The influence of resting period length on jumping performance

The purpose of this study was to determine a resting interval between countermovement jumps (i.e., volleyball spikes) that allows the maintenance of maximal jumping performance. Ten male volleyball players (1.85 +/- 0.05 m, 77.2 +/- 10.6 kg, 21.6 +/- 5.3 years) performed 6 experimental jumping sessions. In the first and sixth sessions, maximal countermovement jump height was measured, followed by submaximal countermovement jumps to the point of volitional fatigue. The number of countermovement jumps was used as a reference to test the effect of rest period between volleyball spikes. From the second to fifth experimental sessions, 30 maximal volleyball spikes were performed with different resting periods (i.e., 8, 14, 17, and 20 seconds) followed by countermovement jumps. Between the 15th and 30th spikes, the blood lactate concentration and heart rate were measured. Because the performance on the first and sixth sessions was the same, no training effects were noticed. During the 8-second resting interval set, the lactate concentration increased significantly between the 15th and 30th spikes (i.e., from 3.37 +/- 1.16 mmol to 4.94 +/- 1.49 mmol); the number of countermovement jumps decreased significantly after spikes compared to those performed without a previous effort (i.e., from 23 +/- 7 jumps to 17 +/- 9 jumps); and these variables were significantly correlated (r = -0.7). On the other hand, the lactate concentration and number of countermovement jumps were stable across the other resting intervals, without a heart rate steady state. The results indicate that an adequate resting period between spikes allowed participants to achieve a lactate steady state in which the performance was maintained during the exercise. These findings show that resting intervals between 14 and 17 seconds, typical during volleyball matches, are indicated to use in volleyball spike drills due to their capacity to maintain maximal jumping performance.     

Relative importance of strength, power, and anthropometric measures to jump performance of elite volleyball players

The purpose of this investigation was to examine the potential strength, power, and anthropometric contributors to vertical jump performances that are considered specific to volleyball success: the spike jump (SPJ) and counter-movement vertical jump (CMVJ). To assess the relationship among strength, power, and anthropometric variables with CMVJ and SPJ, a correlation and regression analysis was performed. In addition, a comparison of strength, power, and anthropometric differences between the seven best subjects and the seven worst athletes on the CMVJ test and SPJ test was performed. When expressed as body mass relative measures, moderate correlations (0.53-0.65; p < or = 0.01) were observed between the 1RM measures and both relative CMVJ and relative SPJ. Very strong correlations were observed between relative (absolute height-standing reach height) depth jump performance and relative SPJ (0.85; p < or = 0.01) and relative CMVJ (0.93; p 相似文献   

Effects of electromyostimulation training and volleyball practice on jumping ability

The aim of this study was to investigate the influence of a 4-week electromyostimulation (EMS) training program on the vertical jump performance of 12 volleyball players. EMS sessions were incorporated into volleyball sessions 3 times weekly. EMS consisted of 20-22 concomitant stimulations of the knee extensor and plantar flexor muscles and lasted approximately 12 minutes. No significant changes were observed after EMS training for squat jump (SJ) and counter movement jump (CMJ) performance, while the mean height and the mean power maintained during 15 seconds of consecutive CMJs significantly increased by approximately 4% (p < 0.05). Ten days after the end of EMS training, the jumping height significantly (p < 0.05) increased compared with baseline also for single jumps (SJ +6.5%, CMJ +5.4%). When the aim of EMS resistance training is to enhance vertical jump ability, sport-specific workouts following EMS would enable the central nervous system to optimize the control to neuromuscular properties.     

Intersession reliability of vertical jump height in women and men

The purpose of the present study was to investigate the intersession reliability of vertical jump height in women and men recorded from a contact mat. Thirty-five women and 35 men performed four testing sessions across a 4-week period, with each session separated by 1 week. Within each testing session, subjects completed three countermovement vertical jumps (CMJs) for maximum height. Reliability statistics were calculated using the highest jump (HIGH) and also from the mean of all three jumps (3 MEAN) during each session. Reliability was calculated as a change in the mean, coefficients of variation (CVs), and intraclass correlations coefficients (ICCs) between testing sessions. For women, jump heights were not substantially different between sessions for either the HIGH or 3 MEAN data. The CVs for women ranged from 4.4 to 6.6% for HIGH and 4.1 to 6.0% for 3 MEAN, with the corresponding ICCs ranging from 0.87 to 0.94 for HIGH and 0.90 to 0.95 for 3 MEAN. For men, jump heights were not substantially different between sessions for HIGH. However, jump heights during session 1 were substantially greater than those during session 2 when using the 3 MEAN data. CVs between sessions for HIGH ranged from 4.0 to 5.6%, and those for 3 MEAN ranged from 4.2 to 5.2%. The ICCs ranged from 0.87 to 0.93 for HIGH and from 0.89 to 0.93 for 3 MEAN. Given the maximal nature of vertical jump tests, it seems appropriate to use the highest jump from a number of trials for women and men when using a contact mat. Practitioners and researchers can use the data to identify the range in which the true value of an athlete's score lies and calculate sample sizes for studies assessing height during CMJs recorded from a contact mat.     

Influence of familiarization on the reliability of vertical jump and acceleration sprinting performance in physically active men

The purpose of the present study was to determine the number of familiarization sessions required to obtain an accurate measure of reliability associated with loaded vertical jump and 20-m sprint running performance. Ten physically active men attended 5 separate testing sessions over a 3-week period where they performed unloaded and loaded (10-kg extra load) countermovement (CMJ) and static (SJ) jumps, followed by straight-line 20-m sprints. Jump height was recorded for the vertical jumps using a jump mat, while the time for 10 m and 20 m was recorded during the sprints using photocells. The highest (jump conditions) and fastest (sprint) of 3 trials performed during each of the 5 testing sessions was used in the subsequent analysis. Familiarization was assessed using the scores obtained during the 5 separate testing sessions. Reliability was assessed by calculating intraclass correlation coefficients (ICCs) and coefficient of variation (CV). No significant differences were obtained between the testing sessions for any of the measures. ICCs ranged from 0.89 to 0.95, while CVs ranged from 1.9 to 2.6%. These results indicate that high levels of reliability can be achieved without the need for familiarization sessions when using loaded and unloaded CMJ and SJ and 20-m sprint performance with physically active men.     

Gender and bilateral differences in single-leg countermovement jump performance with comparison to a double-leg jump

Expectations may be for both legs to function identically during single- and double-leg vertical jumps. However, several reasons might prevent this from occurring. The goals of this investigation were twofold: assess the presence of side-to-side jump height differences during single-leg jumps in a homogenous group of healthy subjects and determine if those with a jump height asymmetry possessed consistent biomechanical differences during single-and double-leg jumps. Thirteen men and 12 women with competitive volleyball experience volunteered for the study. Significance was assessed at p < 0.05. The men jumped significantly higher than the women in all conditions and possessed differences in several anthropometric, kinematic, and kinetic parameters. Based on a three-jump average, all subjects had one leg that they could jump higher with (the dominant leg, DL). The men generated significantly greater maximum ground reaction forces and ankle joint powers on their DL whereas the women had no differences during the single-leg jumps. The only side-to-side differences that existed during the double-leg jumps were in the average ground reaction forces during propulsion. These findings suggest that equality of single-leg jump performance is the exception rather than the norm, with identification of consistent biomechanical attributes difficult within a group.     

Do skill-based conditioning games offer a specific training stimulus for junior elite volleyball players?

This study investigated the specificity of skill-based conditioning games and compared the effectiveness of skill-based conditioning games and instructional training for improving physical fitness and skill in junior elite volleyball players. Twenty-five junior volleyball players (mean age +/- SE, 15.6 +/- 0.1 years) participated in this study. Heart rate data were collected on all players during the Australian Junior Volleyball Championships. After the competition, players were randomly allocated into a skill-based conditioning games group (n = 12) or an instructional training group (n = 13). Each player participated in a 12-week training program that included 3 organized court training sessions per week. No significant differences (P > 0.05) were detected between competition and skill-based conditioning games for the percentage of time spent in low-intensity, moderate-intensity, and high-intensity activities. Skill-based conditioning games induced improvements in vertical jump, spike jump, speed, agility, upper-body muscular power, and estimated maximal aerobic power, whereas technical instruction improved only spike jump and speed. Conversely, instructional training induced meaningful improvements in all measurements of skill, whereas improvements in technical skill after skill-based conditioning games were uncommon and typically small. The results of this study show that skill-based conditioning games offer a specific training stimulus to simulate the physiological demands of competition in junior elite volleyball players. Although the improvements in physical fitness after training were greater with skill-based conditioning games, instructional training resulted in greater improvements in technical skill in these athletes. These findings suggest that a combination of instructional training and skill-based conditioning games is likely to confer the greatest improvements in fitness and skill in junior elite volleyball players.     

Energy expenditure in maximal jumps on sand

The purpose of this study was to comparatively investigate the energy expenditure of jumping on sand and on a firm surface. Eight male university volleyball players were recruited in this study and performed 3 sets of 10 repetitive jumps on sand (the S condition), and also on a force platform (the F condition). The subjects jumped every two seconds during a set, and the interval between sets was 20 seconds. The subjects performed each jump on sand with maximal exertion while in the F condition they jumped as high as they did on sand. The oxygen requirement for jumping was defined as the total oxygen uptake consecutively measured between the first set of jumps and the point that oxygen uptake recovers to the resting value, and the energy expenditure was calculated. The jump height in the S condition was equivalent to 64.0 +/- 4.4% of the height in the maximal jump on the firm surface. The oxygen requirement was 7.39 +/- 0.33 liters in S condition and 6.24 +/- 0.69 liters in the F condition, and the energy expenditure was 37.0 +/- 1.64 kcal and 31.2 +/- 3.46 kcal respectively. The differences in the two counter values were both statistically significant (p < 0.01). The energy expenditure of jumping in the S condition was equivalent to 119.4 +/- 10.1% of the one in the F condition, which ratio was less than in walking and close to in running.     

Changes in skill and physical fitness following training in talent-identified volleyball players

This study investigated the effect of a skill-based training program on measurements of skill and physical fitness in talent-identified volleyball players. Twenty-six talented junior volleyball players (mean +/- SE age, 15.5 +/- 0.2 years) participated in an 8-week skill-based training program that included 3 skill-based court sessions per week. Skills sessions were designed to develop passing, setting, serving, spiking, and blocking technique and accuracy as well as game tactics and positioning skills. Coaches used a combination of technical and instructional coaching, coupled with skill-based games to facilitate learning. Subjects performed measurements of skill (passing, setting, serving, and spiking technique and accuracy), standard anthropometry (height, standing-reach height, body mass, and sum of 7 skinfolds), lower-body muscular power (vertical jump, spike jump), upper-body muscular power (overhead medicine-ball throw), speed (5- and 10-m sprint), agility (T-test), and maximal aerobic power (multistage fitness test) before and after training. Training induced significant (p < 0.05) improvements in spiking, setting, and passing accuracy and spiking and passing technique. Compared with pretraining, there were significant (p < 0.05) improvements in 5- and 10-m speed and agility. There were no significant differences between pretraining and posttraining for body mass, skinfold thickness, lower-body muscular power, upper-body muscular power, and maximal aerobic power. These findings demonstrate that skill-based volleyball training improves spiking, setting, and passing accuracy and spiking and passing technique, but has little effect on the physiological and anthropometric characteristics of players.     

Effect of instantaneous performance feedback during 6 weeks of velocity-based resistance training on sport-specific performance tests

The purpose of this study was to investigate the effect of instantaneous performance feedback (peak velocity) provided after each repetition of squat jump exercises over a 6-week training block on sport-specific performance tests. Thirteen professional rugby players were randomly assigned to 1 of 2 groups, feedback (n = 7) and non-feedback (n = 6). Both groups completed a 6-week training program (3 sessions per week) comprising exercises typical of their normal preseason conditioning program. Squat jumps were performed in 2 of the 3 sessions each week during which both groups performed 3 sets of 3 concentric squat jumps using a barbell with an absolute load of 40 kg. Participants in group 1 were given real-time feedback on peak velocity of the squat jump at the completion of each repetition using a linear position transducer and customized software, whereas those in group 2 did not receive any feedback. Pre and posttesting consisted of vertical jump, horizontal jump, and 10-/20-/30-m timed sprints. The relative magnitude (effect size) of the training effects for all performance tests was found to be small (0.18-0.28), except for the 30-m sprint performance, which was moderate (0.46). The probabilities that the use of feedback during squat jump training for 6 weeks was beneficial to increasing performance of sport-specific tests was 45% for vertical jump, 65% for 10-m sprints, 49% for 20-m sprints, 83% for horizontal jump, and 99% for 30-m sprints. In addition to improvements in the performance of sport-specific tests, suggesting the potential for greater adaptation and larger training effects, the provision of feedback may also be used in applications around performance targets and thresholds during training.     

The influence of familiarization on the reliability of force variables measured during unloaded and loaded vertical jumps

The purpose of this study was to determine the number of familiarization sessions required to obtain an accurate measure of reliability associated with force variables recorded during unloaded and loaded (30 and 60% of 1 repetition maximum squat [1RM]) static vertical jumps (SJ). Nine physically active men attended 4 separate testing sessions over a 2-week period. Force platform recordings of peak force, peak rate of force development (pRFD), average rate of force development, takeoff velocity, average power, and peak power were obtained for each jump. During each of the 4 testing sessions, 3 jumps were performed under each of the load conditions. The average of the force variables were used in the analysis. Familiarization was assessed using the scores obtained during the 4 separate testing sessions. Reliability was assessed by calculating intraclass correlation coefficients (ICCs) and coefficient of variation (CV) associated with the force variables. No significant differences (p > 0.05) were obtained between the testing sessions for any of the force variables. With the exception of pRFD, the force variables showed reasonably good levels of test-retest reliability (ICC range: 0.75-0.99; CV range: 1.2-7.6%). High levels of reliability can be achieved in a variety of force variables without the need for familiarization sessions when performing SJ under unloaded conditions and with loads of 30 and 60% of 1RM squat with physically active men.     

Four weeks of optimal load ballistic resistance training at the end of season attenuates declining jump performance of women volleyball players

Anecdotal and research evidence is that vertical jump performance declines over the competitive volleyball season. The purpose of this study was to evaluate whether a short period of ballistic resistance training would attenuate this loss. Fourteen collegiate women volleyball players were trained for 11 weeks with periodized traditional and ballistic resistance training. There was a 5.4% decrease (p < 0.05) in approach jump and reach height during the traditional training period (start of season to midseason), and a 5.3% increase (p < 0.05) during the ballistic training period (midseason to end of season), but values were not different from start to end of season. These changes in overall jump performance were reflective of changes in underlying neuromuscular performance variables: in particular, power output and peak velocity during loaded jump squats, countermovement jumps, and drop jumps. During the first 7 weeks of traditional heavy resistance training, it appears that the neuromuscular system is depressed, perhaps by the combination of training, game play, and skills practice precluding adequate recovery. Introduction of a novel training stimulus in the form of ballistic jump squats and reduction of heavy resistance training of the leg extensors stimulated a rebound in performance, in some cases to exceed the athlete's ability at the start of the season. Periodization of in-season training programs similar to that used in this study may provide volleyball players with good vertical jump performance for the crucial end-of-season games.     

Low and moderate plyometric training frequency produces greater jumping and sprinting gains compared with high frequency

The purpose of this study was to examine the effect of 3 different plyometric training frequencies (e.g., 1 day per week, 2 days per week, 4 days per week) associated with 3 different plyometric training volumes on maximal strength, vertical jump performance, and sprinting ability. Forty-two students were randomly assigned to 1 of 4 groups: control (n = 10, 7 sessions of drop jump (DJ) training, 1 day per week, 420 DJs), 14 sessions of DJ training (n = 12, 2 days per week, 840 DJs), and 28 sessions of DJ training (n = 9, 4 days per week, 1680 DJs). The training protocols included DJ from 3 different heights 20, 40, and 60 cm. Maximal strength (1 repetition maximum [1RM] and maximal isometric strength), vertical height in countermovement jumps and DJs, and 20-m sprint time tests were carried out before and after 7 weeks of plyometric training. No significant differences were observed among the groups in pre-training in any of the variables tested. No significant changes were observed in the control group in any of the variables tested at any point. Short-term plyometric training using moderate training frequency and volume of jumps (2 days per week, 840 jumps) produces similar enhancements in jumping performance, but greater training efficiency (approximately 12% and 0.014% per jump) compared with high jumping (4 days per week, 1680 jumps) training frequency (approximately 18% and 0.011% per jump). In addition, similar enhancements in 20-m-sprint time, jumping contact times and maximal strength were observed in both a moderate and low number of training sessions per week compared with high training frequencies, despite the fact that the average number of jumps accomplished in 7S (420 jumps) and 14S (840 jumps) was 25 and 50% of that performed in 28S (1680 jumps). These observations may have considerable practical relevance for the optimal design of plyometric training programs for athletes, given that a moderate volume is more efficient than a higher plyometric training volume.     

Changes in strength and power performance in elite senior female professional volleyball players during the in-season: a case study

It is often recommended that in-season training programs aim to maintain muscular strength and power developed during the off-season. However, improvements in performance may be possible with a well-designed training regimen. The purpose of this case report is to describe the changes in physical performance after an in-season training regimen in professional female volleyball players in order to determine whether muscular strength and power might be improved. Apart from normal practice sessions, 10 elite female volleyball players completed 2 training sessions per week, which included both resistance training and plyometric exercises. Over the 12-week season, the athletes performed 3-4 sets of 3-8 repetitions for resistance and plyometric exercises during each training session. All sessions were supervised by one of the investigators as well as by the team head coach. Muscular strength and power were assessed before and after the 12-week training program using 4 repetition maximum bench press and parallel squat tests, an overhead medicine ball throw (BTd), as well as unloaded and loaded countermovement jumps (CMJs). Strength improved by 15% and 11.5% in the bench press and parallel squat, respectively (p < 0.0001). Distance in the BTd improved by 11.8% (p < 0.0001), whereas unloaded and loaded CMJ height increased between 3.8 and 11.2%. The current findings suggest that elite female volleyball players can improve strength and power during the competition season by implementing a well-designed training program that includes both resistance and plyometric exercises.     

Long-term training adaptations in elite male volleyball players

Several investigations have demonstrated differences in anthropometry, jump performance, and strength variables between developmental and elite-level volleyball players. However, within the elite level of play, the magnitude of change that can occur with training is unclear. The purpose of this investigation was to examine the anthropometric, vertical jump, and strength quality changes over 2 years in a group of national team volleyball players. Fourteen national team volleyball players (age, 23.0 ± 4.1 years; height, 1.98 ± 0.07 m; weight, 91.7 ± 7.9 kg) began and completed this study. Participants had all played international matches (representing Australia) before the examination time period and continued to do so during the international season. Anthropometry (stature, mass, and sum of 7 skinfolds), vertical jump measures (countermovement vertical jump; depth jump from 0.35 m, DJ; spike jump, SPJ, all including arm swing), and lower-body power (jump squat at body mass, and jump squat + 50% body weight, JS50) measures were tested before and at the conclusion of the investigation period. Significant (p < 0.05) improvements were observed in sum of 7 skinfolds, DJ, SPJ, and JS50 performance, with large magnitude changes (d > 0.70) in the sum of 7 skinfolds reduction, SPJ, and leg extensor power. This study has demonstrated that elite male volleyball players can improve leanness and power, which contribute to improvements in vertical jump.     

Test-retest reliability of three different countermovement jumping tests

In studies of physical performance comprising muscle strength and power, a vertical jump is a test method that frequently is used. It is important to have access to accurate measuring tools providing data with high reproducibility. Studies have shown that body composition also may play an important part in physical performance. The purpose of this study was to determine test-retest reliability for 3 different kinds of vertical jumps and to correlate jump height with body composition. Thirty-four normally trained subjects (women n = 17) between 18 and 25 years participated. Test-retest, on 3 kinds of vertical jumps, was performed with a median of 7 days between jumps. Methods used were a countermovement jump (CMJ) on a contact mat, with and without arm swing, and an Abalakow jump (AJ) using measuring tape, with arm swing. Body composition was assessed with the use of bioelectric impedance analysis. The results showed that high intraclass correlation coefficients (ICCs) were observed between testing occasions for all 3 vertical jumps (ICC between 0.48 and 0.88). The AJ in women presented the lowest ICC. Also the correlation between CMJ and AJ was high (rs = 0.88). Moderate-to-high correlations could be shown between body composition and CMJ in women (rs = -0.57-0.76). In conclusion, very high test-retest reliability for CMJ on a contact mat was found. For the AJ using a measuring tape, ICC were overall high, but a moderate nonsignificant ICC were found in women, indicating poor reproducibility. The data from the CMJ and AJ may be compared if approximately 25% of the AJ value is subtracted. In practice, this means that vertical jump tests have high reproducibility and can be used as measures of power development.     

The effect of dropping height on jumping performance in trained and untrained prepubertal boys and girls

Plyometric training in children, including different types of jumps, has become common practice during the last few years in different sports, although there is limited information about the adaptability of children with respect to different loads and the differences in performance between various jump types. The purpose of this study was to examine the effect of gender and training background on the optimal drop jump height of 9- to 11-year-old children. Sixty prepubertal (untrained and track and field athletes, boys and girls, equally distributed in each group [n = 15]), performed the following in random order: 3 squat jumps, 3 countermovement jumps (CMJs) and 3 drop jumps from heights of 10, 20, 30, 40, and 50 cm. The trial with the best performance in jump height of each test was used for further analysis. The jump type significantly affected the jump height. The jump height during the CMJ was the highest among all other jump types, resulting in advanced performance for both trained and untrained prepubertal boys and girls. However, increasing the dropping height did not change the jumping height or contact time during the drop jump. This possibly indicates an inability of prepubertal children to use their stored elastic energy to increase jumping height during drop jumps, irrespective of their gender or training status. This indicates that children, independent of gender and training status, have no performance gain during drop jumps from heights up to 50 cm, and therefore, it is recommended that only low drop jump heights be included in plyometric training to limit the probability of sustaining injuries.     

Gender bias in the effects of arms and countermovement on jumping performance

The ability to jump high is considered important in a number of sports. It is commonly accepted that the use of the arms and a counter movement increase jump height. In some sport situations (e.g., volley ball block, basketball rebound), athletes may not be able to utilize a counter movement or arm swing. The purpose of this study is to examine gender differences in the contribution of the arm swing and counter movement to vertical jump height. Fifty college students, 25 men (age = 21.4 +/- 1.7 years, height = 182.2 +/- 8 cm, weight = 83.7 +/- 12.4 kg) and 25 women (age = 20.7 +/- 1.6 years, height = 166.7 +/- 6.3 cm, weight = 61.5 +/- 7.0 kg), performed 4 jumping movements: squat jumps with hands on hips (SNA), counter movement jump with hands on hips (CMNA), squat jump with arm swing (SA), and counter movement with arm swing (CMA). Significant differences were found between men's and women's performance, as well as between each type of jump within each gender. A mixed-model analysis of variance detected gender differences with respect to changes in the jumping movement. For both sexes the jumps in order from worst to best were SNA, CMNA, SA, and CMA. Peak power values for men were 4,057, 4,020, 4,644, and 4,747 W, respectively, for the 4 jumps. The female power values were 2,543, 2,445, 2,842, and 2,788 W, respectively, for the 4 jumps. Arms increased jump height more than a counter movement for both genders, with jump heights for men at 29.6, 31, 36, and 38 cm, respectively, and those of women 21, 22, 26, and 27 cm, respectively. Use of the arms was found to increase the jump height of the men significantly more than that of women. Changes in jumping movements affect men and women differently. The greater increase in jump height for the men when using the arm swing could be because of greater upper body strength of men compared with women. This could have applications to training and upper body strength and also to modeling of jumping movements.     

Vertical jumping tests in volleyball: reliability, validity, and playing-position specifics

Vertical jumping is known to be important in volleyball, and jumping performance tests are frequently studied for their reliability and validity. However, most studies concerning jumping in volleyball have dealt with standard rather than sport-specific jumping procedures and tests. The aims of this study, therefore, were (a) to determine the reliability and factorial validity of 2 volleyball-specific jumping tests, the block jump (BJ) test and the attack jump (AJ) test, relative to 2 frequently used and systematically validated jumping tests, the countermovement jump test and the squat jump test and (b) to establish volleyball position-specific differences in the jumping tests and simple anthropometric indices (body height [BH], body weight, and body mass index [BMI]). The BJ was performed from a defensive volleyball position, with the hands positioned in front of the chest. During an AJ, the players used a 2- to 3-step approach and performed a drop jump with an arm swing followed by a quick vertical jump. A total of 95 high-level volleyball players (all men) participated in this study. The reliability of the jumping tests ranged from 0.97 to 0.99 for Cronbach's alpha coefficients, from 0.93 to 0.97 for interitem correlation coefficients and from 2.1 to 2.8 for coefficients of variation. The highest reliability was found for the specific jumping tests. The factor analysis extracted one significant component, and all of the tests were highly intercorrelated. The analysis of variance with post hoc analysis showed significant differences between 5 playing positions in some of the jumping tests. In general, receivers had a greater jumping capacity, followed by libero players. The differences in jumping capacities should be emphasized vis-a-vis differences in the anthropometric measures of players, where middle hitters had higher BH and body weight, followed by opposite hitters and receivers, with no differences in the BMI between positions.     

Acute effects of plyometric exercise on maximum squat performance in male athletes

This study examines the acute effects of plyometric exercise on 1 repetition maximum (RM) squat performance in trained male athletes. Twelve men (mean age +/- SD: 20.5 +/- 1.4 years) volunteered to participate in 3 testing sessions separated by at least 6 days of rest. During each testing session the 1RM was assessed on back squat exercise. Before all 3 trials subjects warmed up on a stationary cycle for 5 minutes and performed static stretching. Subjects then performed 5 submaximal sets of 1-8 repetitions before attempting a 1RM lift. Subjects rested for at least 4 minutes between 1RM trials. During the first testing session (T1) subjects performed a series of sets with increasing load until their 1RM was determined. During the second and third testing sessions subjects performed in counterbalanced order either 3 double-leg tuck jumps (TJ) or 2 depth jumps (DJ) 30 seconds before each 1RM attempt. The average 1RM lifts after T1 and testing sessions with TJ or DJ were 139.6 +/- 29.3 kg, 140.5 +/- 25.6 kg, and 144.5 +/- 30.2 kg, respectively (T1 < DJ; p < 0.05). These data suggest that DJ performed before 1RM testing may enhance squat performance in trained male athletes.