The purpose of the present study was to investigate the impact force between athletes in the initial phase of Sumo wrestling. The selected six trials in Fifth Sumo World Championships (Amateur) 1997 were filmed from a side view by digital video camera (60 fps). Body mass of the athletes (n=12) ranged from 82 kg to 230 kg. The horizontal velocities of body's center of gravity (CG) were analyzed for 1 s before and after impact. The horizontal velocity of CG just prior to impact ranged from 0.36 to 0.87 m/s. Momentum P (P=mv, m: body mass, v: horizontal velocity of CG), and external force F (F=dP/dt) were determined. The external force F after impact included ground reaction force and force from the opposing athlete. The maximum impact force was 577 N. A more detailed study should include the ground reaction force and a three dimensional analysis.
