On Running (Michaud)

It turns out that moderately flattening our center of mass allows us to maximize efficiency while walking and running. The catch is that the precise movement patterns we need to incorporate in order to adjust the pathway of our center of mass so that we are maximally efficient change depending upon whether we are walking or running. At slower speeds we are most efficient when our legs are stiff and inflexible but at higher speeds we must increase the degree of knee and hip flexion in order to improve shock absorption. These findings correlate with the clinical observation that walking feels more comfortable when moving slowly, while running is more comfortable as speeds increase.

Michaud, Dr. Thomas C. (2014-03-27). Injury-Free Running: How to Build Strength, Improve Form, and Treat/Prevent Injuries (Kindle Locations 557-561). Newton Biomechanics. Kindle Edition.