The Associations Between the Swimming Speed, Anthropometrics, Kinematics, and Kinetics in the Butterfly Stroke.

There is scarce information about what characterizes the swimming speed in the butterfly stroke and the role of thrust in its characterization and prediction. The aim of this study was to compare the fastest and poorest butterfly swimmers based on a set of anthropometric, kinematic, and kinetic variables and to identify the swimming speed predictors. Eight young male swimmers were divided into two equal groups (each group comprising four swimmers). The swimming speed, as well as a set of anthropometric, kinematic, and kinetic variables, were measured. The swimming speed presented significant differences between the groups (<i>p</i> = 0.011, <i>d</i> = 2.18). The stroke frequency (kinematics, <i>p</i> = 0.027, <i>d</i> = 1.69) and thrust (kinetics, <i>p</i> = 0.034, <i>d</i> = 1.57) also presented significant differences between the groups. The swimming speed presented significant correlations with the stroke index (<i>r_s</i> = 0.83, <i>p</i> = 0.011) and thrust (<i>r_s</i> = 0.83, <i>p</i> = 0.011). The swimming speed was predicted by a combination of the stroke frequency and thrust (R² = 0.84, <i>p</i> = 0.010). Coaches and athletes must be aware that combining fast stroke frequencies and the generation of greater thrust leads to the fastest swimming speeds.