Volleyball players require not only technical skills but also individual physical performance capacities because of the characteristics of the volleyball game. The ability to jump is the most fundamental element for performing the spike, block, and jumping serve. Ziv and Lidor (24) suggested that volleyball players in better performing teams have higher vertical jump (VJ) values; strength and conditioning programs that emphasize plyometric training may increase VJ performance and it is important to continue conditioning sessions throughout the season to maintain VJ performance. Furthermore, previous studies reported a relationship between VJ performance and the strength of the lower extremities (4,5,9,11,15,16,19). Although there are some considerable commonalities between the 2 jumps, the spike jump (SPJ) in volleyball differs from VJ from a standing position for the following reasons. Spike jump acquires jumping height by converting horizontal energy obtained by stepping before take-off into vertical energy using take-off movement. Regarding the movement parameters that influence the height of SPJ, Wagner et al. (20) found that the height of SPJ correlated with the maximal horizontal velocity of the center of mass (CM) during SPJ. Although volleyball players are required to generate greater power in the vertical and horizontal directions, the relationships between the height of SPJ, horizontal jumping ability, and lower joint kinetic values of vertical and horizontal jumps have not yet been elucidated.
The standing long jump (SLJ) is a typical measurement test for horizontal jumping ability. Regarding the biomechanical characteristics of SLJ, the optimum take-off angle (21), influence of different starting postures (2), effects of technical training (12) and isokinetic training (14), and the relationship between the kinetic characteristics of SLJ and isokinetic strength of the lower extremities (23) have already been investigated. Moreover, several studies examined differences in kinetic data between VJ and SLJ (7,10,17). The findings obtained suggested that contributions made by the hip, knee, and ankle musculature differ in the 2 types of jumps and that SLJ demonstrates the importance of the hip and ankle musculature in the production of external work in jumping.
The purpose of this study was to examine the relationships among SPJ, SLJ, and VJ performance, and also investigate the influence of the kinetic values of the lower joints in SLJ and VJ on CM velocity in SPJ motion. Because of differences in jump directions between VJ and the standing jump, we hypothesized that a different relationship exists between the kinematic variables of SPJ and the kinematic and kinetic variables of SLJ and VJ. To develop an effective strength training program to enhance SPJ performance, volleyball coaches and strength and conditioning coaches need to understand the various elements affecting SPJ performance. The results of this study may provide insights into training strategies to enhance SPJ performance in female college volleyball players.
Experimental Approach to the Problem
Subjects performed typical warm-up exercises that consisted of jogging, dynamic stretching, agility drills, and short sprints for 30 minutes. These warm-up exercises were performed routinely before volleyball exercise. After a 15-minute recess, they had enough practice of VJ and SLJ, and then performed 3–5 maximal VJ and SLJ on a force plate with an arm swing and 3 maximal SPJ using 3 steps. Subjects who increased their jump height and distance in the third trial performed the fourth trial. The order of the trials performed was as follows. Subjects performed VJ, then SLJ, and lastly SPJ. The highest recorded trial was taken for analyses. The height of VJ using the arm swing and counter movement was calculated using the following equation:V and g represent the vertical velocity of CM at take-off and the acceleration of gravity (9.8 m·s−2), respectively.
The height of SPJ including body height and arm length was measured by Yard Stick (Swift Performance Equipment Inc., Wacol, Australia). Regarding the distance of SLJ, the distance from the tiptoe before jumping to the heel after jumping was measured as performance. Subjects were instructed to jump as far as possible in SLJ, and as high as possible in VJ and SPJ. Recovery for approximately 3 minutes was allowed between trials.
The motion of VJ and SLJ was recorded in the sagittal plane for a motion analysis using a digital video camera (EXILIM EX-100; CASIO Inc., Tokyo, Japan) that was placed at a left angle to the subjects. The sampling frequency was 120 Hz and the exposure time was set at 1/1,000 seconds. The motion of SPJ was recorded in the sagittal plane for a motion analysis using a digital video camera (EXILIM EX-100; CASIO Inc.) that was placed at a right angle to the subjects. A digitizing system (FrameDIAS V; DKH, Inc., Itabashi-ku, Tokyo, Japan) was used to manually digitize 25 points on the body (vertex of the head, ear canal, superior margin of the sternum, acromion, lateral humeral epicondyle, styloid process of the wrist, metatarsophalangeal joint, lowest part of the ribcage, greater trochanter, lateral epicondyle of the femur, lateral malleolus, calcanei, hallux, and tiptoes). In this study, the lengths of 4 control points for calibration were used to obtain 2-dimensional coordinates of digitizing points. The coordinate values were filtered digitally using a Butterworth-type fourth-order low-pass filter. The cutoff frequency for the 2-dimensional coordinate of each digitizing point was calculated and the mean value of the cutoff frequencies was used in this study. The cutoff frequency for the 2-dimensional coordinates was 6 Hz (22). The linear and angular kinematics of the joints and segments were calculated from the smoothed coordinate data, CM, and the inertial properties of each segment were calculated by body segment parameters for Japanese athletes (1). The ground reaction forces of the vertical direction (Fz) and horizontal direction (Fy) in VJ and SLJ were collected from the force plate at 1,000 Hz (9287C; Kistler, Inc., Total Dimension: 900 × 600 mm, Winterthur, Switzerland). Force and the video were synchronized by recording the light of the synchronizer (PTS-110; DKH, Inc.) at the signal.
Joint torques at the ankle, knee, and hip joints were calculated using an inverse dynamic method. The equations of motion for the foot, shank, and thigh were solved from the distal to the proximal end of the support leg using ground reaction force data. The joint power of the leg joints was calculated as a product of the joint torque and joint angular velocity. Mechanical work performed at each joint was calculated using the trapezoidal integration of the power histories beginning at the lowest displacement of CM until the point of take-off (17). Joint torque, joint power, and work divided by body mass were expressed as relative values.
Seventeen female Japanese college volleyball players (mean ± SD; age: 19.6 ± 1.1 years (range: 18–22 years), height: 165.6 ± 5.5 cm, body mass: 61.0 ± 6.2 kg, training experience: 10.7 ± 2.1 years) participated in this study. All subjects were healthy and in good physical condition. Subjects who were unable to exert their maximum effort in trials for this experiment because of injuries did not participate in this study. Strength training and intense aerobic training were not conducted to fine-tune conditioning in subjects 1 week before this study. The trials of this study were conducted during the off-season of the college volleyball league. Sixteen subjects were right-handed and 1 was left-handed. This study was approved by the Ethical Committee of the Department of Health and Sports at Niigata University of Health and Welfare. Subjects were fully informed of the experimental purpose and procedures of this study, after which they provided signed informed consent.
Values for each parameter are presented as the mean ± SD. The normality of the distribution was assessed for all variables using the Kolmogorov-Smirnov test before a comparative analysis. Normally distributed variables between the 2 trials (SLJ and VJ conditions) were compared using the independent t test. Pearson's product-moment correlation coefficients (r) were used to investigate relationships among performance parameters and kinetic and kinematic parameters. A 1-way analysis of variance and Bonferroni's post hoc tests were used to examine differences in the contributions of joints to the work performed for SLJ and VJ. The effect sizes of Cohen (3) were calculated to measure the magnitude of differences in kinematic and kinetic variables between SLJ and VJ. Effect sizes of 0.20–0.49, 0.50–0.79, and ≥0.8 were considered to be small, moderate, and large, respectively (3). All statistical procedures were conducted with SPSS Statistics 22, and significance was set at p ≤ 0.05.
In this study, the jumping distance of SLJ and height of VJ were 2.17 ± 0.12 m and 0.34 ± 0.04 m, respectively. Regarding the normal distribution of data in this study, the normality of all data was confirmed by the Kolmogorov-Smirnov test. Figure 1 shows the mean CM horizontal and vertical velocity-time curves of the 17 subjects and respective SDs for SPJ from 0.33 seconds before first step contact to take-off. The temporal axis was standardized by the time from 0.33 seconds before first step contact to take-off. Mean CM horizontal velocity reached a maximum before second step contact and decreased until take-off. Center of mass vertical velocity sharply increased after third step contact (Figure 1). The relative mean height of SPJ (maximum reaching height using Yardstick/height) was 1.65 ± 0.03 m. The mean CM maximum horizontal velocities, third step contact, and take-off for CM were 3.28 ± 0.31, 2.36 ± 0.25, and 1.17 ± 0.22 m·s−1, respectively. Deceleration of the horizontal velocity of CM from third step contact and take-off was 1.19 ± 0.27 m·s−1. The mean vertical velocity of CM at take-off was 2.87 ± 0.20 m·s−1. The relationships among SPJ height, CM velocities until take-off, and the performance of VJ and SLJ are shown in Figure 2. Center of mass horizontal peak velocity and velocity at take-off did not correlate with SPJ height (r = 0.262, n.s.; r = 0.073, n.s., respectively) (Figures 1 and 2 about here).
Figure 3 shows the mean joint angular velocity, joint torque, and joint power-time curves of the 17 subjects and respective SDs from 1 second before take-off to take-off for SLJ and VJ. The temporal axis was standardized by time from 1 second before take-off to take-off. Based on the torque and power-time curve, the torque and power of the knee joint in VJ had different timings and patterns than those of SLJ (Figure 3 about here).
The hip and ankle peak power and ankle work of SLJ were significantly greater than those of VJ. The knee peak power and work of VJ were significantly greater than those of SLJ. Figure 4 shows the averages and SDs of the percent contributions to work performed by the hip, knee, and ankle joints. A 1-way analysis of variance revealed significant differences in the percent contributions to work for SLJ (F = 37.303, p < 0.001) and VJ (F = 3.832, p ≤ 0.05). Bonferroni's post hoc tests revealed that the percent contributions to work performed by the hip and ankle joints in SLJ were significantly greater than that by the knee joint, and also that the percent contribution to work performed by the hip joint in VJ was significantly greater than that by the knee joint. These results suggested that jump direction affected the contribution of the lower joints (Figure 4 and Table 1 about here).
Table 2 shows the relationship between kinetic parameters in SLJ and VJ and the velocity of CM in SPJ that correlated with SPJ height. These results suggested that hip and ankle joints in the horizontal jump and knee joint in VJ contributed to the velocity of SPJ. Furthermore, knee peak power and work negatively correlated with the deceleration of horizontal velocity from third step contact to take-off. This result indicates that knee power during VJ had a significant effect on the ability to decelerate SPJ (Table 2 about here).
The SPJ height of female volleyball players correlated with CM vertical velocity at take-off, CM horizontal velocity at third step contact, and the deceleration of CM horizontal velocity from third step contact to take-off. Spike jump has only been examined in a few studies (6,8,20), and limited information is currently available on specific training measures to improve SPJ height. Regarding the kinematics of SPJ, the importance of the maximum horizontal velocity of CM during the approach phase of SPJ has already been reported (20). However, CM maximum horizontal velocity did not have a significant influence on SPJ height in this study. These results may reflect differences in CM maximum horizontal velocity (3.28 ± 0.31 m·s−1 in this study vs. 3.71 ± 0.33 m·s−1 in Wagner et al. (20)) or physical abilities between males and females. As an important result of our study, the greater deceleration of horizontal velocity during the approach phase was also an important factor enhancing the height of SPJ. This result suggests the importance of the ability to decelerate horizontal velocity during the approach phase of SPJ, and is useful for devising training strategies to enhance SPJ performance in female college volleyball players.
Spike jump height positively correlated with the distance of SLJ and height of VJ (Figure 2). To the best of our knowledge, the relationship between SPJ height and horizontal jumping ability has not yet been investigated; however, some studies reported that SPJ height correlated with vertical jumping ability (6,8,20). This finding suggests that jumping ability in the horizontal and vertical directions is an important element for enhancing the height of SPJ.
Vertical velocity at take-off of SPJ, which showed the strongest correlation with the height of SPJ, positively correlated with hip work and ankle peak power in SLJ and knee peak power in VJ (Table 2). These results were attributed to the different primary generators of power during the jump movement (Figure 4). Regarding the contribution of the leg joint during SLJ and VJ, several studies (7,17,18) indicated that the hip and ankle musculature in SLJ and knee musculature in VJ were important for the production of external work. We concluded that it is important for volleyball players to enhance horizontal and vertical jumping abilities separately based on an understanding of these mechanisms.
The deceleration of CM horizontal velocity from third step contact to take-off in SPJ negatively correlated with knee peak power and work in VJ, whereas no correlation was observed between the kinetic parameters of SLJ and SPJ (Table 2). These results suggest that the knee joint in VJ may have a different functional role during eccentric lower muscle contraction in SPJ to that in SLJ. A recent meta-analysis suggested that conditioning programs based on plyometric training increase VJ performance by 4.7–8.7% depending on the testing protocol (13). Newton et al. (15) indicated that ballistic resistance training for 8 weeks in NCAA Division I male volleyball players significantly improved counter movement jump and VJ with a 3-step approach. Therefore, the ability of the knee to produce power plays a crucial role in the deceleration phase accompanied by eccentric muscle contraction, and increasing knee power using SSC training such as plyometrics or ballistic training may enhance VJ performance. The main limitation of this study was that subjects only included female volleyball players who showed superior jumping movement. Further studies to elucidate the characteristics of male competitive volleyball players using the same method are warranted.
Spike jump performance is one of the key elements influencing the result of volleyball games. From a practical point of view, our results suggest that horizontal and vertical jumping abilities need to be improved to effectively enhance SPJ performance. Furthermore, this study revealed that power production by the hip and ankle in SLJ and the knee in VJ correlated with the vertical velocity of SPJ at take-off, and also that knee power in VJ correlated with the horizontal velocity change during the deceleration phase of SPJ. These results indicate that the contributions of lower joints to SPJ performance change depending on the jumping direction. Thus, volleyball coaches and strength and conditioning coaches need to be aware of the directions of jumps if jump training for improvements in SPJ is used as a training method. It may be possible to continuously improve SPJ by applying appropriate loads when executing horizontal and VJ movements, according to SLJ and VJ performance levels.
The authors would like to thank Niigata University of Health and Welfare female volleyball team members for their help with data collection.
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