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Original Research

Effect of Potentiating Exercise Volume on Vertical Jump Parameters in Recreationally Trained Men

Khamoui, Andy V; Brown, Lee E; Coburn, Jared W; Judelson, Daniel A; Uribe, Brandon P; Nguyen, Diamond; Tran, Tai; Eurich, Alea D; Noffal, Guillermo J

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Journal of Strength and Conditioning Research: August 2009 - Volume 23 - Issue 5 - p 1465-1469
doi: 10.1519/JSC.0b013e3181a5bcdd
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Abstract

Introduction

A warm-up prior to physical activity, training, and competition has been shown to optimize performance (9,18,22). To elucidate ideal preparation for specific activities, studies have investigated the effect of various warm-up protocols on parameters of athletic performance including speed (17,26), power (9,18,28), and agility (18). The use of high-force activities to evoke postactivation potentiation (PAP) can be a viable warm-up to improve performance (2,4-6,8,20,24,25,29). This is possibly due to phosphorylation of the regulatory myosin light chain of the muscle (4). Heavy-load bench press has served as a potentiating exercise to enhance upper-body power (1), while vertical jump (VJ) and sprint performance also improved following a high-force activity (17,26). Despite the potential benefits associated with PAP, a number of studies have found no significant performance improvements (3,7,10,12,13,16,21,23).

Training status may be a factor of interest as it appears to potentially influence the capacity for PAP. Chiu et al. (4) found athletes to have greater power percent potentiation compared with recreationally trained subjects after a heavy-load back squat. McBride et al. (17) found collegiate football players to decrease 40-m sprint time following a similar intervention. Likewise, Weber et al. (27) observed an increase in squat jump height following a 5 repetition maximum (5RM) back squat in collegiate track and field athletes. Gilbert and Lees (6) found elite throwers and powerlifters to significantly increase countermovement jump height subsequent to a heavy-load back squat, while Saez Saez de Villarreal et al. (22) observed enhanced jumping performance following a heavy back squat intervention in professional volleyball players. Collectively, these studies indicate training status to positively influence the capacity of PAP, with highly trained individuals exhibiting a greater ability to exploit this physiological event. On the other hand, performance enhancement via PAP in recreationally trained men lacks strong support. Several studies have used subjects with a year of back squat experience and found no significant improvements in jumping performance (21,23).

The characteristics of the potentiating exercise may influence the outcome of postintervention performance. Specifically, volume of the potentiating exercise may be of interest when prescribing an intervention designed to induce PAP; however, guidelines eliciting the optimal potentiating effect remain unknown. Previous PAP studies utilizing a heavy-load back squat intervention used varying volumes to improve subsequent performance (4,17,22). McBride et al. (17) observed a potentiating effect using a back squat of 1 × 3 at 90%, while Chiu et al. (4) assigned 5 × 1 at 90% 1 repetition maximum (1RM). Saez Saez de Villarreal et al. prescribed the back squat in clusters of 2 × 4, 2 × 2, and 2 × 1 at 80-95% 1RM. Based on these studies, it appears that a variety of back squat volumes may be assigned to bring about positive results. Therefore, to determine if previous inconsistencies in the capacity for PAP in recreationally trained subjects relates to potentiating exercise volume, the purpose of this study was to investigate the effect of different heavy back squat volume on VJ height, ground reaction force (GRF), impulse (IMP), and takeoff velocity (TOV) in recreationally trained men.

Methods

Experimental Approach to the Problem

To investigate the effect of different potentiating exercise volume on VJ performance in recreationally trained men, we utilized a within-subject design consisting of 5 testing sessions. The first session involved VJ assessment in a test-retest fashion without a back squat intervention (control). The subsequent 4 testing sessions were conducted in a test-retest randomized fashion with 4 different experimental conditions consisting of a back squat intervention. The experimental conditions required subjects to perform the back squat using a load of 85% 1RM (27,29) with volumes of 1 × 2, 1 × 3, 1 × 4, and 1 × 5. Vertical jump parameters were chosen as the dependent measures because they assess lower-body performance and have been used in previous studies that successfully utilized PAP to enhance VJ performance (6,8,20,22,25).

Subjects

Sixteen recreationally trained men (lifting at least twice a week) participated in this study: age 24.56 ± 2.10 years, height 174.53 ± 8.54 cm, mass 84.59 ± 14.75 kg, and 1RM back squat 124.71 ± 17.58 kg. Prior to participating in the study, subjects signed an informed consent document approved by the University Institutional Review Board. All participants had a minimum of 1-year back squat experience and were free of any orthopedic injuries that could hinder their ability to provide maximal effort. A Certified Strength and Conditioning Specialist monitored every session.

Procedures

Subjects completed a total of 5 testing sessions separated by 72 hours' rest over a 3-week period. All subjects were directed to refrain from performing lower-body exercises for the duration of the study. On the first day of testing, subjects performed a warm-up consisting of 5 minutes of submaximal cycling on a stationary cycle at 50 rpm (25 W). After completing the warm-up, subjects performed 3 maximum VJs, 5 minutes of seated rest, followed by 3 more VJs. Fifteen seconds of rest was given between VJs, as it provided sufficient recovery for subsequent jump performance (19). Upon completing the control condition, subjects performed 1RM back squat testing.

The 4 experimental conditions required subjects to perform the back squat at 85% 1RM with 2, 3, 4, or 5 repetitions in randomized order. Upon arriving for these testing days, subjects were again instructed to complete a 5-minute cycle warm-up followed by 3 maximum VJs, each experimental condition, 5 minutes of seated rest, and 3 more VJs. Five minutes' rest post intervention provided adequate recovery in previous studies that successfully enhanced jumping performance (4,22). Peak values for each dependent variable were used for statistical analysis.

Vertical Jump Assessment

Subjects performed a countermovement VJ (to a self-determined depth) with arm swing with the goal of jumping as high as possible. Consistent verbal encouragement was provided. 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 GRF. Jump 2 height on the force platform was calculated via the formula ([a × t2]/8] where ‘a’ is the acceleration due to gravity (9.81 m·s2) and ‘t’ is flight time (second). Takeoff velocity was determined by subtracting body weight from the force-time curve, dividing by body mass, and integrating with respect to time using the trapezoidal rule for numerical integration. Takeoff was defined as the instant mass dropped below 2.2 kg. Impulse was calculated by subtraction of body weight and integration of force-time curve, while jump IMP constituted the difference between positive and negative IMP.

One Repetition Maximum Testing

One repetition maximum testing for the back squat began with a warm-up at a light resistance (5-10 repetitions). The load was increased in 13.64 to 18.18-kg increments until only one successful repetition could be completed. Each subjects' 1RM was determined in approximately 5 attempts. A lift was deemed successful as described by International Powerlifting Federation (11) rules for performing the back squat requiring the subject to descend to a point where the inguinal fold was 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 (Muscle Maxx Power Rack; Power Systems, Inc., Knoxville, TN).

Statistical Analyses

Four 5 × 2 (condition × time) repeated measures analysis of variances were performed to determine differences in each dependent variable with an a priori alpha level of 0.05.

Results

Analysis of variances found no significant (p > 0.05) condition by time interactions for any dependent variable. There was a significant (p < 0.05) main effect for time for both GRF and IMP. Posttest scores were significantly less than pretest scores (Table 1), showing a decrease in VJ performance. There was no difference between pretest and posttest scores for either VJ or TOV (Table 1). Cohen's d effect size was small and medium for GRF and IMP, respectively (Table 1).

Table 1
Table 1:
Results (meanSD) of pretest vs. posttest VJ, GRF, IMP, and TOV.*

Discussion

The purpose of a potentiating exercise was to enhance subsequent performance while minimizing fatigue. This study did not find 2, 3, 4, or 5 repetitions to produce PAP in recreationally trained men, as indicated by the absence of VJ performance enhancements. Furthermore, significant reductions in GRF and IMP from pre- to posttest, collapsed across condition, suggest the potentiation-fatigue balance induced by a heavy-load back squat in this population to favor the latter. Therefore, a potentiating exercise consisting of a back squat at 85% 1RM with 2, 3, 4, or 5 repetitions did not elicit the appropriate response necessary to augment performance in recreationally trained men. Rather, using the back squat at this load produced performance decrements in this particular population.

Training status within the broadly defined recreationally trained classification may have affected the potential for our subjects to benefit from PAP. Young et al. (29) evaluated loaded countermovement jump height following a 5RM back squat intervention in men with at least a year of back squat experience and found that jump height significantly increased (2.8%) following the potentiating exercise. In contrast, Scott and Docherty (23) did not find a 5RM back squat intervention to enhance vertical or horizontal jump performance in “physically active men” with a mean 5RM back squat of 196.9 kg and body mass of 79.3 kg. Despite large lower-body strength, these subjects did not exhibit a propensity to benefit from PAP. Therefore, some unidentified characteristic other than strength may influence the ability of recreationally trained subjects to utilize PAP. Participants in our present study may not harbor that unidentified characteristic, the requisite training background, or the physiological characteristics enabling sensitivity to a potentiating exercise.

Potentiating exercise load could also have influenced the capacity for PAP in our subjects. Previous PAP studies with athletes have utilized variable load within the heavy-load range. Chiu et al. (4) and McBride et al. (17) used a back squat load of 90% 1RM, while Weber et al. (27) used a 5RM intervention (∼85-90%). Gilbert and Lees (6) had elite throwers and powerlifters to squat their 1RM prior to jump assessment. Saez Saez de Villarreal et al. (22) assigned multiset heavy-load progressions beginning with 80-95% 1RM. These studies illustrated performance enhancement with loads ranging from 80 to 100% 1RM in athletes. The back squat intervention of 85% 1RM in our current study may not be appropriate for recreationally trained men based on the loads performed by athletes. In other words, the physical requirements of performing the back squat at 85% 1RM may have evoked fatigue irrespective of volume. Hence, the effectiveness of loading strategies (i.e., decreased load) in generating PAP in recreationally trained men may be worth investigating further.

Rest interval length following a potentiating exercise also merits consideration as a factor influencing the capacity for PAP in our subjects. Kilduff et al. (14) evaluated peak power output during countermovement jumps immediately (within 15 seconds), 4, 8, 12, 16, and 20 minutes after a 3 repetition maximum back squat in professional rugby players and found that peak power output decreased immediately but increased following 8 and 12 minutes' rest, suggesting 8-12 minutes to provide optimal recovery following a heavy-load back squat in professional rugby players. Similarly, Kilduff et al. (15) examined peak countermovement jump height immediately (within 15 seconds), 4, 8, 12, 16, 20, and 24 minutes after a heavy-load back squat of 3 × 3 at 87% 1RM and found that peak jump height occurred 8 minutes post intervention, indicating this rest period to be optimal following a heavy-load back squat. Both studies seem to demonstrate at least 8 minutes of rest after a heavy-load back squat intervention to be optimal for enhanced countermovement jump performance in professional rugby players. The optimal recovery period for recreationally trained men has not been clearly defined, and it may be feasible that recovery requirements differ as a function of training status. Under this premise, the 5-minute rest period provided in our present study may not have been adequate for this subject population to generate and benefit from PAP.

With respect to kinetic data, we observed a significant pre- to postdecrease in GRF and IMP, while VJ and TOV decreased, although not significantly (p = 0.16 and p = 0.12 for TOV and VJ, respectively) collapsed across condition. Collectively, these results indicate the presence of fatigue during postintervention jump assessment. Weber's investigation of a 5RM back squat on squat jump height and GRF in athletes found both variables to significantly increase following the potentiating intervention (27). This illustrates the potentiation-fatigue balance to favor the former in trained athletes following a heavy-load back squat intervention. It also validates the use of a heavy-load back squat to generate PAP and improve performance in athletes while lending support to the potential drawbacks in assigning the same load to recreationally trained men.

Practical Applications

Utilizing a back squat warm-up of 85% 1RM to evoke PAP may not benefit recreationally trained men, regardless of volume. Hence, recreationally trained men should be advised against using the back squat at the volumes and load prescribed in the present study to augment jumping performance as it likely produces fatigue rather than a potentiating effect. In addition, the literature suggests 8 minutes' rest to be optimal following a heavy-load back squat in professional athletes. Therefore, 5 minutes' rest might not be optimal for recreationally trained men to benefit from a potentiating exercise.

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Keywords:

postactivation; back squat; ground reaction force; velocity

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