The present study was designed to investigate the development of a rapidly repeated movement of the whole body observed from center of gravity. Subjects were 130 healthy females aged 5-17 years and were divided into a Fast group (5 females) and a Slow group (5 females) in each age group based on the time required for one set of side jumps. Subjects were measured on their physique (body height, body mass), muscular power (vertical jump, standing broad jump) and the movement of a side jump. The procedure of the side jump was to hop between two parallel lines on the force plate from right to left alternately as quickly as possible. The distance between the lines was fixed at one third of the mean body height at each age. The movement of the side jump was pictured by using a TV camera at the front of the subject, equipping 60 frames per second. The center of gravity (CG) was calculated by using the body segment parameters of Matsui. The CG of the lowest position on the ground and the CG of the highest position in the air calculated the values per unit body height in order to except the effets of aging. Also, the moving distance and the vertical and horizontal displacements calculated the values per line by the same reason. The moving distance of CG per line decreased significantly with age by about 9 years. The lowest position of CG per body height on the ground increased significantly with age by about 9 years. The highest position of CG per body height in the air decreased significantly with age by about 9 years. The vertical and horizontal displacements of CG per line decreased significantly with age by about 9 years. The angular velocity of lower limb increased significantly with age. The CG of the Fast group decreased significantly on the moving distance, the highest position in the air and both vertical and horizontal displacements in comparison with that of the Slow group. And the CG of the lowest position on the ground and the angular velosity of lower limb on the Fast group increased significantly from that of the Slow group. These results suggest that a rapidly repeated ability of the whole body develops by a decrease of the vertical displacement of CG, caused by keeping a high posture on the ground and a low posture in the air, and by a decrease of horizontal displacement of CG caused by increasing the angular velocity of the lower limb.本研究は、全身の急速反復動作であるside jumpの加齢的変化および各年齢における素早さの要因について動作学的に検討することを目的とした。被験者は、5歳～17歳の健常な女子であり、各年齢において反復動作の速い者5名（F群）と遅い者5名（S群）・合計130名を抽出し、形態・瞬発力およびside jumpの測定を実施した。side jumpの測定は、force plate上の2本の平行線（各年齢における身長の標準値の3分の1に設定）をできる限り素早く左右に交互に跳躍させた。side jump中の動作は、被験者の合成重心の算定が可能なように各関節にマークを貼付し、被験者の正面から毎秒60コマのビデオカメラで録画した。なお、本実験における重心の比較は、加齢に伴う影響を消去するために着床時の重心最低位置と離床時の重心最高位置については単位身長あたりの値に、重心の移動距離・鉛直変位・水平変位についてはライン幅あたりの値に換算して処理した。本研究における重心移動距離は、9歳頃まで加齢に伴い有意に減少した。着床時における重心の最低位置は、9歳頃までに加齢に伴い有意に増加し、離床時における重心の最高位置は、9歳頃まで加齢に伴い有意に減少した。鉛直変位と水平変位は、ともに9歳頃まで加齢に伴い有意に減少する傾向を示した。重心まわりの脚角速度は、加齢に伴い有意に増加した。また、本研究における形態・瞬発力は、各年齢においてF群とS群との間にほとんど有意な差は認められなかった。しかし、各年齢におけるF群の重心は、S群に比較して、移動距離が減少し、着床時の最低位置が高く、離床時の最高位置が低く、鉛直変位と水平変位が小さく、脚角速度が大きい値を示した。これらのことから、全身急速反復動作の発達は、着床時における重心を高く、離床時に低くすることによる鉛直変位の減少と、重心まわりの脚角速度の増大に伴う水平変位の減少によって向上し、このような動作を制御する脳幹小脳系の働きが全身急速反復動作の発達に深く関与していることを示唆している。