studies have found that the use of BFRtraining can increase strength and muscle mass invarious populations, ranging from the elderly totrained athletes. Several theories have been putforward regarding mechanisms to explain thebeneficial effects observed following BFR training. It isthought that the mechanisms by which such increasesoccur might include increased fast-twitch fiberrecruitment, metabolic and hormonal alterations,intramuscular signaling, and cellular swelling.However, there is no current strong consensus arounda single, dominant mechanism by which BFR trainingexerts its effects. While there are currently noguidelines available for describing the use of BFRtraining in different populations, it is noted that it maybe possible to achieve gains in muscular size in manyindividuals with lower loads than are typicallyrecommended for resistance-training. The AmericanCollege of Sports Medicine (ACSM) recommends using>60% of 1RM as the desired relative load forincreasing muscular strength and size. However,research indicates that loads of 20 – 50% may beappropriate in combination with BFR. Thus, BFR incombination with resistance-training may be mostuseful for populations who cannot tolerate the largemechanica l loads that are assoc iated withconventional, heavy resistance-training, such as theelderly or infirm.

OBJECTIVE: To present a narrative review exploringthe potential for BFR training as a tool within aprogressive rehabilitation model.

What happened?

Phases of rehabilitationThe researcher proposed that rehabilitation can becategorized into 5 phases: (1) limb immobilization, (2)injury rehabilitation, (3) aerobic exercise, (4) lightload resistance training, (5) heavy load resistancetraining.

Application of BFR in each phaseThe researcher suggested that BFR could be used ineach of these phases. Studies have been performedshowing that the application of vascular occlusioneven without exercise can reduce losses of musclemass during phases in which limb immobilization isneeded. During early-phase rehabilitation, wherebodyweight exercises and walking are incorporated,there are some indications that BFR may help improvegains in strength and size. In all later phases, in whichaerobic exercise, light-load resistance training, andheavy-load resistance training are performed, thereare indications that BFR may enhance gains in musclesize following long-term training.

What did the researcher conclude?The researcher concluded that within all phases ofrehabilitation, BFR may be able to improve outcomesrelating to muscular size. It may enhance theretention of muscle mass during the early phases andthe increase of muscle mass in the later phases.

LimitationsThe article was a narrative review and therefore maynot reflect the views of other researchers in the field.

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Cold vs. heat after exercise – is there a clear winnerfor muscle soreness, by Petrofsky, Khowailed, Lee,Berk, Bains, Akerkar, and Laymon, in Journal ofStrength & Conditioning Research (2015)

BackgroundDelayed onset muscle soreness (DOMS) is frequentlyexperienced by athletes and recreational traineeswhen exposed to either novel resistance-trainingworkouts or a large volume of eccentric muscleactions. Symptoms include soreness, tenderness uponpalpation, and stiffness during movement. DOMSappears to occur reliably between 12 – 24 hours post-workout, with soreness peaking around 48 hours post-workout. There is a lack of consensus regarding theunderlying mechanisms that cause DOMS. Someresearchers consider DOMS to be caused entirely byexercise-induced muscle damage (EIMD). EIMD issimilarly characterized by muscle soreness, muscleswelling, an increase in intramuscular protein andpassive muscle tension, and also involves a reductionin muscular strength and range-of-motion. In thismodel, EIMD causes various disruptive changes,including sarcomere damage, calcium accumulation,protein degradation, and increased osmotic pressure.These changes lead to the sensitization of nociceptorsand other pain receptors, which leads to the sensationof DOMS being experienced. A number of differentinterventions have been tested for reducing both EIMDand DOMS. There is some evidence to support the useof massage and limited evidence to support the use ofself-myofascial release with a foam roller. Themechanisms by which massage or self-massage mightbe effective for reducing DOMS are not well-understood and various possibilities are currentlybeing explored by researchers. One interesting featureof DOMS is that it is dramatically reduced when themuscle has been exposed to a similar stimulus on arecent, previous occasion. This is known as the“repeated bout effect” and indicates that centralfactors may well be involved in addition to local ones.

OBJECTIVE: To compare the effects of applying eithercold or ThermaCare heat wraps either immediately or24 hours post-exercise on muscle soreness (measuredusing a visual analog scale [VAS]), leg strength andpassive stiffness (as measured by knee flexion andextension force using a strain gauge) and myoglobin.

POPULATION: 100 healthy subjects, randomlyallocated into 5 groups: (1) control, (2) cold packimmediately post-exercise, (3) cold pack 24 hourspost-exercise, (4) heat pack immediately post-exercise and (5) heat pack 24 hours post-exercise.

INTERVENTION: All subjects performed an acuteprotocol of squat exercise that was intended to causeDOMS. This protocol involved 5 minutes of continuousbodyweight squats with 1 squat performed every 3seconds. This was repeated for a total of 3 sets with 3minutes of inter-set rest. Where subjects wereallocated to either cold packs or heat packs, thesewere applied at the designated time post-exercise orat 24 hours post-exercise. Cold packs were applied for20 minutes at the designated time but hot packs wereapplied for 8 hours starting at the designated time.

What happened?

Strength lossThe researchers observed that the control groupdisplayed a temporary 24% reduction in leg musclestrength at 24 hours following the DOMS protocol. At24 hours, the reductions in strength observed in thecold (immediate) and hot (immediate) groups weresignificantly less than that in the control group butthere was no significant difference between either thecold (immediate) and hot (immediate) groups. After 3days, strength reductions were still present in the cold(immediate) but not in the hot (immediate) group. Atall time points, the reductions in strength observed inthe cold (24 hours) and hot (24 hours) groups weresignificantly less than that in the control group butthere was no significant difference between either thecold (24 hours) and hot (24 hours) groups.

Muscle soreness and myoglobin changesThe researchers observed that all groups displayed anincrease in muscle soreness (as measured by VAS)that peaked at 2 days post-exercise. At 24 hours,there was no significant difference between the cold(immediate) and hot (immediate) groups. At 3 days,VAS increases were lower in the cold (immediate) thanin the hot (immediate) group. Similar results wereobserved in respect of the cold (24 hours) and hot (24hours) groups. The researchers also observed that allgroups displayed an increase in myoglobin post-exercise but there was no difference between groups.

What did the researchers conclude?The researchers found that cold application appears tobe superior to hot application for reducing DOMS buthot may be superior for reducing strength loss.

LimitationsThe study was limited in that the post-exercise and 24hours post-exercise conditions were not compared.

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An evidence-based review of hip-focused neuro-muscular exercise interventions to address dynamiclower extremity valgus, by Ford, Nguyen, Dischiavi,Hegedus, Zuk, and Taylor, in Open Access Journal ofSports Medicine (2015)

BackgroundNon-contact anterior cruciate ligament (ACL) injury isa very common and quite serious injury that occursfrequently in popular team sports, particularly thosewhich involve lateral pivoting, jump landing or quickdecelerations during sprint running. Previous researchhas identified that ACL injuries occur under twopredominant loading patterns: knee valgus collapse oranterior tibial shear. While there are advocates andadversaries of both mechanisms, studies have shownthat female athletes tend to display greater kneevalgus than males and greater ACL injury incidence.Researchers have also found that the tendency todisplay greater knee valgus is a good predictor of ACLinjury risk. In general, the term “valgus” refers to theoutward angling of the distal segment of a bone.Where a joint or a neighboring joint has more thanone degree of freedom, this outward angling caninvolve movements in transverse, sagittal or frontalplanes. Indeed, research indicates that knee valgus(also called valgus collapse or medial kneedisplacement) actually arises as a result of hip joint orfoot joint actions. Knee valgus in stance is seen inconjunction with a combination of hip joint adductionand hip joint internal rotation and occurs mostfrequently in positions of hip joint flexion. Additionally,foot pronation is commonly observed where kneevalgus occurs. The joint actions at hip and foot appearto lead to a medial displacement of the knee, which isaccompanied by knee joint abduction and knee jointexternal rotation. Various explanations have beenproposed as causes of knee valgus. One popularproposal is that individuals have inadequate hipexternal rotator and hip abductor strength and/orshort, tight or overactive hip adductors and/or hipinternal rotations, leading to a tendency for the hips tomove into hip adduction and hip internal rotation.Another very popular proposal is that ankledorsiflexion mobility is poor or that the lower legmuscles (soleus, gastrocnemius, and anterior tibialis)are short, tight or overactive, which prevents the tibiaand knee from moving forwards and causes the foot tocompensate by pronating. This inward foot movementleads to mirrored movement at the hip (hip internalrotation and hip adduction) and therefore knee valgus.Two less popular proposals are that a lack of eithervastus medialis obliquus strength or a lack of medialhamstrings strength leads to poor knee stabilizationand consequently allows the knee to track inward.Changes of direction during running (cutting) arecommon in many popular team sports and the abilityto perform them quickly is a key attribute ofsuccessful athletes. However, cutting maneuvers arealso associated with knee valgus and consequently anincreased risk of non-contact ACL injury.

OBJECTIVE: To perform a narrative review of long-term trials that have investigated changes in kneevalgus following hip-focused exercise interventions.

What happened?

Study selection and heterogeneityThe researchers identified 10 long-term trials thathave investigated changes in knee valgus as a resultof long-term hip-focused exercise interventions. Theynoted that there was considerable heterogeneity inthis literature. Such heterogeneity can be seen inrespect of the populations being tested (ranging fromhealthy athletes to individuals with patellofemoral painsyndrome [PFPS]), in respect of the duration of theexercise programs (from 4 – 12 weeks), in respect ofthe frequency of training performed (from 2 – 3 timesper week), and in respect of the types of exercise thatwere selected (non-weight-bearing vs. weight-bearingand exercises in single planes [sagittal] vs. multipleplanes [frontal and transverse]).

Effects of hip-focused exercise interventionsThe researchers observed that the programs used inthe 10 long-term trials appeared to produce improvedhip extension, hip abduction, and hip external rotationforce or torque fairly consistently, which indicates thatthe intended purpose of hip strengthening was beingachieved. Moreover, the translation of these gains inhip muscle strength into reduced knee valgus duringlower body movement was also apparent. Certain ofthe studies reported increased peak hip flexion duringdrop landings, decreased hip adduction and hipinternal rotation during single-leg squats, decreasedknee adduction moments in running, and decreasedpeak knee abduction angles and moments in droplandings. Nevertheless, not all of the included studiesreported such changes in lower body biomechanics.

Common exercises used in the programsThe researcher noted that several exercises werecommonly used in many of the programs in the trialsreviewed, including the side-lying hip abduction, pronehip extension, resisted clam-shell, resisted seated hipexternal rotation, single-leg squat, single-leg deadlift,lunge, forward step up, and lateral step-up. Theseexercises may therefore be useful for inclusion ininjury prevention or injury rehabilitation programswhere reduced knee valgus is required.

What did the researchers conclude?The researchers concluded that hip-focused exercisesappear to help reduce knee valgus during a range ofdynamic movements, as indicated by the evidencefrom a small body of long-term trials.

LimitationsThe narrative review was limited in several ways inthat it was not performed as a systematic review withset criteria and did not carry out a quality analysis ofthe included trials.

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Differences and correlations in knee and hipmechanics during single-leg landing, single-leg squat,double-leg landing, and double-leg squat tasks, byDonohue, Ellis, Heinbaugh, Stephenson, Zhu, and Dai,in Research in Sports Medicine (2015)

BackgroundResearchers have found that the tendency to displaygreater knee valgus is a good predictor of ACL injuryrisk. The term “valgus” refers to the outward anglingof the distal segment of a bone. Knee valgus (alsocalled valgus collapse or medial knee displacement)arises as a result of hip joint or foot joint actions.Knee valgus in stance is seen in conjunction with acombination of hip joint adduction and hip jointinternal rotation and occurs most frequently inpositions of hip joint flexion. For a more detailedintroduction to knee valgus and ACL injury risk, seethe previous study review.

OBJECTIVE: To identify differences and correlationsin knee and hip joint angle movements (measuredusing an 8-camera motion analysis system capturingthe positions of reflective markers placed on keyanatomical landmarks) during a single-leg landing, asingle-leg squat, a two-leg drop landing, and a two-legsquat. The primary joint angle movements of interestwere: peak knee flexion angle, peak hip flexion angle,peak knee abduction angle, peak hip adduction angle.Using inverse dynamics, peak external knee abductionmoment was also calculated.

POPULATION: 34 recreational athletes (17 malesand 17 females, aged 21.4 ± 2.0 years.

INTERVENTION: All subjects performed 4 officialtrials each of a two-leg drop landing (from a 30cmbox), a single-leg landing, a two-leg squat, and asingle-leg squat in a randomly selected order.

What happened?

DifferencesThe researchers found significant differences betweenthe 4 conditions for peak knee flexion angles, peak hipflexion angles, peak knee abduction angles, peak hipadduction angles, and peak external knee abductionmoments. Peak knee flexion and peak hip flexionangles were greatest in the order: two-leg squat >two-leg drop landing > single-leg squat > single-legdrop landing. Peak knee abduction angles weregreatest in the order: two-leg squat > two-leg droplanding and single-leg drop landing > single-leg squat.Peak hip adduction angles were greatest in the ordersingle-leg squat > single-leg drop landing > two-legdrop landing and two-leg squat (of which the final twowere hip abduction angles). Peak external kneeabduction moments were greatest in the order: two-leg drop landing > single-leg drop landing and two-legsquat > single-leg squat.

CorrelationsThe researchers found strong, significant correlationsin peak knee and hip flexion angles between the twodrop landings (r = 0.50 – 0.73) and between the twosquats (r = 0.67 – 0.83). They found significantcorrelations in peak knee abduction and hip adductionangles and peak external knee abduction momentbetween the single-leg drop landing and the single-legsquat (r = 0.66 – 0.74).

What did the researchers conclude?The researchers concluded that there exist severalimportant and significant differences in joint anglemovements between single-leg squats, single-leg droplandings, two-leg squats and two-leg drop landings.This implies that a single movement screening test forone of these cannot provide sufficient informationabout the way in which the other movements areperformed.

LimitationsThe study was limited in that only a small number ofjoint angle variables were assessed in a small numberof movements.

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Management of chronic recurrent osteitis pubis/pubicbone stress in a premier league footballer: evaluatingthe evidence base and application of a nine-pointmanagement strategy, by McAleer, Gille, Bark, andRiepenhof, in Physical Therapy in Sport (2015)

BackgroundGroin injuries are relatively common in sports, withadductor strains being the most common category ofgroin injury. However, other common groin injuriesinclude osteitis pubis and sports hernia (athleticpubalgia). Osteitis pubis is a poorly-understood typeof groin injury. It appears to be an inflammation of thepubic symphysis of the pelvis and of the surroundingmuscles. Patients typically present with pain local tothe pubic symphysis but also pain more generallyaround the pelvic area and in the abdomen and hipadductor muscles. Pain is often worse during running,kicking, cutting, or side-lying activities, as well asduring activities involving the diaphragm, such ascoughing. Such features often make it very difficult todistinguish between osteitis pubis and adductor strainsand this difficulty may in fact underlie the differencesin injury incidence reported in the literature betweenclinics. Treatment approaches for osteitis pubis varybut it is believed to be a self-limiting condition thatnevertheless can take up to one year to disappear.Physical therapy tends to focus on improving hipmobility and stretching and strengthening the hipadductor musculature.

OBJECTIVE: To present a clinical example and toillustrate a treatment strategy for the management ofrecurrent chronic groin pain.

POPULATION: one 23-year old professional soccerathlete.

What happened?

Patient historyThe researchers observed that the soccer athletereported the current presence of bilateral adductorand pubic symphysis pain that had developed over theprevious 2 – 3 months, in addition to previous pain inthe lateral part of the rectus abdominis after pre-season training. Previous injuries included osteitispubis (6 years previously), spondylolisthesis (2 yearspreviously), shoulder subluxation (2 years previously),hamstring strain (1 year previously), and Achillestendinopathy (3 months previously).

Return to sport and follow-upThe researchers reported that the athlete returned tofull training and match play within 41 and 50 days,respectively. At 13 month follow-up, there was norecurrence of the injury.

Suggested frameworkThe framework adopted by the clinicians in thetreatment of the athlete was described in 9 stages, asfollows: (1) acute pharmacological pain managementand cessation of aggravating activities, (2) massagetherapy to aid pain relief and promote increasedflexibility, (3) more specific massage therapy toincrease flexibility at hips, pelvis and thorax, (4)increasing adductor strength (using adductor sidebridges, cable-resisted adductor swings, adductorslides and lateral squats), (5) increased movementcontrol (in forward step up and single-leg squat,multidirectional lunges, split squat with thoracicrotation, and unilateral gym ball hip flexion, (6) corestability exercises progressing from supine to standingand moving, (7) improving lumbopelvic control duringstatic and dynamic single-leg joint actions, (8) multi-joint resistance training exercises (including squatsand deadlifts) progressing to plyometrics, and (9)field-based running conditioning.

What did the researchers conclude?The researchers concluded that in this example, theyhave presented a 9-point conservative treatmentstrategy for bilateral adductor pain that was indicativeof chronic recurrent osteitis pubis.

LimitationsThe article was limited in that it was only a case studyand it remains to be ascertained whether the 9-pointframework could be utilized in a larger prospectivetrial involving a larger number of subjects.

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The effectiveness of non-operative rehabilitationprograms for athletes diagnosed with osteitis pubis,by Cheatham, Kolber, and Kumagai, in Journal ofSport Rehabilitation (2015)

BackgroundOsteitis pubis is a poorly-understood type of groininjury. It appears to be an inflammation of the pubicsymphysis of the pelvis and of the surroundingmuscles. For a more detailed introduction to osteitispubis, see the previous study review.

OBJECTIVE: To perform a review to identify studiesassessing the effectiveness of non-operativerehabilitation programs for osteitis pubis in returningathletes to pre-injury levels of participation.

STUDY SELECTION: Searches were performed forpeer-reviewed studies in English that investigated theeffects of non-operative rehabilitation programs onosteitis pubis-related outcomes in athletes.

What happened?

Study selectionThe researchers identified 4 studies that met theinclusion criteria, including 9 athletes (aged 10 – 30years). However, all of these studies were case reportsof athletes in a range of sports, including soccer,basketball, cricket, and Australian Rules football.

Study characteristicsThe researchers reported that all of the describednon-operative rehabilitation programs included manualtherapy, strengthening, stretching, and sports specificexercises.

Study findingsThe researchers reported that 3 of the 4 studiesreported a successful return to pre-injury activities atbetween 4 – 14 weeks and 1 study reported asuccessful return at 30 weeks. None of the 4 casereports observed any unsuccessful attempts to returnto sport. The researchers also noted that 2 of the 4studies observed no recurrence within a follow-upperiod of 6 months while 1 additional study reportedno recurrence within a follow-up period of 18 – 48months.

What did the researchers conclude?The researchers concluded that there is currently nobetter evidence beyond case studies to support theuse of non-operative rehabilitation programs in thetreatment of osteitis pubis in athletes. Future researchis required of a higher quality, including retrospectivecohort trials, prospective cohort trials, and randomizedcontrolled trials.

LimitationsThe review was limited by the severe lack of currentlyavailable research.

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