Kinetic differences of two volleyball jumping techniques.

The vertical component of ground reaction force-time curves for two styles of jumping used in preparation for a spike in volleyball were analyzed in a group of 86 players. The two styles consisted of a hop approach where the player lands simultaneously on both feet prior to take-off, and a step-close (SC) approach where one foot is placed in its take-off position followed by the trailing foot being placed adjacent to it before take-off. A total of 15 variables from the curves for each style were compared using analysis of variance techniques. The hop jump was characterized as having a higher velocity at the end of the approach resulting in a faster and larger absorption impulse. This produced a faster positive impulse with a higher average force, peak force, and acceleration which is consistent with a greater storage and utilization of elastic energy of the muscles. No significant differences were found in the time and average force for the final unweighting phase of the impulse, and no differences were note in take-off velocities. Thus, the hop jump resulted in decreasing the time of the impulse by increasing the average and peak forces during the impulse with no apparent effect on jump height.