Flutter Kicks Provide Propulsion and Postural Stability Through Vertical Vortices

A research team from Meiji University, the University of Tsukuba, and Niigata University of Health and Welfare has scientifically visualized the mechanism of the flutter kick in freestyle swimming. Using Particle Image Velocimetry (PIV) and motion capture, researchers demonstrated that flutter kicks generate three-dimensional vortices that provide propulsion. Unlike the dolphin kick, flutter kicks create asymmetrical vortices and a strong downward flow that lifts the body and counteracts rolling and yawing motions caused by arm strokes, effectively stabilizing the swimmer's posture. This study offers a scientific foundation for improving swimming techniques and coaching methods.