The present study was conducted to determine the contribution of the turning effect of buoyant force for generating bodyroll and its relationship with the subjects' variability in swimming speed at distance pace and sub-maximal sprinting pace. The performances of front crawl swimming performed by 11 skilled swimmers were recorded with two panning periscopes for three-dimensional analysis. The bodyroll (BR) exhibited by each of the 11 male competitive swimmers was determined for every given instant as the time-integral of the conceptual angular velocity of the entire body about the long-axis, which was computed from the angular momentum and the moment of inertia of entire body. The part of BR generated by the buoyancy torque (BR BT) was determined from the moment of inertia of the entire body and the double time-integral of the buoyancy torque. The mean value for the peak-to-peak amplitude of the buoyancy torque was 15Nm at distance pace and 19Nm at sub-maximum sprinting speed. The contribution of buoyancy to BR was significantly greater (p<0.01) than that of the hydrodynamic forces. The individual swimming speed at sub-maximal sprinting pace was positively correlated (p<0.04) with the contribution of buoyancy to BR. These results showed that the skilled swimmers used buoyant force as the primary source of generating BR, and that faster swimmers used buoyant force more effectively to generate BR than slower swimmers. Based on the results and subsequent theoretical analysis, possible patterns of arm-BR coordination that may increase the effectiveness of using buoyant force for BR are discussed.
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