The positive effect of plyometric training on jumping performance has been well established in the literature (13). However, the specifics of plyometric program design remain unclear. The systematic use of periodization, as well as the related concepts of the training taper (1,20) and post-training recovery period (23), is well established for some training modalities such as strength training and may also be applied to plyometric program design.
Results of a meta-analysis demonstrate that plyometric training is effective, although considerable variation exists in the design of plyometric programs employed by researchers (5). Key features of periodized programs such as a systematic decrease in volume or increase in exercise intensity are not used in many plyometric training studies (3,7,8,12,14,15,19,22,24). Nonetheless, some of these studies demonstrate small to moderate improvement in countermovement jump height (3,7,8,14) and power (7,19), whereas others found no improvement in countermovement jump height (22,24) or power (14). In some cases, countermovement jump height and power did not improve, or even decreased, when testing was performed immediately after training, and only improved after a period of recovery (12). Thus, recovery from the plyometric training stimuli may be important.
Matveyev's (16) classic model of periodization indicates that training volume should decrease and intensity should increase over the course of training in order to reduce fatigue and optimize adaptations. Although this model is well understood for modes such as strength training, it has yet to be systematically applied to plyometrics. Popular literature includes recommendations for the increase in plyometric intensity and decrease in volume (18), although the specifics for doing so remain unclear. Previous plyometric research has begun to quantify the intensity of plyometric exercises (6,11), and recommendations have been made for the development of periodized plyometric programs (11).
The training taper before competition is related to periodization in that each share the goal of reducing training volume to maximize performance. Previous reports indicate that performance of a variety of exercise modes may be optimized with a 41-60% reduction in training volume (1). Research examining the post-training recovery period duration demonstrated that 4 days of recovery resulted in greater heel raise strength than 2 or 5 days, whereas isokinetic plantar flexion peak torque was not statistically different at 2, 3, 4 or 5 days of recovery (23). Two studies specifically compared a no training recovery period with a period of reduced volume taper demonstrating superior performance in torque, strength, and power with tapering than with a nontraining recovery period of 10 days (9) or 4 weeks (10).
To date, the application of periodization to plyometric training programs and the value of periodization and post-training recovery has not been investigated. Based on the existing literature, it is possible that the taper-like reduction in training volume inherent in a periodized program may decrease the need for a post-training period of recovery. Therefore, the purpose of this study was to evaluate the effect of a periodized plyometric program and the duration of the post-training recovery period that optimizes jump height and peak power during the countermovement jump.
Experimental Approach to the Problem
This training study used a repeated measures design to assess performance before and at 2, 4, 6, 8, and 10 days after training to evaluate the effect of periodized plyometric training and duration of post-training recovery period. Independent variables included the number of days of recovery after the cessation of training and the presence or absence of periodized plyometric training. Dependent variables included jump height and peak power. The research hypothesis was that periodized plyometric training would reduce the need for a lengthy post-training recovery period.
Fourteen women served as training subjects (mean ± SD, age 19.29 ± 0.91 years; body mass 62.56 ± 7.24 kg; height 167.19 ± 6.51 cm). Controls included 10 women (mean ± SD, age 19.5 ± 1.18 years; body mass 60.41 ± 7.93 kg; height 163.45 ± 6.50 cm). Body mass was assessed for all test sessions, and a repeated measures analysis of variance (ANOVA) showed no change for the training or control groups across any of the test sessions as described in Table 1. Subject exclusion criteria included any history of lower limb pathology that resulted in functional limitation of the training exercises or countermovement jump to be assessed in this study. Before the study, the subjects in the training group participated in an average of 1.7 sports in high school for an average of 3.1 years. None of these subjects were college varsity or club sport athletes. Four subjects participated in intramural sports. None of these subjects were currently participating in resistance or plyometric training, although 13 participated in some form of aerobic conditioning an average of 2.1 times per week. The subjects in the control group participated in an average of 1.6 different sports in high school for an average of 2.6 years. One of these subjects was a college varsity athlete, and 2 previously participated in club sports. Two subjects participated in intramural sports. One of these subjects had been participating in resistance or plyometric training. Seven of 10 subjects participated in some form of aerobic conditioning an average of 1.5 times per week. The subjects were informed of the risks associated with the study and provided informed written consent. The study was approved by the institution's Internal Review Board.
Before all testing and training sessions, subjects warmed up for 3 minutes on a cycle ergometer and performed dynamic stretching exercises including 5 repetitions (reps) of each of the following: slow and fast bodyweight squats, forward and backward walking lunges, walking lateral lunges to the left and right, walking quadriceps and hamstring stretches, side shuffling to the left and right, and skipping. Subjects also performed 5 countermovement jumps of increasing intensity. Subjects rested for 5 minutes after the warm-up, before the testing sessions.
All training and control group subjects were instructed to refrain from physical activity during the 6-week training period. Limited physical activity was confirmed via analysis of subject activity logs. Results revealed that control and training group subjects participated in light aerobic activity 1.5 times per week for an average of 25.8 minutes. Subjects averaged 6.38 minutes of weight training and 5.83 minutes of recreational sports (i.e., volleyball, basketball) per week.
Subjects participated in a pre-training testing session and 5 post-training testing sessions. The post-training testing sessions were performed 2, 4, 6, 8, and 10 days after the 6-week training program for the training subjects and 6 weeks after the pretest for the control subjects. The pre- and post-training testing sessions consisted of 3 reps of the countermovement jump. The countermovement jump testing protocol was limited to 3 reps in order to limit the effect of one post-training testing session on another.
Subjects were randomly assigned to either a nontraining control or plyometric training group. The plyometric training group trained twice per week with 48- to 96-hour recovery between training sessions under the supervision of a certified (NSCA CPT, CSCS, or CSCS*D) professional. A 2-day per week training program was created based on previous research demonstrating the effectiveness of 2 days of training that produced mean and statistically significant greater performances in the countermovement jump compared with 1 and 4 days of training per week, respectively (4). The program was periodized consistent with previous recommendation for decreasing volume and increasing plyometric intensity (18). The daily volume used in the program was in a range that is typically recommended for relatively untrained exercisers (18). The volume was reduced by 40% from a high of 100 foot contacts early in the program to 60 foot contacts near the end of the program. This degree of volume reduction is consistent with the results of a meta-analysis that indicated performance is optimized with this degree of training volume reduction (1). The total volume of the plyometric program was 475 foot contacts. The intensity of the plyometric exercises was determined based on previous research examining ground reaction forces, knee joint reaction forces, and muscle activation (6,11). Subjects rested approximately 30 seconds between sets and 15 seconds between single jumps. The recovery duration between reps and sets was chosen based on previously recommended work to rest ratios of at least 1:5 (18), research that demonstrated that jump performance produces no advantage with rest duration of greater than 15 seconds between reps (21), and the desire to keep the plyometric training session duration no longer than necessary. The specific plyometric exercises, sets, reps, and volume are specified in Table 2.
The countermovement jump tests were assessed with a 60 × 120-cm force platform (BP6001200; Advanced Mechanical Technologies Incorporated, Watertown, MA, USA), which was bolted to the laboratory floor according to the manufacturer's specifications and mounted flush in the center of a 122 × 244-cm weightlifting platform. The force platform was calibrated with known loads to the voltage recorded before the testing session. Kinetic data were collected at 1,000 Hz, real time displayed, and saved with the use of computer software (BioAnalysis 3.1; Advanced Mechanical Technologies, Inc.) for later analysis. Jump height and peak power were analyzed because these variables are frequently used to assess countermovement jump performance (2,12,14,17,19,22). Jump height was calculated from the force-time records consistent with methods previously used (17). Peak power was calculated using the equation proffered by Canavan and Vescovi (2) because this equation was shown to be accurate for monitoring changes in the countermovement jump performance of women subjects after 6 weeks of plyometric training. All values were determined as the average of 3 trials of the countermovement jump for each test session.
All data were analyzed with SPSS 17.0 (IBM Corp., Chicago, IL, USA) using a repeated measures ANOVA to evaluate the differences between countermovement jump height, peak power, and body mass between the pre-training baseline testing and testing sessions performed at 2, 4, 6, 8, and 10 days after training. Significant main effects were further analyzed with Bonferroni-adjusted pairwise comparison to identify the specific differences in jump height, peak power, and body mass between all pre- and post-training testing sessions. The reliability of the trials was assessed using intraclass correlation coefficient, for each of the dependent variables for the pre-training and for the last post-training testing session. Assumptions for linearity of statistics were tested and met. Statistical power (d) and effect size (ηp2) are reported, and all data are expressed as mean ± SD. The a priori alpha level was set at p ≤ 0.05.
Results revealed significant main effects for countermovement jump height (p ≤ 0.001, d = 0.98, ηp2 = 0.41) and peak power (p ≤ 0.001, d = 1.00, ηp2 = 0.56) but not for body mass (p > 0.05), between test sessions, for the subjects in the plyometric training group. Post hoc analysis demonstrated that jump height and peak power were different between the pre-training testing session and all post-training testing sessions, with no difference between any of the post-training testing sessions. Results of post hoc analysis are shown in Tables 3 and 4. No significant main effects were found, demonstrating no differences in countermovement jump height (p > 0.05), peak power (p > 0.05), or body mass (p > 0.05), between testing sessions, for subjects in the control group. Intraclass correlation coefficients are presented in Table 5.
This study demonstrated that periodized plyometric training produces substantial improvement in vertical jump height and peak power. The length of the post-training recovery period does not influence countermovement jump performance, presumably due to the tapering inherent in periodized plyometric training. Thus, the performance of the subjects was optimal within 2 days of training, and performance adaptations were sustained for at least 10 days after training.
The present study demonstrated that periodized plyometric training produced a 25.0% increase in countermovement jump height from pre- to post-training. This improvement is greater than those found in a number of previous studies that demonstrated either no significant increase in countermovement jump height (22,24) or increases that ranged from 2.8 to 10.2% (3,7,8,14). In fact, results of a meta-analysis demonstrate that the pooled mean increase in countermovement jump performance from pre- to post-training is approximately 8.7% (13).
In the present study, countermovement jump peak power increased by 11.61-14.28% from pre- to post-training. The magnitude of this increase is less than the peak power values as shown by Fatouros et al. (7), which were 20.4% higher than pre-training values. It is interesting to note that it is typical for men to attain better power adaptations than women in response to plyometric training (5), potentially explaining the comparatively larger adaptations of the subjects in the study by Fatouros et al. (7) who used men as subjects. Nonetheless, other studies that included only men as subjects demonstrated no significant improvement (14) or increases in countermovement jump peak power in the range of 1.6-2.8% (12,19), which were smaller than the values attained in the present study.
In general, plyometric performance adaptations are known to be a function of increased cross-sectional area of both type I and type II muscles fibers (19), which may potentially explain some of the performance adaptations in the present study. Although the mechanisms underlying the adaptations were not studied, the magnitude of the adaptations demonstrated in the present study exceeds most previously published findings. Possible explanations for this result include the relatively untrained status of the subjects in this study, although these subjects' fitness level and recreational experiences do not appear to be appreciably different than those employed in some previous plyometric studies (4,7,8,12,14,19,22). It is also possible that in the present study, the periodized program design including exercises of known increasing intensity (6,11) and decreasing training volumes in recommended range (18) was more optimal compared with other studies. The present study is the only known periodized plyometric training study and used a daily total volume ranging from as high as 100 foot contacts decreasing to 60 foot contacts over the training program. Most other plyometric programs used no systematic increase in exercise intensity or decrease in volume. In fact, some researchers increased plyometric volumes up to 480 foot contacts per training session over the course of the training program (3). Previous research on tapering of training volume adds to the theoretical foundation for the value of periodization of plyometric programs. Subjects in the present study performed limited concurrent training. Despite being instructed not to perform any concurrent training during the study period, subjects averaged 1.5 weekly session of light aerobic activity and almost no resistance training or other recreational activity. However, the adaptations in jump height and power were not likely enhanced by light aerobic training or an average of a few minutes per week of resistance training or other recreational activity. The limited volume of this concurrent activity did not seem to impair posttest performance as well.
Results of this study confirm, in part, that tapered programs with a 41-60% decline in volume enhance performance as has been reported (1). The present study showed that performance improved with no difference between recovery periods of 2, 4, 6, 8, or 10 days, indicating that tapered programs peak athletes after training and before competitions without the need for a post-training recovery phase. These adaptations are consistent throughout and are retained over at least a 10-day period. Previous research comparing a non-training recovery period with a tapering period of reduced volume demonstrated superior performance in strength and power measures after training with reduced volume tapering than with a non-training recovery period of 10 days (9) or 4 weeks (10). Thus, results of the present study add to the body of literature indicating that systematic volume reduction, and not a non-exercising recovery period, may be more ideal for performance enhancement.
Results of the present study call into question the previously held belief that training programs should be longer than 10 weeks to be highly effective (5). The present study demonstrates that brief moderate-volume periodized plyometric training produces large improvements in countermovement jump performance regardless of the post-training recovery period.
Results of this study demonstrate that periodized plyometric training is effective at improving countermovement jump height and power for relatively untrained women, without the need for and regardless of the length of the recovery period at the end of the training cycle. Practitioners who periodize plyometric training programs by decreasing training volume and increasing plyometric exercise intensity may obtain optimal adaptation without a post-training recovery period before competition.
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