Take-oŠ motion for jumping with an increase in the number of steps in the approach run for the long jump: focusing on the rate of change of take-oŠ action from a short to a long approach jump. Japan J. Phys. Educ. Hlth. Sport Sci. 57: 71 82, June, 2012 AbstractThe aim of this study was to clarify the take-oŠ motion required to perform a longer leap when an athlete increases the number of steps in the approach run for the long jump. Seven senior jumpers performed the long jump using diŠerent

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... mbers of approach-run steps. The number was increased from 6 strides to 16 strides every 2 strides. The following results were obtained. (1) When athletes increased the number of approach-run steps, the change in the approach velocity did not correspond to that of the jump distance. (2) To heighten the increased jump distance when athletes increased the number of approach-run steps, it was necessary to shorten the contact time and gain vertical velocity with less deceleration of horizontal velocity during the take-oŠ phase. (3) To decrease the contact time when athletes increased the number of approach-run steps, it was eŠective to lower the angular deviation of the radius from the center of gravity (c.g.) to the grounding point of the take-oŠ leg and increase the angular velocity during the take-oŠ phase. In order to gain vertical velocity with less deceleration of horizontal velocity, it was necessary to increase the maximal lengthening velocity of the radius during the second half of the take-oŠ phase. These results suggest that when deciding the number of approach-run steps it is necessary to evaluate not only sprint ability, as has been done in the past, but also contact time and take oŠ index, which is deˆned as the value of the vertical velocity at take-oŠ divided by the deceleration of the horizontal velocity during take-oŠ. At the same time, we should also evaluate c.g. behavior because of its relationship to contact time and take-oŠ index. Key wordsjump with a short approach-run, jump with a long approach-run, behavior of center of gravity, approach-run distance, take-oŠ motion キーワード短助走跳躍,長助走跳躍,身体重心の挙動,助走距離,踏切動作  緒 言 陸上競技の走幅跳は,助走において獲得した速 度を踏切で方向転換することで身体の投射運動を 行い,跳躍距離を競う競技種目である.そのため に,走幅跳の跳躍距離には助走速度が大きく影響 を及ぼす(Nigg, 1974; Br äuggeman and Nixdorf,