EVIDENCE OF ENERGY REUSE THROUGH BODY WAVE MOTION IN BUTTERFLY SWIMMING

In butterfly swimming the upper body is raised above the water during the stroke cycle. There is a possibility that oscillations of other body parts out of phase with the oscillations of the shoulders serves to minimise the centre of mass (CM) oscillation and thereby mechanical work. Another possibility is that energy accrued by raising the upper body is transmitted along the body in a caudal direction and contributes to forward propulsion. The purpose of this study was to investigate these possibilities. Digitised data from eight elite male and eight elite female butterfly and individual medley swimmers recorded simultaneously by two above water and two below water video cameras were made available by the International center for Aquatic Research. The vertical oscillations of the vertex, shoulders, hips, knees, ankles, and CM of each swimmer were analysed to determine the phase and amplitude of the first (H 1) and second (H2) Fourier frequencies. The vertical oscillation of the CM was substantial (approx. .08m from maximum to minimum) and there was no evidence to suggest that elite butterfly swimmers minimised the vertical oscillation of the CM by compensatory oscillations of body parts. There was no significant relationship between amplitude of CM oscillation and swimming speed. The HI oscillations had phase differences among body parts that indicated a consistent progression of a 'body wave' in a caudal direction. The average speed of this body wave was faster than the forward motion of the CM by an average of 34m.s-1 for the males and .17ms-1 for the females. The relationship between speed of the body wave and CM motion was significant (pc.01) for males (ra.88) and females (rm.96). The findings supported the possibility that energy accrued by raising the upper body was transmitted caudally and contributed to forward propulsion.