Post-activation potentiation (PAP) is a phenomenon whereby muscular performance is enhanced acutely after an activity executed at a relatively higher intensity (e.g., a 1 repetition maximum (1RM) back squat performed before a vertical jump [VJ]) (11). The mechanisms behind this phenomenon are thought to include phosphorylation of regulatory light chains and an increased recruitment of higher threshold motor units (11). Post-activation potentiation has been demonstrated to increase sprinting (13), jumping (6), and throwing performance (5) and peak power (6).
Achievement of peak performance is dependent on the balance between fatigue and the underlying potentiation mechanisms that are initiated (11). This balance is affected by numerous variables including, but not limited to, training experience, rest period length after a conditioning contraction (CC), and the total volume load and the intensity of the CC performed. Chiu et al. (2) found that athletes who are engaged in regular explosive strength training responded with a 1–3% increase in vertical and drop jump height for 5–7 minutes after a warm-up of 5 sets of 1 repetition, performed at 90% of their 1RM. In contrast, those who were recreationally trained experienced a 1–4% decline in performance. Moreover, there is a moderate correlation (r = 0.63) between strength and countermovement jump potentiation after a high-intensity contraction (5). Stronger more trained individuals likely possess greater fatigue resistance than untrained or recreationally trained athletes. Although fatigue is present early on after a CC, its effects dissipate faster than potentiation. For example, Kilduff et al. (6) examined countermovement jump peak power immediately and at 4, 8, 12, 16, and 20 minutes after a 3RM back squat in professional rugby players. Peak power declined immediately after, but increased and peaked at 8–12 minutes, which suggests that this is an ideal time frame to demonstrate potentiation in a given activity.
The effects of intensity have not yet received adequate attention. For example, Rahimi et al. (7) investigated the effects of 2 sets of 4 repetitions in low-intensity (60% 1RM), moderate-intensity (70% 1RM), and high-intensity back squats (85% 1RM) on subsequent 40-m sprint time. Results indicated that the running speed had improved in an intensity dose-dependent manner (p < 0.05) after low-intensity (−1.9%), moderate-intensity (−2.77%), and high-intensity warm-ups (−2.98%). Unfortunately, because volume load was not controlled for, it is possible that increases in performance were a factor of increases in volume and not intensity. Moreover, it is unknown whether optimal rest period lengths differ from low to high intensities. Therefore, the purpose of this study was to investigate the effects of low, moderate, and high intensities under varying rest period lengths, with the volume load controlled, on VJ height and peak power in trained athletes.
Experimental Approach to the Problem
Achieving maximal performance is key to any exercise bout. Therefore, this study sets out to find what would give an athlete maximal performance while controlling for volume. Previous studies have looked at the effects of low-intensity, moderate-intensity, and high-intensity warm-ups, but the results could be to a simple confound of volume. For that reason, we needed to find out which form of intensity and volume could give the most optimal results when it comes to post-activation potentiation.
Participants completed a total of 4 testing sessions separated by a minimum of 72 hours rest over a 2- to 3-week period. Participants were directed to refrain from performing lower-body exercises 72 hours before testing. The first session involved familiarizing participants with the VJ assessment performed on a force plate and also assessment of their 1RM strength in the back squat. Participants were randomly assigned to one of the experimental conditions in the remaining 3 sessions. The experimental conditions required participants to perform the back squat using a low-intensity load (56% 1RM) for 5 repetitions, a moderate-intensity load (70% 1RM) for 4 repetitions, and a high-intensity load (93% 1RM) for 3 repetitions. These loads and repetitions were chosen as mathematically equivalent volume loads (repetitions Xs weight lifted) regardless of the participants’ 1RM starting strength (Table 1).
Thirteen male participants, aged 21 ± 3 years with a body mass of 84.1 ± 10.4 kg and a height of 179.8 ± 3.1 cm with a minimum of 3 years resistance training and an average relative full squat of 1.7 ± 2 times their body weight, were recruited for this study. All subjects gave informed consent before participating in the study, which was approved by the Institutional Review Board of The University of Tampa.
Participants completed a total of 4 testing sessions conducted at the same time of day (±1 hour) and separated by a minimum of 72 hours rest over a 2–3 week period. All participants were directed to refrain from performing lower-body exercises for a minimum of 72 hours before each experimental trial for the duration of the study while maintaining their usual training regime. During each testing session, participants wore the same clothing, and shoes worn on the first testing day to control any effects that this may have. The first day of testing served as a familiarization session in which participants performed a warm-up consisting of submaximal cycling for 5 minutes on a stationary cycle at 50 rpm (25 W). One minute after completing the warm-up, participants performed 1RM back squat testing. After a 15-minute rest period, participants performed 3 maximum VJs, followed by 5 minutes of seated rest and then finally by 3 more VJs. Fifteen seconds of rest were given between VJs, as it provides sufficient recovery for subsequent jump performance (8).
The 3 experimental conditions required participants to perform the back squat at 56, 70, and 93% of their concentric 1RM in a randomized order. Upon arriving for these testing days, subjects completed a 5-minute cycle warm-up followed by 1 minute latter by 3 maximum VJs. These 3 VJs served as their baseline or control jump height. After one minute, participants performed a warm-up with 50% of their working weight for that day for 10, 8, and 6 repetitions for the low-intensity, moderate-intensity, and high-intensity conditions, respectively. As demonstrated in Table 2, these repetitions and intensities resulted in equal warm-up volumes in each condition. After 5 minutes of rest, the participants performed their working sets at their randomly assigned condition, followed by 3 maximal VJs immediately after and at 2, 4, 8, and 12 minutes. Participants sat quietly between VJs. Peak values for each dependent variable were used for statistical analysis.
Vertical Jump Assessment
Participants performed a countermovement VJ (to a self-determined depth) using an arm swing, with the goal of jumping as high as possible. Consistent verbal encouragement was provided to all participants. All jumps were performed on a multicomponent AMTI force platform (Advanced Mechanical Technology, Inc., Watertown, MA) that interfaced with a personal computer at a sampling rate of 1000 Hz. Data acquisition software (LabVIEW, version 7.1; National Instruments Corporation, Austin, TX) collected values for VJ height and vertical power. Jump height on the force platform was calculated via the formula ([a X t2]/8] where a is the acceleration because of gravity (9.81 m·s−2) and t is flight time (seconds). Peak power was calculated as the peak combination of ground reaction force and peak velocity during the accelerated launch on the platform. Reliability of VJ height and power were 0.97 and 0.96, respectively.
One Repetition Maximum Testing
The concentric 1RM test for the back squat began with a warm-up at a light resistance of 50% 1RM (5–10 repetitions). The load was then increased in 13.64–18.18 kg increments until only 1 successful repetition could be completed. Each participant's 1RM was determined in approximately 5 attempts as all 1RMs were found within these attempts. A lift was deemed successful as described by International Powerlifting Federation rules for performing the back squat requiring the subject to descend to a point where the inguinal fold is lower than the patella and ascend to the starting position without assistance. In the event of a failed 1RM attempt, the weight was decreased by 4.54–9.09 kg until completion of a successful lift. All lifts were performed on a steel power rack (Powerlift Power Rack).
To control for diet, participants kept a record of their diet (all food and beverages) for 24 hours before the first session. The diet was then given to the participant with instructions to replicate the food consumption for 24 hours before the second, third, and fourth trials.
A 3 × 6 (condition × time) repeated-measures analysis of variances was performed using Statistica (StatSoft, Tulsa, OK) to determine differences in each dependent variable with an alpha level of 0.05. A Tukey’s post hoc for pairwise comparisons was run in the event of a significant F-test.
Cohen’s D determined the magnitude of the treatment effect (changes in height and power) using the effect sizes for strength training research according to Rhea (9). Cohen’s D was calculated using the following equation: post-mean − pre-mean/pre-SD. The magnitude of effect was classified by Rhea as trivial if the effect size was <0.25, small if the effect size was between 0.25 and 0.50, moderate if the effect size was between 0.50 and 1.0, and large if the effect size was >1.0.
There was a condition by time effect, in which VJ height did not change at any point in the low-intensity condition, whereas decreasing immediately after squat for both the moderate- and high-intensity conditions. In the moderate-intensity condition, VJ height increased and peaked a minute 4 and returned to baseline by minute 8. However, in the high-intensity condition, VJ height increased and peaked from minutes 4 to 8 and returned to baseline by minute 12 (Figure 1). The effect size for low-intensity VJ height was trivial throughout the 12 minutes, whereas there was a large effect size for both the moderate- and high-intensity conditions (Table 3). There was also a significant condition by time interaction for peak power, in which there was no change at any time point in the low-intensity condition but decreased immediately after (minute 0) both the moderate- and high-intensity conditions. In addition, in the moderate-intensity condition, peak power increased and peaked at minute 4 and returned to baseline by minute 8. In the high-intensity condition, peak power peaked from minutes 4 to 8 and returned to baseline by minute 12 (Figure 2). The effect size for VJ peak power was moderate in the low-intensity condition, whereas there was a large effect size for moderate and high conditions throughout (Table 3).
The main findings in this study were that VJ height and peak power increased to the same extent in the moderate- and high-intensity conditions, with no change found in the low-intensity condition. These changes peaked at minute 4 and returned to baseline values by minute 8 in the moderate-intensity condition. However in the high-intensity condition, these values peaked from minutes 4 to 8 and did not return to baseline until minute 12. These results suggest that high-intensity workloads may prolong the duration of PAP. Our results also seem to indicate that measurements of VJ performance and power is enhanced equally by both moderate and high intensities with equal volume loads.
The outcome in our study of VJ height and power peaking at minutes 4–8 is in line with Kilduff et al. (6) and Jo et al. (4) who found that PAP was optimized at 8–12 minutes and 5–10 minutes, respectively, in trained athletes. These results are also in agreement with Guellich and Schimidtbleicher (3) who demonstrated that the isometric rate of force development significantly increased after a recovery of 4.5–12.5 minutes. In a more sport-specific setting, Wilson et al. (12) investigated the effects of the optimal rest periods after a warm-up with baseball bats of varying weights on peak bat velocity in National Collegiate Athletic Association Division II intercollegiate baseball players. As in this study, these researchers found that velocity peaked at 4–8 minutes after a warm-up.
Our findings suggest that performance enhancement after a high-intensity warm-up are dependent on the rest after that warm-up. These findings are explained by fitness fatigue model of performance by Banister et al. (1). According to this theory, a high-intensity warm-up leads to the build up of fitness (PAP) and fatigue in the athlete (1). After a heavy conditioning mode, fatigue may be elicited in the form of depletion of substrate, a build up of H+ ions, or mechanical disruption of the myofibrillar architecture (12). Short-term gains in fitness after heavy muscle preloading are thought to include phosphorylation of myosin regulatory light chains and thus increased recruitment of higher-order motor units (12). Muscle damage appears to occur proportional to previous contractile intensity. Therefore, according to the model of Banister et al., it could be postulated that a moderately heavy and heavy protocols elicit fatigue and minor MD where as low intensity does not. The performance that results is the difference between these 2 variables. Therefore, rest is also essential to optimize performance. Although the length of PAP manifestation remains unknown, research indicates that the ability to potentiate performance likely dissipates by 30 minutes after a conditioning activity (10). Our current analysis suggests that overall moderate rest period lengths (4–8 minutes) appear to optimally augment power output after a conditioning activity (12). However, our findings also suggested that the duration of PAP lasted longer with high-intensity contractions. While we did not investigate the underlying mechanisms responsible for these findings, it is possible that greater loading schemes enhance motor unit recruitment and thus magnifies the phosphorylation of regulatory light chains (12).
In conclusion, the findings in our study suggest that moderate- or high-intensity training loads are sufficient enough to induce the effects of PAP when volume load is controlled. Additionally, VJ height and peak power appeared to endure longer at higher intensities. However, our results are only applicable to strength-trained men under low volume conditions and are focused on post-activation potentiation involving the lower body. Therefore, future research should investigate PAP effects for other parts of the body and determine responses in duration to greater total volumes of moderate- and high-intensity protocols.
Based on the results of this study, moderate- or high-intensity volume loads may be used by coaches and athletes during warm-up to elicit the effects of PAP. Post-activation potentiation can be used during track events such as the high jump, a atmosphere where testing involves maximal jumps or in any event that requires maximum power for a short burst such as in a baseball while warming up. However, high intensities seem to prolong the duration by which PAP is exhibited. However, we caution that there may be individual differences in responses to PAP and that training experience, rest period length, volume, and intensity should all be taken into consideration when prescribing a protocol intended to exploit the physiological improvements in performance that results from PAP.
The authors declare that they have no conflict of interest. This study was not funded by any company or grant.
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