BUOYANCY: THE PRIMARY SOURCE OF BODYROLL

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The purpose of the study was to determine the rotational effect of buoyant force (buoyant torque) and its contribution to the bodyroll exhibited during front crawl swimming performed at a distance pace. Three-dimensional videography was used to measure the position and orientation of the body segments of eleven competitive swimmers performing at a distance pace. The buoyant torque was computed with the method described by Yanai (1999). The bodyroll generated by the buoyancy torque was determined from the double time-integral of the buoyancy torque and the principal moment of inertia of the body. The buoyancy torque changed in the mean range from –7.7 Nm to 7.7 Nm with a systematic pattern at stroke frequency. The buoyant torque generated the bodyroll of the peak-to-peak amplitude 1.26 radians, accounting for 88 % of the peak-to-peak amplitude (mean = 1.43 radians) of the bodyroll exhibited by the swimmers.