Factors Modulating Post-Activation Potentiation and Its Effect on Performance of Subsequent Explosive Activities

Factors Modulating Post-ActivationPotentiation and its Effect on Performanceof Subsequent Explosive ActivitiesNeale Anthony Tillin1,2 and David Bishop1,3

1 School of Human Movement and Exercise Science, the University of Western Australia, Crawley,

Western Australia, Australia

2 School of Sport and Exercise Science, Loughborough University, Loughborough, Leicestershire, UK

3 Facolta di Scienze Motorie, Universita degli Studi di Verona, Verona, Italy

Contents

Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1471. Post-Activation Potentiation (PAP). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1482. Mechanisms of PAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

2.1 Phosphorylation of Regulatory Light Chains. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1482.2 Increased Recruitment of Higher Order Motor Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1492.3 Changes in Pennation Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

3. PAP and Mechanical Power. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1524. Acute Effects of PAP on Subsequent Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

4.1 PAP versus Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1564.2 Conditioning Contraction Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1574.3 Conditioning Contraction Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1584.4. Subject Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

4.4.1 Muscular Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1604.4.2 Fibre-Type Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1604.4.3 Training Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1614.4.4 Power-Strength Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

4.5 Type of Subsequent Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1625. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

Abstract Post-activation potentiation (PAP) is induced by a voluntary conditioningcontraction (CC), performed typically at a maximal or near-maximal in-tensity, and has consistently been shown to increase both peak force and rateof force development during subsequent twitch contractions. The proposedmechanisms underlying PAP are associated with phosphorylation of myosinregulatory light chains, increased recruitment of higher order motor units,and a possible change in pennation angle. If PAP could be induced by a CC inhumans, and utilized during a subsequent explosive activity (e.g. jump orsprint), it could potentially enhance mechanical power and thus performanceand/or the training stimulus of that activity. However, the CC might alsoinduce fatigue, and it is the balance between PAP and fatigue that will

REVIEW ARTICLESports Med 2009; 39 (2): 147-166

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ª 2009 Adis Data Information BV. All rights reserved.

determine the net effect on performance of a subsequent explosive activity.The PAP-fatigue relationship is affected by several variables including CCvolume and intensity, recovery period following the CC, type of CC, type ofsubsequent activity, and subject characteristics. These variables have notbeen standardized across past research, and as a result, evidence of the effectsof CC on performance of subsequent explosive activities is equivocal. In or-der to better inform and direct future research on this topic, this article willhighlight and discuss the key variables that may be responsible for the con-trasting results observed in the current literature. Future research should aimto better understand the effect of different conditions on the interaction be-tween PAP and fatigue, with an aim of establishing the specific application(if any) of PAP to sport.

1. Post-Activation Potentiation (PAP)

Post-activation potentiation (PAP) or post-tetanic potentiation (PTP) refers to the phenomenaby which muscular performance characteristicsare acutely enhanced as a result of their contrac-tile history.[1,2] The difference between PAP andPTP is defined by the nature of the conditioningcontraction. PTP is induced by an involuntarytetanic contraction, and PAP is induced by avoluntary contraction[3,4] performed typicallyat a maximal or near-maximal intensity. Forsimplicity, this article refers to all potentiationresponses as PAP, and refers to the activity res-ponsible for inducing PAP as a conditioningcontraction (CC).

The presence of PAP in skeletal muscle hasbeen recorded by many studies in both mammalsand humans,[5-17] prompting a discussionamongst recent review articles over the mechan-isms of PAP[1,3] and its application to sportsperformance.[1-3,18] If effectively utilized, PAPcould be implemented into a power-trainingroutine to enhance the training stimulus of aplyometric exercise.[2,18] Inducing PAP prior tocompetition might also prove better than con-ventional warm-up techniques at enhancing per-formance of explosive sports activities such asjumping, throwing and sprinting.[10] Because ofinconsistencies within the literature, research re-mains inconclusive on the possible benefits ofPAP to explosive sports performance and/ortraining. The inconsistencies of past researchare most likely due to the complex interaction

of factors that influence acute performance fol-lowing a CC.[1-3,18] This review discusses theseconfounding factors in greater detail, with thepurpose of helping to inform and direct futureresearch efforts towards establishing the appli-cation (if any) of PAP to performance/training ofexplosive sports activities.

2. Mechanisms of PAP

It has been proposed that two principal me-chanisms are responsible for PAP. One is thephosphorylation of myosin regulatory lightchains (RLC),[1,3,4,11,12,19,20] and the other is anincrease in the recruitment of higher order motorunits.[1,10,20] There is also evidence to suggest thatchanges in pennation angle may contribute toPAP, and this possible mechanism is briefly in-troduced in this article.

2.1 Phosphorylation of Regulatory LightChains

A myosin molecule is a hexamer composed oftwo heavy chains (figure 1).[21] The amino-termini of each heavy chain, classified as themyosin head, contain two RLCs,[9,21] and eachRLC has a specific binding site for incorporationof a phosphate molecule. RLC phosphorylationis catalyzed by the enzyme myosin light chain ki-nase, which is activated when Ca2+ molecules,released from the sarcoplasmic reticulum dur-ing muscular contraction, bind to the calciumregulatory protein calmodulin.[1,5,13,21] RLC

148 Tillin & Bishop

ª 2009 Adis Data Information BV. All rights reserved. Sports Med 2009; 39 (2)

phosphorylation is thought to potentiate sub-sequent contractions by altering the structureof the myosin head and moving it away fromits thick filament backbone.[1,21] It has alsobeen shown that RLC phosphorylation rendersthe actin-myosin interaction more sensitive tomyoplasmic Ca2+.[13] Consequently, RLC phos-phorylation has its greatest effect at relativelylow concentrations of Ca2+, as is the caseduring twitch or low-frequency tetaniccontractions.[1,3,4,22,23]

An acute increase in RLC phosphorylation,and a parallel potentiation of twitch tension fol-lowing tetanic stimulation of specific efferentneural fibres, has been reported by many studiesin skinned animal models[5,7,9,13] (figure 2). Re-latively few studies have attempted to measure asimilar response in human skeletal muscle. Stuartet al.[8] recorded a significantly elevated phos-phate content of RLC in the vastus lateralismuscle (p< 0.01), and a significant potentiation oftwitch tension of the knee extensors, followingone 10-second isometric maximal voluntary con-traction (MVC; p < 0.05). There was also a posi-tive but non-significant correlation between theextent of twitch potentiation and the amount ofphosphate incorporated into individual RLCunits, and between potentiation and percentageof type II muscle fibres (p > 0.05).

Smith and Fry[24] also sampledmuscle biopsiesat the vastus lateralis, and analysed dynamicleg extension performance before and 7 minutesafter a 10-second isometric MVC. The authors

reported no significant change in RLC phos-phorylation or leg extension performance for theentire sample (p > 0.05). The subjects were thensplit into those who responded to theMVCwith asignificant increase, and those who respondedwith a significant decrease in RLC phosphoryla-tion (p < 0.05), but no significant differences in legextension performance were found between thegroups (p > 0.05). Methodological factors anddifferences in fibre-type distribution between an-imals and humans may explain why an observedincrease in RLC phosphorylation following aCC is not as consistent in humans as animals.Nevertheless, the significance of RLC phosphory-lation in human skeletal muscle remains unclear,and Stuart et al.[8] suggest that other factors mayprovide the major contribution to PAP.

2.2 Increased Recruitment of Higher OrderMotor Units

Research on animals has shown that an in-duced tetanic isometric contraction (caused bystimulating specific afferent neural fibres, whichin turn activate adjacent a-motoneurons via anafferent neural volley; figure 3) elevates thetransmittance of excitation potentials acrosssynaptic junctions at the spinal cord. This ac-commodating state can last for several minutesfollowing the tetanic contraction,[10] and as a

Myosin heavy chains

Actin binding site

RLC-2

ATP binding site

Fig. 1. One myosin molecule. Each myosin molecule is composedof two myosin heavy chains. Regulatory light chain (RLC)-2 re-presents a pair of RLCs positioned at the neck of a myosin head.Each RLC can incorporate a phosphate molecule, altering thestructure of the myosin head. At each myosin head there is an actinand adenosine triphosphate (ATP) binding site.

0

0.2

0.4

0.6

0 10 20 70 130 190 250Time (sec)

mol

pho

spha

te/m

ol R

LC

1.0

1.2

1.4

1.6

1.8

2.0

Tw

itch

peak

torq

uepo

tent

iatio

n (p

ost/p

re)Phosphate content

Twitch potentiation

Tetanic contraction

Fig. 2. The time-course of regulatory light chain (RLC) phosphor-ylation and twitch peak torque potentiation, following a 10-secondpre-conditioning tetanus. Potentiation is represented as a ratio of thepost-maximal voluntary contraction (MVC) peak torque value to thepre-MVC peak torque value (post/pre). These results indicatea possible relationship between RLC phosphorylation and twitchtension potentiation (reproduced from Moore and Stull,[7] withpermission).

Post-Activation Potentiation, Theory and Application 149


result there is an increase in post-synaptic po-tentials, for the same pre-synaptic potential dur-ing subsequent activity.[25,26]

Luscher et al.[26] proposed a possible mechan-ism underlying the elevated transmittance of ac-tion potentials across synaptic junctions at thespinal cord. For each parent neural fibre (i.e. Iafibre) numerous synapses project onto eacha-motoneuron. Activation of an a-motoneuronworks in an all-or-none fashion, whereby pre-synaptic transmitter release must coincide withthe post-synaptic receptor sensibility. Transmit-ter failure at various synaptic junctions is acommon occurrence during normal reflex or vo-luntary responses, due to an autonomously pro-tected activation reserve.[26,27] An induced tetaniccontraction is suggested to decrease the trans-mitter failure during subsequent activity, via oneor a combination of several possible responses.These include an increase in the quantity of neuro-transmitter released, an increase in the efficacyof the neurotransmitter, or a reduction in axonalbranch-point failure along the afferent neuralfibres.[28]

Hirst et al.[27] provided evidence to support adecreased monosynaptic transmitter failure dur-ing subsequent activity. They stimulated cat af-ferent neural fibres, and observed a 54% increasein excitatory post-synaptic potentials (EPSPs)for the same pre-synaptic stimulus, following a20-second tetanic isometric contraction. LargerEPSPs represent greater depolarization of thea-motoneuron membrane, which would increasethe likelihood of that a-motoneuron reaching thethreshold required to initiate an action potential,and subsequently contract the muscle fibres ofthat motor unit.

Luscher et al.[26] also measured EPSPs at cata-motoneurons, in response to electrical stimu-lation. They found a significant positive correla-tion between motoneuron input resistances andEPSP amplitude, for a standard stimulus (r= 0.77;p < 0.01; figure 4a), where input resistance wasassociated with the size of the a-motoneuron(with a smaller input resistance representing alarger motoneuron). This suggests that mono-synaptic transmitter failure is greater at largermotoneurons (those responsible for activationof higher order or fast-twitch motor units). Con-versely, when a twitch was stimulated following a10-second tetanic contraction, Luscher et al.[26]

found a significant negative correlation betweenEPSP potentiation and motoneuron inputresistance (r = -0.92; p < 0.001; figure 4b). Thisdemonstrates that a tetanic contraction decreasedthe transmitter failure occurring primarilyat larger motoneurons, which resulted in aconsiderable PAP effect at these motoneurons.If a CC could induce an increase in higher ordermotoneuron recruitment in humans, this effectmight theoretically increase fast-twitch fibrecontribution to muscular contraction, and there-fore enhance performance of a subsequent ex-plosive activity.[10]

Previous studies have measured the H-wave inhumans to investigate the effects of a CC onmotoneuron recruitment.[10,29] The H-wave(H-reflex) is recorded at the muscle fibres usingelectromyography, and is the result of an afferentneural volley in response to single-pulse sub-maximal stimulation of the relevant nerve bundle(see figure 5 for more detail). An increase in

Spinal cord

Alpha motoneuronto synergist

Alpha motoneuronto antagonist

Antagonistmuscle

Synergistmuscle

Agonist muscle

Muscle spindle

Afferent neuralfibre (la)

Alpha motoneuronto agonist

Alpha motoneuronsynapse

Fig. 3. The neural volleys of a Ia afferent fibre. An action potentialgenerated at the Ia afferent neural fibre travels to the spinal cord,where it is transferred to the adjacent a-motoneuron of the agonistmuscle. The action potential then travels directly to the agonistmuscle, initiating the processes of muscular contraction.

150 Tillin & Bishop


H-wave following a CC may therefore representa decrease in transmitter failure at synapticjunctions, and a subsequent increase in higherorder motoneuron recruitment. Gullich andSchmidtbleicher[10] stimulated the tibial nerveand measured changes in H-wave amplitude atthe gastrocnemius before and after five 5-secondisometric MVCs of the plantarflexors. They re-ported a depression in H-wave amplitude 1 minute

after the MVCs (-24%; p < 0.05), but a potentia-tion of H-wave amplitude 5–13 minutes after theMVCs (+20%; p < 0.01). The H-wave, however,was not normalized to maximalM-wave (M-waveis the electrical counterpart of the activation of allmotor units in the pool[30]). Therefore, otherfactors not relating to central activation, such asincreased activity of the Na+-K+ pump at themuscle fibres,[12,14,28] may be responsible for theresults that Gullich and Schmidtbleicher[10] ob-served. Nevertheless, other studies have reporteda potentiation in normalized H-wave amplitude3–10minutes post eight sets of dynamicMVCs,[29]

and 5–11 minutes post a 10-second isometricMVC.[31] Collectively, these results suggest thatPAP increases H-wave amplitude in humans(albeit after sufficient recovery), and this may bethe result of increased higher order motoneuronrecruitment at the spinal cord. Whether or not aCC can enhance motoneuron recruitment andperformance during a subsequent voluntary con-traction is yet to be determined.

The effect of isometric MVCs on subsequentvoluntary motoneuron recruitment has been as-sessed using the interpolated twitch technique(ITT). The ITT can facilitate measurement of

Spinal cord

Electricalstimulation

1st response to the electricalstimulation (M-wave)

2nd response to the electricalstimulation (H-wave)

Afferent neural fibres

Efferent neural fibres

Muscle

Fig. 5. Elicitation of an M- and H-wave. Stimulation of a nerve witha single submaximal electrical impulse evokes two electrical re-sponses at the muscle. The first response (M-wave) is the result ofan action potential travelling directly down the efferent neural fibres(a-motoneurons). The second response (H-wave) is the result of anaction potential travelling along the afferent neural fibres to the spinalcord, where it is transmitted to adjacent efferent neural fibres, anddown to the muscle.

0

6

12

0 1 2 3 4 5

Input resistance (MΩ)

% In

crea

se in

EP

SP

am

plitu

de

Larger motoneurons Smaller motoneurons

0 1 2 3 4 5

Input resistance (MΩ)

Larger motoneurons Smaller motoneurons

a

0

70

140

% In

crea

se in

EP

SP

am

plitu

de

b

Fig. 4. (a) The relationship between input resistances of cat moto-neurons, and amplitude of their excitatory post-synaptic potentials(EPSP) in response to twitch stimulation of the adjacent afferentneural fibres. (b) The relationship between input resistances of catmotoneurons, and the percentage increase (potentiation) in EPSPamplitude, in response to a twitch stimulation of the adjacent afferentneural fibres, following a 10-second tetanus. Although EPSP ampli-tude is greatest at smaller motoneurons (those with greater inputresistances), representing greater transmitter failure at larger moto-neurons (a), potentiation is greatest at larger motoneurons (thosewith smaller input resistances), demonstrating a decreased trans-mitter failure at these motoneurons (b).[22]



motoneuron activation[32] by comparing maximaltwitch amplitude at rest with that evoked whensuperimposed upon an MVC (for more detail ofthe ITT please refer to Folland and Williams[32]

and Shield and Zhou[33]). Using the ITT, Behmet al.[34] reported a decrease in voluntary muscleactivation following 10-second MVCs (p < 0.05).These results are in contrast to the proposedmechanism of PAP, but may demonstrate thedominance of central fatigue observed through-out this study (see section 4.2). Nevertheless, fu-ture research should consider using the ITT toinvestigate the mechanisms of PAP and theircontribution to subsequent performance.

2.3 Changes in Pennation Angle

The pennation angle of a muscle (the angleformed by the fascicles and the inner apo-neurosis) reflects the orientation of muscle fibresin relation to connective tissue/tendon.[35] Thepennation angle will therefore affect force trans-mission to the tendons and bones.[35,36] The sumof the forces of all individual fibres being appliedto the relevant tendon during muscular contrac-tion is reduced by a factor of cosy (where y =pennation angle).[36] Consequently, smaller pen-nation angles have a mechanical advantage withrespect to force transmission to the tendon.[35,36]

Using ultrasonography, Mahlfeld et al.[37] mea-sured resting pennation angle of the vastus la-teralis before and after three 3-second isometricMVCs. Pennation angle immediately after theMVCs (15.7�) had not changed from pre-MVCvalues (16.2�); however, 3–6 minutes after theMVCs, the pennation angle had significantly de-creased (14.4�; p< 0.05). This change would onlybe equivalent to a 0.9% increase in force trans-mission to the tendons, but it is possible that thiseffect may contribute to PAP. Conditioningcontractions, however, are also likely to increaseconnective tissue/tendon compliance,[38] and thismay counter any increase in force transmissioncaused by a decrease in pennation angle. Never-theless, the possibility that changes in musclearchitecture contribute to PAP warrants furtherinvestigation.

3. PAP and Mechanical Power

Performance of explosive sports activities islargely determined by mechanical power.[10,39-43]

Mechanical power can be defined as the rateat which force (F) is developed over a rangeof motion (d), in a specific period of time (t)[P =F ·d/t], or as force multiplied by velocity (v)[P =F · v].[39,40,43] Accordingly, increasing thelevel of force at a given velocity will increasemechanical power, and this has been demon-strated in skinned rat/mouse models.[16,17,22]

Similarly, decreasing the time over which a speci-fic force is applied, without altering the distanceover which that force is applied, will increasevelocity, and consequently mechanical power.PAP could, therefore, increase force and/orvelocity of the muscle contraction, which wouldenhance mechanical power and the associatedsport performance.

To date, there is little evidence that PAP canincrease maximal force. This is consistent withthe observation that increased sensitivity of themyosin-actin interaction to Ca2+ has little or noeffect in conditions of Ca2+ saturation, such asthose caused by higher stimulation frequencies(>20Hz for tetanic, or 200Hz for voluntarycontractions).[9,22] Stuart et al.[8] also found that a10-second isometric MVC of the knee extensorswas unable to increase maximum unloaded velo-city of subsequent dynamic contractions. Al-though PAP appears to have little effect at theextremes of the force-velocity curve (figure 6), ithas been shown to increase rate of force devel-opment (RFD) of tetanic contractions elicited atany frequency.[9] An increase in RFD causes aless concave force-velocity curve (figure 6), re-sulting in a greater velocity for a specific force, orvice versa.[3,44] Therefore, PAP may enhance theperformance of activities that require sub-maximal force and velocity production.[3,11]

Typically, athletes participating in explosivesports activities will not produce maximal forcebecause the mass they are attempting to move isoften relatively small (e.g. body mass), but theymust still overcome that mass so will not achievemaximal unloaded velocity either.[40] Conse-quently, PAP could benefit the performance

152 Tillin & Bishop


of explosive sports activities by increasing RFDand thus mechanical power.[3,11]

There is consensus over the existence of PAP,but if it is to be effectively utilized in performanceand/or training, research must first confirm thatPAP can be induced by an isometric or dynamicvoluntary contraction, and then show that itsbenefits can be realized during a subsequent ex-plosive sports activity. Unfortunately, measure-ment of both PAP and its effect on performanceof a subsequent explosive sports activity inhumans is inconsistent. Furthermore, little isknown about the degree to which the proposedmechanisms underlying PAP may play a role ininducing an elevated neuromuscular response.

4. Acute Effects of PAP on SubsequentActivity

The performance of explosive sports activitiesrelies predominantly on the activation of largemuscle groups (e.g. ankle, knee, hip and/or armand ab/adductors). Therefore, studies assessingthe effect of PAP on smaller muscle groups havebeen excluded from the following sections. Fur-thermore, it has been shown[45,46] and is widelyaccepted that contractions of maximal or nearmaximal intensity (>80% of dynamic or iso-metric MVC) optimize PAP.[4] Therefore, studies

assessing the effects of low-intensity contractionson subsequent performance have also beenexcluded from the following sections. Table Isummarizes the studies that have investigatedthe effects of a voluntary CC on subsequentvoluntary activity in humans.

In agreement with the results produced bystudies conducted on skinned mammalianmodels, research has consistently reported anenhanced twitch response following a CC inhumans. Hamada et al.[12] elicited a twitch reflexat the femoral nerve prior to, 5 seconds after, andthen every 30 seconds for 300 seconds after a10-second isometric MVC of the knee extensors.Twitch Pt (peak torque) was significantly in-creased 5 seconds after the isometric MVC(+71%; p < 0.01); however, by 30 and 60 secondsafter the isometric MVC, twitch Pt potentiationhad decreased to +44% and +31%, respectively(p < 0.01). Potentiation continued to decrease at amore gradual rate for the remainder of the re-covery period, but was still +12% 300 secondsafter the isometric MVC (p < 0.01). Similar find-ings have been reported in other studies,[6,11,59]

demonstrating that peak PAP is achieved im-mediately after a CC, but instantly begins to de-crease. The decrease in PAP is rapid for the firstminute, but then becomes more gradual resem-bling an exponential function (figure 7).

Although an isometric MVC has been foundto consistently enhance subsequent twitch ten-sion, evidence to show that PAP can be effectivelyutilized to enhance the performance of sub-sequent voluntary contractions is not as convin-cing. Gossen and Sale[11] assessed movementmechanics of both twitch and submaximal vo-luntary contractions following a 10-second iso-metric MVC. While the MVC enhanced twitch Pt

(p < 0.01), knee extension peak velocity follow-ing the MVC was significantly lower than kneeextension peak velocity executed in a controlcondition (326.7 vs 341.6�/sec; p < 0.03). Theseresults suggest that although the 10-second MVCinduced PAP, it also induced fatigue, and thatthe latter was more dominant during the volun-tary contractions. It has been proposed, there-fore, that it is the balance between PAP andfatigue that determines whether the subsequent

0

100

0 100Percentage of maximum force

Per

cent

age

of m

axim

um u

nloa

ded

velo

city

Increased RFD

Fig. 6. The relationship between force and velocity. The dotted linerepresents a less concave force-velocity curve due to an increasein rate of force development (RFD) [reproduced from Sale,[3] withpermission].



Table I. A summary of studies that have investigated the effects of a pre-conditioning contraction on a subsequent activity

Study Subjects Pre-conditioning contraction

(condition)

Volume Rest interval Performance test Performance changes

Batista et al.[47] 10 UT M Isovelocity MVC, knee

extension

10 (30 sec RI) 4 min

6 min

8 min

10 min

Isovelocity knee

extensions at all rest

intervals

6% › Pt* at each rest

interval

Behm et al.[34] 9 UT M Isometric MVC, knee

extension

1 · 10 sec

2 · 10 sec

(1 min RI)

3 · 10 sec

(1 min RI)

1, 5, 10, 15 min

for all volumes

Isometric MVC knee

extensions at all rest

intervals

2

2

10-min post: 8.9% fl Pf*15-min post: 7.5% fl Pf *

Chatzopoulos et al.[48] 15 UT M Back-squat 10 · 1 rep 90%1 RM (3 min RI)

3 min

5 min

30-m sprint

30-m sprint

2

3% fl 0–10-m sprint time*,

2% fl 0–30-m sprint time*

Chiu et al.[20] 24; 7 RT, 17 UT

(12 M, 12 F)

Back-squat 90% 1 RM · 5 (2 min RI) 5 min

6 min

7 min

5 min

6 min

7 min

CMJ: 30% 1 RM

50% 1 RM 70% 1 RM

SJ:

30% 1 RM

50% 1 RM

70% 1 RM

RT: 1–3% › , UT: 1–4% fl .

RT > UT*RT: 1–3% › , UT: 1–4% fl .

RT > UT*RT: 1–3% › , UT: 1–4% fl .

RT = UT

RT: 1–3% › , UT: 1–4% fl .

RT > UT*RT: 1–3% › , UT: 1–4% fl .

RT = UT

RT: 1–3% › , UT: 1–4% fl .

RT = UT

Ebben et al.[49] 10 RT M Dynamic bench-press 3–5 RM 0–5 sec Medicine ball BPT 2 GRF

French et al.[50] 14 RT (10 M,

4 F)

Isometric MVC, knee

extension

3 sec · 3 (3 min RI)

5 sec · 3 (3 min RI)

0–5 sec CMJ

DJ

5 sec C-sprint

Isovelocity KE CMJ DJ

5 sec C-sprint isovelocity

KE

2

5.0% › * (4.9% › GRF*)

2 6.1% › Pt * 2

2

2

3.0% fl Pt *

Gilbert et al.[51] 7 RT M Back-squat 100% 1 RM · 5 (5 min RI) 2 min

10 min

15 min

20 min

30 min

Isometric MVC at all rest

intervals5.8% fl RFD

5.8% fl RFD

10.0% › RFD

13.0% › RFD*2

Gossen and Sale[11] 10 UT (6 M,

4 F)

Isometric MVC, knee

extension

10 sec 20 sec

40 sec

Dynamic KE

Dynamic KE

2

2

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Table I. Contd

Study Subjects Pre-conditioning contraction

(condition)

Volume Rest interval Performance test Performance changes

Gourgoulis et al.[15] 20 M (11 RT,

9 UT)

Back-squats 2 reps of: 20%, 40%,

60%, 80%, and 90% 1RM

(5 min RI)

0–5 sec CMJ 2.4% › RT + UT*RT: 4.0% ›UT: 0.4% ›

Gullich and

Schmidtbleicher[10]

Study 1: 34 RT

(22 M, 12 F)

Study 2: 8 RT

Isometric MVC, leg press

Isometric MVC, plantarflexion

3 · 5 sec (5 min RI)

5 · 5 (1 min RI)

3 min, then every

20 sec. 8 jumps

measured

1 min, then every 2nd

min for 13 min

CMJ and DJ

Isometric MVC,

plantarflexion

3.3% › CMJ*. › DJ*13% fl RFD 1 min post*.

RFD 3 min post. 19% ›RFD 5–13 min post*

Hanson et al.[52] 30 UT (24 M,

6 F)

Back-squats 4 reps of 80% 1 RM 5 min CMJ 2

Jenson and Ebben[53] 21 RT (11 M,

10 F)

Back-squats 5 RM 10 sec

1 min

2 min

3 min

4 min

CMJ

CMJ

CMJ

CMJ

CMJ

4–13% fl *2

2

2

2

Kilduff et al.[54] 23 RT M Dynamic back-squats

Dynamic bench-press

1 · 3RM

1 · 3 RM

15 sec

4 min

8 min

12 min

16 min

20 min

15 sec

4 min

8 min

12 min

16 min

20 min

CMJ

CMJ

CMJ

CMJ

CMJ

CMJ

Barbell BPT

Barbell BPT

Barbell BPT

Barbell BPT

Barbell BPT

Barbell BPT

2.9% fl Pp*2

6.8% › Pp*8.0% › Pp *2

2

4.7% fl Pp *2

2.8% › Pp*5.3% › Pp*0.8% › Pp*

Magnus et al.[55] 10 UT M Back-squats 90% 1 RM 3 min CMJ 2

Rahimi[45] 12 RT M Back-squats 2 · 4 reps of 80%1 RM (2 min RI)

4 min 40-m sprint 3% fl 0–40 m sprint time*

Rixon et al.[56] 30 UT (15 M,

15 F)

Dynamic back-squats

Isometric MVC back-squats

3 RM

3 · 3 sec (2 min RI)

3 min

3 min

CMJ

CMJ2.9% › JH *, 8.7% › Pp *2 JH, 8.0% › Pp *

Robbins and

Docherty[57]

16 UT M Isometric MVC back-squats 3 · 7 sec (8 min

between each set)

4 min CMJ after each set of

isometric MVC

2

Young et al.[58] 10 UT M Back-squats 5 RM 4 min LCMJ 2.8% › *BPT = bench press throw; CMJ = counter movement jump; C-sprint = cycle sprint; DJ = drop jump; F = females; GRF = ground reaction force; JH = jump height; KE = knee extensions;

LCMJ = loaded counter movement jump; M = males; MVC = maximum voluntary contractions; Pf = peak force; Pp = peak power; Pt = peak torque; RFD = rate of force development;

RI = rest interval; RM = repetition maximum; RT = resistance/athletically trained; SJ = squat jump; UT = un/recreationally trained; ›› indicates increase; flfl indicates decrease;

2 indicates no differences; * p < 0.05.

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contractile response is enhanced, diminished orunchanged.[2]

4.1 PAP versus Fatigue

The balance between PAP and fatigue and itseffect on subsequent explosive contractions hasbeen observed by several studies. Immediatelyafter a CC, Gullich and Schmidtbleicher[10] andGilbert et al.[51] reported a decrease or no changein isometric RFD, but following a sufficient re-covery (4.5–12.5 minutes[10] and 15 minutes[51])isometric RFD was significantly increased(+10–24%; p< 0.05). The same pattern of nochange/decrease followed by an increase incounter-movement jump (CMJ) peak power(+7–8%; p< 0.05)[54] and 30-m sprint perfor-mance (2–3%; p < 0.05)[48] 8–12 minutes and5 minutes, respectively, following a CC have alsobeen reported. Collectively, these results suggestthat although twitch studies have reported max-imal PAP immediately after a CC (described insection 4; see figure 7), fatigue is also presentearly on. Furthermore, fatigue seems moredominant in the early stages of recovery and,consequently, performance of subsequent volun-tary activity is diminished or unchanged. How-ever, fatigue subsides at a faster rate than PAP,and potentiation of performance can be realizedat some point during the recovery period. Figure 8illustrates the PAP-fatigue relationship and

shows how the net affect on subsequent volun-tary contractions might be very different to theeffect of a MVC on subsequent twitch contrac-tions (represented in figure 7).

There is also evidence that a recovery periodmay not be required to benefit from PAP, or thateven with a recovery period performance ofa subsequent voluntary activity may remainunchanged/diminished. French et al.[50] did notutilize a recovery period, but still observed a sig-nificant increase in both drop jump (DJ) heightand isovelocity knee extension Pt (+5.0% and+6.1%, respectively; p < 0.05), immediately afterthree sets of 3-second isometric MVC knee ex-tensions. Likewise, Gourgoulis et al.,[15] reporteda significant increase in CMJ height (+2.4%;p < 0.05) immediately after two back-squats per-formed with 90% of one repetition maximum(1RM). Conversely, Chiu et al.[20] were unable todetect a significant improvement in peak powerof three CMJs or three loaded squat jumps (SJ)[p > 0.05], even though they were performed aftera recovery period of 5, 6 and 7 minutes, respec-tively, following five sets of one back-squat, with90% 1RM. The three CMJs (5, 6 and 7 minutespost-activation), were executed with different

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

0 30 60 90 120 150 180 210 240 270 300Time immediately after a 10-sec isometric MVC (sec)

Tw

itch

peak

torq

ue p

oten

tiatio

n (p

ost/p

re)

Fig. 7. The time-course of twitch peak torque potentiation im-mediately after a 10-second isometric maximal voluntary contraction(MVC).[12] Potentiation is represented as a ratio of the post-MVCpeak torque value to the pre-MVC peak torque value (post/pre).

0

1

2

Pot

entia

tion

(pos

t/pre

)

Window1 Window 2

Condition volume Recovery time

Peak PAP

Peak fatigue

Performance

Fig. 8. A model of the hypothetical relationship between post-activation potentiation (PAP) and fatigue following a pre-conditioningcontraction protocol (condition).[3] When the condition volume is low,PAP is more dominant than fatigue, and a potentiation in subsequentexplosive performance (post/pre) can be realized immediately (win-dow 1). As the condition volume increases, fatigue becomes domi-nant, negatively affecting subsequent performance. Following thecondition, fatigue dissipates at a faster rate than PAP, and a po-tentiation of subsequent explosive performance can be realized atsome point during the recovery period (window 2).

156 Tillin & Bishop


loads (30%, 50% and 70% of 1RM, respectively),which may have affected peak power output, andmakes it difficult to compare differences in perfor-mance over the time-course. However, these re-sults were supported by those ofMangus et al.,[55]

who reported no change in CMJ height 3 minutesafter one back-squat with 90% 1RM. Finally,Behm et al.[34] observed no change in isometricpeak force immediately after three 10-secondMVCs;however, after a 10- to 15-minute recovery period,maximal force had decreased (7–9%; p< 0.05).These contradictory findings suggest that thePAP-fatigue relationship and its effects on sub-sequent voluntary activity are multi-faceted.

In summary, it has been suggested that fol-lowing a CC an optimal recovery time is requiredto diminish fatigue and realize PAP; however,evidence is inconsistent in support of this theory.There are a number of possible explanations forthe contrasting results produced by the afore-mentioned studies. The relationship betweenPAP and fatigue, and the overall effect of con-tractile history on subsequent performance, isinfluenced by a combination of factors.[2] Theseinclude: volume of the CC (e.g. sets, repetitionsand rest interval between numerous sets); in-tensity of the CC (although there is consensusthat maximal-intensity contractions optimizePAP), the type of CC performed (e.g. dynamic orisometric); subject characteristics (e.g. muscularstrength, fibre-type distribution, training statusor power-strength ratio), and the type of activity

performed after the CC.[1,2] Figure 9 illustratesthe interaction of these complex factors and thefollowing sections discuss them in more detail.

4.2 Conditioning Contraction Volume

The effect of the CC volume on the interactionbetween PAP and fatigue is highlighted by oneparticular study. Hamada et al.[14] used a fati-guing protocol of 16 5-second isometric MVCknee extensions, with each MVC separated bya 3-second rest interval. A twitch response wasstimulated at the femoral nerve pre-MVCs, bet-ween each MVC, 1 minute after the MVCs, andthen every second minute after the MVCs, for13 minutes. Twitch Pt gradually augmented overthe first three MVCs, peaking at a 127% increasefrom baseline values (p < 0.05). This demon-strates that PAP was more dominant than fati-gue, after the first three MVCs when the MVCvolume was small. For the remainder of the fati-gue protocol, however, twitch Pt progressivelydecreased, and by the sixteenth MVC measured32% below baseline-values (p < 0.05). This de-monstrates that as the volume of MVCs con-tinued to increase, so did the dominance offatigue. Following the fatigue protocol twitch Pt

gradually increased, and exceeded baseline valuesafter 30–120 seconds of recovery (+32%; p< 0.05).This demonstrates that fatigue dissipated at afaster rate than PAP and, consequently, there wasa potentiation in twitch Pt during the recovery

Conditionintensity

Conditionvolume Performance

Condition type:• Dynamic• Isometric

Mechanisms of PAP:• RLC phosphorylation• ↑ higher order motor-unit recruitment• ↓ pennation angle

Mechanisms of fatigue:• Central• Peripheral

Subject characteristics:• Muscular strength• Fibre type distribution• Training level• Strength-power ratio

Recoverytime

Type ofexplosiveactivity

Fig. 9. The complex factors influencing performance of a voluntary explosive activity following a conditioning contraction (condition). Con-dition intensity, volume and type will affect individuals differently, depending on their subject characteristics. Collectively, these factors willinfluence the extent to which the mechanisms of post-activation potentiation (PAP) and fatigue are affected. The interaction between themechanisms of PAP and fatigue will determine whether subsequent performance is potentiated, and the recovery period required to realizepotentiation. Regardless of the previous interactions, however, the response of some explosive activities to the condition may be different tothe response of other explosive activities. RLC = regulatory light chain.



period. An adaptation of these results is presentedin figure 10. These findings were supported inanother study.[6] They recorded twitch tensionin the dorsiflexors before and immediatelyafter five isometric dorsiflexion MVC protocols,where each protocol differed in MVC dura-tion (volume). Accordingly, each protocol in-duced a different level of PAP, with a 10-secondisometric MVC eliciting the greatest potentia-tion (twitch Pt: after a 1-second MVC = +43%;after a 3-secondMVC = +130%; after a 10-secondMVC = +142%; after a 30-second MVC = +65%;after a 60-second MVC = +14%). Again, theimportant question is whether or not a similareffect will occur during performance of voluntaryexplosive activities?

French et al.[50] assessed the effect of differentCC volumes on performance of subsequent vo-luntary explosive activities. They measured asignificant increase in isovelocity knee-extensionPt immediately after three 3-second isometricMVCs (+6.1%; p < 0.05), but reported a sig-nificant decrease in isokinetic knee-extension Pt

immediately after three 5-second isometricMVCs (3%; p < 0.05). In contrast, Behm et al.[34]

measured isometric MVC peak force after one,two and three sets of 10-second isometric MVCs,and the only effect reported was an 8–9%

decrease in peak force 10–15 minutes after threesets ofMVCs. As discussed in section 3, PAP is notexpected to enhance isometric peak force (whichrepresents maximal force), so Behm et al.[34] mayhave observed potentiation had they measuredvoluntary RFD or dynamic performance. Ad-ditionally, the smallest CC volume used by Behmet al.[34] (10-second isometric MVC) is arguablylarger than the smallest CC volume used byFrench et al.[50] (three 3-second isometric MVCsseparated by 3 minutes), and may therefore haveinduced a greater degree of fatigue. Furthermore,due to the various other measurements takenby Behm et al.[34] during the recovery period(including high-frequency tetanic contractions,twitches, 30% isometric MVC and ITT), fatiguemay have continued to accumulate, thus reducingany opportunity to realize PAP.

The results of the four aforementioned stu-dies[6,14,34,50] demonstrate the influence of CCvolume on the PAP-fatigue relationship. Theyalso present the possibility that PAP developsquicker than fatigue and may therefore be uti-lized immediately after a relatively low CC vo-lume (window 1 in figure 8). In contrast, as theCC volume increases so does fatigue and itsdominance in the PAP-fatigue relationship, andtherefore a recovery period may be required be-fore PAP is realized (window 2 in figure 8). Thespecific recovery period required for differentCC volumes is yet to be determined and it is dif-ficult to compare the results of individual studiesbecause methodologies have not been standar-dized. If future research intends to infer the idealwarm-up and/or training protocol for optimizingPAP, CC volume and recovery between theCC and subsequent activity should be assessedtogether.

4.3 Conditioning Contraction Type

Although, to varying degrees, any type ofcontraction is likely to activate the mechanisms ofPAP,[4] the degree of potentiation achieved islikely to be related to contraction type. Conse-quently, the use of different types of CC hasprobably contributed to the inconsistent resultsthat have already been discussed. As past research

−40

−20

0

20

40

60

80

100

120

140

Cha

nge

in tw

itch

torq

ue (

%)

Fatigueprotocol Recovery period

Time (min)

0 2 7

Fig. 10. The time-course of knee extensor twitch torque during afatigue protocol and throughout a subsequent 5-minute recoveryperiod. The fatigue protocol consisted of 16 5-second MVCs sepa-rated by 3 seconds of recovery. A twitch contraction was recordedpre-fatigue protocol, between each MVC, 5 seconds post-fatigueprotocol, and then every 30 seconds throughout the recovery period.Twitch torque is given as percentages of pre-fatigue values.[14]

158 Tillin & Bishop


has typically used either isometric or dynamic CC,this article will only discuss the differences be-tween these two types of contractions.

Several studies have investigated the effects ofisometricMVCs on subsequent explosive activity,and whilst two reported an increase,[10,50] othersreported no change in performance.[11,34,57] Paststudies have also used dynamic maximal/nearmaximal voluntary contractions to induce PAP,and again, some recorded potentiation of asubsequent explosive activity[15,45-48,54,58] andothers did not.[20,49,52,53,55] These conflicting re-sults (see table I for results) present no clear re-lationship between contraction type (isometric vsdynamic) and PAP-response, and only one study(to our knowledge) has directly compared iso-metric and dynamic CC with respect to theireffects on performance of a subsequent explosiveactivity.[56] This study reported that while asignificant increase in CMJ height (2.9%; p< 0.01)and peak power (8.7%; p< 0.001) was observed3 minutes after three 3-second isometric MVCback-squats, no change in CMJ height (p> 0.05)but a significant increase in CMJ peak power(8.0%; p< 0.001) was measured 3 minutes after a3RM dynamic back-squat set. The authors con-cluded that their isometric condition induced agreater PAP-response than their dynamic condi-tion. The two conditions, however, were notmatched with respect to volume or frequency, andas a result, it is difficult to make a direct com-parison between their effects.

Theoretically, different types of contractionwould have different effects on neuromuscularfatigue.[60,61] Babault et al.[60] assessed neuro-muscular fatigue during a dynamic contractionfatiguing protocol and an isometric contractionfatiguing protocol, where the two protocols werematched in terms of Pt decrement. The authorsreported that early fatigue during the dynamicprotocol was preferentially peripheral in origin(peripheral fatigue defined as a decrease in forcegenerating capacity due to action potential fail-ure, excitation-contraction coupling failure, orimpairment of cross-bridge cycling in the pre-sence of unchanged or increased neural drive[61]),while central fatigue (defined as a reduction inneural drive to muscle[61]) developed towards the

end of the dynamic fatiguing protocol. The iso-metric protocol, however, produced the oppositeprofile, whereby fatigue was firstly central andthen peripheral in origin.

Babault et al.[60] proposed that the differencein fatigue development between isometric andconcentric contractions might be associated withmuscle metabolite accumulation, which is sug-gested to activate and/or sensitize groups of smalldiameter (III and IV) afferent neural fibres.[60,62,63]

This would in turn cause central fatigue by in-hibiting a-motoneuron activation, and/or redu-cing the supraspinal descending drive,[60,63] and/ordecreasing motoneuron firing rate.[64] The inter-mittent nature of dynamic contractions may fa-vour blood flow, subsequently aiding the removalof metabolic by-products. Accordingly, metabo-lite accumulation would be greater during iso-metric contractions, resulting in greater centralfatigue. Conversely, lactate accumulation has beenreported to alleviate peripheral fatigue.[65] Thismight account for the slower development of per-ipheral fatigue during isometric contractionswhen compared with dynamic contractions.[60]

If isometric and dynamic contractions can in-duce different fatigue responses, then it is fair toassume that they might also have different effectson the mechanisms of PAP. For example, the ec-centric motion of dynamic contractions (but notisometric contractions) increases muscle spindlefiring, activating group Ia neural fibres.[63] Inturn, this might enhance the afferent neural volleyat the spinal cord. Consequently, decreased trans-mission failure from Ia neural fibres to adjacenta-motor units, resulting in increased higher ordermotor unit activation during subsequent activity,might be greater after dynamic contractions. Onthe other hand, isometric contractions activate agreater number of motor units than dynamiccontractions.[66] Consequently, more muscle fi-bres might be involved during an isometriccontraction, and this might result in a greaterpercentage of RLC phosphorylation, and greaterchanges in muscle architecture.

In summary, preliminary evidence suggeststhat isometric CCs may induce greater centralfatigue, but are more likely to activate the per-ipheral mechanisms of PAP. In contrast, dynamic



CCsmay induce greater peripheral fatigue, but arepossibly more likely to activate the central me-chanisms of PAP (table II). The manner in whichthese mechanisms interact has not yet been de-termined, but it is fair to assume that isometric anddynamic contractions will have different effects onsubsequent explosive activities. The differencesbetween isometric and dynamic contractions willalso influence the volume and recovery period re-quired to potentiate subsequent explosive activity.Future research should investigate the effects ofcontraction type on the mechanisms of PAP andfatigue, whilst standardizing CC volume and re-covery period. It is also not known whether a CCof any type is more beneficial than conventionalwarm-up methods,[18] and although one studysuggested that it is,[46] their results were specific tothe individuals and protocols assessed. Future re-search should compare the potentiating effects ofCC to conventional warm-up techniques.

4.4. Subject Characteristics

The subject characteristics that have beensuggested to affect an individual’s PAP-fatigueresponse include muscular strength, fibre-typedistribution, training level and power-strengthratio. These factors are discussed in more detail inthe following sections.

4.4.1 Muscular Strength

There is evidence to suggest that an in-dividual’s muscular strength might partly de-termine their PAP response following a CC.Gourgoulis et al.[15] observed a 4% increase inCMJ height (p < 0.05) following five sets of back-squats in those subjects able to squat a load of>160 kg. Conversely, those subjects unable to

squat loads of >160 kg, only recorded a 0.4% in-crease in CMJ height (p > 0.05). Similarly, Kilduffet al.[54] reported a correlation between muscularstrength (absolute and relative) and CMJ peakpower potentiation 12 minutes after a 3RMback-squat set (r = 0.63; p< 0.01). A possibleexplanation for these findings might be asso-ciated with subject fibre-type distribution. Thepositive linear relationship between muscularstrength and percentage of type II muscle fibresis well documented (r = 0.5–0.93; p< 0.05),[67-69]

and type II muscle fibres display the greatestincrease in RLC phosphorylation following aCC.[7] Furthermore, subjects with a higher per-centage of type II muscle fibres would pre-sumably have a greater number of higher ordermotor units in reserve, which could be activatedvia decreased transmitter failure, following a CC.The combined effect of a greater RLC phos-phorylation and a greater increase in higher-order motor unit recruitment would theoreticallypredispose individuals with a higher percentageof type II muscle fibres to a greater PAP re-sponse. Consequently, it could be speculated thatthe stronger subjects in the two studies discussedabove[15,54] had a higher percentage of fast-twitchmuscle fibres, and thus achieved a greater PAPresponse.

4.4.2 Fibre-Type Distribution

Hamada et al.[14] provided evidence to supporta relationship between fibre-type distribution andPAP. They separated their subjects into twogroups: one with predominantly fast-twitch (typeII) muscle fibres (T-II; n = 4), and a second, withpredominantly slow-twitch (type I) muscle fibres(T-I; n = 4). They reported a greater Pt response inthe T-II group during a 3-second isometric MVC(250.0 vs 171.0 N �m; p < 0.01). Furthermore, inresponse to a fatigue protocol of 16 5-secondisometric MVCs of the knee extensors, the T-IIgroup showed significantly greater twitch tensionpotentiation during the early stages of the fatigueprotocol (+127% vs +40% increase in Pt after thethird MVC; p< 0.05). However, the T-II groupalso had a greater decrease in both twitch Pt andMVC Pt during the later stages of the fatigueprotocol (p < 0.05). Therefore, although subjects

Table II. An illustration of the hypothetical effects of isometric and

dynamic conditioning contractions on the central and peripheral

mechanisms of post-activation potentiation (PAP) and fatigue

Type of

conditioning

contraction

The mechanisms of

PAP predominantly

induced

The mechanisms of

fatigue predominantly

induced

Isometric Peripheral Central

Dynamic Central Peripheral

160 Tillin & Bishop


with a greater percentage of type II muscle fibreselicited a greater PAP response, they also eliciteda greater fatigue response following a high-volume CC protocol.

There are a number of possible reasonswhy Hamada et al.[14] observed a greater fatigueresponse in the T-II group. As stated, Hamadaet al.[14] reported a greater Pt production in the T-IIgroup during the early stages of the fatigue pro-tocol. Therefore, according to the force-fatiguerelationship,[70] a greater fatigue response in theT-II group would be expected. Additionally, anegative correlation has been reported betweeninitial glycolytic rate and fatigue during inter-mittent exercise.[71] The specific task employed byHamada et al.[14] (16 5-second isometric MVCs,with 3 seconds of rest between MVCs) would relypredominantly on a high anaerobic adenosinetriphosphate (ATP) turnover rate, especially insubjects with a higher percentage of type II mus-cle fibres.[72,73] Therefore, although subjects witha higher percentage of type II muscle fibres areexpected to produce a larger MVC Pt, due to ahigher initial anaerobic ATP turnover rate, theyare also likely to show greater Pt decrements, dueto a greater utilization of anaerobic energy storesand the production of metabolites associatedwith fatigue.[74,75]

4.4.3 Training Level

An individual’s training level may also influ-ence PAP and fatigue responses following a CC.Chiu et al.[20] separated a sample of 24 subjectsinto athletes who were training and participatingin a sport at national and/or international level(RT; n = 7), and those who participated in re-creational resistance training (UT; n = 17). Fivesets of one back-squat with 90% 1RM and 5–7minutes of subsequent recovery induced a 1–3%increase in CMJ and SJ height in the RT group.In contrast, the UT group reacted to the samecondition with a 1–4% decrease in CMJ and SJheight. Chiu et al.[20] suggested that those subjectstraining at higher levels of resistance would de-velop fatigue resistance as an adaptation of theirintensive training regimens, and were more likelyto realize PAP. Chiu et al.,[20] however, did not

measure fibre-type distribution, so it is possiblethat a greater percentage of fast-twitch musclefibres in the RT group also contributed to theeffects observed in this study.

4.4.4 Power-Strength Ratio

There is also evidence to suggest that a sub-ject’s power-strength ratio will influence theirPAP response to a CC. Schneiker et al.[76] re-ported a significant negative correlation betweenpower-strength ratio and potentiation of peakpower during loaded CMJ, executed 2–4 minutesafter one set of 6RM back-squats (r2 = 0.65;p < 0.05). Furthermore, when the sample ofstrength-trained subjects were separated intothose with a power-strength ratio of <19W/kg(group 1) and those with a power-strength ratioof >19W/kg (group 2), group 1 had a significantnegative correlation between power-strengthratio and peak power potentiation (r2 = 0.91;p < 0.05). In contrast, group 2 showed no re-lationship between power-strength ratio andpeak power potentiation (p > 0.05). These resultssuggest that those subjects less able to effectivelyconvert their strength into power are more likelyto benefit from PAP than those that can. In ad-dition, it appears that there may be a power-strength ratio threshold above which subjects donot benefit from PAP.

In summary, several subject characteristicshave been suggested to affect an individual’sPAP-fatigue response, and this may partly ex-plain the inconsistencies of past research. Evi-dence suggests that individuals most likely tobenefit from PAP include those with a greatermuscular strength, a larger percentage of typetwo fibres (although fatigue may also be greaterin these individuals), a higher level of resistancetraining, and a smaller power-strength ratio.Further research, however, is required to validatethese findings as well as determine the possibleeffects of other subject characteristics such asmuscle and/or lever lengths. For coaches con-sidering the implementation of CC prior to ex-plosive activities (in training or performance), itmay be pertinent to first assess each athlete’s sus-ceptibility to PAP during the off-season period.



4.5 Type of Subsequent Activity

An additional explanation for the inconsistentresults of past research is the different types ofsubsequent explosive activities used to determinethe acute effects of PAP. The types of subsequentexplosive activities employed by previous studieshave included isometric MVCs,[10,34,51] isolateddynamic contractions (e.g. isovelocity kneeextensions),[11,47,50] and compound ballisticactivities (e.g. CMJ and DJ).[10,15,46,49,52-58] It ispossible that a specific CC will not have the sameeffect on different explosive activities.

With regard to differences between isometricand dynamic explosive contractions, previousstudies have reported moderate to strong corre-lations between isometric and dynamic RFD(r = 0.65–0.75),[77] and moderate to strong corre-lations between isometric and dynamic peakforce (r= 0.66–0.77).[77,78] These results indicate aclear relationship between tests measuring isometricand dynamic strength and power. There are,however, a number of differences in the neuraland mechanical processes involved in isometricand dynamic activities. For example, the motorunit recruitment and rate coding for an isometriccontraction will probably be regulated by the sizeprinciple,[79] whereby motor units are recruited ina hierarchical order of small, followed by higherorder units. On the other hand, dynamic con-tractions might display a specific pattern of mo-tor unit recruitment relevant to joint angle andposition through the range of motion.[80] Ad-ditionally, the eccentric movement involved indynamic contractions, but not isometric con-tractions, would result in a greater afferent(group Ia neural fibres) input from musclespindles.[61,81] As a result, the a-motoneuron ac-tivation responses for isometric and dynamiccontractions would be different.[82] Furthermore,utilization of elastic strain energy (stretch-shortening cycle), stored in the muscles during aneccentric contraction, provides a significant con-tribution to overall performance of dynamicmovements.[83-85] The stretch-shortening cycle,however, is not utilized during an isometric con-traction and, consequently, isometric contrac-tions may not reflect the muscles capabilities for

dynamic situations.[82] Finally, PAP is greatestwhilst the muscle is shortening[86] and extends tohigher stimulation frequencies in concentricwhen compared with isometric contractions.[22]

This suggests that PAP may have a performance-enhancing effect beyond what would be expectedbased on isometric contractions.

It is also likely that whilst a specific CC mightenhance performance of a particular dynamicactivity, it might decrease or have no effect on theperformance of a different dynamic activity.French et al.[50] analysed isovelocity knee exten-sion, CMJ, DJ and 5-second cycle sprint perfor-mance before and immediately after three3-second MVC knee extensions. They reportedsignificant improvements in DJ height, DJ RFDand knee extension Pt (+5.0%, +9.5% and +6.1%,respectively; p < 0.05) after the MVCs, but foundno significant effect in any of the other activities(p > 0.05). French et al.[50] used time-motionanalysis to explain their results. They reportedthat the DJ and knee extension MVC had amuscle activation period of £0.25 seconds. Incontrast, the CMJ and 5-second cycle sprint hada muscle activation period of ‡0.25 seconds. Ex-plosive muscle actions have previously beendefined as those that have an activation periodof £0.25 seconds.[77] French et al.[50] thereforeconcluded that PAP was only effective in tasksdefined as explosive muscle actions. The conclu-sions of French et al.,[50] however, should beinterpreted with caution. Some studies have re-corded a potentiation effect in CMJ performance,as well as other activities that otherwise might notfall under the above definition of explosive mus-cle action.[10,15,46,51,54,56,58] In addition, Frenchet al.[50] only measured exercise performance im-mediately after the CC, and a rest interval mayhave been needed for a potentiation effect to berealised. Finally, the CC exercise was an isola-tion exercise targeting the knee extensors alone.The DJ may load the knee extensors to a greaterextent than the CMJ and 5-second cycle sprint,which would explain the increase in DJheight/RFD. The CMJ and 5-second cycle sprint,however, may rely on the contribution of variousother large muscle groups, which due to thekinematics of the CC, had not been potentiated.

162 Tillin & Bishop


These results therefore highlight the importanceof closely matching the kinematics of the CC tothose of the subsequent explosive activity. Bydoing so, an individual is more likely to activatethe higher order motor units, phosphorylate theRLC and change the architecture of those musclefibres specifically associated with the subsequentactivity.

The aim of recent research has been to estab-lish the application of PAP to specific explosivesports activities. Explosive sports activities aredynamic in nature so, for the reasons discussedabove, isometric responses to a CC should not beused to infer effects of the same CC on sub-sequent sports activities. If researchers are in-vestigating the application of PAP to a trainingscenario, the reported effects of a CC on sub-sequent ballistic activities (e.g. CMJ and DJ) maybe useful, as ballistic exercises are used in power-training programmes. On the other hand, whilstPAP may sometimes be effective in enhancingperformance of a ballistic exercise, it may nothave the same ergogenic effect on performance ofa specific explosive sports activity (e.g. sprinting,long jump). If PAP is to be utilized in competi-tion, research must first determine its effectsbeyond those reported for ballistic training ex-ercises. Two recent studies have shown that PAPcan enhance performance of a specific explosivesports activity, reporting a decrease in sprint time(-3% over 10m,[48] -2% over 30m,[48] and -3%over 40m;[45] p < 0.05) 4–5 minutes after theexecution of near maximal (>80% 1RM) back-squats. Nevertheless, further research is requiredto establish the application of PAP to many dif-ferent explosive sports activities. Furthermore,even if PAP is consistently shown to enhanceperformance of different explosive sports activ-ities, several practical implications would need tobe addressed to effectively apply PAP to a com-petitive scenario (such as the need for possibleequipment in the warm-up area and the require-ment to compete within the optimal recoveryperiod following activation). As a result of theseimpracticalities, the application of PAP toperformance has been challenged,[18] but withreported increases in performance by >3%,further investigation is warranted.

5. Conclusion

It may be possible to effectively utilize PAP toenhance mechanical power and therefore perfor-mance and/or the training stimulus of an explo-sive sports activity. Evidence over the practicalapplication of PAP to explosive activities is,however, inconclusive. The inconsistent results ofpast research appear to be due to the complexinteraction of several factors that determine thedegree to which the different mechanisms of PAPand fatigue are affected. Greater CC volumes andintensities are expected to induce greater levels ofboth PAP and fatigue. However, the rates atwhich PAP and fatigue develop and dissipatemay differ, resulting in two windows of oppor-tunity to potentiate performance; immediatelyafter a low-volume CC, or after a specific re-covery period following a high-volume CC. Thetype of CC may also have different effects on themechanisms of PAP and fatigue. For example,isometric MVCs may induce central fatigue, butperipheral PAP, whilst dynamic MVCs may in-duce the opposite response. The interaction ofthese different mechanisms would, in turn, de-termine the optimal CC volume and recoverytime required to potentiate (if at all) subsequentperformance. Regardless of the above factors, anindividual training at a higher level, with a greatermuscular strength, a greater fast-twitch fibredistribution and a lower power-strength ratiomay be more likely to benefit from PAP than anindividual without these characteristics. Wheninterpreting results, consideration should also begiven to the specific application of PAP in sport.If the intention is to utilize PAP in competition,only the results of studies reporting the effects ofa CC on performance of a specific explosivesports activity should be considered. Althoughstandardization of these various factors providesfuture research with an extremely arduous task,the results of studies showing 2–10% increases inperformance suggests further investigation ofPAP may be worthwhile. It may be pertinent,however, for research to first establish how themechanisms of PAP and fatigue interact underdifferent conditions before applying PAP tosport.



Acknowledgements

No sources of funding were used in the preparation of thisreview and the authors have no conflicts of interest that aredirectly relevant to the contents of the review.

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Correspondence: Mr Neale A. Tillin, School of Sport andExercise Science, Loughborough University, Ashby Road,Loughborough, Leicestershire, LE11 3TU, UK.E-mail: [email protected]

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Documents

Factors Modulating Post-Activation Potentiation and Its Effect on Performance of Subsequent Explosive Activities