Postactivation potentiation (PAP) is a phenomenon by which a previous voluntary maximal or near maximal muscular action acts to induce an acute improvement of the following exercise (typically explosive or sprinting activities) (18). Despite the appeal of the potential PAP effect for athletes, researchers have found contradictory findings. For example, heavy back squats have been reported to improve subsequent vertical jump performance (25), whereas other studies have reported no benefits (8). The inconsistencies in these findings may arise from a number of sources influencing the balance between fatigue and potentiation (30). This balance is affected by numerous factors including, but not limited to, training experience (9), rest period length (20), type and mode of exercise, training intensity, and the volume of the conditioning activity (29).
Shorter rest periods (<1 minute) have been shown to be effective to elicit potentiation after low-volume (LV) protocols (e.g., 3 maximal voluntary contractions) (30), whereas longer intervals (>3 minutes) would be required to enhance performance after a multiple set of potentiating exercise (31). Some studies using whole body vibration (WBV) platforms (e.g., maintain an isometric half squat position for 30 seconds at frequencies of 30–40 Hz and 2- to 8-mm amplitude) found acute positive effects on jumping performance immediately (12) or 1 minute after the stimulating exercise (4).
Regarding the type of exercise used to elicit PAP effects, recent studies have analyzed the effectiveness of WBV to acutely enhance subsequent explosive strength performance. Although some studies found no acute effects of WBV on maximal isometric force (15), jump, sprint, or agility performance (10), positive results on vertical jump performance have been observed when combining frequencies between 30 and 50 Hz with 2- to 4-mm and 4- to 6-mm amplitude (1) and by using 30 Hz with 6.5 mm (14) or 2.5 mm (12) of vertical amplitude. Combining resistance training and WBV methods would induce a more pronounced neuromuscular acute response compared with performing only resistance exercise or WBV (22). This enhancing effect would occur because of an increase in gravitational load caused by performing resistance exercise onto a WBV platform. Of note, there are 2 types of WBV platforms, namely, those that uniformly oscillate vertically (i.e., synchronous) WBV and those that rotate around a central axis causing an alternate vertical displacement of the legs (i.e., oscillatory). Rittweger et al. (26) observed no potentiation effects on vertical jump height or isometric endurance after squatting with an extra load of 40% body weight onto a side alternating WBV (oscillatory) Galileo device with 26 Hz and 12-mm peak-to-peak amplitude. Despite the popularity of WBV synchronous platforms, to our knowledge, no studies have investigated the acute effects of performing resistance exercise with an external load on a synchronous WBV platform on subsequent muscular performance in athletes. Therefore, the aim of the present investigation was to examine the acute effects of different parallel squat (PS) PAP protocols with and without WBV using both a high-volume (HV) and an LV protocol on jumping performance in male college athletes. Additionally, the effectiveness of a short (1 minute) or long (4 minutes) rest period between stimulating and explosive exercises to elicit PAP effects will be analyzed. It was hypothesized that when PS is performed with WBV, regardless of volume protocol and because of the high gravitation stimulus, longer recovery time (4 minutes) would be needed for enhancing jumping performance.
Experimental Approach to the Problem
We analyzed the acute effects of different PAP protocols involving PS with 80% 1 repetition maximum (1RM) performed alone or combined with WBV on countermovement jump (CMJ) and best drop jump (BDJ) performance. This study included a randomized repeated measures counterbalanced design, whereby participants served as their own controls. After a familiarization period, participants performed 3 repetitions of a CMJ and BDJ as measurements of performance after 3 conditions (parallel squat without vibration [NV-PS], parallel squat onto a whole body vibration platform [WBV-PS], and control [C]) that were performed under HV and LV and short (1 minute) and long (4 minutes) recovery time. In addition, to check any training effects, pre- (T1) and postintervention measures (T2) were considered.
Fifteen male college athletes (8 American football and 7 baseball) (20.3 ± 1.3 years [SD], height 179.50 ± 5.3 cm, body mass 81.0 ± 10.8 kg) with at least 2 years of resistance training experience and no experience using WBV participated in this study. Written informed consent was obtained from all participants before the start of the study. All subjects were notified of the research procedures, protocols, benefits, and risks before providing written consent. Experimental procedures were evaluated and approved by the Institutional Review Board for Human Subjects at the College. A health history questionnaire was used to ensure that participants were healthy and free of any musculoskeletal injury or cardiovascular disease.
The study was carried out during the end of the preseason toward and the start of competition period. Participants reported to the laboratory on 19 separate occasions. To ensure the proper use of the WBV platform and correct PS technique under both NV-PS and WBV-PS conditions, the first 3 nonconsecutive sessions were allocated for familiarization purpose. During the second week, 2 testing sessions (T1) were performed. Day 1 consisted of body composition measurements and the determination of the 1RM on the PS. The second testing day involved a maximal CMJ test and the determination of the BDJ. The 8 PAP and 4 control protocols (12 sessions) were performed on nonconsecutive days during the third to the sixth week. To assess the influence of any training effects during the intervention period, a second 2-day testing session (T2) was carried out during the seventh week. To minimize any diurnal effects on performance, testing time was constant throughout the study period. Figure 1 depicts a schematic representation of the study design.
Condition and Protocol Descriptions
All participants performed 3 different main conditions: (a) PS with 80% 1RM without vibration (NV-PS), (b) PS with 80% 1RM on a whole body vibration platform (WBV-PS), and (c) a control condition (C). Each condition was performed using both LV and HV protocols involving 1 set of 3 repetitions or 3 sets of 3 repetitions with 2-minute rest between sets, respectively. In addition, all protocols were assessed after short (1 minute) or long (4 minutes) recovery periods.
Participants were instructed to squat with the maximum possible velocity during the concentric phase and control the decent phase until they reached the final flexed position with their posterior thigh parallel to the floor. One qualified instructor controlled the appropriate range of motion during the squat exercise for both NV-PS and WBV conditions. In the case of C, participants were required to maintain a stationary standing position on the weightlifting platform for the same period as required to complete the sets for the LV or HV protocols. Based on previous pilot measurements with the same participants, 10 seconds and 3 periods of 6 seconds with 2 minutes of active rest were, respectively, established for LV and HV control condition protocols. Table 1 summarizes all conditions and protocols tested in this study.
Consideration was given to the rest intervals between testing sessions, with each protocol being carried out every 48–72 hours. Participants were instructed to avoid any additional resistance training or complementary explosive exercises during the study period but were permitted to continue with their regular sport-specific training sessions and dietary habits for the duration of the study.
Before testing the effects of any protocol, participants carried out a standardized warm-up consisting of light dynamic calisthenics followed by 2 sets of 5 repetitions on the PS with 50% of 1RM and 3 submaximal trials with the CMJ and BDJ. After 10 minutes of recovery, participants performed one of the protocols before performing 3 maximal consecutive CMJs and 3 BDJs with 5-second rest in between jumps. The rest period between CMJs and drop jumps (DJs) was 60 seconds.
Whole Body Vibration
Whole body vibration was conducted using a Power Plate platform (Power Plate North America, Inc., Northbrook, IL, USA). This device used a triplaner action, but the majority of the vibration is directed up and down within the Z plane in a synchronous manner.
As recommended by Marin and Rhea (23), the frequency in the current study was set to 40 Hz. Following the recommendation provided by the manufacturer, the higher peak-to-peak amplitude of the vibration platform used in this study was 1.963 mm. The resulting peak acceleration (apeak) measured at platform level in unloading condition was 124 m·s−2. In addition, this stimulus was used in preliminary pilot studies where participants did not show any difficulty for squatting with additional external free weight load. In this study, participants squatted with 80% 1RM while maintaining the same PS technique as the stable condition. Participants stood on the center of the vibration platform with their feet parallel and shoulder width apart on either side on the central axis behind a predetermined mark that divided the platform into a front and rear quadrant. Volunteers wore the same athletic shoes during all trials.
Body mass and height were determined on a standard scale and stadiometer according to the methods described by Ross and Marfell-Jones (28). Lean body mass and fat mass was determined using a 4-electrode bioimpedance body scale (Tanita BC 418 MA; Tanita Corp., Tokyo, Japan).
The 1RM PS was determined according to the methodology proposed by Baechle et al. (2). The PS was chosen because it is a common exercise that has been shown to potentiate performance in athletes (20).
Countermovement Jump Test
From standing erect position, participants descended to a self-selected depth and immediately jumped upward as high as possible. To exclude the influence of arm swing, subjects were instructed to keep their hands on hips (17). Participants performed 3 consecutive CMJs. Based on the height, the best of the 3 was chosen for the analysis.
Best Drop Jump Test
The optimal vertical starting height that elicited maximal height performance during the DJ was examined using a progressive height test by which participants dropped down from 0.10-, 0.20-, 0.30-, 0.40-, 0.50-, and 0.60-m-high platforms (5). Volunteers were instructed to place their hands on their hips and step off from the platform with the leading leg straight to avoid any initial upward propulsion. They were instructed to jump for maximal height and minimal contact time, leaving the platform with knees and ankles fully extended and landing in a similarly extended position to ensure the validity of the test. Three repetitions were performed from each drop height with 5-second rest between trials. Based on the jump height, the best of 3 trials was recorded. The drop height that produces the highest DJ performance was determined as the BDJ and assigned for the analysis.
Determination of Jumps Height, Peak Force, and Peak Power
Countermovement jump and DJ were performed on an AMTI force platform (Advanced Mechanical Technology, Inc., Watertown, MA, USA) with a sampling rate of 1,000 Hz where vertical forces were recorded. Jump height was calculated from the difference between maximum height of the center of mass (apex) and the last contact of the toe on the ground during the takeoff. Peak force (PF) and peak power (PP) during the push-off phase were also obtained (6).
Test-retest reliability coefficients (intraclass correlation coefficients [ICCs]) for the day-to-day reproducibility of each of the dependent performance measures were recorded at ICCs ≥ 0.90, and the coefficients of variation ranged from 1.0 to 2.5%.
Paired samples t-tests were used to determine the training effect from T1 to T2 and for the comparison between each condition with both T1 and T2. Cohen’s d was also used as a measure of standardized effect size (ES), using the reference values of small (d = 0.2), medium (d = 0.5), and large (d = 0.8) (11).
Repeated-measures analysis of variance (ANOVA) 3 × 2 × 2 (Conditions × Intensity × Rest Period) was used to assess the effects over CMJ and BDJ. Repeated measures 1-way ANOVA was used to compare the maximum values of CMJ and BDJ in NV-PS, WBV-PS, and C conditions.
Eta-squared (η2) was used as a measure of standardized ES, using the values of small (η2 = 0.01), medium (η2 = 0.06), and large (η2 = 0.14) (11).
The alpha level of 0.05 was adjusted using the Bonferroni’s method for all ANOVA pairwise comparisons. Statistical power for the evaluations ranged from 0.80 to 1.00. All values were expressed in mean ± SD.
The 1RM PS was 131.1 ± 24.9 kg (1.61 ± 0.16 kg·body weight−1) at T1 and 134.9 ± 24.5 kg (1.65 ± 0.16 kg·body weight−1) at T2. The CMJHt, countermovement peak force (CMJPF), and countermovement peak power (CMJPP) were 0.36.2 ± 0.04.5 and 0.36.7 ± 0.04.2 m, 1,779.2 ± 234.2 and 1,728 ± 296.8 N, and 4,034.6 ± 691.7 and 4,014.1 ± 603.1 W, respectively. The optimal drop height that maximizes DJ performance was 0.427 ± 0.07 m for both T1 and T2. The BDJHt, best drop jump peak force (BDJPF), and best drop jump peak power (BDJPP) were 0.217 ± 0.036 and 0.214 ± 0.037 m, 3,331.7 ± 551.2 and 3,332.1 ± 635.3 N, and 2,429.7 ± 486.7 and 2,425.9 ± 516.4 W.
No significant difference (p > 0.05) was observed between all variables analyzed at T1 and T2 and when comparing the data obtained at both T1 and T2 with the performance analyzed in all experimental protocols performed with the 3 main conditions (S-PS, WBV-PS, and C). All determined ESs were small (d < 0.5).
Comparison Between Conditions
Table 2 shows the descriptive values obtained for all conditions. No significant main effects of condition (NV-PS, WBV-PS, or C) × volume (LV or HV) × rest period interaction (1 or 4 minutes) were observed for all the variables assessed for CMJ or BDJ.
The only main effect for rest period was significant for CMJHt (F1,14 = 1.134, p = 0.005, η2 = 0.600) and BDJHt (F1,14 = 6.662, p = 0.0022, η2 = 0.256). These results suggest a better performance after 4-minute rest regardless of the protocol. Post hoc comparisons revealed that CMJHt was significantly higher for the NV-PS condition at LV (p = 0.015) but not at HV; meanwhile, BDJHt showed a significantly greater value for the WBV-PS condition in both LV (p = 0.022) and HV (p = 0.010) protocols.
Moderate to large standardized ESs were observed for condition (NV-PS or WBV-PS) effect (CMJHt η2 = 0.163; CMJPP η2 = 0.222; CMJPF η2 = 0.100; BDJHt η2 = 0.311; BDJPF η2 = 0.132; BDJPP η2 = 0.370), volume effect (CMJPP η2 = 0.200; CMJPF η2 = 0.166), and rest period effect (CMJPF η2 = 0.104; BDJPF η2 = 0.265; BDJPP η2 = 0.216). These individual effects are also large when combined for volume × rest period interaction effect (CMJPF η2 = 0.216; BDJPF η2 = 0.171), condition × rest period interaction effect (CMJHt η2 = 0.159; BDJHt η2 = 0.382; BDJPF η2 = 0.224; BDJPP η2 = 0.288), and condition × volume × rest period interaction effect (CMJPP η2 = 0.166; CMJPF η2 = 0.340; BDJPF η2 = 0.172).
When comparing maximum values obtained at the NV-PS, WBV-PS, and C conditions regardless of volume or rest period, significant differences (F2,13 = 3.457, p = 0.063, η2 = 0.117) were observed only for CMJHt. The post hoc analysis showed no differences between NV-PS and WBV-PS, whereas C reached significantly lower performance compared with NV-PS (p = 0.025) (Figure 2). The nonsignificant difference observed between WBV-PS and C is likely because of larger SD observed in V compared with S.
The primary finding of this investigation was that a 1-minute rest period was not enough to restore both CMJ and BDJ performance after all PAP protocols tested in this study. Conversely, a 4-minute rest was adequate for recovery of CMJ or BDJ performance after NV-PS and WBV-PS conditions, which included both LV and HV protocols. The standardized ES analysis confirmed the acute potentiation effects observed after the LV protocol (p = 0.015) with a 4-minute rest period on CMJHt (η2 = 0.600) for both NV-PS and WBV-PS compared with C. In addition, our findings indicate that a 4-minute rest period after an LV protocol could also improve CMJPF (η2 = 0.200) and CMJPP (η2 = 0.166).
The higher BDJHt performance observed after WBV-PS condition for both LV (p = 0.022) and HV (p = 0.010) protocols after 4 minutes compared with 1 minute could be because of a reduced BDJHt performance observed after 1 minute rather than a PAP effect. Standardized ES analysis confirms these results when lower BDJHt, BDJPF, and BDJPP values measured after WBV-PS condition for both LV and HV protocols after 1 minute were compared with those measured after 4 minutes of recovery. Therefore, regardless of the condition (NV-PS or WBV-PS), it seems that to potentiate CMJ performance, an LV PAP protocol involving 3 repetitions of PS with 80% 1RM and 4 minutes of recovery could be the best strategy. Conversely, in the case of BDJ, 4 minutes of rest seems to be required for restoring the performance capacity after all the PAP protocols were used in our study.
The potentiation effects observed in CMJHt after 4-minute protocol are consistent with previous investigations (13,24,25). However, not all studies have reported significant potentiation effects after 4 minutes of rest after similar squat LV (19) or HV protocols (20). Dabbs et al. (14) reported large individual differences in the optimal rest interval needed to elicit a positive potentiation effect on vertical jump height after an acute exposure of 4 bouts of 30 seconds on WBV with 30 Hz and 6.5 mm peak-to-peak displacement. Thus, PAP seems to be a highly individualized phenomenon whereby some individuals may experience a greater PAP effect than fatigue, whereas others experience the opposite effect for the same protocol (16). Both conditions (NV-PS and WBV-PS) and volume protocols (LV and HV) used in our study may have induced fatigue after only 1 minute of rest for both exercises CMJ and BDJ. Conversely, 4 minutes of recovery may have been sufficient to induce PAP for enhancing CMJHt but long enough not to produce the same effects on CMJPF, CMJPP, and for all BDJ-measured variables.
When considering only the maximum values regardless of the condition and protocol, only CMJHt showed significantly better performance after NV-PS compared with C (p = 0.025). The large interindividual variability observed for the WBV-PS condition may have influenced these observations (Figure 2). If we consider the phenomenon of PAP as a physiological neuromuscular capacity inherent in all individuals regardless of performance level and training experience (3), all participants in our study should be able to elicit some degree of potentiation but of different magnitudes and times according to their individual response under each experimental condition. In fact, when analyzing the individual responses, we found that after the NV-PS, 11 participants (73%) attained their highest CMJHt after 4 minutes of recovery, whereas 4 of them (27%) achieved their best CMJHt performance after 1 minute. A similar scenario was observed for the WBV-PS condition with 10 participants (67%) having their best CMJHt performance after 4 minutes and 5 participants (33%) after 1 minute of recovery. Therefore, regardless of the condition, a few athletes (27–33%) peaked at 1 minute, whereas the majority of them (67–73%) peaked at 4 minutes. In the current study, 4 minutes seemed to be a more appropriate recovery period to restore and possibly elicit some degree of performance enhancement. Clearly, individualization of the recovery period between stimulating and potentiated exercises warrants special consideration.
The lack of potentiation effects observed on BDJ performance could, in part, be explained by the limited experience of the participants performing DJ as a training exercise. It is possible that the execution of the CMJ before the DJ may have also affected subsequent BDJ performance. Additionally, potentiation effects have been shown to be more effective when some degree of similarities exist between the movement patterns (13). This may explain why we found significant PAP effects on CMJ because it is biomechanically similar to PS. Additionally, despite the significant increases in CMJHt occurred after NV-PS condition, there were no concurrent significant enhancements in CMJPF or CMJPP (Table 2). The mechanical and temporal variables obtained from the force plate in our study highlighted the potentiation effects observed after 4 minutes of recovery in CMJHt in the NV-PS group, which could be a consequence of modified jump technique rather than an increased capacity to develop greater PF or PP.
Whole body vibration devices increase the gravitational load on the subject while exercising or standing on the vibrating platform (7). As the movement of the power plate device is sinusoidal, the maximal acceleration (a max) is calculated as a max = Axω2 = Ax (2πƒ)2. Therefore, exercising at a frequency (ƒ) of 40 Hz with an amplitude (A) of 1.963 mm gives a stimulus equal to 12.6 times the normal gravitational load (27). Hence, when participants performed the PS with 80% 1RM onto the vibration platform, they were exposed to a greater overload that leads to a higher neuromuscular stimulation compared with the NV-PS condition. The great variability observed in CMJHt after WBV-PS compared with NV-PS condition could be explained by the superior overload. It is possible that for some athletes in our study, performing PS with 80% 1RM on a WBV device set at 40 Hz and 1.963 mm peak-to-peak displacement may have been an excessive overload that negatively affected motor control during CMJ. In fact, the range of maximum values after WBV-PS conditions regardless of volume or rest period protocols were larger (0.30–0.50 m) compared with NV-PS (0.305–0.46 cm) and C (0.30–0.45 m). After WBV-PS, 5 subjects (33%) showed lower maximum CMJHt values in respect to those measured after C. However, only 3 of them also produced inferior maximum CMJHt value when performing NV-PS condition compared with C. For these athletes, the level of overload applied under WBV-PS or even NV-PS conditions may have hindered jump motor control (e.g., altered Ia- and Ib-afferent central nervous system inputs from muscle spindles and Golgi organs, respectively) and reduced performance instead of eliciting potentiation (21). In conclusion, PAP was effective for enhancing CMJHt after NV-PS and possibly WBV-PS conditions when an LV and a recovery period of 4 minutes were applied. Additionally, 4 minutes of recovery was more effective than 1 minute for restoring BDJ performance capacity. Because of the observed interindividual variability in performance outcomes, PAP strategies should be personalized according to each athlete’s training history and individual responses to different PAP protocols.
To acutely enhance jumping performance in male college athletes, a PS PAP protocol using NV-PS or WBV-PS conditions combined with an LV (e.g., 3 repetitions with 80% 1RM) followed by 4 minutes of recovery should be considered over other strategies with higher volumes and shorter rest periods. Although analysis of the data revealed both positive and negative responses to the same protocol, 4 minutes of recovery seems to be more appropriate for avoiding performance decrements and possibly eliciting PAP in a majority of the male college athletes studied in our investigation. Nevertheless, to elicit the greatest potentiating effects, it is recommended that each individual’s optimal response under different conditions, volume, and rest time should be determined along the training process. For example, only the athletes who positively respond to WBV-PS would train under this special condition. Additionally, different recovery times would be prescribed according to the athlete’s individual’s response after similar potentiation protocol.
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