Kyle Kortegaard and Sasho MacKenzie Kyle Kortegaard and Sasho MacKenzie Department of n Kinetics Department of Human Kinetics St. Francis Xavier University, Antigonish, Nova Scotia The volleyball serve is often considered the first offensive action in every rally (Masumura et al., 2007), as the ultimate goal is to present the defense with a difficult passing scenario (Penning et al., 2006). The defense’s reaction time dictates whether or not the serve will be successfully received, and so flight time of the ball should be minimal. Flight time of a serve is governed by the ball’s velocity and flight path. Competitive volleyball is currently dominated by the jump spin serve, a service technique that permits a favourable contact position (high above the court), and thus a maximum serve speed and optimal trajectory. However, its vast popularity in today’s game has led to defensive adaptation. A traditional “toss-focused” (TF) jump float serve is used to confuse the defense with unpredictable ball movement patterns, but the associated contact position is not optimal. A novel service technique, the “jump- focused” (JF) jump float serve, incorporates the spike approach of the spin serve and the random flight patterns of the float serve. The current study investigated the offensive potential of the JF jump float serve. Testing was conducted at St. Francis Xavier University and Dalhousie University. Differences between the TF and JF service techniques were examined using a repeated measures study design. Testing consisted of filming all participants (N=9) perform both service techniques using a SONY ® high definition digital video camera. Training and practice sessions ensured familiarity with both the TF and JF techniques prior to data collection. A total of 232 serves were captured. The five best TF and JF serves from each player were selected for analysis based on a preliminary qualitative assessment (the ball had to be served in the correct plane, land in, and have no spin). Ninety serves were analyzed in total. Contact positions (Fig.1), initial serve velocities and trajectories, and pre-contact vertical ball velocities were quantified through digitization using the computer analysis program MaxTRAQ ®. Student’s paired t-tests were conducted to test for any statistical significance among initial serve conditions. Forthomme, B., Croisier, J., Ciccarone, G., Crielaard, J., & Cloes, M. (2005). Factors correlated with volleyball spike velocity. The American Journal of Sports Medicine, 33(10), Harman, E. A., Rosenstein, M. T., Frykman, P. N., & Rosenstein, R. M. (1990). The effects of arms and countermovement on vertical jumping. Medicine and Science in Sports and Exercise, 22(6), Huang, C., & Hu, L. (2007). Kinematic analysis of volleyball jump topspin and float serve. XXV ISBS Symposium 2007, Masumura, M., Marquez, W., & Koyama, H. (2007). A biomechanical analysis of serve motion for elite male volleyball players in official games. Journal of Biomechanics, 40(2). Pennings, T., Lithio, D., Webb, E. (2006). Optimizing a volleyball serve. A Biomechanical Evaluation of Two Methods of the Jump Float Serve in Volleyball JUMP-FOCUSED METHOD DISCUSSIONINTRODUCTION METHODS Fig. 1 Horizontal and vertical components of contact position. REFERENCES TOSS-FOCUSED METHOD RESULTS DyDy DyDy The ball is tossed as the right foot is forward (for right-handed players) with a low trajectory. Immediately after the left foot comes forward, the server must jump to contact the falling toss. The ball is struck in front of the server’s body with an open palm so as to impart no spin on the ball. This approach eliminates the possibility of using an arm swing to facilitate a maximal jump. The mean contact height for JF serves was 5.5% (16 cm) higher than the contact height for TF serves (Fig. 2A). The paired t-test indicated that this difference was statistically significant, t(8) = -4.12, p = The associated effect size (d = 0.72), suggests that the higher contact height achieved with the jump-focused technique is meaningful from a practical perspective. Players served the ball with 24 % more velocity (3.3 m/s) with the JF technique, which was significantly greater than the TF technique, t(8) = -4.71, p = 0.006, d = The JF method also yielded significantly flatter initial trajectories (5.9º) relative to the TF technique (8.2º), t(8) = -4.71, p =.006, d = Significant differences were alos found in the vertical ball velocity prior to contact, t(8) = 2.53, p =.036, d = 2.86, illustrating a meaningful difference in the difficulty of contacting the ball with the JF method (Fig. 2B) ●Harman et al. (1990) concluded that the countermovement and arm swing are both important contributing factors to jump height. A countermovement increases the athlete’s jump time, while the arm swing maximizes the ground reaction force acting at the athlete’s feet. These features together increase the impulse acting on the athlete [Impulse = Force × time]. ●The JF service approach resulted in a significantly higher contact position than the traditional TF technique. This was expected because the arm swing and countermovement inherent in the JF technique theoretically increase the impulse acting on the server, maximizing take-off velocity and thus jump height. ●A significantly greater initial serve velocity was found with the JF technique. This was consistent with Forthomme et al. (2005) who found that post-spike ball velocity was directly related to height of impact. Also, Huang & Hu (2007) linked greater contact heights to a higher probability of the ball landing in the court, likely due to a decreased initial angle of ball flight. This was seen in the current study, as initial serve trajectories were significantly flatter in the JF condition. ●The significantly greater pre-contact vertical ball velocity evident with the JF toss has implications on the difficulty level in performing this type of serve. Since the ball is tossed much higher, the force of gravity has more time to act on the ball, resulting in a prolonged downward acceleration and a toss that is moving much faster just before impact. This suggests that practice may be required to establish the correct timing in coordinating a successful ball contact. Fig. 2 (A) Mean contact heights for the TF and JF service techniques. (B) Mean pre-contact vertical ball velocities of TF and JF tosses. (A) (B) Fig. 3 (A) Toss-focused service approach. (B) Jump-focused service approach. (A)(B) VyVy The JF jump float serve is characterized by a much higher toss that occurs earlier in the approach than the TF method. The ball is tossed with the left leg forward (for right-handed players). The higher toss allots the server sufficient time to then execute a two-step spike approach, which allows the player to perform a countermovement and an exaggerated arm swing prior to take-off, resulting in a potentially greater jump. DxDx DyDy VyVy