Al~tract--In this study it was hypothesized that elite butterfly performance is characterized by wave
motions with particular frequency, amplitude, and phase characteristics. Particular emphasis was accorded
the question of whether 'waves' travel along the body during the butterfly stroke. Selected body landmarks
and the center of mass (CM) of eight elite males and eight elite female swimmers were quantified. Fourier
analysis was conducted to determine the frequency, amplitude, and phase characteristics of the vertical
undulations of the vertex of the head, shoulders, hips, knees, and ankles. The differences in phase between
these landmarks for the first (HI) and second (H2) Fourier frequencies were investigated to establish
whether waves travelled along the body in a caudal direction. The absolute average velocity of H1 wave
travel from vertex to ankle was found to be a mean of 0.34 m s- 1 faster than the forward velocity of the CM
for the male swimmers and 0.17 m s- 1 faster for the female swimmers. There was a very strong relationship
(p < 0.01) between velocity of HI wave travel and CM velocity. There was no evidence to suggest that elite
swimmers timed their actions to minimise vertical CM displacement to reduce mechanical work. In fact, the
phase relationships among adjacent segments suggested that energy gained by raising the CM was
transmitted caudally and contributed to a propulsive 'whip-like' action.