Volleyball is one of the most popular team sports in the world. The game is characterized by short, explosive movement patterns, quick, agile positioning, jumps, and blocks. Although a match may last for up to 3 hours, volleyball is considered an anaerobic sport, with metabolic demands met mainly by phosphagen energy processes (15). Along with a technical and tactical knowledge, appropriate morphological features (e.g., a lean body with greater height), speed and agility, and jumping ability are the key elements for success in volleyball for both sexes (1,16), because game play is oriented around a net whose top height is set at 2.43 m (men) and 2.24 m (women). Consequently, athletes and coaches in volleyball should pay special attention to testing and developing characteristic vertical jumping abilities (16) that will allow the player to compete at a more advanced level. A volleyball team consists of 12 players in the following positions: opposite hitter, middle hitter, libero, setter, and receiver. Given the specialized role and tasks players are involved in (7), it is generally accepted that different morphological (11), fitness (18) and physiological (23) are associated with the different playing positions. However, the specific jumping abilities required by the different volleyball positions have rarely been studied. In short, Marques et al. (18) found no significant differences between the playing positions in terms of jumping ability when measured using the countermovement jump (CMJ), whereas Duncan et al. (5) found no differences in vertical jumping capacity between playing positions among elite junior players.
Vertical jumping performance can be assessed using a variety of tools, ranging from sophisticated electronic measuring instruments (e.g., force platforms, contact mats, or photocells) to popular field-testing procedures (e.g., the Sargent jump test or the Abalakov test). In such assessments, different types of jumps may be performed (e.g., squat jumps [SJs], CMJs, or repeated jumps). In volleyball, there are some specific movement patterns associated with jumping, namely, a block jump (BJ) and an attack or spike jump (AJ). When performing a defensive BJ, a player starts from the characteristic stable position, with the knees slightly bent and arms in front of the chest. When performing a BJ, the athlete must jump as quickly as possible, meaning that he or she does not have time to perform a classic CMJ but instead uses a somewhat shortened version of the CMJ technique. In addition because the hands must be positioned in front of the chest to perform the block, there is no time for a full arm swing. A full countermovement and arm swing would almost certainly result in a jump of greater height, but the blocking would be delayed, and consequently, the defense would be unsuccessful. The AJ is a combination of a drop jump and a CMJ with an arm swing. The player generally uses a 2- to 3-step approach, performing a half-drop jump (sometimes referred to as a ''bounce drop jump" ) followed by a countermovement arm swing and an eccentric contraction that exploits the stretch-shortening cycle of the activated muscles (13). The movement finishes with a maximal vertical jump accompanied by a forceful backward arm swing to enable a subsequent spike. The pattern of this final movement probably has a slight negative influence on jumping performance (i.e., the maximum jump height would probably be more higher if the strong backward arm swing were not performed), but as stated above, such movement patterns are characteristic of volleyball. It is absolutely crucial, therefore, that they be included in any volleyball-specific testing procedure.
Standard vertical jumping test procedures have been validated extensively for a variety of purposes (4,17,19,24). However, we have found no studies that deal with the reliability and validity of volleyball-specific jumping performance or volleyball-specific jumping tests. Additionally, studies that have dealt with volleyball playing positions (5,18) and their jumping abilities have used standard (i.e., CMJ) and not volleyball-specific (i.e., AJ or BJ) jumping procedures. The sample of subjects in these studies was also smaller than our sample (see Discussion), which possibly influenced their results and conclusions.
The aims of this study were (a) to determine the reliability and factorial validity of 2 volleyball-specific jumping tests, the block jump test and the attack jump test, relative to 2 frequently used and systematically validated jumping tests, the CMJ and SJ tests and (b) to determine position-specific differences in jumping abilities among high-level male volleyball players and their anthropometric characteristics.
Experimental Approach to the Problem
In our professional experience, we have observed the measurement of jumping abilities as an index of the performance status in volleyball. This is especially true for volleyball-specific jumping techniques that, to the best of our knowledge, have not been studied for the reliability and validity of their respective tests. Additionally, studies focusing on volleyball have heretofore rarely noted positional differences with respect to jumping capacities. We hypothesized that systematic training and specific game performance would lead to significant differences between playing positions regarding the players' jumping performance. At the same time, selection processes would probably lead to differences in the anthropometric measures between playing positions. As a result, this study consists of 2 separate methodologies. The first part of this study focuses on the reliability and validity of the jumping tests (see Statistical Analyses). The second part of the study seeks to determine the differences in jumping tests and anthropometric measures (dependent variables) between different playing positions in volleyball (independent variable).
A total of 95 high-level volleyball players participated in this study. The subjects were all men between the ages of 18 and 30 years. The subjects' heights ranged from 177 to 207 cm (mean 189.1 cm), and their body weights ranged from 57.2 to 128.6 kg (mean 85.1 kg). All the participants were members of the teams that competed in the Slovenian National Championship (first and second Divisions) during the 2008–2009 season. Testing included 96% of all the players participating in the highest level of the National competition and 12 members of the National team. Thus, one-third of the subjects were international-level players who played in the European Championship and the European League. All the subjects underwent a preseason preparation period of at least 1 month before the testing was performed. Only the subjects who had no injuries and illnesses for 30 days before the experiment were included in this investigation (based on a health history questionnaire completed before testing). None of the players were taking exogenous anabolic-androgenic steroids or other substances that might be expected to affect their physical performance during the course of the study. The players were categorized as opposite hitters (OPPOSITE, n = 15); middle blockers (MIDDLE, n = 26); liberos (LIBERO, n = 11); setters (SETTER, n = 19); and outside receivers (RECEIVER, n = 24).
All the participants were fully informed about the nature and demands of the study and the possible health risks. Written information and oral instructions were given to each participant before the testing, and all the participants gave oral consent to participate. The Institutional Ethical Board was introduced to the testing methods and the complete experiment and gave written consent for the investigation.
All the subjects had been playing volleyball for at least 5 years. Apart from standard technical and tactical practice sessions (1–4 hours per day) and competitions, the subjects were involved in upper-lower body resistance training programs in the gymnasium (1–3 sessions per week), plyometric and medicine ball training (1–3 sessions per week), and proprioceptive balance training (0–3 sessions per week). In general, resistance training included free-weight and machine-based exercises that lasted 45–75 minutes on average, incorporating 10–15 minutes of abdominal and lower back (core) exercises on the mat and Swiss ball. The plyometric sessions consisted of loaded and unloaded drop jumps and medicine ball throws and lasted 30–45 minutes in addition to the warm-up. Most of the athletes (70%) participated in the regular proprioceptive exercises, which lasted 15–30 minutes and included unstable wobble board, BOSU and AIREX mat, and Swiss ball exercises. The average training frequency for all the subjects ranged from 4 to 10 training sessions per week, with an average of 5–6 sessions weekly.
The variables in this study included 4 types of vertical jump, the CMJ; the SJ, the BJ, and the attack jump (AJ); and 2 anthropometric measures, body height (BH), and body weight (BW).
The subjects were invited to participate through the Slovenian National Volleyball Federation. The response rate was >95%. The testing was conducted during June and July 2009. It was conducted in a closed, ventilated facility with a temperature ranging from 20 to 23°C in the morning (from 10 AM to 1 PM). Before testing, the athletes were suggested to be properly but not excessively hydrated. Each subject underwent all the tests during 1 session. The BH and BW of the participants were tested before the warm-up when they were in shorts and with no shoes. For the rest of the testing, the subjects wore volleyball shorts and shirts and their standard playing shoes. After a 6-minute warm-up on a stationary bicycle using progressive resistance (50–100 W) and 1 minute of hamstring stretches, each subject performed 3 trials for each of the 4 types of jump. The ordering of the different types of jump was assigned randomly for each participant. Between the testing trials and different tests, each subject paused for a self-defined period, which was limited to 3–5 minutes. All the jumps were measured using the Optojump system (Microgate, Bolzano, Italy). The Optojump is a dual-beam optical device that measures ground contact and flight time during a jump or series of jumps. The flight time (Tf) and the acceleration due to gravity (g) were used to calculate the vertical rise (h) of the center of gravity of the body:
There producibility of the vertical jump test results using the Optojump device has been shown to be excellent (10), and it has been used in other studies (20).
The CMJ test begins with the subject standing in an upright position. A fast downward movement to about 90° knee flexion is immediately followed by a quick upward vertical movement as high as possible, all in one sequence. The test is performed with a full arm swing.
The SJ test begins with the subjects in a stance with 90° knee flexion, with the feet hip-width apart. Their hands remain on the hips throughout. From this static position (with no prestretching), the subjects perform a quick upward vertical jump as high as possible.
The BJ is performed in a defensive volleyball position. The subjects in our study were instructed to visualize preparing for a defensive block during a game. In this situation, the hands are positioned in front of the chest in the most convenient position. From this position, the participants perform a CMJ-type technique with self-determined countermovement depth and the amount of arm swing that is typical for their individual volleyball technique during a game or practice. The subject performs the vertical jump with full arm extension, trying to reach as high as possible.
In the AJ test, the subject uses an individually determined 2- to 3-step approach, performing a bounce jump with an arm swing. This movement is followed by a quick upward vertical jump as high as possible, accompanied by a forceful backward arm swing. (Note that the photocells do not include the very beginning stage of the AJ procedure.) The subjects were instructed to perform the jumping procedure in the way that they found most convenient, similar to their personal technique during a volleyball game or practice.
Because we asked the subjects to use their usual individual procedures for performing the AJ and BJ tests, their specific procedures were relatively nonstandardized. Because the main intention of this investigation was to construct and validate volleyball-specific vertical jumping tests, it was necessary to acknowledge that each of the tested players had characteristic individual movement patterns (length of approach, foot positioning, arm swing, etc.). Because all the tested subjects were high-level volleyball athletes, further standardization would have almost certainly had a negative influence on their jumping performance during the AJ and BJ tests.
The BH and BW were assessed using a Seca stadiometer and weighing scales (Seca Instruments Ltd., Hamburg, Germany). Body mass index (BMI) was calculated as the ratio of the BW (kilograms) and squared BH (meters).
The playing positions were self-reported using a multiple choice questionnaire form in which the subjects were asked to determine their primary playing position as opposite hitters (OPPOSITE), middle blockers (MIDDLE), liberos (LIBERO), setters (SETTER), and outside hitters/receivers (RECEIVER). This information was verified by a team official (coach and team manager).
Descriptive statistical parameters (mean, SD, minimum, and maximum) were calculated for each individual trial (each item) and for the overall results (case-specific maximal results) of all of the tests conducted. An analysis of variance (ANOVA) for repeated measures and a Tukey post hoc test were used to detect any systematic bias between the individual trials (items) for each test. Average interitem correlation coefficients (IIR) and Cronbach's alpha reliability coefficients (CA) were used to determine the between-subject reliability of the jumping tests. The within-subject variation for each of the tests was determined by calculating the coefficient of variation (CV). To determine the factorial validity of the jumping tests, the intercorrelation matrix for the 4 tests was factorized using a principal-components factor analysis. The number of significant components was determined using the Kaiser-Guttman criterion. The correlations between tests and factors were used to determine the factorial validity of the tests. Differences between playing positions in anthropometric measures and jumping tests were determined using the ANOVA with a Unequal-n post hoc test. All the coefficients were considered significant at 95% (p ≤ 0.05).
The parameters of reliability for the tests (Table 1) 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 between-subject reliability was found for the newly constructed volleyball-specific tests (0.97 and 0.99 for Cronbach's alpha, 0.94 and 0.97 for interitem correlation). We observed no systematic differences between the trials for any of the tests.
The correlations between tests were high, ranging from 0.75 (SJ and AJ) up to 0.89 (CMJ and BJ). Factor analysis extracted one significant component (F1) with high correlations for all the applied tests. This component accounts for 86% of the common variance, meaning that only 14% of the variance among the tests cannot be explained by calculated linear combination (F1). All these results indicated the high validity of the applied tests for this subject sample (Table 2).
MIDDLE players are the tallest and heaviest, followed by OPPOSITEs and RECEIVERs. LIBERO players are the shortest of all and lighter than the OPPOSITEs and MIDDLEs. No significant differences between positions were found for BMI. The differences in jumping abilities reached statistical significance for the SJ and CMJ, where RECEIVERs had higher average jumps than did the SETTERs, and for the AJ, where RECEIVERs had higher average jumps than did the LIBEROs. Finally, LIBEROs performed significantly better than did the SETTERs in the BJ (Table 3).
The CMJ data are similar to those previously reported for high-level volleyball players (18), but the jumping abilities of our subjects are evidently far better than those reported in previous studies (17,24) for physically active and trained subjects (20–25% greater for volleyball players). Our subjects achieved the greatest heights in the AJ test (24, 31, and 40% higher than for the BJ, CMJ and SJ tests, respectively). This finding can be explained by the biomechanical characteristics of the AJ. In this jump, a multistep approach results in additional acceleration during the bounce drop jump (i.e., the eccentric contraction) through an intensive stretch-shortening cycle that is effectively transformed into concentric vertical jumping performance (13). However, we believe that such superior results on AJ tests should be expected only for experienced athletes who are able to use all the muscular capacities relevant to this sport-specific jumping technique (e.g., high-level volleyball and handball players). The BJ test results are approximately 9% higher than the results for the CMJ test (in our case, the CMJ was performed without an arm swing, and the BJ was performed as a CMJ with a partial arm swing). Interestingly, previous studies noted a larger difference between vertical jumps performed with and without arm swing. When comparing the CMJ with and without an arm swing, Slinde et al. (24) found a 14% difference for both men and women. In addition, a 13% difference was found in the Abalakov jumping test (17). We consider it probable that the limited arm swing performed during a BJ led to the relatively smaller difference between the BJ and the CMJ found in our investigation.
The CMJ and SJ tests have been used extensively, and there have been a number of studies that have checked their reliability (2,12,17,24). However, the CMJ and BJ tests are standard rather than sport-specific jumping tests, and most of these studies involved physically active individuals instead of high-level athletes. In our study, we focused on high-level volleyball players, and therefore, high reliability for the jumping tests was hard to be expected. In brief, the numerical values of the reliability coefficients rely on 2 descriptive statistical parameters: the correlation between items (IIR) and the difference between single-item and overall (in this case, 3-item) variance (CA and CV). When testing high-level athletes in a specific sport for characteristic sport-specific achievement measures (e.g., jumping performance in volleyball), less single-item variance should be expected (21). This lower variance leads to (a) lower numerical values for the correlation coefficients (i.e., small differences between the results for different test items are statistically penalized) and (b) a higher possibility that the single-item variance and the overall variance will differ significantly, which will consequently decrease the CA and CV values. In view of these considerations, we judge the reliability coefficients found in our study to be very high. We found no significant differences between trials of the jumping test procedures, which accords with the findings of previous studies in which participant familiarity with the jumps has not been discussed in relation to tests of jumping performance (9). However, we must note that we sampled high-level athletes; thus, their specific motor knowledge of the types of jumps that we tested should be considered high and stable. Additionally, the participants were instructed to adhere to their usual routine when performing a BJ and an AJ, which almost certainly influenced the high stability of results. Because volleyball players are specialized for certain positions, we hypothesized that our tests might identify 2 separate factors for jumping performance. However, this was not the case. In fact, the results of the correlation analysis indicate that the volleyball-specific tests are highly intercorrelated (Table 2). Generally, the test intercorrelations are notably higher than those previously noted for nonvolleyball-specific tests. Furthermore, our factorial validity supports the findings of previous studies in which researchers performed factor analyses and identified a single latent dimension for explosive power in well-trained male subjects (17). At this time, we are not positing any ranking between the tests with regard to their factorial validity. Because of the high correlations between tests and the extracted latent dimension, any such interpretation would be partially speculative.
Our results showed significant differences between playing positions with respect to anthropometric measures and jumping abilities, which will be discussed in parallel. In general, RECEIVERs are superior in most of their jumping capacities, but these findings should not be oversimplified. Although better in jumping performance, RECEIVERs do not jump frequently during game play because of their lower BH (in comparison with other teammates) and because of their tactical position in the game (relatively far from the net). However, it is generally accepted that RECEIVERs are technically the most advanced of all players and must participate in diverse tactical situations during game play. It is possible that such diversity in their training stimuli partially explains their dominance of the jumping tests that we studied. In short, the different actions that they are involved in during games and training sessions ensure a wide range of training stimuli, which allows RECEIVERS to develop superior physical capacities to their teammates. Our finding accords with the findings of previous studies in which authors have demonstrated the superiority of RECEIVERs in the parallel squat (lower body strength), although differences for CMJ in their study did not reach statistical significance (18) (see text given later for more details). The relationship between BH and muscle mass is generally curvilinear and not linear. Much the same explanation can be offered when addressing LIBEROs' jumping capacities (note that LIBEROs are the second most successful of all playing positions studied behind RECEIVERs). Because LIBEROs are the shortest of all the groups, their jumping reach height is insufficient for a successful jumping performance in a volleyball game. However, their BH is probably one of the most important reasons for their advancement in jumping tests. Previous studies of volleyball players (22) have found that the “best” and the “worst” CMJ performers differ significantly in their BH (e.g., the “best performers” are significantly shorter), which could be explained by the fact that the relationship between BH and muscle mass is generally curvilinear and not linear (21) (e.g., the development of the muscle tissue as a generator of force does not linearly follow advancement in BH among adults). However, in volleyball, all previously discussed should be judged by emphasizing the differences in BH and the correlated arm length and reach height differences (14). More precisely, MIDDLE players are by far the most advanced in their body length dimensions (see BH results), which certainly makes up for their average results in the jumping tests that we conducted and allows them to achieve a superior performance at the net. In light of the relatively greater BH of MIDDLE players in comparison with that of LIBEROs and SETTERs, one should also observe the jumping performance of the OPPOSITE players. The relative inferiority of the SETTERs in the jumping performance is not surprising because this playing position is known to be relatively more “tactical” than “physical” in volleyball.
Most of the previous studies that have dealt with the physical capacities of volleyball players have studied female and junior volleyball athletes (6–8,11) and have rarely identified >3 playing positions (e.g., MIDDLE, SETTER, and OUTSIDE ). In one of the rare studies that studied 5 playing positions with respect to jumping ability, Marques et al. (18) found no significant differences between positions in their CMJ performance. However, the numerical differences between playing positions for the CMJ in their study were almost identical to those we have reported here. It is likely that the number of subjects (95 subjects in this study vs. 35 subjects in Marques et al.) should be regarded as a significant factor in investigations that deal with positional differences in team sports.
Based on the results studied and discussed, we emphasize 2 groups of important practical considerations.
First, this study found that all the test procedures showed high reliability and validity. Additionally, the subjects involved in this investigation (i.e., high-level volleyball players) were highly consistent in their sport-specific jumping tests (i.e., AJ and BJ) and in the standard jumping tests (i.e., CMJ and SJ). Generally, the newly constructed tests (AJs and BJs) showed a relatively higher between-subject reliability than did the standard tests (CMJs and SJs). However, the differences in reliability parameters between the tests of standard jumping procedures and the tests of volleyball-specific jumping procedures were very small. Therefore, we conclude that these newly constructed volleyball-specific tests, which simulate real-game situations of defense and attack, captured appropriate metric characteristics and should be used to test volleyball athletes for sport-specific jumping abilities in the future.
Second, the data presented for the different playing positions should be observed as the numerical norms and achievement standards for the tests we have studied herein. They should be used in 2 separate ways. First, they should be used as orientation values that will allow coaches to compare the achieved results of their players with the results presented here and to emphasize the need for specific training. This comparison will allow strength and conditioning specialists to design appropriate training programs aimed at improving the specific jumping abilities of athletes at different positions, keeping in mind their morphological features (e.g., BH and BW). Finally, using the results presented here, volleyball coaches will be able to place their players in the most appropriate playing positions according to their jumping capacities and anthropometric characteristics.
Support of the Ministry of Education and Sport of Republic of Slovenia (project no. v5-0233) and Ministry of Science, Education, and Sport of Republic of Croatia (project no. 315-1773397-3407) is gratefully acknowledged. The authors declare that they have no conflict of interest relevant to the content of this manuscript. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.
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