High vertical jumping performance is not only of importance for success in both sport games and other athletic activities but is also related to other important physical abilities, such as sprint running and agility (11,22). Regarding the role of anthropometric measures, the effect of body size on muscle strength and power output has been discussed since the time of Galileo (27). The general effects of body size on various physical performance variables have been extensively studied over the past several decades, and various methods for physical performance normalization have been proposed (18,19,27). In particular, the most prevalent scaling models based on the presumption of geometric similarity have revealed that while the jumping height could be independent of body size, muscle strength increases proportionally to body mass on power 2/3 (18). However, relatively few studies have explored the effects of body composition on the performance of vertical jumps and other rapid movements, and their findings have been generally inconsistent. For example, although the percent muscle may not be a relevant predictor of the jumping performance in relatively lean population of physically active individuals (36), a moderately negative relationship could exist between the percentage fat and the jump height (35). Therefore, although the equipment for a quick and reliable assessment of body composition has recently become widely available, practitioners still lack knowledge regarding not only the general role of body composition in rapid movement performance but also whether that role differ across various populations.
One of the most frequently studied factors that could contribute to high jumping performance has been the strength of the lower limb muscles. Both individual muscles groups (4,31,36) and leg extensors as a whole, such as through the maximum leg press or squat performance (12,29,30,37), have been tested for the maximal voluntary force (F) and, less frequently, for the rate of force development (RFD). The outcomes were thereafter related with the maximum jumping performance typically assessed through the maximum jump height (8,25,31). However, the findings have been generally inconclusive because both medium-to-strong (29,30) and weak (25,36) relationships between the assessed muscle strength and jumping performance variables have been reported. As a result, it still remains unknown whether muscle strength should be targeted by the training procedures aimed toward increasing the jumping ability, whereas the validity of routine testing of F and RFD for the prediction of jumping and other rapid movement performance also remains questionable.
A relatively underexplored factor that could play a role in the above-discussed relationships could be the population tested. Namely, the samples of the tested subjects could be widely different regarding their athletic proficiency, muscle strength, body size, and body composition (13,16). For example, the samples of top-level athletes are more homogeneous regarding their anthropometric measures and physical abilities than the samples of participants obtained from the general populations (33,38). Differences in ranges of the assessed variables inevitably affect the relationships among them. Top-level athletes also typically pass through specific training and selection procedures that predictably affect their particular strength and other qualities (4). These qualities could be even position specific, such as the documented positional differences in volleyball (26,34). As a result, the strength of the relationship of the jumping performance with both body composition and muscle strength variables could also differ both among top-level athletes of different specialization and between the athletes and nonathletes. Therefore, the tested population could be considered as an important confounding factor affecting the studied relationships, but that problem has been rarely explored through direct comparisons.
To address the discussed problems, we have designed a study to explore the relationship between the jumping performance and both the body composition and the leg extensor strength. In particular, 2 groups of participants with different levels of fitness and skills were tested on maximum countermovement jumps (CMJs), F and RFD of leg extensors, and percent muscle and body fat. Our first hypothesis was that both body composition and strength variables would be predictors of jumping performance. Our second hypothesis was that the studied relationships would be stronger in nonathletes than in a homogeneous group of top-level volleyball players (VP). The expected finding could aid to our understanding of the factors contributing to performance of jumping and other explosive movements, as well as aid in further refining of early selection, training, and testing procedures in various sports.
Experimental Approach to the Problem
A cross-sectional experimental design was applied to assess the role of body composition and muscle strength in vertical jump performance in 2 distinct subject groups (i.e., elite female VP and physically active nonathletes). A single session included the body composition, vertical jump tests, and the muscle strength measurement. The relationships between the jumping performance (jump height) and both body composition (percent body fat [%BF] and percent of muscle mass) and muscle strength (maximum force and its RFD) were assessed and thereafter compared between the 2 groups.
To elucidate the differences in the hypothesized relationships between the individuals of different jumping abilities, we recruited 2 groups of participants. Because both weak and moderate relationships between the evaluated variables have been reported in the literature, we recruited relatively large samples of participants to secure a sufficient statistical power. As representatives of elite athletes, we selected a group of elite VP whose game success markedly depends on the vertical jumping performance. In particular, VP consisted of elite females athletes (age, 22.0 ± 3.7, range 16–29 years; training experience, 11.8 ± 4.0 years; N = 35) where 16 players were the members of the national Olympic team, whereas the remaining 19 players were members of the national super league clubs. The second group consisted of physically active females (PA: age, 21.3 ± 1.2 years, range 20–24 years; N = 21) all of whom were the students of the university's Sport and Physical Education program. Although none of them had been a former active athlete, they participated in different fitness programs 2–3 times a week for at least 6 months before the testing. Note that the same subjects had passed the academic entrance examination that was partly based on their physical abilities.
In line with the Helsinki Declaration and ACSM's guidelines for exercise testing and prescription (1), the participants formally agreed to participate in this research and signed informed consent approved by the Institutional Review Board. Parental/guardian consent was obtained for 4 VP athletes who were younger than 18 years at the time of testing.
The testing protocol consisted of a single experimental session. The body composition and the jumping performance were followed by the leg press strength test. The testing session was carried out during morning hours between 9:00 and 11:00 AM, which corresponded to their seasonal training schedule. All subjects were asked not to engage in strenuous exercise for at least 48 hours and not to eat for 2 hours before the testing. Because VP were familiar with vertical jumping performance, only PA participants underwent a 30-minute familiarization session 2 or more days before the test.
Body Composition Test
Body composition was estimated by an 8-polar bioimpedance method using a multifrequency current (InBody720; Biospace Co., Seoul, Korea). All body composition measurements were performed and analyzed by the same investigator throughout the study period. Bioelectrical impedance analysis measurements (BIA) were performed in the postabsorptive state. All metal items were removed from the participants to ensure the accuracy of the measurement, and subjects were in light clothing. Before the test, subjects were instructed to excrete and to wipe their palms and foot soles with an electrolyte cloth provided by the manufacturer. Body height, age, and gender were entered to the device by the research personnel. Subjects stood with the ball and heel of each foot on 2 metal electrodes on the floor scale and held handrails with metal grip electrodes. Arms were fully extended and abducted approximately 20° laterally.
Vertical Jump Performance
The testing was preceded by a standard warm-up procedure (5-minute cycling and 10 minutes of callisthenic and dynamic stretching). Each subject performed 1 practice and 2 experimental trials of consecutive maximum countermovement jumps performed either without (CMJn; arms placed akimbo) or with arm swing (CMJa) in random sequence (see Figure 1 for illustration). The higher jump was used for further analysis. In line with previous studies, 1 minute of rest was allowed between consecutive trials, and 2–3 minutes between the series of different jumps, to minimize the effects of fatigue (25,35). The force plate (AMTI, Inc., Newton, MA, USA; sampling frequency 5,000 Hz) was mounted and calibrated according to the manufacturer's specifications. Custom-designed software (LabVIEW, version 8.2; National Instruments, Austin, TX, USA) was used to record and process the vertical component of the ground reaction force (GRF). This system has been demonstrated to be reliable for the measurement of flight time (20,23).
Leg Extensor Strength
After the vertical jump tests, muscle strength was assessed through a standard bilateral leg press test. We selected the isometric leg press test instead of the frequently applied standard unilateral isokinetic and isometric tests of individual muscle groups for several reasons. First, it assessed the strength of leg extensors through a single bilateral trial. Second, in addition to its relative simplicity, leg press could also have the property of ecological validity because of the leg position that closely corresponds to the leg posture during vertical jumping (21). The leg press test is also a multiple-joint exercise that is more similar to vertical jumping than single-joint tests. Third, note that the leg press is typically conducted isometrically because very few laboratories have available leg press devices that allow for accurate control of leg extension kinematic and kinetic. Subjects were seated on a bench of a custom-designed leg press device with their hip, knee, and ankle extension angles at 110°, 120°, and 90°, respectively. They were specifically instructed to exert their maximal force both as strong and as quickly as possible. Subjects performed 4 consecutive trials of force exertion lasting 4 seconds with 1 minute of rest between them. The last 3 trials were used for the assessment of reliability, whereas the trial with the highest maximum voluntary force (F) was taken for other analyses. Strain-gauge transducers recorded the force-time series at a rate of 2,000 Hz (10,16,32). The data were digitized (National Instruments) and recorded for further analysis.
Body composition data were electronically imported to Excel using the standard Lookin'Body software. The values of %BF and percent skeletal muscle mass (%SM) were calculated relative to body mass using the standard manufacturer software. Jump height (h) was calculated from the flight time (tf) using the standard formula h = g × tf2/8, where g corresponds to acceleration due to gravity (8). The leg press test provided F as the highest value of the force recorded during the bilateral isometric leg extension, expressed in N (Figure 2B). To assess the RFD as an index of muscular quickness that could be of importance for rapid movement performance (3,6), we obtained not only the most often maximum calculated of F derivative (RFDmax; in N·s−1) but also the force exerted 200 milliseconds after the trial initiation (RFD200ms; in N). The validity of RFD200ms has been justified by the fact that 200 milliseconds closely corresponds to the typical time interval that elapses between the minima and maxima of GRF exerted during vertical jumping (2,9). All 3 strength variables (i.e., F, RFDmax, and RFD200ms) were normalized for body size using the standard scaling formula that recommends dividing the strength variables by body mass on power 2/3 (17,19,27).
A descriptive statistical analysis provided means and SDs of all obtained variables. To assess the reliability of the strength variables, we calculated the intraclass correlation coefficients (ICC), coefficients of variation (CV%), and SEM (15). Two-group t-test was used to assess the differences between VP and PA participants. Finally, the relationships between the jump height and both body composition and strength were assessed by the Pearson's correlations and the corresponding 95% confidence intervals. All statistical procedures were carried out by the Microsoft Office Excel (Microsoft Co., Seattle, WA, USA) and the SPSS for Windows, Release 17.0 (IBM, Armonk, NY, USA). Alpha was set at 0.05.
Table 1 presents descriptive statistics of the anthropometric and body composition variables of both subject groups. Note that VP were significantly taller and heavier than the PA participants. Volleyball players also revealed a higher %SM and lower %BF.
Regarding the jumping performance, VP revealed significantly higher CMJn (29.4 ± 4.3 vs. 23.0 ± 4.4 cm; p < 0.01) and CMJa (34.2 ± 4.5 vs. 26.8 ± 4.8 cm; p < 0.01) than PA. Table 2 shows the descriptive data and the indices of reliability of the strength variables obtained from both groups through the leg press test. Regarding the reliability (data shown only for nonnormalized variables), note that CV and SEM were relatively high in both RFDmax and RFD200ms. This observation was particularly prominent in the PA subjects. Nevertheless, all ICC values in both groups remained above 0.80 suggesting high reliability of the measured strength variables. Finally, none of the strength variables normalized for body size revealed significant differences between the 2 groups.
The main finding of the study is shown in Figure 3. The relationships of the jumping performance with the body composition variables were moderate-to-strong (range, 0.39–0.76), whereas the same relationships with the strength variables were average moderate (0.33–0.64). The relationships were significant excluding 3 of 4 correlation coefficients obtained from F that were somewhat below the level of significance. Of particular importance could be the differences observed between the 2 groups. A consistent set of data shown in Figure 3 revealed that the body composition variables could be better predictors of jumping performance in PA than in VP groups. Conversely, none of the relationships between the strength variables and jumping performance showed differences between the tested groups.
Within this study, we aimed to explore the relationship of the body composition and leg strength variables with the performance of 2 partly different vertical jumps in 2 distinctive groups of participants. The findings proved to be mainly in line with the 2 hypotheses. Specifically, most of the tested relationship proved to be not only significant but also moderate-to-high, whereas the body composition variables were stronger predictors of jumping performance in physically active individuals than in a group of elite VP. However, none of the strength variables revealed the differences between the tested subjects. Of potential importance could also be the lack of differences in muscle strength between the 2 groups despite marked differences in the jumping performance.
Despite being of apparent importance for athletic training and testing, the importance of body composition for rapid movement performance has been profoundly neglected in literature, particularly when compared with the same role of muscle strength, power, body size, and other potentially important variables. In this study, we observed the relationships between the body composition variables and jumping performance that were on average higher than reported by earlier studies (35,36). Note that the discussed finding was obtained from the groups of participants who were relatively lean, as compared with general population. Specifically, their average BMI of about 21 inevitably implies low variability of %BF and possibly %SM. It is also plausible to assume that the relationship between body composition and jumping performance we observed would be even higher if obtained from a number of other populations. Therefore, the obtained findings generally suggest that the body composition variables could be relatively strong predictors of jumping performance and, possibly, other rapid movements. However, the data also suggest that the importance of body composition for jumping performance could be lower for elite athletes than physically active individuals. One could speculate that the discussed finding could result from a lower variance of body composition in VP than in PA subjects, but the observed phenomenon apparently requires further research.
Regarding the possible role of the leg extensor strength, the observed relationships suggest that both the maximum force and its rate of development could be moderate predictors of jumping performance. The differences in the observed relationships between the tested strength variables in 2 jumps were mainly nonsignificant. The only exception was F obtained from VP in CMJn that revealed a weaker relationship with the jumping performance than either of RFD variables. This finding supports the concept that F and RFD variables may assess the same mechanical property of tested muscles (5,14,31,33,34). Regarding our second hypothesis, the data revealed no significant differences in the studied relationships between VP and PA. Therefore, the findings obtained generally suggest that the leg extensor strength (as assessed either by F or by RFD) should be not only targeted by training procedures but also assessed for the prediction of the maximum jumping performance in both elite athletes and nontrained individuals.
Although the above-discussed findings were mainly hypothesized, the lack of differences in the normalized muscle strength between the elite athletes and physically active individuals could be considered as somewhat unexpected. Namely, the jumping performance was prominently better in VP than in PA despite the lack of significant differences in muscle strength between the 2 groups. Moreover, note that the applied strength normalization was based on body mass, rather than on muscle content that was markedly higher in VP. The lack of the strength differences between the 2 groups could have originated from the relatively intense physical activity of the PA. Namely, through their academic curriculum they had been involved in several classes of various physical activities per day, 2–3 times a week, that also involved strength training. Therefore, we believe that the advantage in jumping performance of VP over PA could originate from both the overall physical fitness and jumping skill. An alternative explanation could be based on a close relationship observed between the jumping performance and normalized muscle power (13,24,28). Specifically, it remains possible that the better performance of VP was based on a higher power output of their lower limb muscles (not assessed in this study), rather then on their higher strength.
An apparent limitation of this study is the number of variables assessed. For example, although for the sake of both the ecological validity and simplicity we tested the strength through the maximum leg press exertion, the strength testing could be extended to both isometric and isokinetic tests of individual leg extensor groups (4,26,31,36). Another limitation originates from the cross-sectional design that does not allow for discerning the effects of physical activity from the initial selection of the subjects. Furthermore, the performance of other jumps and various rapid movements could also be assessed (6,7,39). Finally, note that both of the tested groups could be considered as lean and, therefore, relatively homogeneous regarding both their body composition and leg extensor strength. As a result, it remains questionable to what extent the present findings could be generalized to other populations. Namely, it is plausible to assume that the observed differences between the tested populations would be even more prominent if PA group consisted of more typical recreationally active individuals instead of both partly selected and highly physically active students of a sport and physical education program.
To conclude, the data suggest that not only the leg extensor strength but also the generally neglected body composition variables could be valid predictors of jumping performance. Specifically, the %BF and %SM could be particularly strong predictors of the jumping performance in nontrained women, as compared with elite female athletes whose activity is considerably based on vertical jumping. However, the lack of differences in the strength between the 2 groups strongly suggests that the role of other factors that contribute to performance of both jumping and other rapid movements still deserves further research.
Importance of both the body composition (i.e., assessed through the muscle and fat content) and leg strength variables (i.e., the ability to rapidly exert high muscle forces) should be taken into account when designing various training and testing procedures that target the performance of jumping and, possibly, other rapid and explosive movements. Specifically regarding the strength measures, the RFD could be a better predictor of jumping performance than the maximum force. However, the body composition, as seen through a large content of muscle and low content of fat tissue, could be a particularly strong predictor of rapid movement performance in nonathletes as compared with elite athletes. Therefore, to improve the performance of various jumps and other explosive movements in various populations, the practitioners should target their interventions to improve sport specific muscle strength. However, for the same purpose, the improvement in body composition should be specifically targeted in recreationally active individuals, rather than in a more homogeneous population of elite athletes.
The study was supported in part by grant III47015 of the Research Council of Republic of Serbia.
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