Spring-Like Properties of Muscles and Reflexes in Running

The idea that running is essentially bouncing may be an ancient one, but the first good quantitative evidence for it was presented by Cavagna et al. (1976). Force-plate measurements of steady- speed human walking and running were used to calculate fluctuations of the kinetic energy and the gravitational potential energy of the body’s center of mass. In walking, the calculations showed that changes in forward kinetic energy were out of phase with changes in gravitational potential energy, so that the total mechanical energy of the center of mass was nearly steady throughout a walking step. In running, the kinetic and gravitational energy fluctuations were found to be in phase, so that large changes in the sum of the two took place during a step. A simple way to put this is to say that in walking, the body is highest at the moment the forward kinetic is least, in mid-step (when the hips pass over the ankles). In running, as may be seen in the strobe photograph in Figure 37.1, the body is lowest in mid-step, when the forward kinetic energy is least.