The purpose of this study was to determine the effects of thrower-discus system rotation on performance in discus throwing. The resultant angular momentum of the thrower-discus system and direction cosines of the angular momentum vector were calculated from kinematic data at five critical instants of discus throwing for 28 female and 15 male elite discus throwers, and compared between their long and short trials in actual competition. Compared to short trials, elite female throwers long trials had significantly less angular momentum at right foot takeoff and left foot takeoff (P=0.023), and significantly less top-to-left rotation at right foot takeoff, left foot takeoff, left foot touchdown, and release (P=0.007), and significantly greater right-to-left rotation at left foot touchdown and release (P=0.009) in long trials. Compared to their short trials, elite male throwers had significantly less top-to-left and top-to-front rotations at left foot touchdown (P=0.042), and significantly less total angular momentum at release (P=0.043) in long trials. Elite discus throwers should control the amount of rotations of the thrower-discus system to reduce the top-to-left roll of the discus during the flight to extend the aerodynamic distance.
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