In the last 2 decades, the use of the repeated sprint test (RST) has gained popularity among coaches and athletes as a valid (2,13) and reliable (9,20) method of evaluating repeated sprint ability. Such tests usually involve repetitions of short sprints, with variable recovery periods in-between. Different protocols for this test consist, for example, of eight to ten 5-second sprint repetitions starting every 30 seconds, (2) six 40-m maximal sprints starting every 30 seconds, or twelve 20-m sprints starting every 20 seconds (17). The specific test protocol can be easily adapted to suit the specific needs and activity patterns of intermittent-type sports. Thus, RSTs are most commonly used in multisprint sports, such as soccer, rugby, and hockey.
To date, most repeated sprint studies have used running (13,17,20) or cycling (2,9) as the exercise mode. However, certain sports are characterized by intense intermittent activities other than running. One such sport is volleyball, where jumping is the leading type of action, and running for more than few steps is hardly performed during the game (8). Previous studies have shown that 20 to 30 jumps per set are performed by a single player in a volleyball game, although this depends on the player's role in the team (1,23). The importance of jumping to volleyball was demonstrated in various studies where jump height was found to be significantly higher in elite compared with semielite and novice players (10) and in trained players compared with nonplayers of all ages (14). Therefore, it is not surprising that vertical jump serves as a major training method for improving the volleyball player's relevant fitness capabilities. For example, reports of the 1981 U.S. Olympic Volleyball Team training revealed that about 200 maximal jumps were performed per training session during the early phase of the program and increased to 400 maximal jumps per session during the heavy phase of training (16). In view of this information, it seems that the use of a repeated running protocol to test anaerobic capabilities of volleyball players is inappropriate. Instead, a more specific test that uses the activity pattern of volleyball and includes repeated jumps seems more appropriate.
Previous studies suggested that a higher level of aerobic fitness is required for improved performance during repeated sprint activity (RSA) (11,24). However, the correlation between V[Combining Dot Above]O2max and indices of RSA were found inconsistent, and although some authors reported significant correlations between the two (4), others failed to do so (25). Possible reasons for this inconsistency may be the use of different RSA protocols, differences in the participants' fitness levels, or the different exercise modes used in previous studies. Further research is needed to investigate the relationship between aerobic fitness and RSA, especially using exercise modes other than running or cycling.
The aim of this study, therefore, was to determine performance indices of repeated jump test (RJT) and to examine their relationships with RST performance indices and with aerobic fitness among trained volleyball players. We hypothesized that significant correlations will be found between performance indices of the RST and RJT, and between performance indices of the 2 repeated tests and aerobic fitness of the players.
Experimental Approach to the Problem
To date, most repeated sprint studies used running (13,17,20) as the exercise mode. However, in sports of an intense intermittent nature, activity may be performed in different forms. For example, in volleyball, jumping is the dominant action, whereas running of more than a few steps is rare during a game. Thus, although RST is a popular and a common testing methodology to evaluate anaerobic capabilities in intermittent sports, such as soccer, rugby, or basketball, its use to test anaerobic capabilities of volleyball players seems inappropriate.
To investigate the relationships between performance indices of 2 different forms of repeated activity—running and jumping—players performed RST (6 × 30-m all-out sprints with 30-second rest periods between runs) and RJT (6 sets of 6 consecutive power jumps with 30-second rest periods between sets). The 2 protocols, although different in activity form (running vs. jumping), were premeditated to match activity structure where the total time of activity, the number of leg-ground contacts, and the number of sets were matched. Given that, both tests were supposed to measure similar anaerobic capabilities and performance indices reflecting similar physiological properties.
An aerobic 20-m shuttle run test was also performed by the players to evaluate their aerobic fitness. To assess the importance of aerobic capacity to power maintenance during the different forms of repeated activity, predicted V[Combining Dot Above]O2max was correlated with performance indices of both repeated activity tests (RATs).
Sixteen trained male volleyball players (age 25.9 ± 4.9 years, body mass 83.9 ± 6.9 kg, height 192 ± 6.1 cm, body fat 11.8 ± 2.8%), members of a first division Israeli league team, participated in the study. The team was consistently ranked among the first 5 teams in the league. The players trained 5 days per week and competed during the weekend. The study was performed in the middle of the competition season, when the players were assumed to be in their top physical shape. Most training sessions at this time of the year were devoted to specific tactic drills and game skills with the use of balls. Two resistance training sessions, without aerobic training, were performed per week during that period.
A standard calibrated scale and stadiometer were used to determine height and body mass. Skinfolds measurement at 4 sites (triceps, biceps, subscapular, and suprailiac) was used to calculate percent body fat. The study was approved by the institution's ethical committee, the testing procedure was explained, and a written informed consent was obtained from all players. As all players were older than 18 years, and no parents' permission for participation was needed.
The participants performed 3 tests in random order, separated by 4–5 days from each other and at least 48 hours before or after a match. The 3 tests included an aerobic power test, RST, and RJT.
To prevent unnecessary fatigue effect, players and coaches were instructed to avoid intense training 24 hours before each testing session. The aerobic power test and the 2 RATs were performed in the team home sports arena. All tests were performed about 4 hours after lunch and 30 minutes after drinking 500 mL of water. All tests were performed in the afternoon, in a comfortable average air temperature of about 24° C. None of the participants were taking any medication or food supplements during the study period.
Before each RAT, participants performed a 20-minute warm-up. Participants started the warm-up with 5 minutes of jogging followed by 8 minutes of stretching exercises, and then performed specific drills—2 all-out 20-m sprints or 4 maximal jumps—before starting the RST and the RJT, respectively.
Repeated Sprint Test
The RST protocol included a series of six 30-m maximal sprints with 30-second rest periods between runs. A photoelectric cell timing system (Alge-Timing Electronic, Vienna, Austria) linked to a digital chronoscope was used to record each sprint and rest interval time, with an accuracy of 0.001 seconds. During the recovery period between sprints, participants tapered down from the sprint they had just completed and walked back to the next starting point. Two sets of timing gates were used, working in opposite directions, to allow participants to start the next run from the ending point of the preceding sprint, thus eliminating the need to hurry back to the initial starting point. A standing start, with the front foot placed 30 cm behind the timing lights, was used for all sprints. Timing was initiated when the participant broke the light beam. An experimenter was placed at each end of the track to provide strong verbal encouragement to the participants at each sprint.
The 3 measures for RST were the ideal 30-m run time (IS), the total run time (TS) of the 6 sprints, and the performance decrement (PD) during the test. The fastest 30-m sprint time multiplied by 6 calculated the IS value. The sum of all sprint times calculated the TS value. Performance decrement was used as an indication of fatigue and was calculated as ([TS/IS] × 100) − 100 (9). The test-retest reliability of running RST is 0.942 for TS and 0.75 for PD (9,20).
Repeated Jump Test
The RJT protocol included 6 sets of 6 consecutive maximal jumps, with 30-second rest periods between sets. Participants were instructed to perform each set rapidly and in a continuous manner. The number of jumps per set was chosen based on previous experience to match the number of ground contact (6 times for each leg) and the performance time (about 5 seconds) of each set of RJT and RST. Strong verbal encouragement was given to each participant at each set. All jumps were performed on a 60 × 40 cm force platform (Kistler 9286; Kistler Instrument, Corp., Amherst, MA, USA) connected to a digital timer that recorded the flight time of all jumps. The flight time was used to calculate the change in the height of the body's center of gravity. During the recovery period between sets, participants were instructed to walk around the jumping area. Before the first jump in each set, participants stood in an erect position, moved into a semisquat position, and then used a vigorous double-arm swing for maximal jump. Free vigorous arm activity was allowed throughout all jumps to replicate the jumping technique in the game.
The 3 measures for RJT were the ideal jump height (IJ), the total jump height (TJ), and the PD during the test. Ideal jump height was calculated as the highest sum of 6 jumps in each set multiplied by 6. Total jump height was calculated as the sum of all jump heights in all sets. PD was used as an indication of fatigue and was calculated as ([TJ/IJ] × 100) − 100. These calculations were adapted from the commonly used calculations to assess anaerobic capabilities in repeated maximal running and cycling tests (9).
Each participant performed an all-out 30-m maximal sprint and 1 maximal vertical jump before the performance of the RST and the RJT, respectively. The time of the maximal sprint or the height of the maximal vertical jump was used as a criterion score for the upcoming test. In the first sprint of the RST or the first jump of the RJT, participants were required to achieve at least 95% of their criterion score. If 95% of the criterion score was not achieved, the participant was required to restart the test. Accordingly, the participants were instructed by the coaches and the investigators to produce maximal effort during each sprint or jump and to avoid pacing themselves. All participants met the required criterion (95% of maximal score in the first sprint/jump), and no 1 had to restart the test.
Aerobic Power Test—Twenty-Meter Shuttle Run Test
The 20-m shuttle run test is a field test that predicts aerobic fitness (V[Combining Dot Above]O2max) and has been shown to be a reliable and valid indicator of aerobic power in various populations (21). The test consisted of shuttle running at increasing speeds between 2 markers placed 20 m apart. A portable compact disc (Sony CFD-V7) dictated the pace of the test by emitting tones at appropriate intervals. The subject was required to be at one of the ends of the 20-m course at the signal. A start speed of 8.5 km·h−1 was maintained for 1 minute and was increased by 0.5 km·h−1 every minute thereafter. The test score achieved was the number of 20-m laps completed before the subject either withdrew voluntarily from the test or failed to arrive within 3 m of the end line on 2 consecutive tones. V[Combining Dot Above]O2 was derived by the formula: Y = 6.0X − 24.4, where Y equals the predicted V[Combining Dot Above]O2max and X equals the maximum speed achieved (21).
Blood lactate concentration was measured by fingerprick 2 minutes after the completion of each repeated test, using a portable lactate analyzer (Accusport, Boehringer Mannheim, Germany). Heart rate was measured using a Polar heart rate monitor (Polar Accurex Plus; Polar Electro, Woodbury, NY, USA) immediately upon completion of each repeated test. Rate of perceived exertion (RPE) was determined using the modified Borg scale (3) at the end of each repeated test.
Paired t-test was used to compare differences between physiological responses (i.e., heart rate and blood lactate), RPE and PD of the RST and the RJT. Assumptions of linear statistics were met, and Pearson's correlations were computed between performance indices of the RST (IS, TS, PD) and the RJT (IJ, TJ, PD), and between the performance indices of the 2 RATs and the calculated peak V[Combining Dot Above]O2 from the 20-m shuttle run. Data are presented as mean ± SD. Significance level for all variables was set at p ≤ 0.05.
Physiological responses (i.e., heart rate, blood lactate), RPE, and performance indices of the study participants after the RST and the RJT are summarized in Table 1. As premeditated in the structure of the 2 protocols, there was no significant difference in the total performance time and the total ground contacts between the RST and RJT. Heart rate, RPE, and PD were significantly higher after the RJT compared with the RST. There was no statistically significant difference in blood lactate level after the RST and RJT.
No significant correlations were found between performance indices (IS, TS, PD and IJ, TJ, and PD) of the RST and the RJT (Table 2). Significant correlations were found between performance indices of the RST (IS, TS, and PD) and predicted V[Combining Dot Above]O2max calculated from the 20-m shuttle run test. In contrast, there were no significant correlations between performance indices of the RJT (IJ, TJ, and PD) and predicted V[Combining Dot Above]O2max calculated from the 20-m shuttle run test (Table 3).
This study examined the relationships among performance indices of 2 different RATs and aerobic fitness in a group of trained volleyball players. In contrast to our hypothesis, no significant correlations were found between any matched performance indices of the 2 RATs (i.e., IS, TS, PD and IJ, TJ, PD in the RST and RJT, respectively, Table 2). These results are surprising because both tests were supposed to measure similar anaerobic capabilities and performance indices (highest work output, total work output, and fatigue index), reflecting similar physiological properties (maximal muscle power and capacity).
The 2 protocols, jumping and running, were designed to match activity structure (e.g., time of activity, number of leg-ground contact, and number of sets; Table 1). However, despite the similarity between the 2 tests, the results of this study suggest that each of the current tests imposes different physiological demands on the working muscles, and thus may reflect different performance capabilities of the players. It seems that the mechanical load of the vertical motion, especially during the eccentric phase of muscle contraction during landing in the RJT, was greater than the muscle load during the horizontal motion of running in the RST (5). Consequently, the RJT may create greater local fatigue in the leg muscles compared with the RST. An indication of this may be seen by the higher PD value after the RJT compared with the RST (Table 1). This may also explain the significantly higher RPE and heart rate responses after the RJT compared with the RST (Table 1). In agreement with this, Drinkwater et al. (7) found that repeated plyometric jumps led primarily to peripheral fatigue and to substantial impaired force and rate of force development. Similarly, electromyography muscle activation was associated with a substantial acute decrement after jumping exercise (15,19). Thus, the findings of this study may emphasize the need for careful selection of an appropriate RAT protocol. Such protocol should match the activity patterns and physiological demands of the relevant sport. The protocol selection should acknowledge not only the work-rest pattern and the total amount of work but also the specific technique and mode of exercise used in the sport.
The contribution of aerobic energy sources to power maintenance during intermittent activity was evaluated in this study by the correlations between performance indices of each of the RATs (IS, TS, PD and IJ, TJ, PD in the RST and RJT, respectively) and the participants predicted peak V[Combining Dot Above]O2. The assumption that the aerobic energy system is important for the recovery from intense activity and therefore assists in power output maintenance during RST relies on the fact that creatine phosphate (CP) resynthesis is mediated primarily by oxidative processes (11,24). However, although some previous studies reported significant correlations between the two (4), others have failed to do so (25). One possible reason for this inconsistency is the use of different RST protocols, with large variations in the number and time of repetitions and rest periods. In this study, significant correlations were found between PD, IS, and TS in the RST protocol and peak V[Combining Dot Above]O2 (r = −0.60, −0.75, and −0.77, respectively). In contrast, no significant correlations were found between PD, IJ, and TJ in the RJT protocol and peak V[Combining Dot Above]O2. Given that the 2 RAT protocols in this study were matched in time of activity and resting intervals, the results may suggest that the mode of exercise and specific activity form was the main cause for the evident difference in the correlations between peak V[Combining Dot Above]O2 and performance indices of the 2 current RATs. In this context, previous studies showed that plyometric jumping resulted in substantial peripheral fatigue and slowed contraction velocity (7,18). Although it is believed that the cause of fatigue in this type of exercise is related mainly to mechanical or neuromuscular factors, the precise mechanism is unclear. It was suggested that fatigue during jumping may result from possible exhaustion and structural damage of extrafusal and intrafusal muscle fibers, temporary changes in structural protein and muscle-tendon interaction, or supraspinal neural adjustments (18). These structural and functional changes were noticed even when jumping exercises were not performed to exhaustion (7). However, the causes of fatigue in running activity were found to be mainly metabolic and include muscle CP stores depletion and accumulation of muscle and blood lactate (12). Although comprehensive procedures to evaluate these mechanisms were not performed in this study, the significant correlations between peak V[Combining Dot Above]O2 and performance indices of the RST but not the RJT suggest that the involvement of the aerobic system in the energy regulation of intense repeated activity is more important in running than in jumping activity, mainly through the CP resynthesis process. It is also possible that the relatively low peak V[Combining Dot Above]O2 of the volleyball players in this study (compared with soccer players, for example) increased the relative metabolic load on the aerobic system during the RATs. However, this was associated with significant correlations only between peak V[Combining Dot Above]O2 and performance indices of the RST but not the RJT. Therefore, because the typical activity pattern in the game of volleyball is characterized by frequent jumps rather than short sprints (8), aerobic fitness seems to plays a relatively negligible role in performance maintenance during a volleyball game. Instead, aerobic fitness may be important to other ball games, such as soccer, where short repeated sprints are frequently performed throughout the game (6). As mentioned earlier, professional soccer players tend to have higher V[Combining Dot Above]O2max than volleyball players, and V[Combining Dot Above]O2max was shown to correlate positively with the distance covered during a soccer game (22). This may have a significant implication for the design of training programs in these sports. However, because the correlations between peak V[Combining Dot Above]O2 and performance indices of RSTs are only moderate (4,17), additional factors are likely to be important for recovery and power output maintenance even in sports characterized by intermittent sprint activity.
The significant higher performance decrement and the higher maximal heart rate and RPE that was found after the RJT compared with the RST may indicate that RJT create greater local fatigue in the leg muscles compared with the RST.
In addition, the lack of significant correlations between any of the matched performance indices of the RST and RJT may imply that the 2 tests, using different exercise modes, probably impose different physiological demands on the working muscles and therefore may reflect different performance capabilities. This emphasizes the need for an accurate and a careful selection of an appropriate RAT protocol, 1 that will match the activity patterns and physiological demands of the given sport. Specifically, this study suggested that a distinct RJT, rather than the classic RST, is more appropriate for assessing the anaerobic capabilities of trained volleyball players.
Significant correlations were found between peak V[Combining Dot Above]O2 and all performance indices of the RST protocol but not the RJT protocol. Because the typical activity pattern in the game of volleyball is characterized by frequent jumps rather than by short sprints, it is suggested that aerobic fitness plays only a minor role in performance maintenance throughout the jumping-type volleyball game compared with running-type ball games such as soccer. Volleyball coaches may, therefore, considered focusing on anaerobic and volleyball-specific drills during the competitive season rather than on aerobic workout.
The authors wish to thank the Hapoel Kfar-Saba Volleyball Club for its cooperation in the study. The authors also wish to thank each of the players and the coaches for their efforts in completing the physical tasks needed for the study.
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Keywords:Copyright © 2015 by the National Strength & Conditioning Association.
sprint; jumps; fatigue; anaerobic capabilities; technique