跑步时，人体的动力是靠两腿的后蹬来提供的。根据物理学中力的分解来分析后蹬动作时，就可以把支撑反作用力分解为垂直分力与水平分力两个力，其中的水平分力是动力，是推动人前进的。只有当水平分力的方向与跑动方向一致时，水平分力才能够全面用于推进人体向前运动。如果水? When running, the body’s power is provided by the rear legs of the legs. According to the decomposition of force in physics to analyze the pedaling action, the supportive reaction force can be decomposed into two forces of vertical component force and horizontal component force. The horizontal component force is the motivation to promote people to move forward. Only when the horizontal component of the direction of the same direction and running, the horizontal component can be fully used to promote the human body to move forward. If water?