The necessity for power development in sports needs no debate. As such, coaches, athletes, and certified strength and conditioning specialists dedicate a significant amount of their time working on muscular power development. Present training programs to improve power are comprised of resistance and/or plyometric techniques. Investigators have studied the effects of both forms of training individually and in combination on factors such as vertical jump height (VJH), hip and thigh power, and one-repetition maximums. It has been shown that the combination of resistance training and plyometric training yields greater results than either method alone (1-3,6). The combination appears to maximize power output by increasing both muscle fiber hypertrophy and neuromuscular adaptations (1,4,9,13).
Two forms of combination training have been developed: Complex and Compound training. Complex training alternates between resistance exercises and biomechanically similar plyometric exercises within a single exercise session. Complex training is believed to be more effective at improving power production than other training program designs, due to an enhanced neuromuscular environment (16). Compound training is another form of combination training in which resistance exercises are performed in sessions separate from plyometric exercises. For example, leg resistance exercises are performed on one day and depth jump exercise on another day. Compound training is believed to increase contractile proteins while also improving the stretch reflex of a muscle (9,13).
Training studies have not yet determined the optimum combination of resistance and plyometric exercises needed to cause the best muscular power production (2). While there are numerous research studies comparing different types of combination training to either plyometric or resistance training programs alone, very few studies have been done which directly compare two different types of combination training programs against one another (5,20). Furthermore, there is a need for combination training studies which compare programs that have been equated for total work done (9). Since coaches and athletes are often restricted to a short preseason, which is especially true in collegiate club and high school athletics, a better understanding of the effects of a shorter training period in the context of the aforementioned study designs is an important and logical next step. Therefore, the primary purpose of this study was to compare short-term VJH and lower-body power output gains from four weeks of training between complex and compound training programs. The secondary purpose of the study was to determine if gains in VJH and power output occur faster with one form of combination training over the other.
Experimental Approach to the Problem
This prospective study was designed to investigate whether a four-week complex training program was more effective at improving VJH and lower body muscular power than compound training in a cohort of competitive club volleyball players. Two different combination training programs were designed with equal volumes of work in order to address the purpose of this study. Six exercises (squat, depth jump, single leg lunge, split squat jump, deadlift, and double leg bounds) were used in each training program to develop lower body power. In order to assess the time at which point improvements in either of the training program became statistically significant, we employed a repeated measures design on our two dependent outcome measures (VJH and power output).
The subjects were volunteers from a competitive Division I club volleyball program. All subjects participated in volleyball practice at least twice a week and were regularly involved in jumping activities for the previous 3 months. Eleven men and 20 women were divided into either the complex or compound groups. Men and women were divided into the two groups by gender matching them on pretraining VJH as close as possible. Acknowledging an uneven number of men in our sample, the eleventh male subject was randomly assigned to the compound training group. The age, height, mass, and BMI for each subject are presented in Table 1. Subjects provided written informed consent that was previously approved by the university's institutional review board.
During the pre-assessment, subjects completed their informed consent and medical history questionnaires. Subjects who had sustained a lower extremity injury within the past 3 months that prevented them from participating in their sport, were unable to attain a squat depth of at least 90 degrees of knee flexion, were not comfortable jumping from a height of 30 cm, or were deemed at risk of injury based on answers provided by the medical history questionnaire were asked to not participate.
Vertical ground reaction forces were measured using a 0.6 m × 0.4 m Bertec 4060-08 piezoelectric force sensor platform (Bertec Corp.; Columbus, OH). The force platform was interfaced with a personal desktop computer via a 12-bit, 64-channel analog to digital (A/D) interface unit (Peak Performance Technologies, Inc.; Englewood, CO, U.S.A.). All data was recorded using the Peak Motus 3D Motion Analysis System Software Version 5.1 (Peak Performance Technologies, Inc.; Englewood, CO). Force platform data was collected at a sampling frequency of 1000 Hz. Actual standing VJH was recorded using a Vertec measuring device (Sports Imports, Columbus, OH).
Vertical Jump Testing Protocol
Vertical jump testing sessions were performed pretraining, postweek 1, 2, 3, and 4 of training. From a standing position on the force platform, subjects performed a vertical jump using initial countermovement (with an arm swing) reaching up and striking the highest possible vein of a Vertec measuring device and landing back on the force platform. A 2-foot takeoff and landing was required in order to retain the data from each trial. Prior to testing, subjects performed three warm-up vertical jumps at submaximal effort off the platform (15). Subjects then performed 3 maximal vertical jumps (3 minute rest between each jump) on the force platform with the peak performances being recorded for that session (15).
The week prior to the start of the respective training programs, subjects' pretraining maximal VJH were recorded. They also completed a 10-Repetition Maximum squat test to ensure appropriate training intensities were prescribed during the respective interventions, and that participants were matched on group assignment. Participants trained twice per week (on Tuesday and Thursday) for the duration of this study, regardless of group assignment (Table 2). The complex group completed both plyometric and resistance training exercises on each day, with the compound group performing resistance training exercises solely on Tuesdays and plyometric exercises solely on Thursdays. Resistance exercises included the squat, the single leg lunge, and the deadlift (8,9,18). The intensity for the resistance exercises was optimal for the development of power, as subjects performed 3 sets of 6 repetitions at 60% of his or her 1-Repetition maximum (3,6). Plyometric activities included 3 sets of 6 repetitions of depth jumps, split squat jumps, and double leg bounds (1,8,9). In order to equate overall workload, participants in the compound training group simply repeated these same 3 resistance exercises in succession on Tuesdays and repeated the plyometric exercises on Thursday. Subjects were informed to perform both resistance and plyometric activities as “explosively” as possible with high-speed contractions. All resistance exercises were performed using free weights. A breakdown of each training session for the two groups is provided in Table 3. The number of sets (3) and repetitions (6) were based on previous research (17,19). Rest periods between sets lasted 60 seconds; whereas, rest periods between individual exercises lasted 2 minutes (10). If a subject missed a session, it was made up within 24 hours and there was always a rest window of 48 hours between the two sessions. This only occurred once during the entire study. All training sessions were observed by one of the investigators to ensure the quality of the workout.
Data collected from the force platform was filtered and reduced by a custom Matlab computer program (Matlab 7; The Mathworks, Inc.; Natick, MA). Actual VJH measurements were also recorded from the Vertec measurement device for each individual trial. Estimated VJH measurements from the force platform (measured in cm) and Power (W) were computed using the following equations. Power was also estimated using the same formula found below using actual Vertec-measured VJH.
For all subjects, descriptive statistics were calculated for age (years), height (cm), mass (kg), and Body Mass Index (BMI; kg/m2). A 2 × 5 ANOVA was used to compare the VJH and power data collected from the force platform to the data measured directly from the Vertec. A 3-way Mixed Model Analysis of Variance was used to find statistical significance between and within the group and time measures, as well as between genders, for VJH and power. If a significant interaction effect was observed (P ≤ 0.05), then a Tukey's post hoc analysis was performed to determine at what time during the training significant changes between or within the groups occurred. The independent variables in this study were training group, gender, and time; whereas, the dependent variables were VJH and power. Intraclass correlation coefficients (ICC2, k) were computed to assess the reliability of the VJH and power measures. Standard error of measurement (SEM) for VJH and power were also computed to relate the precision of the measurements.
Five men and 10 women were assigned to the complex training group (CPX) while 6 men and 10 women were assigned to the compound training (CPD) group. All subjects were screened the week prior to the start of the intervention training and again each week during the intervention. Throughout the 5 testing sessions, 2 subjects missed the 4th session (postweek 3 testing session), while 2 subjects missed the 5th session (posttraining testing session). Three of those 4 were from the CPX training group.
Vertec vs. Force Platform
Analyses of variance were run comparing the estimated VJH and power output computed from the force platform and Vertec. Vertical jump height and power production estimates were significantly lower than outcome measures obtained directly from the Vertec (P < 0.0001). The force platform estimates were consistently 0.17-0.19 m (38-42%) lower in VJH and ∼1100 Watts (∼30%) lower for power output. Provided that the Vertec data was a direct measure of the actual jump, and not a prediction as determined from the force platform, it was decided to present results based on the data produced by using the Vertec measuring device.
Vertical Jump Height and Power Output
Results of a 3-way mixed model ANOVA (group × gender × time) revealed that both groups significantly improved VJH (P < 0.0001) and power production (P < 0.0001) over the 4 weeks of training (Figures 1 and 2). The CPX training group increased their VJH from 48.2 ± 8.6 cm to 50.9 ± 9.3 cm (∼5.4%), while the CPD training group increased VJH from 47. 8 ± 8.0 to 52.6 ± 8.4 cm (∼9.1%). The CPX training group increased mean power output from 3865 ± 874 to 4060 ± 896 W (∼4.8%), while the compound training group increased mean power output from 3765 ± 770 to 4072 ± 738 W (∼7.5%). There was no significant difference in the rates at which the two groups improved over the course of the study (P > 0.05). Compared to pre-intervention measures, both groups significantly increased VJH and power in the postweek 3 and 4 sessions. A significant difference between the postweek 3 testing session and postweek 4 was also evident. Furthermore, high intraclass correlation coefficients were observed for VJH (ICC2, k = 0.943; SEM = 2.017 cm) and power (ICC2,k = 0.968; SEM = 143.41 W).
Vertical jump heights were significantly higher for men in both groups (P < 0.0001), with men jumping 24.8% and 22.3% higher than their female counterparts in the CPX and CPD groups, respectively. Consequently, power outputs were significantly higher for the men in both groups (P < 0.0001): CPX = 31.4% greater and CPD = 26.4% greater. There was, however, no significant difference in the rate at which improvements in VJH or power output occurred between genders (P > 0.05).
The results of this study showed that significant improvements in VJH and power output were achieved 3 weeks into a 4-week training program consisting of complex and compound training as part of a competitive volleyball training regimen. However, this study was unable to demonstrate a significant difference in gains for VJH or power output over the 4 weeks between the two forms of combination training programs. In addition, this study also found no significant difference in the rate at which gains were achieved within the two training programs as both groups showed significant improvements after the 3rd and 4th weeks of training.
The major finding of this study was that 3 weeks of both CPX and CPD training significantly improved VJH. In the present study, the complex training group improved VJH by ∼5% while the compound training group improved VJH by ∼9%. A 5% increase in the complex group represented a mean increase of 2.7 cm; the 9% increase in the compound training group represented a mean increase 4.77 cm. Although no statistically significant differences were observed between the two training groups, a 2-cm difference in the context of VJH performance is quite appreciable to the certified strength and conditioning specialist charged with improving the physical performance of volleyball players and other athletes requiring repetitive maximal vertical jump efforts. These results support the majority of existing literature in that combination training is effective for improving muscular power (13,17,19). For example, an 8-week study on NCAA Division I volleyball players found combination training improved VJH by 5.9% and peak power by 8% over an 8-week squat training program (17). Two other studies of 8 and 9 weeks duration found that combination training improved VJH by 6% (13,19). In contrast, another 8-week study by Fatouros et al. (9) yielded far greater results, as it was found that combination training improved VJH by 13% and power production by 28%. The Fatouros et al. study differed from ours on two accounts: resistance exercises were performed 2 hours following plyometric exercises, and the duration was twice as long.
Another significant finding in this study was that CPX and CPD training improved VJH and power production. In comparison, a 7-week study also found no significant differences in VJH or power production between complex and compound training programs (5). However, the latter study compared forms of complex and compound training that were slightly different from the designs used in this study. In our study, complex training consisted of alternating between resistance and plyometric exercises during each training sessions, while compound training consisted of performing resistance or plyometric exercises in 2 separate training sessions. In contrast, one of the first studies to compare complex and compound training programs found 14 weeks of complex training to be superior to compound training in developing leg power (20). Their study compared 2 forms of compound training-one in which plyometrics were performed before resistance exercises, and another in which plyometrics were performed after resistance exercises-to complex training. However, no numerical data was provided in this study and no interim measures (e.g., 4 wk, 8 wk) were reported; thus making comparisons to our current study difficult.
A focus of our study was to determine if CPX training improved VJH and power at a faster rate than CPD training. The observed increase in both VJH and power from week 3 to 4 in this study suggests that short-term training programs can begin to yield significant improvements in athletic performance; this is especially true of sports that require maximal vertical jump efforts such as volleyball. The literature in this area suggests that if our program were continued, differences between the CPX and CPD may have been noted (1,4,8,9). Future research should take duration of training into consideration, as it may play an important factor. While most literature agrees that 4 weeks is a sufficient period of time to yield performance enhancements due to training, few studies have reported outcome measures on a weekly basis (1,2,7,10,15). This makes the determination of improvement rates in these studies difficult. Due to the repeated measures research design we implemented in our study, we were able to observe significant improvements following the third week of the 4-week training program. These observed changes in vertical jump height and power output performance were most likely neural in nature. Continued training may likely have resulted in more pronounced physiological changes such as increased physiological cross-sectional area of the muscles, changes in histochemical properties of the tissues, and continued neuromuscular improvements. We acknowledge that factors beyond training can influence how an individual responds to a particular training program. Clearly, motor recruitment patterns and fiber types differ between individuals and may differ between genders. Although most short-term improvements are likely attributable to neural changes, we observed improved power output over the training period in 28 out of 31 of our participants. As such, training did have an effect on power output regardless of the individual variability of motor unit arrays and fiber types we would expect between athletes. We believe, however, studies using training programs presented in this study over a longer period of time are definitely warranted in future studies.
This study also supported the finding that men had significantly higher absolute VJH and power production than their female counterparts, regardless of training group. Studies have consistently reported women capable of producing roughly two-thirds as much absolute power as men (12,14). This seems to be confirmed as power production for the men were 26-31% higher than the women in our study. More importantly, gains in VJH and power occurred at a similar rate when analyzed within each gender. Similarly, Jenson and Ebben's study also found no significant difference in vertical or power gains between genders following complex training (11). Thus, complex and compound training appears to influence both genders similarly.
The concurrent use of the force platform combined with the Vertec may have restricted jumping performances. A small number from our sample reported awkwardness in having to jump straight up and down onto the force platform, stating that volleyball players usually land 6-8 inches in front of their takeoff spots. This may have influenced the results of the study by inhibiting some subjects from achieving their true maximal verticals. However, this restriction was consistent across our sample for all trials, so increases in VJH and power in our study are still comparable to those in other studies. Subjects were permitted 3 jumps as a warm-up prior to data collection each week they were tested. Future studies should investigate the effects of differing warm-ups on vertical jump height performance. Our study evaluated improvements in VJH performance in competitive Division I club volleyball players. Since training experience and skill in Division I varsity athletes or high school athletes can differ from our cohort, careful consideration should be afforded by certified strength and conditioning specialists prior to generalizing the results of our experiment to other populations. Our results would seem to suggest that, regardless of training experience, enhancements in VJH performance can still be expected. Future studies should evaluate the effects of prior and concurrent resistance training in future cohorts, noting that our sample did not undergo concurrent resistance training with the exception of regular practices. We compared estimated VJH computed from force platform measures to actual jump performance using a Vertec; we noted force platform measures based on formulae previously reported in this journal consistently underestimate actual VJH performance. Future studies should acknowledge this or continue to develop mathematical models for better predicting VJH.
Our study found that both complex and compound training programs resulted in similar gains in vertical jump height and power in as little as 3 weeks of training. Moreover, vertical jump height and power production following the final week of training (posttraining testing session) was significantly greater than the week before (postweek 3 testing session), suggesting that gains in performance may continue with longer training programs. This is very beneficial for coaches or athletes who only have a brief period of time to train before competition, such as in high school athletics. The study also found that both forms of training resulted in similar improvements in vertical jump height and power for both genders. Thus, it appears that for training volleyball players, either type of training can be effectively used. The choice of training program may be dependent upon how the resistance training and plyometrics fit best into the overall training program.
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