b y A a r o n B u b b i c o a n d L e n K r a v i t z , P h D

QUIZ 2:PAGE 85

Muscle HypertrophyNew insights and training recommendations.

Muscle hypertrophy, or muscle cell en-largement, is a topic of great debate andinterest in all fields of health, fitness andsports. How the body responds to muscu-lar overload to elicit muscle growth is stillunder much scientific investigation.

Many types of training educe musclehypertrophy. This is evidenced by thefact that athletes in numerous sportsexhibit wonderful muscular develop-ment even though they follow differenttraining protocols. With this in mind, itmakes sense to examine contemporaryunderstandings of muscle hypertrophyand highlight some effective trainingapproaches.

Muscle HypertrophyMuscle hypertrophy is an increase inmuscle fiber size, observed when themuscle achieves a larger diameter orthickness. New muscle fibers are not cre-ated during hypertrophy in humans, al-though Paul and Rosenthal (2002) notenew-fiber creation has been observed insome animal studies, owing to uniquestructural differences in muscle anatomybetween species.

With muscle hypertrophy at the cellu-lar level in humans, the actin and myosincontractile proteins increase in size andnumber (Schoenfeld 2010). In addition, asSchoenfeld explains, there is an increase inthe fluid (sarcoplasm) and noncontractileconnective tissues interspersed withinmuscle, a concept collectively referred toas sarcoplasmic hypertrophy. In eccentrictraining, which overloads the muscle dur-ing lengthening, muscle cells also add sar-comeres (the smallest functional unit ofmuscle fibers) longitudinally, thus addinglength to the muscle fiber as well (Proske& Allen 2005).

It is important to note that strengthgains made in the first couple of months oftraining are primarily neural adaptations(Schoenfeld 2010). Gabriel, Kamen andFrost (2006) explain that in early trainingphases, the muscle is acquiring greaterneural input, referred to as neural drive.Underlying this greater neural input arethe motor unit recruitment patterns ofmuscle fiber types (see Figure 1 for an ex-planation of motor unit recruitment). Eachmotor unit represents a single nerve andthe many muscle fibers it innervates.

Satellite Cells, Cytokinesand Hornnones: ExploringNew Insights Into MuscleHypertrophy MechanismsSatellite cells are the "stem" cells of skeletalmuscle (Schoenfeld 2010). Like stem cells,satellite cells have unique physiologicalcharacteristics and functions. They can becharacterized as small, mononuclear cellslocated between the basement membraneof a muscle fiber (called the basal lamina)and the sarcolemma (the polarized plasmamembrane). They function to repair dam-aged muscle tissue and trigger skeletalmuscle growth after any type of overload.Once satellite cells are stimulated by mus-cular overload, they fuse to the musclefiber and facilitate muscle hypertrophy byforming a new nucleus. Uniquely to hu-man physiology, muscle fibers have nu-merous nuclei. Each nucleus is responsiblefor a finite area of volume and tissue withinthe muscle fiber, a concept called myonu-clear domain (Schoenfeld 2010).

The exercise-induced stimulus fromresistance exercise activates a complexresponse of cellular messaging pathways,cytokines and hormones that set muscle

November-December 2011 IDEA Fitness Journal 23

hypertrophy in motion (see Figure 2). Threedistinct messaging pathways (calcium-de-pendent pathway, mitogen-activated pro-tein-kinase pathway and rapamycinpathway) shift the cell into a protein synthe-sis condition while also inhibiting proteinbreakdown (Schoenfeld 2010). Cytokinesare messaging proteins from the immunesystem that interact with specialized recep-tors on muscle to promote tissue growth.Significantly, some anabolic (musclegrowth-promoting) hormonesincludinginsulin-lce growth factor, testosterone andgrowth hormoneplay a primary role inpromoting hypertrophy (Schoenfeld 2010).

Some Distinctive TrainingMethodsThat PromoteHypertrophySchoenfeld (2011) explains that eventhough direct research is lacking, severalbodybuilding training methods appear to

promote muscle growth because theyincite one or all of the factors that activatehypertrophy in muscle (see the sidebar "5Questions About Muscle Hypertrophy").

Descending-Weight or Drop SetsCountless variations are possible ondescending-weight or drop sets. For ex-ample, an exerciser might do 8 repetitionsof a dumbbell lateral raise with 35 poundsto failure, put those dumbbells down andcomplete 8 repetitions with 25 pounds tofailure, and then drop to 8 repetitionswith 15 pounds to failure. Depending onthe exerciser, a sequential drop of10%-25% in weight would be appropri-ate for this technique.

Alternating Rest PeriodsBetween Multiple SetsTypically, three types of rest periods areused in resistance exercise: short (30 sec-

onds or less), moderate (60-90 seconds)and long (3 minutes or more) (Willardson2006). Short rest periods may cause a sig-nificant amount of metabolic stress, whichis now believed to be a potent stimulator forhypertrophy (Schoenfeld 2011). However,with shorter rest periods (between multi-ple sets) it is harder to obtain the higherworkloads needed to really overload mus-cle. By alternating rest periods (betweenmultiple sets), the exerciser may be able tocreate more metabolic stress in some setsand more mechanical tension in others,both of which promote hypertrophy.

IEccentric TrainingAs highlighted by Schoenfeld (2011), asignificant amount of research has shownthat eccentric training leads to great gainsin muscle hypertrophy (for a completereview of eccentric training, read"Eccentric Training" in October 2010

Figure 1.Motor UnitRecruitmentMotor units for the mostpart are recruited in orderof increasing size, becausethe size (in diameter) ofthe motor unit Is directlyreiated to its force-producing capabiiity.A lighter force demandplaced on the muscle wiiiemphasize activation ofsiow-twitch fype 1 fibers(see A). As the force onmuscle increases, thefast-twitch type lia fibersare activated with thehelp of type I fibers (see B).With the most challengingdemands of muscie, themost powerful (and largest)type lib fibers are triggeredto fire, with the help of typei and type lia fibers (see C).

Source: Enoka 1995. Adapted froman illustration by Lyman Dally.

Type I Type IIA Type IIB

nerve and muscle fibers innervated by nerve

IType I Type IIA Type IIB

November-December 2011 IDEA Fitness Journal

c. Satellite cell donates nuclei to fiber.

d. Signaling pathways shift fiber intoprotein synthesis balance.

e. Cytokines promote protein synthesis.

Figure 2. iVIeciianisms of iViuscie i^Ypertropily

a. Overloading exercise triggers hypertrophy mechanismin muscle fiber to start.

b. Satellite cell fuseson nnuscle fiber.

f. Anabolic hormones regulate amount of growth; activate DNA changes for

protein synthesis; increase uptake of

glucose and fatty acidsfor grovirth fuel needs;and

increase amino acidsinto muscle fiber forprotein synthesis.

Source: Schoenfeld 2010.

IDEA Fitness Journal). One popular ec-centric training technique is the "supra-maximal technique," in which the clientlifts a weight (with the aid of a personaltrainer) that is 105%-125% ofthat per-son's normal load and then lowers theweight eccentrically in 3-4 seconds.

Forced RepetitionsWith spotting from a personal trainer, theclient completes 2-4 extra repetitionsafter reaching momentary muscularfatigue during a set.

SupersetsSupersets, or paired sets, consist of anytwo sets performed in sequence (with norest between exercises). Schoenfeld(2011) notes that the metabolic stress in-duced by this technique may be responsi-ble for the hypertrophie gains it canproduce. Possible superset strategies (andexamples of each) include agonist/antag-onist (e.g., biceps curl and triceps exten-sion), opposite action (e.g., chest flye andseated row), upper body/lower body (e.g.,chest press and leg press), lower bodyonly (e.g., lunge and heel raise) and upperbody only (e.g., fiye and chest press).

Concluding ConnmentsIt is remarkable to see how scientists arenow beginning to understand and explainmany hypertrophy techniques that have

1 . What are the most important factors for promoting hypertrophy?Mechanical tension, muscle damage and metabolic stress are the three primary factorsthat promote hypertrophy from exercise (Schoenfeld 2011). Mechanical tension isdirectly related to exercise intensity, which is the key to stimulating muscle growth.Muscle damageleading to muscle soreness from exercise traininginitiates aninflammatory response, which activates satellite cells' grovyth processes. And metabolicstress, a result of the byproducts of anaerobic metabolism (i.e., hydrogen ions, lactate,inorganic phosphates), is now also believed to promote hormonal factors leading tomuscle hypertrophy.

2. Which tend to show hypertrophy faster: the upper extremities or the lowerextremities?The upper extremities tend to show more growth faster than the lower extremities(Schoenfeld 2011).

3. What is the ideal intensity for maximizing hypertrophy?Maximal growth occurs with loads between 80%-95% of 1 -repetition maximum(Fry 2004).

4. How do weightlifters, power lifters and bodybuilders differ in their hypertrophieresponses to training?According to Fry (2004), weightlifters and power lifters show more favorable hypertrophyof type II (fast-twitch) muscle fibers, whereas bodybuilders appear to have comparablehypertrophy in both type I (slow-twitch) and type II muscle fibers.

5. Which are better for developing hypertrophy: single- or multiple-joint exercises?Multijoint exercises have been shown to produce larger increases of anabolic hormonescompared with single-joint exercises and thus should be prioritized (Hansen et al. 2001).

November-December 2011 IDEA Fitness Journal 2S

Balzarni.fied Personal Traner

111

The ACE Way

That Other Way

Align With the BestForget the Rest

The antagonistic personal trainer barking in people's facesmay benefit TV producers, but that's no way to earn thetrust and loyalty of clients. With ACE, you'll receive real-world solutions you won't find elsewhere to ensure yourclients achieve lasting results. And with our history rootedin progressive education and forward-thinking thoughtleadership, we'll equip you with the latest training tools,research-proven techniques and knowledgeable staff toguide you in your career.

Join our team of 50,000-(- fitness professionals!www.acefitness.org/thoughtleaders

Personal Training. Reinvented^

been used for decades. The physiologi-cal responses to training vary accordingto a persons age, fitness level, hormonallevels, gender and tolerance for mechan-ical overload. It is always a major respon-sibility of the personal trainer to assesswhat strategies to use and how muchtraining is best to help clients attain theirmuscular fitness goals.

Aaron Bubbico is working on his master'sdegree in exercise science at the Universityof New Mexico, Albuquerque (UNM). Heowns and operates Quality Fitness Trainingin Albuquerque. His research interestsinclude eccentric load training, hyper-trophic adaptations and mechanisms, andperiodization. | '

Len Kravitz, PhD, is the program coordina-tor of exercise science and a researcher atUNM, where he has won the OutstandingTeacher of the Year award. He was honoredwith the Can-Fit-Pro Lifetime AchievementAward in 2008 and received the 2010Aquatic Exercise Association Glohal Award.

Take CECwww.ideafjt.com/noveniber-2011 -courses

or maii Hie quit on page BS.

ReferencesBnoka. R.M. 1995. Morphological features and activa-

tion patterns of motor units. Journal of ClinicatNeurophysiohgy. 12 (6), 538-59.

Fry, A.C. 2004. The role of resistance exercise inten.sityon muscle fibre adaptations. Sports Medicine, 34 (10).663-79.

Gabriel, D.A., Kamen, G., & Prost, G. 2006. Neural adap-tations to resistive exercise: Mechanisms and recom-mendations for training practices. Sports Medicine, .6(2), 131-49.

Hansen, S., et al. 2001. The effect of shorl-term strengthtraining on human skeletal muscle: The importance ofphysiologically elevated hormone levels. Scandinaviantournai of Medicine & Science in Sports, /) (6), 347-54.

Paul, A.C., & Rosenthal, N. 2002. Different modes of hy-pertrophy In skeletal muscle fibers. The journal of CellBiology, 156 (4), 751-60.

Proske, U, & Allen, T.J. 2005. Damage lo skeletal mus-cle from eccentric exercise. Exercise and Sports ScienceKfvfews, 33(2),9-104.

Schoenfeld, B.I. 2010. The mechanisms of muscle hy-pertrophy and their application to resistance training.Journal of Strength ami Conditioning Research, 24 {]()),2857-72.

Schoenfeld, B.J. 2011. The use of specialized trainingtechniques to maximize muscle hypertrophy. Strengthand Conditioning journal, 33 (4), 60-65.

Willardson, l.M. 2006. A brief review: Factors affectingthe length of the rest interval between resistance ex-ercise sets, journal of Strength Conditioning Research,20 (4), 978-84.

M 2011 by lUKA Health & 1-ilnes.s Inc. All rights reserved.Reproduction without permission is strictly prohinited.

November-December 2011 IDEA Fitness Journal

Copyright of IDEA Fitness Journal is the property of IDEA Health & Fitness, Inc. and its content may not becopied or emailed to multiple sites or posted to a listserv without the copyright holder's express writtenpermission. However, users may print, download, or email articles for individual use.