Post Activation Potentiation (PAP)
- PART III - 

By Dr. Joel D. Seedman PhD
See Part I and Part II

Rest and Fatigue: The Perfect Balance

The idea of post activation potentiation has been a topic of great interest to researchers not only because of its seeming effectiveness for improving performance but also because of the challenge involved in balancing fatigue and rest.  Researchers have concluded most forms of muscular contractions produce both fatigue and potentiation to varying degrees. Because post activation potentiation relies on a form of short term synaptic plasticity to induce rather immediate effects on physiological performance there appears to be a specific time-frame for maximizing the potentiation response.  Unfortunately this window may be smaller than previously thought as too much rest may cause the heightened response of the CNS to diminish relatively quick yet insufficient rest will not allow fatigue to adequately dissipate.   Therefore the contractile history plays a significant role for determining the net balance between fatigue and potentiation with higher intensities inducing more fatigue yet greater potentiation and lower intensities producing less potentiation and less fatigue.  It is for these reasons that many researchers and strength coaches have found balancing these factors to be the true art associated with producing post activation potentiation from strength training.

The rest period used between the PAP-inducing activity and the assessment of the PAP response appears to be one of the most commonly manipulated and investigated variables by researchers.  Chatzopoulos et al. [1], and Esformes et al. [2] found 5 minutes to be effective for producing post-activation potentaition with heavy barbell squats.  Similarly Crewther et al. [3] and Lowery et al. [4] found 4-8 minutes as being the desirable rest period following heavy squats for producing improvements in jump performance although 8-12 minutes produced similar improvements.  Finally other investigations have concluded that longer rest periods (5-20 minutes) may be equally or more effective for producing PAP [5] [6].   Finally, shorter rest periods such as 0-3 minutes has in most cases shown to be ineffective or inferior for producing post tetanic potentiation when compared to longer durations of rest [7, 8]. 

In essence much of the literature suggests that 4-8 minutes is sufficient and ideal for most training conditions [3, 4, 9].  Lastly it should be noted that other factors and training variables such as mode of exercise, upper vs. lower body movements, volume of exercise, training experience, strength levels, and intensity of exercise may each play a substantial role when determining the ideal duration of rest for PAP protocols.  Future research will hopefully shed further light on this topic and give better insight into how these variables interact with each other as well as clarify optimal conditions for maximizing the balance between rest and fatigue.
 

Repetition Protocol

The appropriate repetition range is directly related to training intensity and loading parameters. Furthermore repetition protocol may have a similar effect on rest and fatigue as that previously described with training intensity.  In order to maximize the potentiation response and minimize the degree of fatigue most research points to the fact that a lower repetition range may be more suitable for producing PAP.  A majority of investigators such as West et al. [10] Lim et al. [11] and Kilduff et al. [12] have utilized 3 repetitions for their research.  However multiple studies such as those performed by Weber et al. [13] and Mitchel et al. [9] have successfully used 5 repetitions to induce a post activation potentiation response.  Finally other investigations have discovered that using heavy singles (1 repetition) with heavy loads has been an effective PAP protocol [1].   Lastly it should be re-emphasized that many of the repetition protocols used in these studies were a direct result of the load being used.  In other words lower repetitions (1-3) were usually a result of heavy loads (87-93% 1RM) whereas higher repetitions (4-5) were typically a result of lighter loads (60-85%).

In regards to isometric training conditions, repetition protocols were similar to those involving isotonic movements although there were distinct differences.  Most notably, the time under tension for each repetition or the duration of MVC varied amongst the studies.  Requena et al. [14] used the longest MVC’s inducing a significant improvement in jump performance with a single 10-second maximal isometric contraction.  Similarly Esformes et al. [15] produced post activation potentiation using a single 7-second isometrics.  Other researchers such as Rixon et al. [16] and French et al. [17] have utilized moderate volume (3 sets) combined with shorter duration isometrics (3 seconds) to create a potentiation response.  Finally results from a study performed by Pearson et al. [18] suggest that 5-second isometrics may be superior to 3 and 7-second isometrics.
 

Training Volume

Overall volume may play a critical role when trying to elicit the strongest post activation potentiation response.  Although varying degrees of training volume have been employed by researchers, current literature appears to have semi-conclusive information pertaining to this topic.  Numerous studies have demonstrated the effectiveness of utilizing a single set for post activation potentiation protocols [3, 6, 9, 19].  However multiple studies have also produced significant PAP using three sets rather than one [10, 12, 16].  Although most researchers have used a low to moderate volume of training (1-3 sets) a unique study by Chatzopoulos et al. [1] signifies that larger volumes (10 sets of 1 rep at 90% 1RM) can serve as an effective means for producing significant potentiation.  Finally it should be noted that some research indicates lower volume (1-2 sets) may be superior to higher (4-10 sets) or moderate volume (3 sets) [8].
 

Performance Outcome Measures and Dependent Variables

The theory of post activation potentiation has been examined solely on its effectiveness to elicit temporary increases in factors associated with force production.  Many if not all outcome measures that have been investigated include, speed, power, explosiveness, force, torque and other related variables all of which are directly related to force development.  A majority of these performance-related factors have been measured using some form of vertical jump assessment [4, 19] or sprint test variation [1, 11].  Other studies have utilized more controlled tests such as maximal twitch peak torque [14, 18] to determine PAP, a common laboratory assessment of potentiation.  Yet several studies particularly those involving upper body PAP have appropriated more unique assessments such as a ballistic bench press throw to measure maximal launch distance, peak power, peak force, and rate of force development [10, 15]. 

Although there appears to be moderate variability in outcome measures used to assess post activation potentiation, current research has only investigated factors directly linked to force production while altogether ignoring more complex bio-motor abilities such as balance, stability, symmetry, and mobility.  However many kinesiologists have hypothesized that these performance markers are likely linked to strength and force production in a similar yet more indirect manner as power and rate of force production [20].  If this is true then it is not irrational to conclude that if specific training protocols can induce temporary improvements in force production, power, and torque, then other factors such as stability, symmetrical loading, sway, and mobility may be similarly enhanced.  However future research is needed to validate such assumptions.
 

Static Stretching and its Anti-Potentiation Effect

For some, the idea of post activation potentiation can be difficult theory to accept.  However research examining the short-term effects of static stretching on force production may give greater credibility to the idea of PAP.   Numerous investigations such as those by Kay et al. [21], Samuel et al. [22], and Simic et al.  [23] have demonstrated the deleterious effects of short-term long duration static stretching on various markers of performance associated with power and force production. Various explanations have been constructed to support these findings with rationale similar to that used for explaining post activation potentiation.  It appears that stretching may have a similar yet opposite effect on recruitment and neural drive as witnessed for PAP with long duration static stretching causing acute neural inhibition, muscular relaxation, and overall decreased motor unit recruitment [23, 24].  While strength training may have a potentiating effect on the nervous system that appears to be witnessed almost immediately post activation, static stretching may have an inhibiting effect immediately after.  In essence long duration static stretching may have an inverse or antagonistic PAP effect.
 

Other Factors

Although research regarding post activation potentiation appears promising, offering great value to athletes and fitness enthusiasts alike there are various factors that require further investigation.  First, most studies suggest that not all individuals benefit similarly from post activation potentiation protocols [25].  A large majority of investigations have drawn similar conclusions demonstrating relatively small yet significant portion of research participants as being non-responders (those that produce no PAP effect) [26].  Even the most promising studies with large effect sizes consistently display non-responders.   Researchers suggest that multiple variables including gender, training experience, level of strength, muscle fiber type (slow vs. fast twitch athletes), and age could play significant roles in determining which individuals display the strongest postactivation potentiation response.

A study by Hamada et al. [27] demonstrated that individuals with greater percentage of fast twitch muscle fibers produce a more significant post activation potentiation response than those with greater percent of slow twitch fibers.  A meta-analysis by Wilson et al. [25] highlights specific findings suggesting those with greater training experience producing more significant levels of PAP with the response being similar between male and females.  Finally, Arabatzi [28] and his colleagues made several key discoveries in their investigation.  First, men and women both displayed post activation potentiation in response to maximal isometric squats.  However, more significant levels of PAP occurred in men.  Age also was a significant variable with no post activation potentiation response occurring in children (10-15 years of age). 

Although other factors may play a substantial role in determining the effectiveness of post activation potentiation, further research is needed to determine what variables significantly modulate the PAP response.
 

Conclusion

Post activation potentiation induced by heavy resistance training appears to be an effective method for temporarily increasing markers of force and power output.  Isotonic resistance in the form of barbell back squats or barbell bench press using 60-93% of 1RM appear to be the most common modes and intensities of exercise used to create a PAP effect on explosive movements such as jumping, throwing, and sprinting.  Furthermore studies indicate that full-range of motion activities may be a more effective method for creating potentiation than partial-range of motion movements.  Although findings are somewhat conflicting in regards to optimal rest between the PAP-inducing protocol and the assessment period, 4-8 minutes appears to be ideal although longer durations may be effective.  Finally, low to moderate volume in the form of 1-3 sets of 1-5 repetitions should be incorporated in order to achieve optimal potentiation while avoiding unnecessary fatigue.


References

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