BUOYANCY: THE PRIMARY SOURCE OF BODYROLL IN FRONT CRAWL SWIMMING

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. KEY WORDS: angular velocity, buoyant force, 3D videography, principal axis, torque INTRODUCTION: In front crawl swimming, swimmer’s body rolls from one direction to the other about its long-axis. This rolling action of the body is called bodyroll. Whereas the functions of the bodyroll have been described frequently, the mechanical cause of th