Power can be defined as the rate of work or the product of force and velocity. There are a number of sports that require a high degree of lower-body power. Thus, for many sports, it can be considered the most important determinant of performance. Because of its impact on sports performance, the examination of power outputs during various types of resistance exercise is a heavily researched area (5,8,18,27). Many of these studies have focused on assessing the optimal intensity for maximizing power output during low-volume exercise (6,13,22,29,31). However, there has been significantly less research conducted examining power output during high-volume exercise. This may be because of some evidence that suggests power output preceded by high-volume endurance training is detrimental to high-speed strength performance (1,21). Additionally, high-repetition, hypertrophy-oriented, resistance training preceding a power training set was found to significantly decrease power output by more than 15% (3). Thus, it has been postulated that low repetitions are necessary to maximize power output (5).
The recommended number or repetitions varies with some studies using a low-to-moderate range (e.g., 2–6 repetitions; (2,4)) to a higher number of repetitions (e.g., 6–10 repetitions; (12,19)). Additionally, because the purpose of many studies has been to assess the optimal intensity that produces maximal power output, few researchers have used protocols consisting of multiple sets. Consequently, the effects of a multiple set high-repetition resistance training bout on power output are not clearly understood. Although power output would expectedly decrease during a high-repetition set, due to fatigue, it is unknown what effect the additional later repetitions would have on the initial repetitions of subsequent sets. The purpose of this study was to examine power output during a high-volume power-oriented back squat protocol and determine whether the performance of additional repetitions was detrimental to the power output of subsequent sets. We hypothesized that, as long as appropriate rest periods were provided, the completion of a higher repetition protocol would not be detrimental to the power output of subsequent sets.
Experimental Approach to the Problem
Resistance-trained individuals performed a power-oriented back squat protocol consisting of 5 sets of 16 repetitions to determine the effects of a high-volume exercise bout on power output throughout the duration of the protocol. Each subject visited the laboratory on 2 occasions; each separated by at least 4–7 days. During the first visit, subjects performed a 1 repetition maximum (1RM) test for the back squat and were familiarized with the back squat protocol cadence. Peak power (PP) during the performance of the squat protocol was examined for each subject on the second visit. All subjects performed the squat protocol to a regulated depth of 90°-knee flexion and a metronome-controlled cadence. Power output during each repetition was measured allowing within- and between-set analyses of power output decline. Furthermore, between-set comparisons of the highest repetition power output during each set were made to determine how power output was affected throughout the duration of the protocol.
Nineteen resistance-trained men between the ages of 19 and 25 (mean ± SD: age = 22.68 ± 2.98 years, mass = 85.94 ± 10.52 kg, stature = 174.71 ± 8.23 cm, squat 1RM = 149.60 ± 23.35 kg) volunteered to participate in this study. Inclusion criteria consisted of at least 6 months of lower-body resistance training experience with the inclusion of the back squat exercise being performed at least once per week. None of the subjects reported taking any ergogenic supplements (i.e., supplemental protein or creatine) before the study, nor reported any musculoskeletal injuries of the lower extremities, within 1 year before testing. All subjects were instructed to refrain from any caffeine consumption and vigorous physical activity within 12 hours of each session. Each subject signed an informed consent approved by the University's Institutional Review Board for human subjects before participation.
One Repetition Maximum Testing
All 1RM and squat protocol testing were performed in a multipurpose adjustable Commercial Power Rack (RockSolid Fitness, Rutland, VT, USA) with a standard 20-kg Olympic barbell. A light 5-minute aerobic warm-up was performed on a cycle ergometer at 50 rpm before each testing session. A successful 1RM attempt required each subject to descend at a metronome-controlled tempo of 2 seconds until a 90° angle at the knees was achieved. An elastic band was positioned across the power rack designating the bar height associated with the necessary squat depth. This provided subjects with a kinesthetic feedback when 90° was reached. The back squat 1RM testing began with a warm-up, consisting of 10 repetitions at approximately 50% of the subject's estimated 1RM load. After an adequate rest period of 3 minutes, the back squat 1RM was determined by selecting an initial load that the subject estimated to be approximately 90% of their 1RM, and subsequently applying light loads until the subject could not complete a repetition using proper technique through the full range of motion or failed to maintain the cadence. Additional trials were performed until the 1RM was determined within 2.27 kg (i.e., 5 lb), and using these procedures the 1RM was always achieved in ≤5 trials. A 3-minute rest period was allowed between all trials, and each subject's 1RM was used to determine the load for the squat protocol.
Back Squat Protocol
All subjects performed the squat protocol within 4–7 days of 1RM testing. Before the protocol, a 5-minute aerobic warm-up and a specific back squat warm-up consisting of 10 repetitions at 50% of their 1RM were performed by each subject. Upon 2 minutes of rest, subjects performed the squat protocol consisting of 5 sets of 16 repetitions at an intensity of 40% of the subject's 1RM. This intensity was based on previous research that suggests an intensity of 30–45% 1RM during resistance training to maximize the power output (8,14,17,23,27). Subjects were given 2 minutes of rest between each set, and the same cadence used for 1RM testing was also enforced for the eccentric phase of each repetition. However, subjects were instructed to perform the concentric phase of each repetition with maximal quickness by accelerating from 90°-knee flexion to complete extension as rapidly and explosively as possible, while maintaining flat feet.
The PP of each repetition during the concentric phase of the back squat was assessed with a Tendo weightlifting analyzer (Tendo Sports Machines, Trencin, Slovak Republic) that was attached to the barbell by means of a tether using previously reported procedures (16,28). The Tendo unit was placed on the floor in a position that would allow the cord to be extended perpendicular to the floor during the back squat exercise in accordance with the manufacturer's User Guide (11). The Tendo unit uses the tether displacement time and the manually entered load to calculate PP. Jennings et al. (15) demonstrated high test-retest reliability (intraclass correlation coefficient = 0.97) using these procedures for the assessment of muscular power during a multiple-joint exercise.
A 2-way [repetitions (minimum vs. maximum) × set (1–5)] repeated-measures analysis of variance (ANOVA) with a Greenhouse-Geiser correction was used to analyze the within- and between-set differences in PP. The highest repetition PP (PPmax) and the lowest repetition PP (PPmin) from each set for each subject were used for the within-set assessment. Percent decline was calculated using the following formula: (PPmax − PPmin)/PPmax ×100. Five separate correlations were performed to examine the decline across repetitions within each set. The repetition number and group mean PP for each repetition were used for these correlations. Statistical analyses were performed using PASW software version 21.0 (SPSS, Inc., Chicago, IL, USA), and an alpha level of 0.05 was used to determine statistical significance.
The 2-way ANOVA revealed a lack of a set × repetition interaction (p = 0.355). There was no main effect for set (p = 0.493), but there was a significant main effect for repetitions (the within-set measure: p < 0.001). Therefore, PP decreased significantly within each set (PPmax > PPmin), but this decrease was independent of set number (set 1 = 2 = 3 = 4 = 5). The group mean PP for each repetition is shown in Figure 1A and the percent decline for each set is given in Figure 1B. The overall percent decline in PP was 31.3% when using PPmax and PPmin across the entire protocol (i.e., from any set).
In this study, PP was assessed during a high-volume power-oriented back squat protocol consisting of 5 sets of 16 repetitions at an intensity of 40% 1RM in resistance-trained men. To the author's knowledge, this is the first attempt to examine power output over the duration of a maximal-effort high-volume back squat protocol. The significant decrease in PP that was observed within each set (p < 0.001) was most likely due to fatigue. Few studies have examined power output during high-repetition power-oriented resistance training exercise.
One study, Baker and Newton (5), using a high-repetition protocol examined power output during a single set of 10 jump squats in professional rugby players. Although an absolute load of 60 kg was used during the jump squat for all subjects, it was determined that this represented an average of 35% 1RM for all subjects. The jump squat exercise produces higher PP than the traditional squat used in this study and lacks a deceleration phase during the concentric portion of the movement unlike the traditional squat. Nevertheless, similar to our findings, Baker and Newton (5) reported a significant decline in power output after the fifth repetition. Furthermore, by the 10th repetition, a 5.0% decline was observed for the jump squat. This is minimal compared with the percent decline demonstrated in this study for the first set (17.9%). Of course, this difference is most likely because of the discrepancy in duration (15 seconds vs. 60 seconds) and number of repetitions performed between protocols (10 vs. 16).
The results of this study and Baker and Newton (5) provide evidence that power output is negatively affected during a high-repetition set. Previous research examining power output during high-volume exercise suggests possible causes for the within-set fatigue induced throughout the 16 repetitions such as peripheral fatigue or a dampening effect of the stretch-shortening cycle (SSC). Smilios et al. (25) observed significant decreases in power output during the last 2 sets of a submaximal (40–50%) endurance-oriented back squat protocol consisting of 4 sets at 20 repetitions, whereas the electromyographic amplitude of the leg extensors demonstrated a gradual increase from set to set. Furthermore, an increase in blood lactate levels upon completion of the protocol was observed despite already having high values (10 mmol·L−1) after the first 2 sets, indicating that peripheral fatigue may have been the predominant cause for power decrements. Similarly, Tesch et al. (26) reported decreases in torque within and between each set during a maximal isokinetic protocol consisting of 32 concentric contractions at 180°·s−1 for 3 sets. Researchers concluded that there was no decrease in neural drive and that declines in torque were a result of peripheral fatigue. Pasquet et al. (24) observed torque decrements from set to set during 5 sets of 30 isokinetic concentric contractions at 50°·s−1 of the dorsiflexors. The authors concluded that peripheral changes, such as decreases in excitation-coupling intensity, led to the fatigue-induced torque decrements. Of course, it is impossible to make comparisons between previous findings and this study because no neuromuscular or metabolic measurements were obtained in the latter. However, previous findings are indicative of potential causes for the decreases in power output observed within each set. Finally, another plausible reason for the decrements in power output in this study may be because of progressive inefficiency of the SSC. Baker and Newton (5) concluded that decreases in power output observed during the performance of 10 jump squats were because of the continual use of the SSC during a high-repetition protocol which leads to a decreased ability to use stored muscle energy. Briefly, this impairment has been described as a fatigue-induced reduction in energy transfer between the eccentric and concentric phases resulting from repeated SSC movements (10). In a study comparing mechanisms of fatigue between a single set of back squats at 65% 1RM and continuous drop jumps, Wadden et al. (30) concluded that the fatigue and recovery patterns after slow (resistance training) and rapid (plyometric) SSC movements are similar. Thus, similar to Baker and Newton (5), impaired SSC function may have been the reason for the within-set power output decrements demonstrated in this study.
An important finding in this study was the lack of difference in PPmax between the sets (p = 0.493), indicating that subjects were able to sufficiently recover between sets when performing a high-volume power-oriented back squat protocol. Previous research has suggested restricting maximal power training to 6 repetitions or less (2,4,5,20). However, there have been few studies conducted for the purpose of examining power output during a high-volume, specifically high-repetition resistance training protocol. In this study, as expected, power output declined significantly within each set. However, as indicated by PPmax being similar between sets, the subjects were able to recover from the fatigue produced within each set. In other words, performing additional repetitions within each set did not affect the subjects' power output during the early repetitions of subsequent sets. This is in contrast to Smilios et al. (25) who found power output to be significantly higher during the first and second sets compared with the third and fourth sets, although this was most likely because of reductions in the load used in the third and fourth sets so subjects would be able to complete all repetitions. Therefore, it is difficult to make comparisons between these findings. Nevertheless, 2 minutes of rest between the sets was sufficient for recovery, allowing subjects to produce analogous PPmax values for each of the 5 sets. This finding demonstrates the likelihood of training at optimal power output levels over multiple sets during a maximal-effort back squat protocol. Thus, a protocol of this nature may be beneficial when the goal is to improve intermediate-term anaerobic performance (lasting between 60 and 90 seconds) (7), specifically intermittent weightlifting anaerobic endurance (9). Although we have shown that the additional repetitions within each set were not harmful to maximal power production, further intervention-based research is warranted to determine their efficacy.
In conclusion, few studies have examined power output over the course of a maximal-effort high-volume resistance training exercise. This study demonstrated a significant decline in power output within each set, most likely a result of peripheral fatigue. However, maximal power output was not diminished between sets indicating that a 2-minute recovery period was sufficient. The evidence shown in this study suggests that a high-volume protocol is conducive to power-oriented training for longer durations.
This study provides evidence indicating that a high-volume power-oriented back squat protocol can be performed without detrimental effects on the maximum power output capacity within each set. Although PP during resistance training is generally reached within the first several repetitions, it may be possible to achieve alternative adaptations by incorporating a higher repetition scheme. A protocol of this nature may be favorable for strength and conditioning professionals when training to improve weightlifting-specific anaerobic endurance. An improvement in this kind of performance may be of interest to coaches of sports such as soccer or rugby in which repeated explosive performances of the lower body are necessary.
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