Flow fields around a swimmer are extremely unsteady. Top swimmers are expected to swim using effectively unsteady flow force. A motion analysis can evaluate the unsteady motion of swimmer quantitatively. In addition, PIV (Particle Image Velocimetry) can visualize the unsteady flow field. With this method, the vortex motion around a hand can be evaluated quantitatively. Our study is to clarify the relationship between the vortex behavior and the motion of a hand in crawl swimming by using the motion analysis combined with PIV. The analysis is made for two subjects ; one is a male with no competitive career and the other a female Olympic swimmer. It was found that the hand motion in swimming was closely related to the vortex generation.
