Abstract
The purposes of the present study were (1) to investigate the relationship between posture and ground reaction force (GRF) produced by the joint torque, and (2) to clarify the posture used to orient the GRF forward during the first stance from a crouch start. Thirty-six male track and field athletes volunteered, and the participants sprinted 10 m from starting blocks. The GRFs of the leg in the first and second stance phases were determined using a force platform (1000 Hz). Simultaneously, three-dimensional coordinates were recorded with a motion analysis system (250 Hz) using 20 cameras (MX-T20). The support leg joint torque was calculated using inverse dynamics. On the basis of the collected data, sprint motions that changed the joint angle were created with kinematic simulation. In the simulated motion, the contribution of the GRF produced by the joint torque of the support leg was calculated by solving equations of motion for the whole body system. We investigated the relationship between posture and GRF produced by the joint torques. The main results were as follows: (1) The ankle joint plantar flexion torque of the support leg was the main generator of GRF. (2) When the shank of the support leg leaned forward, the propulsive force produced by the plantar flexion torque was bigger and the upward force was smaller.
A previous study has suggested that the GRF of a good sprinter is characterized by a forward-oriented GRF. The
present study clarified that a forward-oriented GRF is attained by forward leaning of the shank segment.
