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Original Research

Postactivation Potentiation Enhances Swim Performance in Collegiate Swimmers

Hancock, Andrew P.1; Sparks, Kenneth E.2; Kullman, Emily L.2

Author Information
Journal of Strength and Conditioning Research: April 2015 - Volume 29 - Issue 4 - p 912-917
doi: 10.1519/JSC.0000000000000744
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Abstract

Introduction

Understanding how the contractile properties of muscle fibers influence performance can provide coaches and athletes with additional options when devising training programs. Of particular interest to this study is the concept of postactivation potentiation (PAP), which has been shown to provide an ergogenic effect on athletic performance (13,16,20,21,25). Postactivation potentiation is characterized by an increased rate of force development (RFD) and has been observed after both voluntary (8,11) and electrically stimulated muscle contractions (11). The increased RFD while the muscles are under a potentiated condition is accompanied by a decreased time to peak force and has been theorized to enhance performance in subsequent athletic activities that use the potentiated muscle groups. The underlying physiology of PAP involves transient phosphorylation of the regulatory myosin light chains of the contracted skeletal muscles, essentially priming the muscle for enhanced RFD for a brief period for successive contractions (7,26).

Postactivation potentiation has been observed after conditioning contractions of 4–10 seconds in duration, and its effect has been observed from 4 to 12 minutes after the conditioning contraction (1,6,12,13,15). Studies have investigated performance enhancement and PAP after maximal muscle contractions of many varieties, including isometric, dynamic, and electrical stimulation (1,11–13,16,19,21,23–25), with several relating PAP to a direct performance improvement in subsequent athletic activity (2,13,16,21,24,25).

The practical application of PAP can be seen in the training philosophy known as complex training, which provides both short- and long-term benefits (4,16,25). Complex training is practiced in numerous sports and involves loading the muscle with a resistive activity before performing a sport-specific activity involving similar muscle groups. After a maximal or near-maximal muscle contraction, the muscles are in both a fatigued and potentiated state (10). The potentiated state remains for a period after fatigue subsides and provides a “window of opportunity” during which the athlete may be able to take advantage of an ergogenic benefit from the potentiated state (10) (Figure 1).

Figure 1
Figure 1:
Schematic highlighting the time line of fatigue vs. muscle potentiation after a maximal loading protocol. The area in gray represents the optimal window of opportunity during which fatigue has diminished but potentiation remains.

A common example of complex training is that of using a squat protocol (either isometric or dynamic) as the loading mechanism, followed by a series of countermovement jumps (CMJs) (8,21,22,29). Studies have been equivocal as to the performance benefit to be gained using this protocol, with some showing a demonstrated increase in performance following the loading protocol (21) and others showing no increase (8,22), or even a decline (29). The squat/CMJ protocol attempts to take advantage a delayed increase in muscular power, as opposed to an immediate increase in power with the stretch-recoil properties harnessed in plyometric movements.

Complex training is widely practiced in the sport of swimming, and it is gaining popularity at all levels of the sport from the novice to Olympic level. Although numerous studies have examined the longitudinal effects of complex training on swimming performance (5,18,27), the only one to examine the immediate effect of PAP on performance focused solely on the start (12). Thus, this study sought to quantify what effect, if any, could be seen by athletes completing a PAP loading protocol before a swimming sprint. The 100-m freestyle is a swimming event that lasts for less than 1 minute at the elite level and was chosen for this study because it requires a substantial application of anaerobic power.

Methods

Experimental Approach to the Problem

A test/retest protocol was followed, which allowed the subjects to act as their own controls. Each trial was separated by precisely 48 hours. During the experimental trials swimmers performed a maximal 100-m freestyle sprint, which was preceded by either a standard 900-m swimming warm-up or a standard 900-m swimming warm-up plus a PAP loading protocol. The standard swimming warm-up for both conditions consisted of an 800-m freestyle swim proceeded by 4 × 25-m freestyle sprints with a 40-second send-off. Subjects rested for 6 minutes before completing each maximal 100-m freestyle sprint trial. To avoid order effect, half of the subjects performed the control trial first and half performed the PAP trial first. Numerous biomechanical markers described below were measured to observe the response to the PAP loading protocol.

Subjects

Subject characteristics are presented in Table 1. Thirty healthy volunteers (15 men and 15 women; age range was 19-22 years old) from a collegiate varsity swim team provided informed consent before participation in the study, which was approved by the university's institutional review board. The subjects possessed a wide variety of training and stroke backgrounds: 7 subjects had a sprint training background, 7 of the subjects had a distance training background, and 16 of the subjects had a mix of some sprint and some distance training. The testing occurred during a general conditioning phase of the swimming season, and the subjects were 4 weeks removed from any competitions at the time of the study.

Table 1
Table 1:
Physical characteristics of subjects (mean ± SD).

Procedures

Before completing the swimming trials, the subjects had the following biometric data collected: height, weight, and body composition. Body composition was assessed through air displacement plethysmography (Bod Pod; COSMED USA, Chicago, IL, USA). The subjects then performed the 2 randomly ordered counterbalanced swimming trials, with 48 hours in between trials. During the control trial, the subjects were administered a standard 900-m swimming warm-up similar to their precompetition warm-up. After a 6-minute rest interval, the subjects performed a 100-m freestyle sprint from a dive start. During the PAP trial, the subjects were administered the same 900-m freestyle warm-up and immediately moved to the PAP loading protocol. A 6-minute rest interval was again observed before the subjects performed a 100-m swim sprint. The 6-minute rest interval falls within the range of 4–12 minutes shown by previous studies to provide adequate recovery time to take full advantage of the ergogenic effects of PAP (1,12,13). Subjects performed a 100-m cooldown after each test.

The PAP loading protocol was designed to produce a window of opportunity (Figure 1) during which the subjects could experience an ergogenic effect on their performance. This was accomplished using dynamic resistive sprints while attached to a Total Performance Power Rack (Total Performance, Inc., Mansfield, OH, USA). The power rack uses a pulley system, which loads the muscles with weighted resistance as the subject swims approximately 10 m. Subjects performed 4 repetitions at the calculated load, 1 minute apart, to satisfy the loading protocol.

Power rack load was individually prescribed based on a formula that was derived to handicap each power rack swim to a duration of ∼7 seconds, which was sought as a result of the duration of conditioning contractions used in previous studies (19,28) in addition to the swimmers' own experience when using the equipment. The formula derived was L = (0.2)(LBM)(100/t), where L is the load in kg, LBM is the lean body mass in kg, and t is the subject's best 100-m freestyle time in seconds. Lean body mass was included in an effort to correct for the physiological differences between genders, and the subjects' best time (t) was included in an effort to correct for differing athletic ability levels. As the denominator, t served the purpose of increasing the load for faster swimmers (smaller numbers) and decreasing the load for slower swimmers (larger numbers). A correction factor of 0.2 was used to bring the largest majority of athletes in line with the target time of ∼7 seconds.

Measurements

Times for the tests were obtained electronically using a System 6 electronic timing console and touch pads (Colorado Time Systems, Loveland, CO, USA). Daily calibration of the timing system was performed before data collection. Data collected using the timing console included total 100-m freestyle time, first 50-m split, and second 50-m split. The 50-m splits allowed for a more detailed analysis of the effects of PAP during various phases of the 100-m effort. Posttest blood lactates were obtained 2 minutes after the completion of each trial using a Lactate Plus instant lactate analyzer (Nova Biomedical, Waltham, MA, USA). The duration of each conditioning swim during the PAP loading protocol timed by hand, and the results were used to analyze the effectiveness of the loading formula.

Statistical Analyses

Descriptive statistics were obtained for all measures. An independent t-test was used to analyze any differences between genders for both the load assigned and the time for each conditioning swim. A repeated-measures analysis of variance (ANOVA) was used to examine differences in time between trials for the 100-m time, first 50-m split, and last 50-m split. The ANOVA also examined any differences between genders in response to the loading protocol. A paired samples t-test was used to examine any differences in lactate measures between the 2 trials. The level of significance for this trial was set at p ≤ 0.05, and all statistics were performed using SPSS 18.0 (SPSS, Inc., Chicago, IL, USA).

Results

Swimming Performance

The mean time for the PAP trial of 62.91 seconds was significantly faster than the time for the control trial of 63.45 seconds (p = 0.029; Table 2). The mean values for the first 50-m were 29.78 seconds for the control and 29.52 seconds for the PAP trial. Although the PAP trial was faster by 0.26 seconds, this was only a trend (p = 0.051). The means for the second 50-m of each trial were 33.67 for the control trial and 33.40 for the PAP trial. The PAP trial was 0.27 seconds faster, but again, this difference was only a trend (p = 0.058).

Table 2
Table 2:
Swimming performance for 100- and 50-m splits for all subjects (N = 30).

Gender Comparisons

There was no significant gender interaction in response to the PAP loading protocol. Table 3 summarizes the times of the genders for each performance measure. Both men and women showed improvements during the PAP trial relative to their control trials.

Table 3
Table 3:
Gender comparisons for biomechanical time markers.

Duration of Conditioning Swims

The time for each conditioning swim undertaken during the loading protocol was recorded, and the mean of each athlete's 4 repetitions was analyzed. The mean repetition times were 6.66 seconds for men and 7.95 seconds for women. The difference between genders of 1.29 seconds was significant (p = 0.001). The mean for the entire sample was 7.30, or 0.3 seconds slower than the target of ∼7 seconds.

Blood Lactates

Lactate readings tended to be higher after the PAP trial (12.3 mmol·dl−1) compared with the control trial (11.5 mmol·dl−1), although the difference was not significant (p = 0.099).

Discussion

The results of this study show that 100-m freestyle performance can be improved as a result of a PAP loading protocol performed before the event (Table 2). The mean time for the PAP trial (62.91 seconds) was significantly faster than the mean time for the control trial (63.45 seconds), with an improvement of 0.54 seconds. This is consistent with the results from other studies, which found that a resistance loading protocol was sufficient to produce PAP (1,11–13,16,19,21,25), and can subsequently enhance performance (13,16,21,25). Statistical significance aside, an improvement of 0.54 seconds is a very substantial margin in competitive swimming and precisely represents the difference between first place and seventh place in the men's 100-m freestyle at the 2012 Olympic Games.

The 50-m splits of each trial were also examined to determine whether the performance effect of PAP is achieved at a specific phase of a race. A major difference between the PAP response during each 50-m split could guide future research toward different events such as the 50-m freestyle (which requires more power) or the 200-m freestyle (which requires more anaerobic endurance). The PAP trial showed a trend for improvement in the first 50-m of 0.26 seconds over the control trial, which is a large margin in sprint swimming where races are routinely decided by tenths and hundredths of a second. The results for the second 50-m split were similar to those of the first, with the PAP trial being 0.27 seconds faster than the control trial. This improvement in time was also only a trend but again represents a margin that can and often times does decide sprint races. The improvement in the second 50-m split is particularly noteworthy considering previous applications of PAP that have only been investigated in short-duration (15 seconds or less) events, such as 10-m running sprints, maximal contractions, and muscular power measures. Our findings suggest that properly executed conditioning exercise may provide PAP-related enhancements that persist for 1 minute or longer, indicating that the application of PAP conditioning exercises may not solely apply to short-duration power performances.

Although there have been several reports of performance improvements from PAP, there are also numerous accounts indicating a lack of performance enhancement after PAP. There are likely many reasons for these discrepancies from our findings, including the intensity, timing, and nature of contraction of the conditioning exercise, as well as the training background of the study population. The intensity of the conditioning swim was designed to maximally challenge the swimmer over a 10-m swim, with a goal time of 7 seconds for each of the 4 repetitions. This was based on the findings of Requena et al. (19), who achieved PAP as measured by isometric torque using a ∼7-second duration for the conditioning exercise. Robbins and Docherty (22) also used a contraction length of ∼7 seconds, but in contrast to Requena et al. and this study, failed to induce PAP as measured by maximal CMJs. Both of these studies used a conditioning exercise consisting of 1 maximal isometric contraction. However, the measurement of PAP effectiveness differed between the 2 studies, and an improvement in muscular force production may not always translate into performance improvement as demonstrated by Kilduff et al. (12). Moreover, we had our athletes perform 4 repetitions of the conditioning exercise, which proved to successfully achieve PAP-related performance enhancement. However, Matthews et al. (15) used only a single 10-m resisted sprint on ice in competitive ice hockey players and showed a significant improvement in 25-m sprint speed on ice. This leads to the question of whether fewer conditioning repetitions would achieve the same magnitude of performance enhancement among collegiate swimmers or whether more repetitions could further improve PAP.

Rest interval between conditioning exercise and measurement of performance outcome is also a point of contention in the determination of the most effective use of PAP. We found that 6 minutes of rest was allowed between the conditioning swims, and the 100-m swim was adequate to enhance swim performance. However, some have suggested that true muscle potentiation dissipates as quickly as 5 minutes after a conditioning exercise (14), whereas a recent meta-analysis indicates that a rest interval of 8–12 minutes provides the greatest benefit (6). Thus, future studies need to be directed at investigating varying rest intervals to determine the best balance between fatigue recovery and peak muscle potentiation for collegiate swimmers.

Training status can also have a substantial impact on the effectiveness of PAP, with trained individuals showing a greater benefit from PAP than untrained. In a cross-sectional comparison of weightlifters vs. untrained individuals, the weightlifters exhibited an enhanced response to PAP (21). Recently, Miyamoto et al. (17) determined that the effect of PAP is augmented after a 12-week resistance training protocol. The extensive training background of our swimmers may have magnified the potency of the conditioning exercise and subsequent PAP.

Previous studies have indicated that there may be an influence of gender on the effectiveness of PAP (3,21). Boelk et al. (3) found that the power rack was insufficient to improve the power characteristics of female sprinters compared with a non–power rack swim, which begs the question as to whether there may be more effective methods of PAP loading for females than the power rack. We also had gender-related concern when devising the formula for conditioning swim load, questioning whether LBM would not correct enough for the performance differences between men and women when using the power rack, particularly given prior research suggesting that men are better suited to anaerobic performance in swimming (9). The mean contraction time for men was 6.66 ± 0.59 seconds, significantly faster than the time of 7.95 ± 1.18 seconds recorded for women. Furthermore, a much larger standard deviation for women indicates a greater degree of variability in the loading times. However, we found that this did not translate to a gender-related performance difference between our swimmers during the 100-m swim. The PAP loading protocol produced improvements for both men and women for the 100-m swim by 0.42 and 0.64 seconds, respectively. There was no significant gender interaction for 100-m swim performance, and this is in agreement with Witmer et al. (29) who observed no gender differences in PAP performance. Rixon et al. (21) hypothesized that women would see performance benefits resulting from PAP because of greater resistance to fatigue than men, which may explain why the 100-m performance of women still substantially improved in this study despite the longer duration of their conditioning swims.

There are a few limitations to this study worthy of mentioning for the purpose of directing future studies on this topic. The accuracy of timing of the 100-m swim is highly dependent on how the swimmer touches the touch pad and therefore presents a potential source of error between trials. However, it was assumed that each swimmer used the same technique each trial when touching the touch pad. The other limitations of this study are particularly associated with aspects of direct cellular mechanisms responsible for performance enhancement. We did not perform any invasive techniques beyond the fingerstick for lactate measurements. Given the substantial improvement of swim time, further investigation of the role of independent cellular components in performance enhancement is warranted. For instance, the use of muscle biopsies could confirm increased phosphorylation of regulatory myosin light chains, as seen with PAP. Measurement of muscle twitch characteristics after the conditioning swims is needed to verify enhanced RFD and thus true PAP. Furthermore, we cannot rule out the effect of increased muscle temperature as a result of the conditioning swims on performance improvement. However, it has previously been shown that muscle temperature did not play a role in performance in a study after a similar warm-up and conditioning scheme (24).

Practical Applications

This study indicates that 100-m freestyle performance can be improved in response to a PAP loading protocol performed 6 minutes before the swim. The improvement in this study of 0.54 seconds is a major difference in a sport that routinely has races decided by hundredths of a second. There are limitations in this investigation pertaining to the precise mechanisms responsible for swim improvement. Nonetheless, this study demonstrates a substantial and immediate improvement in swimming performance as a result of a PAP loading protocol and serves as a starting point to examine different distances, strokes, and loading methods to find the most effective ways to use PAP to improve swimming performance.

Acknowledgments

The authors extend their thanks to the swimmers and coaches of the swim team for their effort and time given for this investigation. No funding was received for this investigation. The results of this study do not constitute endorsement by the authors or the National Strength and Conditioning Association.

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Keywords:

sprint swimming; freestyle; power rack; competition

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