| Summary: | The kick-start is one of the commonly used block start techniques in competitive swimming. Since swimmers push off first with the rear leg and then with the front leg during the kick-start, leg extension timings relative to the rear leg push-off would affect horizontal take-off velocity. The purpose of this study was to investigate the effects of leg extension timings during kick-start on swimming start performance. Based on the empirically obtained human body kinematic data during kick-start, the whole body was modeled as nine rigid-body segments to simulate kick-start performance for five Japanese collegiate male swimmers. Front leg extension timing was adjusted by shifting the time-series data of the front foot segment, front lower segment and front thigh segment angles were shifted 0.01 to 0.04 sec (T-0.01 to T-0.04) earlier from the original data (T0). The kick-start motion was simulated using both forward and inverse kinematics under some simplifying assumptions with geometric constraints. As a result, the horizontal take-off velocity increased for three swimmers, whereas it decreased for the other two swimmers when front leg extension timing became earlier. The vertical take-off velocity and take-off angle increased as front leg extension timing became earlier. These results indicate that front leg extension timings would either positively or negatively affect horizontal take-off velocity depending on vertical take-off velocity. Therefore, for the swimmer take-off downward, earlier front leg extension timing would allow them to generate a greater horizontal take-off velocity on kick-start.
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