Postactivation Potentiation: A Brief Review

The goal of many researchers, strength
and conditioning professionals and personal trainers is to enhance the acute
and chronic effects of resistance training on a person’s overall athletic
performance. To that end, many resistance training methods, strategies and
ergogenic aids have been investigated. Some of the underlying mechanisms of
these strategies include increased
motor unit recruitment, muscle spindle firing and activity of the synergist
musculature; reduced
inhibition of the Golgi tendon organ; and a phenomenon called
postactivation potentiation (Hilfiker et al. 2007).

Postactivation potentiation (PAP) has recently gained popularity
in the strength training community because it offers a proposed approach for
optimizing muscle force and power production above and beyond performance
achieved through traditional training methods (Robbins 2005). This phenomenon
describes the enhanced and immediate muscle force output of explosive movements
after a heavy
resistance exercise is performed (Robbins 2005). The PAP phenomenon can
potentially maximize performance of explosive-based activities such as
weightlifting, sprinting, jumping and throwing activities (French, Kraemer
& Cooke 2003; Hilfiker et al. 2007).

Two Theories of
PAP

The underlying principle surrounding PAP
is that prior heavy loading induces a high degree of central nervous system
stimulation, resulting in greater motor unit recruitment and force, which can
last from 5 to 30 minutes (Chiu et al. 2003; Rixon, Lamont & Bemben 2007).
There are two proposed theories for PAP. The first involves an increased
phosphorylation (addition of a phosphate for the production
of ATP) of myosin
regulatory light chains (proteins of muscle contraction)
during a maximum voluntary contraction (MVC). This allows the actin
(the other protein of muscle contraction) and myosin binding (for
muscle contraction) to be more responsive to the calcium ions released (from
the sarcoplasmic reticulum), triggering a cascade of events leading to enhanced
muscle force production at the structural level of muscle (Hamada, Sale &
MacDougall 2000). The greater the muscle activation, the greater the duration
of calcium ions in the muscle cell environment (referred to as sarcoplasm)
and the greater the phosphorylation of the myosin light chain protein (Rixon,
Lamont & Bemben 2007). As a result, faster contraction rates and faster
rates of tension develop (Chiu et al. 2003).

The second theory involves the Hoff­mann reflex (H-reflex),
named after the scientist Paul Hoffmann who first described it. The H-reflex is
an excitation of a spinal reflex elicited by the Group Ia afferent muscle
nerves (specialized nerves conducting impulses to muscle). It is theorized that
the PAP intervention enhances the H-reflex, thus increasing the efficiency and
rate of the nerve impulses to the muscle (Hodgson, Docherty & Robbins
2005).

Muscle Fiber Type and PAP

It has been assumed that muscles with
shorter twitch contraction times show predominance in fast-twitch (type II)
muscle fibers and exhibit greater force than muscles with longer twitch
contraction times, such as slow-twitch (type I) fibers. It was the purpose of a
study conducted by Hamada et al. (2000) to investigate the correlation between
muscle fiber type distribution and PAP in human knee extensor muscles. The
study was completed in two phases. The first phase tested a group of 20 male
subjects. The subjects were measured by a dynamometer and were hooked up to an
EMG machine that measured muscle twitch response to a 10-second MVC.

In the second phase of the study, four subjects with the highest
and lowest PAP scores underwent a needle biopsy of the vastus lateralis to
determine the distribution of fiber type. The results showed that PAP is most
effective when type II fibers are a greater percentage of the muscles being
used. Thus, this phenomenon can be correlated to improved performance in
athletes and recreational enthusiasts who rely on shorter twitch contraction
times for optimal athleticism in spurt activities such as sprinting, jumping
and throwing.

Athletes vs. Recreationally Trained Individuals and PAP

A study conducted by Chiu and colleagues
(2003) investigated the impact of training status on the response to PAP in
athletes involved in explosive strength activities compared with individuals
involved in recreational training. Over four sessions, 12 men and 12 women
performed jump squats 5 minutes and 18.5 minutes after a controlled
(moderate-intensity) or heavy (high-intensity) PAP intervention. The study
found that recreationally trained athletes exhibited fatigue 5 minutes after
the acute heavy-resistance stimulus, and thus showed no enhanced performance.
However, in the athletically trained individuals, the heavy PAP stimulus
enhanced power performance during both tests (5 and 18.5 minutes after the
intervention). The authors concluded that PAP enhances explosive strength
performance in highly trained individuals, largely because of their
fatigue-resistant, high level of conditioning.

PAP Effects on Endurance Training

Endurance athletes typically have lower
percentages of type II muscle fibers compared with type I muscle fibers. Past
research has shown a greater PAP response in individuals engaging in activities
that involve more type II fiber types (Hamada, Sale & MacDougall 2000).
However, the same study revealed that endurance-trained individuals also show
an increase in the maximum shortening velocity of their type I fibers after a
PAP intervention. Additionally, the study authors concluded that endurance
athletes may have an increased resistance to fatigue, allowing the PAP effect
to prevail over fatigue.

Subjects in this trial were triathletes, distance runners, active
controls and sedentary individuals. Each group contained 10 subjects who
performed 10-second maximal isometric contractions of the elbow extensors and
ankle plantar flexors. Twitch responses were then elicited at 5 seconds and 1,
3 and 5 minutes post-MVC. Results showed that the triathletes, who trained both
the upper- and lower-body muscles, had an enhanced PAP response in both the
elbow extensors and plantar flexors compared with sedentary individuals. The
runners, who trained only lower-body muscles, were found to have an enhanced
PAP reaction in the plantar flexors but not in the elbow extensors.

The active control group, who trained both upper- and lower-body
muscles, had an enhanced PAP effect in both muscle groups, but the increases
were not as significant as those observed in the triathletes. The authors
concluded that PAP can indeed enhance endurance athletes’ performance by
offsetting fatigue. However, this enhancement is limited to the muscle groups
that are trained and is somewhat proportional to the training status of the
individual.

Incorporating PAP

Research has shown that PAP can enhance
athletic performance by increasing force development (rate and quantity) to
maximize explosive power. There are a variety of differing strategies and
methods for eliciting PAP, with no known approach being identified as the most
preferred. However, the conclusion of the studies examined in this brief review
point out a few concrete concepts. First, PAP is best for activities that
require explosive power movements, such as sprinting, high jumping, ski
jumping, weightlifting and boxing (French, Kraemer & Cooke 2003; Hilfiker
et al. 2007). Second, the PAP ergogenic stimulus has been found to last 2–30
minutes (Chiu et al. 2003; Rixon, Lamont & Bemben 2007). Last, the
preconditioning load amount appropriate in the PAP intervention is dependent on
the type of contractile activity used, a point that needs further elucidation
through research (Hilfiker et al. 2007). From this review it can also be
concluded that each individual athlete is uniquely different, and what works
for one athlete might not work for another.

As scientists advance and develop more consistent PAP usage
strategies, they will surely present (as they have done with periodization
models) methods of adaptation that will also help recreationally trained
clients optimally enhance their muscular fitness performance. n

SIDEBAR: Complex Training

The theory of complex training incorporates a training stimulus that involves coupling heavy and light loads alternately in an orderly sequence to lead to a higher PAP response (French, Kraemer & Cooke 2003). For example, a typical complex training exercise could pair a maximal-contraction exercise, such as a squat, immediately followed by a plyometric exercise, such as a depth jump (stepping off a box and then exploding upward upon ground contact). This training protocol offers an exercise sequence that enhances the involvement of the nervous system by heightening central nervous system excitability (French, Kraemer & Cooke 2003). Although some research into complex training has been completed, much more study is needed.

Roxanne Horwath, ATC, LAT, is a licensed and certified athletic
trainer. She is a graduate student at the University of New Mexico, Albuquerque
(UNMA), currently majoring in exercise science. She plans to pursue a degree
and a career as a physician assistant after completing her master’s program.

Len Kravitz, PhD, is the program coordinator of exercise
science and a researcher at UNMA, where he recently won the Outstanding Teacher
of the Year Award. In 2006 he was honored as the Can-Fit-Pro Specialty
Presenter of the Year and as the ACE Fitness Educator of the Year.

References

Chiu, L.Z., et al. 2003. Postactivation
potentiation response in athletic and recreationally trained individuals. Journal of Strength
and Conditioning Research, 17 (4), 671–77.

French, D.N., Kraemer, W.J., &
Cooke, C.B. 2003. Changes in dynamic exercise performance following a sequence
of preconditioning isometric muscle actions. Journal of Strength and Conditioning
Research, 17 (4), 678–85.

Hamada, T., et al. 2000. Postactivation
potentiation, fiber type, and twitch contraction time in human knee extensor
muscles. Journal
of Applied Physiology, 88, 2131–37.

Hamada, T., Sale, D.G., &
MacDougall, J.D. 2000. Postactivation potentiation in endurance-trained male
athletes. Medicine
& Science in Sports & Exercise, 32 (2), 403–11.

Hilfiker, R., et al. 2007. Effects of
drop jumps added to the warm-up of elite sport athletes with a high capacity
for explosive force development. Journal of Strength and Conditioning
Research, 21 (2), 550–55.

Hodgson, M., Docherty, D., &
Robbins, D. 2005. Post-activation potentiation: Underlying physiology and
implications for motor performance. Sports Medicine, 35 (7), 585–95.

Rixon, K.P., Lamont, H.S., &
Bemben, M.G. 2007. Influence of type of muscle contraction, gender, and lifting
experience on postactivation potentiation performance. Journal of Strength
and Conditioning Research, 21 (2), 500–505.

Robbins, D.W. (2005). Postactivation
potentiation and its practical applicability: A brief review. Journal of Strength
and Conditioning Research, 19 (2), 453–58.