Objective: lt is well known in judo that a player becomes immobile when he/she is leaning. The purpose of this study was to clarify the relationship between the inclination of the body and strength exertions. Methods: Subjects were seven university students. COP (center of pressure) and push and pull strengths were measured. The COP is a projection of the COM (center of mass) obtained from three-dimensional motion analysis onto the floor. Push and pull strengths were measured by a dynamometer using the Ioad cell (1kN). Subjects were conducted in both natural and defense postures. We analyzed the relationship between the COP and push or pull strength, and the difference between the two different postures. Results and Discussion: 1. The push strength tended to become weaker as the COP approached the heel line. On the contrary, The pull strength gradually weakened as the COP approached the toe line. These trends were similar in the natural and defense postures. Strength exertion associated with body collapse was identified. The most likely explanation is that one cannot exert strength if exerting more strength would cause one's own body to collapse and fall over. For example, when the body is leaning backward, one cannot push because if one pushes, one's own body will fall over. 2. The push and pull strengths of the defense posture are exerted stronger than the natural posture. Compared to the natural posture, the defense posture had a Iower center of mass and a wider stance, thus it had a higher degree of stability. Therefore, it is clear that the defense posture is exerted more strongly than the natural posture.
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