VERTICAL JUMPING PERFORMANCE: ONE - FOOT VS. TWO- FOOT TAKEOFF TECHNIQUES Peter F. Vint, M.S. Introduction considerable amount of literature documents investigations of jumping mechanics and the factors which determine jumping performance. While several researchers have examined biomechanical aspects of either one-foot vertical jumping or two-foot vertical jumping, few have specifically investigated the differences between the two styles. As the one-foot slide attack gains popularity, coaches, athletes and trainers should understand the inherent strengths and weaknesses of each technique. This article reviews the biomechanical factors which contribute to vertical jumping performance, emphasizing the differences between one-foot and two-foot jumping techniques. Factors in Vertical Jumping Performance In a maximum vertical jump, the goal is simply jump- ing and reaching as high as possible. In volleyball, the height to which an athlete can jump and reach is often critically im- portant. In the absence of air resistance and other external forces, the upward projection of the whole body center of mass (CM) is completely determined by the vertical velocity at the instant of takeoff and the acceleration due to gravity. However, this quantity does not completely describe the overall jump and reach height which is observed. A simple model shows that on individual's maximum jump and reach height, may be described by the sum of four lesser heights: takeoff height, flight height, reach height and loss height (see Figure 1). Takeoff height may be defined as the height of the CM at the instant the individual leaves the ground. Flight height refers to the actual height to which the CM is elevated during the in-flight phase of the jump. Reach height describes the vertical distance from the CM to the fin- gertips at the instant the maximum jump and reach height is evaluated. Loss height refers to the difference between the peak height of the CM and the height of the CM at the instant the maximum jump and reach height is evaluated. This last factor can usually be attributed to mistiming the final reach (usually by contacting the ball on the way down from the peak of the jump). In standing two-foot vertical jumps (similar to block jumps), takeoff height, flight height and reach height account for 41, 17, and 42 percent, respectively, of the overall jump A BGN INT ADV P ERFORMANCE C ONDITIONING A NEWSLETTER DEDICATED TO IMPROVING VOLLEYBALL PLAYERS www.performancecondition.com/volleyball VOLLEYBALL Jump and Reach Height Takeoff Height Flight Height Reach Height Loss Height Reach Height Loss Height Flight Height Takeoff Height Jump and Reach Height CM Figure 1 - Deterministic model and illustration of simple factors which determine overall jump and reach height. Note: relative pro- portions of the four sub-heights are drawn approximately to scale.