This study aimed to clarify how pivot leg kinetics influence body rotation during the osoto-gari throw by comparing black- and white-belt judokas. Twenty male judokas (10 black and 10 white belts) performed osoto-gari. Three-dimensional coordinate data were acquired using a Mac3D motion analysis system (250 Hz), and the ground reaction force (GRF) of the pivot leg was measured using a force plate (1,000 Hz). During the throwing phase, the angular impulse of the tori was greater in black belts than in white belts (p = 0.043). Black belts exhibited a significantly higher external moment generated from the pivot leg`s GRF between 50% and 65% of the throwing motion (p < 0.001). Additionally, the upward GRF, ankle plantar flexion moment, and ankle positive power of the pivot leg were significantly greater in the black belts during 60-84%, 56-88%, and 59-64% of the throwing motion. These findings highlight the critical role of the ankle plantar flexor force in modulating external moment and enhancing whole-body rotation, which is essential for the effective execution of the osoto-gari throw.
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