In this study it was hypothesized that elite butterfly performance is
characterized by wave motions with particular frequency, amplitude, an
d 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 ma
les and eight elite female swimmers were quantified. Fourier analysis
was conducted to determine the frequency, amplitude, and phase charact
eristics of the vertical undulations of the vertex of the head, should
ers, hips, knees, and ankles, The differences in phase between these l
andmarks for the first (H1) and second (H2) Fourier frequencies were i
nvestigated to establish whether waves travelled along the body in a c
audal 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) fas
ter for the female swimmers. There was a very strong relationship (p <
0.01) between velocity of H1 wave travel and CM velocity. There was n
o evidence to suggest that elite swimmers timed their actions to minim
ise vertical CM displacement to reduce mechanical work. In fact, the p
hase relationships among adjacent segments suggested that energy gaine
d by raising the CM was transmitted caudally and contributed to a prop
ulsive 'whip-like' action.