7. Walking

This chapter describes the basic mechanism of walking in adult humans, in children during growth and in some animal species. This is done by measuring the changes in kinetic energy of forward motion and gravitational potential energy of the center of mass of the body during the step. These changes are in opposition of phase as in a pendulum with the result that the changes in the total mechanical energy of the center of mass, kinetic plus potential, and as a consequence the external work done to maintain locomotion, is conveniently reduced. The potential-kinetic energy exchange by this pendular mechanism is quantitatively measured (recovery) and found to attain a maximum at an ‘optimal’ walking speed similar to the speed where the external work per unit distance is at a minimum in humans, turkeys, rams, rhea and elephants. This ‘optimal’ speed is also similar to the speed where the metabolic energy expenditure was found to be at a minimum in adult humans; in children, it increases with age and equals the freely chosen walking speed; in parabolic flight maneuvers it increases with gravity. The recovery, measured at each instant within the step, is greater in load-carrying African women than in control subjects explaining their greater economy in carrying loads. The step frequency where the total, external plus internal, work is at a minimum is found to be related to the freely chosen step frequency. The mechanics of competition walking is analyzed and a method is shown evidencing anomalies of pathological gait.