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Journal of Science and Medicine in Sport journal homepage: www.elsevier.com/locate/jsams
Original research
Analysis of the association between isokinetic knee strength with offensive and defensive jumping capacity in high-level female volleyball athletes Tine Sattler a , Damir Sekulic b,c,∗ , Michael R. Esco d , Ifet Mahmutovic e , Vedran Hadzic a a
University of Ljubljana, Faculty of Sport, Slovenia University of Split, Faculty of Kinesiology, Croatia c University of Split, University Department of Health Care Studies, Croatia d University of Alabama, Department of Kinesiology, USA e University of Sarajevo, Faculty of Physical Education and Sport, Bosnia and Herzegovina b
a r t i c l e
i n f o
Article history: Received 13 May 2014 Received in revised form 31 July 2014 Accepted 2 August 2014 Available online xxx Keywords: Eccentric strength Concentric strength Discriminant analysis Jumping performance
a b s t r a c t Objectives: Isokinetic-knee-strength was hypothesized to be an important factor related to jumping performance. However, studies examining this relation among elite female athletes and sport-specific jumps are lacking. This investigation determined the influence of isokinetic-knee flexor/extensor strength measures on spike-jump (offensive) and block-jump (defensive) performance among high-level female volleyball players. Design: Cross-sectional laboratory study. Methods: Eighty-two female volleyball athletes (age = 21.3 ± 3.8 years, height = 175.4 ± 6.76 cm, and weight = 68.29 ± 8.53 kg) volunteered to participate in this study. The studied variables included spikejump and block-jump performance and a set of isokinetic tests to evaluate the eccentric and concentric strength capacities of the knee extensors (quadriceps – Q), and flexors (hamstring – H) for both legs. Both jumping tests showed high intra-session reliability (ICC of 0.87 and 0.95 for spike-jump and block-jump, respectively). The athletes were clustered into three achievement-groups based on their spike-jump and block-jump performances. Results: For the block-jump, ANOVA identified significant differences between achievement-groups for all isokinetic variables except the Right-Q-Eccentric-Strength. When observed for spike-jump, achievementgroups differed significantly in all tests but Right-H-Concentric-Strength. Discriminant canonical analysis showed that the isokinetic-strength variables were more associated with block-jump then spike-jumpperformance. The eccentric isokinetic measures were relatively less important determinants of blockjump than for the spike-jump performance. Conclusion: Data support the hypothesis of the importance of isokinetic strength measures for the expression of rapid muscular performance in volleyball. The results point to the necessity of the differential approach in sport training for defensive and offensive duties. © 2014 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
1. Introduction Volleyball is one of the most popular sports in the world. Although a match may last up to 3 h, volleyball is a sport that involves a significant energy contribution of the phosphagen system. This is mostly due to the primary anaerobic bouts of exertion during game-play such as, explosive movement patterns, quick and agile positioning, jumps and blocks.1,2 Volleyball is oriented
∗ Corresponding author. E-mail addresses: [email protected], [email protected] (D. Sekulic).
around a net that is 2.43 or 2.24 meters high for men or women, respectively; hence, vertical jumping performance is particularly important.3–5 Since optimal jumping ability underpins advancedlevel play, athletes and coaches pay special attention toward testing and developing this characteristic feature.6–8 Sport-specific tests are known to be more applicable in defining real-game performance compared to standard, non-specific assessment protocols.9–11 In volleyball, the primary focus should be placed on testing sport-specific jumping achievements, such as the block-jump and spike-jump.4,12,13 In short, spike-jump is a common jumping technique used during offense (in attack).14–16 On the contrary, the block-jump technique is used in defensive
http://dx.doi.org/10.1016/j.jsams.2014.08.002 1440-2440/© 2014 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Sattler T, et al. Analysis of the association between isokinetic knee strength with offensive and defensive jumping capacity in high-level female volleyball athletes. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2014.08.002
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duties, when an athlete tries to prevent an opponent’s spiking attack. Both advanced jumps require simultaneous biomechanical co-ordination of both the lower and upper body for successful execution. However, elite volleyball players have a high level of technical proficiency. Therefore, it is important to find specific factors which directly contribute to optimal jumping ability. Isokinetic-dynamometry is a safe and reliable method for estimating maximal muscular strength.17–19 Apart from a concentric activation, isokinetic diagnostics allow identification of eccentric muscular abilities that are difficult to observe through traditional resistance measuring protocols such as free weights and machines.20 Isokinetic strength may serve as a valuable predictor of jumping performance, but the findings of current literature are controversial.21 For instance, some authors demonstrate moderate to strong relationships between isokinetic knee measures and jumping performance,22–25 while others report low or negligible associations.26,27 However, it is evident that most of the research in this area has focused on non-specific jumps such as squat-jump and CMJ, even those studies that have included well trained, competitive athletes.21,24,27 Previous investigation has rarely tested sport-specific jumping protocols.23 There appears to be no studies that have examined the relationship between isokinetic muscular properties of the knee and jumping performance in advanced female athletes. Therefore, the aim of this investigation was to determine the association of selected isokinetic strength measures on spike-jump and block-jump performance in high-level female volleyball players. In the first phase of the study, we assessed the reliability of the volleyball-specific jumping protocols. Due to the dependence on muscular strength for rapid and explosive performance, it is reasonable to hypothesize that the measured muscular strength of knee extensors and flexors derived by the isokinetic testing will relate to vertical jumping performance in the volleyball athletes. Isokinetic equipment provides safe and reliable testing methods, while also serving as effective modalities of training specific musculature. Determining the relationship between isokinetic knee flexor/extensor measures and volleyball-specific jumping performance could provide important information regarding the development of effective training and/or recovery methods for advanced volleyball players.
2. Methods This cross-sectional laboratory study included two phases. The first phase assessed the reliability of the spike-jump and blockjump performances. The second phase involved separating the participants into three groups based upon the results of the jumping tests and examining the between-group differences in isokinetic strength variables. The participants in this study consisted of 82 female volleyball athletes (age = 21.3 ± 3.8 years, height = 175.4 ± 6.76 cm, and weight = 68.29 ± 8.53 kg). All athletes involved in the investigation competed in the Slovenian National Championship (1st and 2nd Division). While testing included the majority of the players participating in the highest level of National Competition, athletes were only included if they were 18 years or above and had no injuries or illnesses for at least 30 days prior to the commencement of the study based on the health history questionnaires. The players were categorized as outside receivers (n = 14); liberos (n = 16); middle blockers (n = 12); opposite hitters (n = 22); and setters (n = 18); and. All participants underwent a one-month preparation period prior to the testing. Testing was done at the beginning of the competitive season. Testing protocols and associated risks were explained to all participants. The participants were asked to maintain a normal diet during the course of the study. Prior to testing, the athletes were
suggested to be properly hydrated. The Commission for Medical Ethics of Republic of Slovenia approved the experiment and each participant provided written consent. Testing was done throughout one session. All athletes were tested in a ventilated facility with temperature ranging from 20◦ to 23◦ Celsius, between the hours of 10 am to 1 pm. Body mass and height were measured prior to the warm-up protocol while wearing their volleyball jerseys but no shoes using a stadiometer and weighing scale, respectively, by Seca (Seca Instruments Ltd., Hamburg, Germany). For the remainder of the testing, the athletes wore their jerseys and standard playing shoes. At the beginning of testing session athletes warmed-up. The warm-up protocol was standardized and consisted of: (i) 6 min of exercise on a stationary bicycle using progressive resistance (from 50 to 100 W) and (ii) hamstring stretching. Then, each athlete performed 3 trials for each of the jumps, while the order of the jump testing was randomly assigned for each athlete. Pause between jump testing trials was limited to 3–5 min. Optojump System (Microgate, Bolzano, Italy) was used as a measuring device for jumping tests. Optojump is dual-beam optical measuring system that measures ground-contact and flight-time during a jump or series of jumps. Flight time (Tf) and gravity acceleration (g) were used to calculate the vertical rise (h) of the body’s center of gravity with the following equation: h=
Tf 2 × g 8
For the block-jump (i.e. defensive jump) athletes were asked to visualize and mimic defensive block performance during a volleyball match. More specifically, the hands were positioned in front of the chest. Then, the athletes performed a technique similar countermovement-type-jump with a most-convenient depth and arm swing movement. The vertical jump was done with full arm extension attempting to reach as high as possible. Athletes familiarized themselves with block-jump performance 2–3 times before measurement. The spike-jump (i.e. offensive jump) was tested while using three Opto-jump units (each of 1 m in length) which covered 3-meters distance. The athletes positioned them-selves behind the Opto-jump, with some participants choosing a strict-forward approach while others approached from an angle. Distance between the cells was 3 meters to accommodate the diversity of approaches. As a result participants performed spike-jump within a 3 m × 3 m square. The athletes’ self-determined two-to-three-step approach, performing a bounce-jump with an arm swing. It was followed by a quick maximal vertical jump, with arm swing. The athletes were instructed to mimic a spike-like action at the point of peak jump height and to perform the jumps as close to their personal technique during a volleyball game or practice. Athletes familiarized themselves with spike-jump performance 4–5 times before the measurement. After the jumps, the athletes paused for 15–20 min before isokinetic testing. Isokinetic testing was performed to determine concentric and eccentric strength for the knee-extensors (i.e. quadriceps – Q) and flexors (hamstring – H) using TechnoGym REV 9000 isokinetic dynamometer (TechnoGym, Gambet-Tola, Italy). The athletes were tested in a seated position. Two straps secured to the isokinetic device were positioned around the pelvis and upper thoracic region to prevent unnecessary upper body movement. The thigh of the tested leg was also secured using an additional strap that was attached to the lower portion of the isokinetic device to prevent unwanted movement of the femur in the frontal plane. The participants provided verbal feedback concerning the level of comfort for each strap. The athletes were instructed to keep arms folded across the chest during isokinetic testing and were not allowed to grasp onto the handles of the device. The axis of rotation of the
Please cite this article in press as: Sattler T, et al. Analysis of the association between isokinetic knee strength with offensive and defensive jumping capacity in high-level female volleyball athletes. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2014.08.002
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knee joint was identified through the lateral femoral condyle and positioned in alignment with the motor axis using a laser beam that was pre-installed to the dynamometer. A range of motion of 60◦ was set from 30◦ to 90◦ knee flexion with full extension being considered as 0◦ . The rate was set at 60◦ per second for both concentric and eccentric contraction modes for Q and H. Gravity error torque was recorded for every athlete. For familiarity, each participant performed 2 submaximal repetitions and 1 maximal repetition at a given velocity and mode of contraction. Those participants who experienced pain or discomfort during the trial repetitions were not included in the study (n = 3) Next, each participant performed the following: (i) five consecutive concentric Q and H contractions followed by a 60 s pause, (ii) five eccentric Q contractions followed by a 60 s pause, (iii) five eccentric H contractions. When testing of one side was completed, a 3-minute rest period was allowed.19 During this time period, the machine setting was changed to accommodate the opposite leg. The testing order for each leg was randomly assigned for each athlete. Verbal coaching or cueing was not provided to the athletes during the testing repetitions. From the isokinetic testing, the following eight variables were recorded as follows: right (RHecc) and left (LHecc) hamstring eccentric strength, right (RHconc) and left (RHconc) hamstring concentric strength, right (RQecc) and left (LQecc) quadriceps eccentric strength, and right (RQconc) and left (LQconc) quadriceps concentric strength. The main outcome measure was peak torque (PT) which was later normalized for body mass and expressed as PT/kg. The coefficient of variation (CV) and intra-class coefficient (ICC) were calculated as measures of reliability for each jumping-test. Additionally, repeated measures analysis of variance (ANOVA) procedure with a Scheffe Post hoc test was used to detect any systematic bias between the individual trials (items). Descriptive statistics (mean and standard deviation) were calculated. For the purpose of this study, the athletes were divided into achievement groups according to their performance on two studied jumps. The low-achievement group compromised one-third of the athletes with the lowest jumping performance (n = 28), the average-achievement group consisted of those athletes who were ranked between 33rd and 66th percentile (n = 27), and the highachievement group comprised one-third of the best performers (above 67th percentile; n = 27). Such a grouping was performed independently for spike-jump- and block-jump-performance. The breakdown for positions into achievement groups is presented in Table 1. The breakdown of the achievement-groups was not different between playing positions. Univariate differences between achievement-groups were determined using a one-way ANOVA with a Scheffe’s Post hoc follow-up test. To define multivariate differences between the groups a discriminant canonical analysis (DISCRA) was calculated. Statistical significance was pre-determined as p < 0.05. Statistica, ver. 11 (Statsoft, Tulsa, OK) was used for all statistical calculations.
3. Results Reliability results for the block-jump and spike-jump showed CV values of 3% and 4%, respectively, and ICCs of 0.95 and 0.87, respectively. There were no significant differences between the three testing trials for the block-jump (F test = 1.86; df = 2; p > 0.05). However, the difference between testing-trials of the spike-jump was significant (F test = 4.33; df = 2; p < 0.05). Follow-up procedures showed the 1st trial was significantly lower (40.22 ± 7.07 cm) compared to the following trials (41.09 ± 6.42 cm and 41.11 ± 7.01 cm for the 2nd and 3rd trial respectively), with no significant difference between the 2nd and 3rd trials. Therefore, the final achievement was defined as the personal best result across the three trials.
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Significant differences between the three block-jump achievement-groups were found for all isokinetic variables except RQecc (Table 2). When the participants were divided into the three achievement-groups according to their spike-jumpperformance, significant differences were found in all tests but RHconc (Table 3). The DISCRA procedure found significant differences between the achievement-groups based on block-jump-performance. The LQconc contributed most significantly to differentiation of the high- and low-performers. At the same time RQconc, and LHconc contributed less to block-jump performance (Table 3). The classification was correct for 63% of athletes (60% of low performers, 49% of average-performers, and 80% of high-performers). The DISCRA procedure identified LQconc, RHecc, and LHecc as the most significant discriminators between the groups based on spike-jump performance. Meanwhile, RQecc and LHconc contributed less to the discrimination of the spike-jump achievement-groups (Table 3). In total, 56% of the athletes were successfully classified (i.e., 46%, 49% and 72% for low-achievement-, average-achievement- and high-achievement-group, respectively) (Table 4).
4. Discussion Previous research has consistently found sport-specific testing procedures to be highly applicable in defining strength and conditioning capacities relative to the particular sport of interest.9 Therefore, we consider the finding of strong reliability of the volleyball-jumping tests to be highly important. Vertical jumping tests are often investigated with regard to reliability, and reports of good consistency across the tests are common.28 However, since reliability directly depends on the variability of the results and the tests conducted in the current study were performed by high-level athletes (i.e. where variance of the results is naturally truncated), the findings of strong reliability are even more encouraging.11 The reliability results showed that performance in spike-jump did not stabilize until the third testing trial even though the athletes were familiarized with the procedures. This finding is possibly due to the fact that during the familiarization session the athletes were asked to perform several jumps using a submaximal level of exertion. Thus, it is likely that the familiarization effort which was non-maximal was not substantial enough to achieve stabilization of spike-jump performance. Furthermore, since we used an optical measuring device to test jumping performance over 3 meters in length, the athletes’ orientation in space was possibly another contributing factor to the lack of stability. Since the athletes had to subjectively locate the optimal distance and approach speed, their ability to concentration on exerting full effort may have been obscured, and jumping performance throughout the first testing trials was limited. However, since performance eventually stabilized in the study, a three-trial testing design may be adequate enough to achieve an optimal level of spike-jump performance. Previous instigations defined high consistency and low measurement error of concentric and eccentric knee-strength when testing was done in similar conditions as those in our study (i.e. asymptomatic subjects, measured by same evaluator).29 Additionally, we have observed relatively large sample of high-level athletes. Therefore, in this study we have not evaluated reliability of the isokinetic testing. Other studies that investigated the association between isokinetic strength variables and jumping performance in various populations has provided controversial results.21,24,27 However, it seems that relative isokinetic strength measures are significantly related to jumping achievement in participants who possess stable and high technical quality of jumping performance.21,23,24 This
Please cite this article in press as: Sattler T, et al. Analysis of the association between isokinetic knee strength with offensive and defensive jumping capacity in high-level female volleyball athletes. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2014.08.002
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Table 1 Break-down for positions into achievement groups for block-jump and spike-jump performance. Block jump
Setters Opposite hitters Middle blockers Outside receivers Libero players
Spike jump
Low achievers (n = 28)
Average achievers (n = 27)
High achievers (n = 27)
Low achievers (n = 28)
Average achievers (n = 27)
High achievers (n = 27)
7 9 4 3 5
6 7 5 5 5
5 7 3 6 6
7 7 2 5 6
6 6 5 5 5
5 8 5 4 5
Table 2 Univariate differences between achievement groups defined on a basis of the block-jump performance.
Age (years) Body height (cm) Body mass (kg) Block-jump (cm) LQconc (PT/kg) RQconc (PT/kg) LQecc (PT/kg) RQecc (PT/kg) LHconc (PT/kg) RHconc (PT/kg) RHecc (PT/kg) LHecc (PT/kg)
Low-achievers (n = 28)
Average-achievers (n = 27)
High-achievers (n = 27)
Analysis of variance
Mean ± SD
Mean ± SD
Mean ± SD
F test
p
0.90 2.42 1.24 94.08 18.79 10.21 5.28 3.24 5.35 2.62 8.41 6.94
0.40 0.07 0.29 0.01 0.01 0.01 0.01 0.06 0.01 0.08 0.01 0.01
20.76 175.21 71.05 26.03 2.06 2.09 2.19 2.26 1.12 1.17 1.23 1.21
± ± ± ± ± ± ± ± ± ± ± ±
2.36 6.88 12.58 2.95¶ , 0.30 0.26 0.57 0.48 0.22 0.14 0.16 0.26
22.47 174.90 68.93 32.10 2.22 2.16 2.37 2.35 1.18 1.22 1.35 1.37
± ± ± ± ± ± ± ± ± ± ± ±
3.66 5.85 9.07 2.36¥ , 0.21 0.31 0.55 0.49 0.18 0.17 0.27 0.19
22.24 172.89 65.08 38.20 2.54 2.5 2.74 2.67 1.3 1.28 1.52 1.48
± ± ± ± ± ± ± ± ± ± ± ±
4.88 6.49 4.34 3.07¥ , ¶ 0.28¥ , ¶ 0.39¥ , ¶ 0.56¥ , ¶ 0.64 0.17 0.18 0.26¥ 0.25¥
Block-jump, performance of the block jump; LQconc, left quadriceps concentric strength; RQ conc, right quadriceps concentric strength; LQecc, left quadriceps eccentric strength; RQecc, right quadriceps eccentric strength; LHconc, left hamstring concentric strength; RHconc, right hamstring concentric strength; RHecc, right hamstring eccentric strength; LHecc, left hamstring eccentric strength. ¥ Significantly different from low achievement group. ¶ Significantly different from average achievement group. § Significantly different from high achievement group. Table 3 Univariate differences between achievement groups defined on a basis of the spike-jump performance.
Age (years) Body height (cm) Body mass (kg) Spike-jump (cm) LQconc (PT/kg) RQconc (PT/kg) LQecc (PT/kg) RQecc (PT/kg) LHconc (PT/kg) RHconc (PT/kg) RHecc (PT/kg) LHecc (PT/kg)
Low-achievers (n = 28)
Average-achievers (n = 27)
High-achievers (n = 27)
Analysis of the variance
Mean ± SD
Mean ± SD
Mean ± SD
F test
p
0.24 0.34 4.09 157.51 16.18 7.41 3.59 1.89 9.25 4.51 9.87 10.81
0.78 0.65 0.02 0.01 0.01 0.01 0.03 0.16 0.01 0.01 0.01 0.01
21.40 174.34 72.00 26.92 2.00 2.13 2.11 2.32 1.04 1.16 1.25 1.15
± ± ± ± ± ± ± ± ± ± ± ±
2.44 7.07 14.51 2.87¶ , 0.25 0.25 0.43 0.47 0.16¶ , 0.15 0.13 0.20
22.23 174.34 69.66 32.69 2.21 2.13 2.4 2.32 1.20 1.18 1.28 1.33
± ± ± ± ± ± ± ± ± ± ± ±
4.87 6.67 8.01 1.05¥ , 0.27 0.32 0.69 0.53 0.20¥ , 0.15 0.26 0.21
21.70 173.27 64.39 38.89 2.50 2.46 2.64 2.61 1.30 1.29 1.53 1.5
± ± ± ± ± ± ± ± ± ± ± ±
3.43 6.25 4.69¥ 2.47¥ , ¶ 0.29¥ , ¶ 0.39¥ , ¶ 0.59¥ 0.64 0.16¥ , ¶ 0.17¥ 0.25¥ , ¶ 0.25¥ , ¶
Spike-jump, performance of the spike jump; LQconc, left quadriceps concentric strength; RQ conc, right quadriceps concentric strength; LQecc, left quadriceps eccentric strength; RQecc, right quadriceps eccentric strength; LHconc, left hamstring concentric strength; RHconc, right hamstring concentric strength; RHecc, right hamstring eccentric strength; LHecc, left hamstring eccentric strength. ¥ Significantly different from low achievement group. ¶ Significantly different from average achievement group. § Significantly different from high achievement group.
is a particularly important yet known phenomenon, as all sportspecific performances (i.e. jumps, throws, serves, etc.) depend primarily on skill level. It is reasonable to suggest that other cofactors (i.e. anthropometrics, motor qualities, etc.) may influence jumping performance among participants who do not differ in their level of technical proficiency.9 However, when skill proficiency is inconsistent, then technical quality may account for the greatest variation in performance with less of an influence from other co-variables such as those mentioned above. The results of our analyses show that isokinetic-kneestrength is more strongly associated to block-jump than to spike-jump performance. This finding is most likely related to the
differentiation of the achievement groups in the discriminate analysis. There are several possibilities to explain why isokineticstrength is more strongly related to block-jump compared to the spike-jump. First, the spike-jump is a more complex and technically advanced movement than the block-jump.4 Consequently, it is reasonable to assume that there are a number of other factors that influence spike-jump performance, such as arm swing, the length of the limbs, and appropriate timing of execution.16 Meanwhile, the block-jump is a relatively simple movement that may not be as influenced by confounding factors. In addition, volleyball-playing positions differ with regard to their game-play duties. While some players perform the spike-jump often (i.e.
Please cite this article in press as: Sattler T, et al. Analysis of the association between isokinetic knee strength with offensive and defensive jumping capacity in high-level female volleyball athletes. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2014.08.002
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Table 4 Multivariate differences (canonical discriminant analyses) between achievement groups formed on a basis of the block-jump and spike-jump performance. Block-jump
LQconc (PT/kg) RQconc (PT/kg) LQecc (PT/kg) RQecc (PT/kg) LHconc (PT/kg) RHconc (PT/kg) RHecc (PT/kg) LHecc (PT/kg) Eigenvalue Canonical R Wilk’s lambda Chi square p Centroid: Low achievers Centroid: Average achievers Centroid: High achievers
Spike-jump
Root 1
Root 2
Root 1
Root 2
0.87 0.58 0.59 0.40 0.34 0.32 0.58 0.53 0.53 0.59 0.64 56.03 0.00 −0.93 −0.20 0.94
0.24 −0.04 −0.11 0.03 −0.04 −0.45 −0.49 −0.52 0.02 0.16 0.97 3.42 0.84 0.19 −0.20 0.07
0.87 0.57 0.49 0.36 0.42 0.46 0.69 0.60 0.36 0.46 0.71 45.66 0.00 −0.61 −0.27 0.62
−0.02 −0.14 0.24 0.04 0.60 0.06 0.00 0.72 0.06 0.24 0.94 7.32 0.40 −0.30 0.31 −0.08
LQconc, left quadriceps concentric strength; RQ conc, right quadriceps concentric strength; LQecc, left quadriceps eccentric strength; RQecc, right quadriceps eccentric strength; LHconc, left hamstring concentric strength; RHconc, right hamstring concentric strength; RHecc, right hamstring eccentric strength; LHecc, left hamstring eccentric strength; Root, structure of the canonical root.
outside hitter, middle blocker), others do it rarely (i.e. setter, libero) which may demonstrate that technical efficacy is specific to position. On the contrary, block-jump technique is relatively consistent across volleyball playing positions.4 In other words, the spike-jump is complex and multifaceted with some players (depending on the position) lacking the technical skills that are required to competently perform the movement. Although concentric properties appear to be more important than the eccentric activations for the performance of both observed jumps, this difference is more evident for block-jump than for the spike-jump performance. The block-jump starts from a two-stance stable position in which the athlete then performs a shortened version of the CMJ jumping technique with no full arm swing followed by a maximal vertical displacement. In our study, all participants were instructed to perform both jumps while using their individualized technique. As a result, some athletes executed block-jump with no preceding eccentric phase (i.e. downward phase). They actually performed somewhat of a “squat-jump” technique starting with 30–40 degrees static squat and concentrically activated quadriceps for the vertical displacement. Consequently, the concentric properties are most important in execution of the block-jump, since the eccentric phase of the movement is minimal. The differences in the findings related to the association of eccentric muscular activation and jumping performance could be explained by the discrepancy of execution between the two jumps.4 Eccentric muscular strength is highly challenged during the phase of the spike-jump that precedes maximum concentric contraction (i.e., “bounce-jump” phase). During the spike-jump, the athlete’s ability to decelerate during downward momentum and transition into an explosive vertical jump is highly dependent on eccentric strength capacity.7,14,30 Alternatively, the eccentric phase of the block-jump is not as expressed because the jump begins from a two-stance, stable position without a preceding “drop-jump”. Moreover, some athletes perform block jump with practically no downward momentum (i.e. no eccentric phase, see previous text). Due to this, the force applied in the downward movement is not as intensive when compared to the same phase of the spike-jump. Logically, the concentric qualities of the block-jump are more important determinants of performance than eccentric qualities. There are several limitations of this investigation. First, we investigated high-level female athletes, which limit the ability to generalize the findings toward other populations. Second,
isokinetic testing is often criticized as being non-functional hence limiting the applicability in the real world. However, isokinetic testing allows determination of eccentric muscular properties which is difficult to be observed throughout other measuring protocols (free weights, machines, etc.). Third, we did not observe dominant vs. non-dominant leg of the athletes. However, we are of the opinion that this limitation does not influence our findings. Mainly, the difference in leg dominance will not contribute to the findings of multivariate analysis (i.e. discriminant analysis), and block-jump (i.e. as a two-leg jump). Also, less than 10% of athletes were left handed. Therefore, it is reasonable to suggest that majority of the studied athletes were left leg dominant. Finally, in this study we have been focused solely on knee-joint while volleyball jumps involve multiple joints. However, while isokinetic testing is time-consuming and exhaustive, we were limited in doing additional tests and consequently more profound analyses. 5. Conclusion This study demonstrated that relative isokinetic strength variables are more strongly related to block-jump performance than to spike-jump performance. The block-jump performance is primary related to concentric qualities of quadriceps. The eccentric isokinetic measures of hamstring and quadriceps were relatively less important determinants of the efficient execution of the blockjump than for the spike-jump. There were some indices in the study to suggest that technical quality of the execution (i.e. characteristic motor skill) is highly important for spike-jump performance. Further studies should evaluate the importance of multiple-joint-isokinetic-strength while focusing on the typical joint angles of specific jumping performance in volleyball. This is particularly important for athletes with high technical proficiency. Practical implications • In volleyball athletes whose game-duties are oriented toward attack and spike jumping, both eccentric and concentric muscular capacities are equally important determinants of performance. • Strength and conditioning training programs for volleyball athletes should include both concentric (e.g., free-weight, machine-based) and eccentric (e.g., plyometric) exercise modalities.
Please cite this article in press as: Sattler T, et al. Analysis of the association between isokinetic knee strength with offensive and defensive jumping capacity in high-level female volleyball athletes. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2014.08.002
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• Since block-jump was found to be more associated to concentric compared to eccentric strength, it may be best that athletes who are more often involved in defensive duties (i.e. middle blockers) should emphasize training concentric muscular strength for improving performance. Acknowledgements The study was supported by the Slovenian Research Agency and Slovenian Ministry of Sport and Education within the project “The prevention of sport injuries in the Republic of Slovenia” (V5-0233) and partially by Croatian Ministry of Science, Education and Sport (Project No. 315-1773397-3407). References 1. Dal Pupo J, Gheller RG, Dias JA et al. Reliability and validity of the 30-s continuous jump test for anaerobic fitness evaluation. J Sci Med Sport 2013 [Epub ahead of print]. 2. Mok K, Jarning J, Hansen B et al. Identification of jumping activity in volleyball by using accelerometer. Br J Sports Med 2014; 48(7):640. 3. Lamontagne-Lacasse M, Nadon R, Goulet E.D. Effect of creatine supplementation on jumping performance in elite volleyball players. Int J Sports Physiol Perform 2011; 6(4):525–533. 4. Sattler T, Sekulic D, Hadzic V et al. Vertical jumping tests in volleyball: reliability, validity, and playing-position specifics. J Strength Cond Res 2012; 26(6):1532–1538. 5. Tillman MD, Hass CJ, Brunt D et al. Jumping and landing techniques in elite women’s volleyball. J Sports Sci Med 2004; 3(1):30–36. 6. Malatesta D, Cattaneo F, Dugnani S et al. Effects of electromyostimulation training and volleyball practice on jumping ability. J Strength Cond Res 2003; 17(3):573–579. 7. Sheppard JM, Dingley AA, Janssen I et al. The effect of assisted jumping on vertical jump height in high-performance volleyball players. J Sci Med Sport 2011; 14(1):85–89. 8. Voelzke M, Stutzig N, Thorhauer HA et al. Promoting lower extremity strength in elite volleyball players: effects of two combined training methods. J Sci Med Sport 2012; 15(5):457–462. 9. Peric M, Cavar M, Zenic N et al. Predictors of competitive achievement among pubescent synchronized swimmers: an analysis of the solo-figure competition. J Sports Med Phys Fitness 2014; 54(1):16–26. 10. Uljevic O, Spasic M, Sekulic D. Sport-specific motor fitness tests in water polo: reliability, validity and playing position differences. J Sports Sci Med 2013; 12(4):646–654. 11. Uljevic O, Esco MR, Sekulic D. Reliability, validity and applicability of isolated and combined sport-specific tests of conditioning capacities in top-level junior water polo athletes. J Strength Cond Res 2014; 28(6):1595–1605.
12. Sharma A, Geovinson SG, Singh Sandhu J. Effects of a nine-week core strengthening exercise program on vertical jump performances and static balance in volleyball players with trunk instability. J Sports Med Phys Fitness 2012; 52(6):606–615. 13. Hughes G, Watkins J. Lower limb coordination and stiffness during landing from volleyball block jumps. Res Sports Med 2008; 16(2):138–154. 14. Wagner H, Tilp M, von Duvillard SP et al. Kinematic analysis of volleyball spike jump. Int J Sports Med 2009; 30(10):760–765. 15. Borras X, Balius X, Drobnic F et al. Vertical jump assessment on volleyball: a follow-up of three seasons of a high-level volleyball team. J Strength Cond Res 2011; 25(6):1686–1694. 16. Sheppard JM, Cronin JB, Gabbett TJ et al. Relative importance of strength, power, and anthropometric measures to jump performance of elite volleyball players. J Strength Cond Res 2008; 22(3):758–765. 17. Dekerle J, Barstow TJ, Regan L et al. The critical power conin cept all-out isokinetic exercise. J Sci Med Sport 2013. http://dx.doi.org/10.1016/j.jsams.2013.09.003 [Epub ahead of print]. 18. Hadzic V, Sattler T, Veselko M et al. Strength asymmetry of the shoulders in elite volleyball players. J Athl Train 2014 [Epub ahead of print]. 19. Hadzic V, Sattler T, Markovic G et al. The isokinetic strength profile of quadriceps and hamstrings in elite volleyball players. Isokinet Exerc Sci 2010; 18(1): 31–37. 20. Edouard P, Codine P, Samozino P et al. Reliability of shoulder rotators isokinetic strength imbalance measured using the Biodex dynamometer. J Sci Med Sport 2013; 16(2):162–165. 21. Harrison B, Firth W, Rogers S et al. The relationship between isokinetic performance of hip and knee and jump performance in university rugby players. Isokinet Exerc Sci 2013; 21(2):175–180. 22. Tsiokanos A, Kellis E, Jamurtas A et al. The relationship between jumping performance and isokinetic strength of hip and knee extensors and ankle plantar flexors. Isokinet Exerc Sci 2002; 10(2):107–115. 23. Saliba L, Hrysomallis C. Isokinetic strength related to jumping but not kicking performance of Australian footballers. J Sci Med Sport 2001; 4(3): 336–347. 24. Ispirlidis I, Malliou P, Beneka A et al. Jumping ability and kinetic knee extensors’ performance in elite soccer players. J Hum Mov Stud 2004; 46(6): 483–491. 25. Pua YH, Koh MTH, Teo YY. Effects of allometric scaling and isokinetic testing methods on the relationship between countermovement jump and quadriceps torque and power. J Sports Sci 2006; 24(4):423–432. 26. Alemdaroglu U. The relationship between muscle strength, anaerobic performance, agility, sprint ability and vertical jump performance in professional basketball players. J Hum Kinet 2012; 31:149–158. 27. Iossifidou A, Baltzopoulos V, Giakas G. Isokinetic knee extension and vertical jumping: are they related? J Sports Sci 2005; 23(10):1121–1127. 28. Markovic G, Dizdar D, Jukic I et al. Reliability and factorial validity of squat and countermovement jump tests. J Strength Cond Res 2004; 18(3): 551–555. 29. Sole G, Hamren J, Milosavljevic S et al. Test–retest reliability of isokinetic knee extension and flexion. Arch Phys Med Rehabil 2007; 88(5):626–631. 30. Sheppard JM, Newton RU. Long-term training adaptations in elite male volleyball players. J Strength Cond Res 2012; 26(8):2180–2184.
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Journal of Science and Medicine in Sport journal homepage: www.elsevier.com/locate/jsams
Original research
Analysis of the association between isokinetic knee strength with offensive and defensive jumping capacity in high-level female volleyball athletes Tine Sattler a , Damir Sekulic b,c,∗ , Michael R. Esco d , Ifet Mahmutovic e , Vedran Hadzic a a
University of Ljubljana, Faculty of Sport, Slovenia University of Split, Faculty of Kinesiology, Croatia c University of Split, University Department of Health Care Studies, Croatia d University of Alabama, Department of Kinesiology, USA e University of Sarajevo, Faculty of Physical Education and Sport, Bosnia and Herzegovina b
a r t i c l e
i n f o
Article history: Received 13 May 2014 Received in revised form 31 July 2014 Accepted 2 August 2014 Available online xxx Keywords: Eccentric strength Concentric strength Discriminant analysis Jumping performance
a b s t r a c t Objectives: Isokinetic-knee-strength was hypothesized to be an important factor related to jumping performance. However, studies examining this relation among elite female athletes and sport-specific jumps are lacking. This investigation determined the influence of isokinetic-knee flexor/extensor strength measures on spike-jump (offensive) and block-jump (defensive) performance among high-level female volleyball players. Design: Cross-sectional laboratory study. Methods: Eighty-two female volleyball athletes (age = 21.3 ± 3.8 years, height = 175.4 ± 6.76 cm, and weight = 68.29 ± 8.53 kg) volunteered to participate in this study. The studied variables included spikejump and block-jump performance and a set of isokinetic tests to evaluate the eccentric and concentric strength capacities of the knee extensors (quadriceps – Q), and flexors (hamstring – H) for both legs. Both jumping tests showed high intra-session reliability (ICC of 0.87 and 0.95 for spike-jump and block-jump, respectively). The athletes were clustered into three achievement-groups based on their spike-jump and block-jump performances. Results: For the block-jump, ANOVA identified significant differences between achievement-groups for all isokinetic variables except the Right-Q-Eccentric-Strength. When observed for spike-jump, achievementgroups differed significantly in all tests but Right-H-Concentric-Strength. Discriminant canonical analysis showed that the isokinetic-strength variables were more associated with block-jump then spike-jumpperformance. The eccentric isokinetic measures were relatively less important determinants of blockjump than for the spike-jump performance. Conclusion: Data support the hypothesis of the importance of isokinetic strength measures for the expression of rapid muscular performance in volleyball. The results point to the necessity of the differential approach in sport training for defensive and offensive duties. © 2014 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
1. Introduction Volleyball is one of the most popular sports in the world. Although a match may last up to 3 h, volleyball is a sport that involves a significant energy contribution of the phosphagen system. This is mostly due to the primary anaerobic bouts of exertion during game-play such as, explosive movement patterns, quick and agile positioning, jumps and blocks.1,2 Volleyball is oriented
∗ Corresponding author. E-mail addresses: [email protected], [email protected] (D. Sekulic).
around a net that is 2.43 or 2.24 meters high for men or women, respectively; hence, vertical jumping performance is particularly important.3–5 Since optimal jumping ability underpins advancedlevel play, athletes and coaches pay special attention toward testing and developing this characteristic feature.6–8 Sport-specific tests are known to be more applicable in defining real-game performance compared to standard, non-specific assessment protocols.9–11 In volleyball, the primary focus should be placed on testing sport-specific jumping achievements, such as the block-jump and spike-jump.4,12,13 In short, spike-jump is a common jumping technique used during offense (in attack).14–16 On the contrary, the block-jump technique is used in defensive
http://dx.doi.org/10.1016/j.jsams.2014.08.002 1440-2440/© 2014 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
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duties, when an athlete tries to prevent an opponent’s spiking attack. Both advanced jumps require simultaneous biomechanical co-ordination of both the lower and upper body for successful execution. However, elite volleyball players have a high level of technical proficiency. Therefore, it is important to find specific factors which directly contribute to optimal jumping ability. Isokinetic-dynamometry is a safe and reliable method for estimating maximal muscular strength.17–19 Apart from a concentric activation, isokinetic diagnostics allow identification of eccentric muscular abilities that are difficult to observe through traditional resistance measuring protocols such as free weights and machines.20 Isokinetic strength may serve as a valuable predictor of jumping performance, but the findings of current literature are controversial.21 For instance, some authors demonstrate moderate to strong relationships between isokinetic knee measures and jumping performance,22–25 while others report low or negligible associations.26,27 However, it is evident that most of the research in this area has focused on non-specific jumps such as squat-jump and CMJ, even those studies that have included well trained, competitive athletes.21,24,27 Previous investigation has rarely tested sport-specific jumping protocols.23 There appears to be no studies that have examined the relationship between isokinetic muscular properties of the knee and jumping performance in advanced female athletes. Therefore, the aim of this investigation was to determine the association of selected isokinetic strength measures on spike-jump and block-jump performance in high-level female volleyball players. In the first phase of the study, we assessed the reliability of the volleyball-specific jumping protocols. Due to the dependence on muscular strength for rapid and explosive performance, it is reasonable to hypothesize that the measured muscular strength of knee extensors and flexors derived by the isokinetic testing will relate to vertical jumping performance in the volleyball athletes. Isokinetic equipment provides safe and reliable testing methods, while also serving as effective modalities of training specific musculature. Determining the relationship between isokinetic knee flexor/extensor measures and volleyball-specific jumping performance could provide important information regarding the development of effective training and/or recovery methods for advanced volleyball players.
2. Methods This cross-sectional laboratory study included two phases. The first phase assessed the reliability of the spike-jump and blockjump performances. The second phase involved separating the participants into three groups based upon the results of the jumping tests and examining the between-group differences in isokinetic strength variables. The participants in this study consisted of 82 female volleyball athletes (age = 21.3 ± 3.8 years, height = 175.4 ± 6.76 cm, and weight = 68.29 ± 8.53 kg). All athletes involved in the investigation competed in the Slovenian National Championship (1st and 2nd Division). While testing included the majority of the players participating in the highest level of National Competition, athletes were only included if they were 18 years or above and had no injuries or illnesses for at least 30 days prior to the commencement of the study based on the health history questionnaires. The players were categorized as outside receivers (n = 14); liberos (n = 16); middle blockers (n = 12); opposite hitters (n = 22); and setters (n = 18); and. All participants underwent a one-month preparation period prior to the testing. Testing was done at the beginning of the competitive season. Testing protocols and associated risks were explained to all participants. The participants were asked to maintain a normal diet during the course of the study. Prior to testing, the athletes were
suggested to be properly hydrated. The Commission for Medical Ethics of Republic of Slovenia approved the experiment and each participant provided written consent. Testing was done throughout one session. All athletes were tested in a ventilated facility with temperature ranging from 20◦ to 23◦ Celsius, between the hours of 10 am to 1 pm. Body mass and height were measured prior to the warm-up protocol while wearing their volleyball jerseys but no shoes using a stadiometer and weighing scale, respectively, by Seca (Seca Instruments Ltd., Hamburg, Germany). For the remainder of the testing, the athletes wore their jerseys and standard playing shoes. At the beginning of testing session athletes warmed-up. The warm-up protocol was standardized and consisted of: (i) 6 min of exercise on a stationary bicycle using progressive resistance (from 50 to 100 W) and (ii) hamstring stretching. Then, each athlete performed 3 trials for each of the jumps, while the order of the jump testing was randomly assigned for each athlete. Pause between jump testing trials was limited to 3–5 min. Optojump System (Microgate, Bolzano, Italy) was used as a measuring device for jumping tests. Optojump is dual-beam optical measuring system that measures ground-contact and flight-time during a jump or series of jumps. Flight time (Tf) and gravity acceleration (g) were used to calculate the vertical rise (h) of the body’s center of gravity with the following equation: h=
Tf 2 × g 8
For the block-jump (i.e. defensive jump) athletes were asked to visualize and mimic defensive block performance during a volleyball match. More specifically, the hands were positioned in front of the chest. Then, the athletes performed a technique similar countermovement-type-jump with a most-convenient depth and arm swing movement. The vertical jump was done with full arm extension attempting to reach as high as possible. Athletes familiarized themselves with block-jump performance 2–3 times before measurement. The spike-jump (i.e. offensive jump) was tested while using three Opto-jump units (each of 1 m in length) which covered 3-meters distance. The athletes positioned them-selves behind the Opto-jump, with some participants choosing a strict-forward approach while others approached from an angle. Distance between the cells was 3 meters to accommodate the diversity of approaches. As a result participants performed spike-jump within a 3 m × 3 m square. The athletes’ self-determined two-to-three-step approach, performing a bounce-jump with an arm swing. It was followed by a quick maximal vertical jump, with arm swing. The athletes were instructed to mimic a spike-like action at the point of peak jump height and to perform the jumps as close to their personal technique during a volleyball game or practice. Athletes familiarized themselves with spike-jump performance 4–5 times before the measurement. After the jumps, the athletes paused for 15–20 min before isokinetic testing. Isokinetic testing was performed to determine concentric and eccentric strength for the knee-extensors (i.e. quadriceps – Q) and flexors (hamstring – H) using TechnoGym REV 9000 isokinetic dynamometer (TechnoGym, Gambet-Tola, Italy). The athletes were tested in a seated position. Two straps secured to the isokinetic device were positioned around the pelvis and upper thoracic region to prevent unnecessary upper body movement. The thigh of the tested leg was also secured using an additional strap that was attached to the lower portion of the isokinetic device to prevent unwanted movement of the femur in the frontal plane. The participants provided verbal feedback concerning the level of comfort for each strap. The athletes were instructed to keep arms folded across the chest during isokinetic testing and were not allowed to grasp onto the handles of the device. The axis of rotation of the
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knee joint was identified through the lateral femoral condyle and positioned in alignment with the motor axis using a laser beam that was pre-installed to the dynamometer. A range of motion of 60◦ was set from 30◦ to 90◦ knee flexion with full extension being considered as 0◦ . The rate was set at 60◦ per second for both concentric and eccentric contraction modes for Q and H. Gravity error torque was recorded for every athlete. For familiarity, each participant performed 2 submaximal repetitions and 1 maximal repetition at a given velocity and mode of contraction. Those participants who experienced pain or discomfort during the trial repetitions were not included in the study (n = 3) Next, each participant performed the following: (i) five consecutive concentric Q and H contractions followed by a 60 s pause, (ii) five eccentric Q contractions followed by a 60 s pause, (iii) five eccentric H contractions. When testing of one side was completed, a 3-minute rest period was allowed.19 During this time period, the machine setting was changed to accommodate the opposite leg. The testing order for each leg was randomly assigned for each athlete. Verbal coaching or cueing was not provided to the athletes during the testing repetitions. From the isokinetic testing, the following eight variables were recorded as follows: right (RHecc) and left (LHecc) hamstring eccentric strength, right (RHconc) and left (RHconc) hamstring concentric strength, right (RQecc) and left (LQecc) quadriceps eccentric strength, and right (RQconc) and left (LQconc) quadriceps concentric strength. The main outcome measure was peak torque (PT) which was later normalized for body mass and expressed as PT/kg. The coefficient of variation (CV) and intra-class coefficient (ICC) were calculated as measures of reliability for each jumping-test. Additionally, repeated measures analysis of variance (ANOVA) procedure with a Scheffe Post hoc test was used to detect any systematic bias between the individual trials (items). Descriptive statistics (mean and standard deviation) were calculated. For the purpose of this study, the athletes were divided into achievement groups according to their performance on two studied jumps. The low-achievement group compromised one-third of the athletes with the lowest jumping performance (n = 28), the average-achievement group consisted of those athletes who were ranked between 33rd and 66th percentile (n = 27), and the highachievement group comprised one-third of the best performers (above 67th percentile; n = 27). Such a grouping was performed independently for spike-jump- and block-jump-performance. The breakdown for positions into achievement groups is presented in Table 1. The breakdown of the achievement-groups was not different between playing positions. Univariate differences between achievement-groups were determined using a one-way ANOVA with a Scheffe’s Post hoc follow-up test. To define multivariate differences between the groups a discriminant canonical analysis (DISCRA) was calculated. Statistical significance was pre-determined as p < 0.05. Statistica, ver. 11 (Statsoft, Tulsa, OK) was used for all statistical calculations.
3. Results Reliability results for the block-jump and spike-jump showed CV values of 3% and 4%, respectively, and ICCs of 0.95 and 0.87, respectively. There were no significant differences between the three testing trials for the block-jump (F test = 1.86; df = 2; p > 0.05). However, the difference between testing-trials of the spike-jump was significant (F test = 4.33; df = 2; p < 0.05). Follow-up procedures showed the 1st trial was significantly lower (40.22 ± 7.07 cm) compared to the following trials (41.09 ± 6.42 cm and 41.11 ± 7.01 cm for the 2nd and 3rd trial respectively), with no significant difference between the 2nd and 3rd trials. Therefore, the final achievement was defined as the personal best result across the three trials.
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Significant differences between the three block-jump achievement-groups were found for all isokinetic variables except RQecc (Table 2). When the participants were divided into the three achievement-groups according to their spike-jumpperformance, significant differences were found in all tests but RHconc (Table 3). The DISCRA procedure found significant differences between the achievement-groups based on block-jump-performance. The LQconc contributed most significantly to differentiation of the high- and low-performers. At the same time RQconc, and LHconc contributed less to block-jump performance (Table 3). The classification was correct for 63% of athletes (60% of low performers, 49% of average-performers, and 80% of high-performers). The DISCRA procedure identified LQconc, RHecc, and LHecc as the most significant discriminators between the groups based on spike-jump performance. Meanwhile, RQecc and LHconc contributed less to the discrimination of the spike-jump achievement-groups (Table 3). In total, 56% of the athletes were successfully classified (i.e., 46%, 49% and 72% for low-achievement-, average-achievement- and high-achievement-group, respectively) (Table 4).
4. Discussion Previous research has consistently found sport-specific testing procedures to be highly applicable in defining strength and conditioning capacities relative to the particular sport of interest.9 Therefore, we consider the finding of strong reliability of the volleyball-jumping tests to be highly important. Vertical jumping tests are often investigated with regard to reliability, and reports of good consistency across the tests are common.28 However, since reliability directly depends on the variability of the results and the tests conducted in the current study were performed by high-level athletes (i.e. where variance of the results is naturally truncated), the findings of strong reliability are even more encouraging.11 The reliability results showed that performance in spike-jump did not stabilize until the third testing trial even though the athletes were familiarized with the procedures. This finding is possibly due to the fact that during the familiarization session the athletes were asked to perform several jumps using a submaximal level of exertion. Thus, it is likely that the familiarization effort which was non-maximal was not substantial enough to achieve stabilization of spike-jump performance. Furthermore, since we used an optical measuring device to test jumping performance over 3 meters in length, the athletes’ orientation in space was possibly another contributing factor to the lack of stability. Since the athletes had to subjectively locate the optimal distance and approach speed, their ability to concentration on exerting full effort may have been obscured, and jumping performance throughout the first testing trials was limited. However, since performance eventually stabilized in the study, a three-trial testing design may be adequate enough to achieve an optimal level of spike-jump performance. Previous instigations defined high consistency and low measurement error of concentric and eccentric knee-strength when testing was done in similar conditions as those in our study (i.e. asymptomatic subjects, measured by same evaluator).29 Additionally, we have observed relatively large sample of high-level athletes. Therefore, in this study we have not evaluated reliability of the isokinetic testing. Other studies that investigated the association between isokinetic strength variables and jumping performance in various populations has provided controversial results.21,24,27 However, it seems that relative isokinetic strength measures are significantly related to jumping achievement in participants who possess stable and high technical quality of jumping performance.21,23,24 This
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Table 1 Break-down for positions into achievement groups for block-jump and spike-jump performance. Block jump
Setters Opposite hitters Middle blockers Outside receivers Libero players
Spike jump
Low achievers (n = 28)
Average achievers (n = 27)
High achievers (n = 27)
Low achievers (n = 28)
Average achievers (n = 27)
High achievers (n = 27)
7 9 4 3 5
6 7 5 5 5
5 7 3 6 6
7 7 2 5 6
6 6 5 5 5
5 8 5 4 5
Table 2 Univariate differences between achievement groups defined on a basis of the block-jump performance.
Age (years) Body height (cm) Body mass (kg) Block-jump (cm) LQconc (PT/kg) RQconc (PT/kg) LQecc (PT/kg) RQecc (PT/kg) LHconc (PT/kg) RHconc (PT/kg) RHecc (PT/kg) LHecc (PT/kg)
Low-achievers (n = 28)
Average-achievers (n = 27)
High-achievers (n = 27)
Analysis of variance
Mean ± SD
Mean ± SD
Mean ± SD
F test
p
0.90 2.42 1.24 94.08 18.79 10.21 5.28 3.24 5.35 2.62 8.41 6.94
0.40 0.07 0.29 0.01 0.01 0.01 0.01 0.06 0.01 0.08 0.01 0.01
20.76 175.21 71.05 26.03 2.06 2.09 2.19 2.26 1.12 1.17 1.23 1.21
± ± ± ± ± ± ± ± ± ± ± ±
2.36 6.88 12.58 2.95¶ , 0.30 0.26 0.57 0.48 0.22 0.14 0.16 0.26
22.47 174.90 68.93 32.10 2.22 2.16 2.37 2.35 1.18 1.22 1.35 1.37
± ± ± ± ± ± ± ± ± ± ± ±
3.66 5.85 9.07 2.36¥ , 0.21 0.31 0.55 0.49 0.18 0.17 0.27 0.19
22.24 172.89 65.08 38.20 2.54 2.5 2.74 2.67 1.3 1.28 1.52 1.48
± ± ± ± ± ± ± ± ± ± ± ±
4.88 6.49 4.34 3.07¥ , ¶ 0.28¥ , ¶ 0.39¥ , ¶ 0.56¥ , ¶ 0.64 0.17 0.18 0.26¥ 0.25¥
Block-jump, performance of the block jump; LQconc, left quadriceps concentric strength; RQ conc, right quadriceps concentric strength; LQecc, left quadriceps eccentric strength; RQecc, right quadriceps eccentric strength; LHconc, left hamstring concentric strength; RHconc, right hamstring concentric strength; RHecc, right hamstring eccentric strength; LHecc, left hamstring eccentric strength. ¥ Significantly different from low achievement group. ¶ Significantly different from average achievement group. § Significantly different from high achievement group. Table 3 Univariate differences between achievement groups defined on a basis of the spike-jump performance.
Age (years) Body height (cm) Body mass (kg) Spike-jump (cm) LQconc (PT/kg) RQconc (PT/kg) LQecc (PT/kg) RQecc (PT/kg) LHconc (PT/kg) RHconc (PT/kg) RHecc (PT/kg) LHecc (PT/kg)
Low-achievers (n = 28)
Average-achievers (n = 27)
High-achievers (n = 27)
Analysis of the variance
Mean ± SD
Mean ± SD
Mean ± SD
F test
p
0.24 0.34 4.09 157.51 16.18 7.41 3.59 1.89 9.25 4.51 9.87 10.81
0.78 0.65 0.02 0.01 0.01 0.01 0.03 0.16 0.01 0.01 0.01 0.01
21.40 174.34 72.00 26.92 2.00 2.13 2.11 2.32 1.04 1.16 1.25 1.15
± ± ± ± ± ± ± ± ± ± ± ±
2.44 7.07 14.51 2.87¶ , 0.25 0.25 0.43 0.47 0.16¶ , 0.15 0.13 0.20
22.23 174.34 69.66 32.69 2.21 2.13 2.4 2.32 1.20 1.18 1.28 1.33
± ± ± ± ± ± ± ± ± ± ± ±
4.87 6.67 8.01 1.05¥ , 0.27 0.32 0.69 0.53 0.20¥ , 0.15 0.26 0.21
21.70 173.27 64.39 38.89 2.50 2.46 2.64 2.61 1.30 1.29 1.53 1.5
± ± ± ± ± ± ± ± ± ± ± ±
3.43 6.25 4.69¥ 2.47¥ , ¶ 0.29¥ , ¶ 0.39¥ , ¶ 0.59¥ 0.64 0.16¥ , ¶ 0.17¥ 0.25¥ , ¶ 0.25¥ , ¶
Spike-jump, performance of the spike jump; LQconc, left quadriceps concentric strength; RQ conc, right quadriceps concentric strength; LQecc, left quadriceps eccentric strength; RQecc, right quadriceps eccentric strength; LHconc, left hamstring concentric strength; RHconc, right hamstring concentric strength; RHecc, right hamstring eccentric strength; LHecc, left hamstring eccentric strength. ¥ Significantly different from low achievement group. ¶ Significantly different from average achievement group. § Significantly different from high achievement group.
is a particularly important yet known phenomenon, as all sportspecific performances (i.e. jumps, throws, serves, etc.) depend primarily on skill level. It is reasonable to suggest that other cofactors (i.e. anthropometrics, motor qualities, etc.) may influence jumping performance among participants who do not differ in their level of technical proficiency.9 However, when skill proficiency is inconsistent, then technical quality may account for the greatest variation in performance with less of an influence from other co-variables such as those mentioned above. The results of our analyses show that isokinetic-kneestrength is more strongly associated to block-jump than to spike-jump performance. This finding is most likely related to the
differentiation of the achievement groups in the discriminate analysis. There are several possibilities to explain why isokineticstrength is more strongly related to block-jump compared to the spike-jump. First, the spike-jump is a more complex and technically advanced movement than the block-jump.4 Consequently, it is reasonable to assume that there are a number of other factors that influence spike-jump performance, such as arm swing, the length of the limbs, and appropriate timing of execution.16 Meanwhile, the block-jump is a relatively simple movement that may not be as influenced by confounding factors. In addition, volleyball-playing positions differ with regard to their game-play duties. While some players perform the spike-jump often (i.e.
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Table 4 Multivariate differences (canonical discriminant analyses) between achievement groups formed on a basis of the block-jump and spike-jump performance. Block-jump
LQconc (PT/kg) RQconc (PT/kg) LQecc (PT/kg) RQecc (PT/kg) LHconc (PT/kg) RHconc (PT/kg) RHecc (PT/kg) LHecc (PT/kg) Eigenvalue Canonical R Wilk’s lambda Chi square p Centroid: Low achievers Centroid: Average achievers Centroid: High achievers
Spike-jump
Root 1
Root 2
Root 1
Root 2
0.87 0.58 0.59 0.40 0.34 0.32 0.58 0.53 0.53 0.59 0.64 56.03 0.00 −0.93 −0.20 0.94
0.24 −0.04 −0.11 0.03 −0.04 −0.45 −0.49 −0.52 0.02 0.16 0.97 3.42 0.84 0.19 −0.20 0.07
0.87 0.57 0.49 0.36 0.42 0.46 0.69 0.60 0.36 0.46 0.71 45.66 0.00 −0.61 −0.27 0.62
−0.02 −0.14 0.24 0.04 0.60 0.06 0.00 0.72 0.06 0.24 0.94 7.32 0.40 −0.30 0.31 −0.08
LQconc, left quadriceps concentric strength; RQ conc, right quadriceps concentric strength; LQecc, left quadriceps eccentric strength; RQecc, right quadriceps eccentric strength; LHconc, left hamstring concentric strength; RHconc, right hamstring concentric strength; RHecc, right hamstring eccentric strength; LHecc, left hamstring eccentric strength; Root, structure of the canonical root.
outside hitter, middle blocker), others do it rarely (i.e. setter, libero) which may demonstrate that technical efficacy is specific to position. On the contrary, block-jump technique is relatively consistent across volleyball playing positions.4 In other words, the spike-jump is complex and multifaceted with some players (depending on the position) lacking the technical skills that are required to competently perform the movement. Although concentric properties appear to be more important than the eccentric activations for the performance of both observed jumps, this difference is more evident for block-jump than for the spike-jump performance. The block-jump starts from a two-stance stable position in which the athlete then performs a shortened version of the CMJ jumping technique with no full arm swing followed by a maximal vertical displacement. In our study, all participants were instructed to perform both jumps while using their individualized technique. As a result, some athletes executed block-jump with no preceding eccentric phase (i.e. downward phase). They actually performed somewhat of a “squat-jump” technique starting with 30–40 degrees static squat and concentrically activated quadriceps for the vertical displacement. Consequently, the concentric properties are most important in execution of the block-jump, since the eccentric phase of the movement is minimal. The differences in the findings related to the association of eccentric muscular activation and jumping performance could be explained by the discrepancy of execution between the two jumps.4 Eccentric muscular strength is highly challenged during the phase of the spike-jump that precedes maximum concentric contraction (i.e., “bounce-jump” phase). During the spike-jump, the athlete’s ability to decelerate during downward momentum and transition into an explosive vertical jump is highly dependent on eccentric strength capacity.7,14,30 Alternatively, the eccentric phase of the block-jump is not as expressed because the jump begins from a two-stance, stable position without a preceding “drop-jump”. Moreover, some athletes perform block jump with practically no downward momentum (i.e. no eccentric phase, see previous text). Due to this, the force applied in the downward movement is not as intensive when compared to the same phase of the spike-jump. Logically, the concentric qualities of the block-jump are more important determinants of performance than eccentric qualities. There are several limitations of this investigation. First, we investigated high-level female athletes, which limit the ability to generalize the findings toward other populations. Second,
isokinetic testing is often criticized as being non-functional hence limiting the applicability in the real world. However, isokinetic testing allows determination of eccentric muscular properties which is difficult to be observed throughout other measuring protocols (free weights, machines, etc.). Third, we did not observe dominant vs. non-dominant leg of the athletes. However, we are of the opinion that this limitation does not influence our findings. Mainly, the difference in leg dominance will not contribute to the findings of multivariate analysis (i.e. discriminant analysis), and block-jump (i.e. as a two-leg jump). Also, less than 10% of athletes were left handed. Therefore, it is reasonable to suggest that majority of the studied athletes were left leg dominant. Finally, in this study we have been focused solely on knee-joint while volleyball jumps involve multiple joints. However, while isokinetic testing is time-consuming and exhaustive, we were limited in doing additional tests and consequently more profound analyses. 5. Conclusion This study demonstrated that relative isokinetic strength variables are more strongly related to block-jump performance than to spike-jump performance. The block-jump performance is primary related to concentric qualities of quadriceps. The eccentric isokinetic measures of hamstring and quadriceps were relatively less important determinants of the efficient execution of the blockjump than for the spike-jump. There were some indices in the study to suggest that technical quality of the execution (i.e. characteristic motor skill) is highly important for spike-jump performance. Further studies should evaluate the importance of multiple-joint-isokinetic-strength while focusing on the typical joint angles of specific jumping performance in volleyball. This is particularly important for athletes with high technical proficiency. Practical implications • In volleyball athletes whose game-duties are oriented toward attack and spike jumping, both eccentric and concentric muscular capacities are equally important determinants of performance. • Strength and conditioning training programs for volleyball athletes should include both concentric (e.g., free-weight, machine-based) and eccentric (e.g., plyometric) exercise modalities.
Please cite this article in press as: Sattler T, et al. Analysis of the association between isokinetic knee strength with offensive and defensive jumping capacity in high-level female volleyball athletes. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2014.08.002
G Model JSAMS-1078; No. of Pages 6
ARTICLE IN PRESS T. Sattler et al. / Journal of Science and Medicine in Sport xxx (2014) xxx–xxx
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• Since block-jump was found to be more associated to concentric compared to eccentric strength, it may be best that athletes who are more often involved in defensive duties (i.e. middle blockers) should emphasize training concentric muscular strength for improving performance. Acknowledgements The study was supported by the Slovenian Research Agency and Slovenian Ministry of Sport and Education within the project “The prevention of sport injuries in the Republic of Slovenia” (V5-0233) and partially by Croatian Ministry of Science, Education and Sport (Project No. 315-1773397-3407). References 1. Dal Pupo J, Gheller RG, Dias JA et al. Reliability and validity of the 30-s continuous jump test for anaerobic fitness evaluation. J Sci Med Sport 2013 [Epub ahead of print]. 2. Mok K, Jarning J, Hansen B et al. Identification of jumping activity in volleyball by using accelerometer. Br J Sports Med 2014; 48(7):640. 3. Lamontagne-Lacasse M, Nadon R, Goulet E.D. Effect of creatine supplementation on jumping performance in elite volleyball players. Int J Sports Physiol Perform 2011; 6(4):525–533. 4. Sattler T, Sekulic D, Hadzic V et al. Vertical jumping tests in volleyball: reliability, validity, and playing-position specifics. J Strength Cond Res 2012; 26(6):1532–1538. 5. Tillman MD, Hass CJ, Brunt D et al. Jumping and landing techniques in elite women’s volleyball. J Sports Sci Med 2004; 3(1):30–36. 6. Malatesta D, Cattaneo F, Dugnani S et al. Effects of electromyostimulation training and volleyball practice on jumping ability. J Strength Cond Res 2003; 17(3):573–579. 7. Sheppard JM, Dingley AA, Janssen I et al. The effect of assisted jumping on vertical jump height in high-performance volleyball players. J Sci Med Sport 2011; 14(1):85–89. 8. Voelzke M, Stutzig N, Thorhauer HA et al. Promoting lower extremity strength in elite volleyball players: effects of two combined training methods. J Sci Med Sport 2012; 15(5):457–462. 9. Peric M, Cavar M, Zenic N et al. Predictors of competitive achievement among pubescent synchronized swimmers: an analysis of the solo-figure competition. J Sports Med Phys Fitness 2014; 54(1):16–26. 10. Uljevic O, Spasic M, Sekulic D. Sport-specific motor fitness tests in water polo: reliability, validity and playing position differences. J Sports Sci Med 2013; 12(4):646–654. 11. Uljevic O, Esco MR, Sekulic D. Reliability, validity and applicability of isolated and combined sport-specific tests of conditioning capacities in top-level junior water polo athletes. J Strength Cond Res 2014; 28(6):1595–1605.
12. Sharma A, Geovinson SG, Singh Sandhu J. Effects of a nine-week core strengthening exercise program on vertical jump performances and static balance in volleyball players with trunk instability. J Sports Med Phys Fitness 2012; 52(6):606–615. 13. Hughes G, Watkins J. Lower limb coordination and stiffness during landing from volleyball block jumps. Res Sports Med 2008; 16(2):138–154. 14. Wagner H, Tilp M, von Duvillard SP et al. Kinematic analysis of volleyball spike jump. Int J Sports Med 2009; 30(10):760–765. 15. Borras X, Balius X, Drobnic F et al. Vertical jump assessment on volleyball: a follow-up of three seasons of a high-level volleyball team. J Strength Cond Res 2011; 25(6):1686–1694. 16. Sheppard JM, Cronin JB, Gabbett TJ et al. Relative importance of strength, power, and anthropometric measures to jump performance of elite volleyball players. J Strength Cond Res 2008; 22(3):758–765. 17. Dekerle J, Barstow TJ, Regan L et al. The critical power conin cept all-out isokinetic exercise. J Sci Med Sport 2013. http://dx.doi.org/10.1016/j.jsams.2013.09.003 [Epub ahead of print]. 18. Hadzic V, Sattler T, Veselko M et al. Strength asymmetry of the shoulders in elite volleyball players. J Athl Train 2014 [Epub ahead of print]. 19. Hadzic V, Sattler T, Markovic G et al. The isokinetic strength profile of quadriceps and hamstrings in elite volleyball players. Isokinet Exerc Sci 2010; 18(1): 31–37. 20. Edouard P, Codine P, Samozino P et al. Reliability of shoulder rotators isokinetic strength imbalance measured using the Biodex dynamometer. J Sci Med Sport 2013; 16(2):162–165. 21. Harrison B, Firth W, Rogers S et al. The relationship between isokinetic performance of hip and knee and jump performance in university rugby players. Isokinet Exerc Sci 2013; 21(2):175–180. 22. Tsiokanos A, Kellis E, Jamurtas A et al. The relationship between jumping performance and isokinetic strength of hip and knee extensors and ankle plantar flexors. Isokinet Exerc Sci 2002; 10(2):107–115. 23. Saliba L, Hrysomallis C. Isokinetic strength related to jumping but not kicking performance of Australian footballers. J Sci Med Sport 2001; 4(3): 336–347. 24. Ispirlidis I, Malliou P, Beneka A et al. Jumping ability and kinetic knee extensors’ performance in elite soccer players. J Hum Mov Stud 2004; 46(6): 483–491. 25. Pua YH, Koh MTH, Teo YY. Effects of allometric scaling and isokinetic testing methods on the relationship between countermovement jump and quadriceps torque and power. J Sports Sci 2006; 24(4):423–432. 26. Alemdaroglu U. The relationship between muscle strength, anaerobic performance, agility, sprint ability and vertical jump performance in professional basketball players. J Hum Kinet 2012; 31:149–158. 27. Iossifidou A, Baltzopoulos V, Giakas G. Isokinetic knee extension and vertical jumping: are they related? J Sports Sci 2005; 23(10):1121–1127. 28. Markovic G, Dizdar D, Jukic I et al. Reliability and factorial validity of squat and countermovement jump tests. J Strength Cond Res 2004; 18(3): 551–555. 29. Sole G, Hamren J, Milosavljevic S et al. Test–retest reliability of isokinetic knee extension and flexion. Arch Phys Med Rehabil 2007; 88(5):626–631. 30. Sheppard JM, Newton RU. Long-term training adaptations in elite male volleyball players. J Strength Cond Res 2012; 26(8):2180–2184.
Please cite this article in press as: Sattler T, et al. Analysis of the association between isokinetic knee strength with offensive and defensive jumping capacity in high-level female volleyball athletes. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2014.08.002
