Abstract: The purpose of the present study was to utilise a spring-mass model to (1) continuously measure vertical stiffness (Kvert) and leg stiffness (Kleg) over an entire 400m sprint, and (2) investigate the relationship between leg spring stiffness (Kvert and Kvert) and the performance characteristics of mean forward running velocity (Vforwad), mean stride frequency (fstride), and mean stride length (Lstride). Eight well-trained male athletes performed a 400m sprint with maximal effort on an...