ENERGETIC COST AND STABILITY DURING HUMAN WALKING AT THE PREFERRED STRIDE FREQUENCY

The possibility that preferred modes of locomotion emerge from dynamic al and optimality constraints and the energetic and dynamical constrai nts on preferred and predicted walking frequency are explored in this article. Participants were required to walk on a treadmill at their pr eferred frequency, at a frequency predicted as the resonance of a hybr id pendulum-spring model of the legs, and at frequencies +/-15%, +/-25 %, +/-35% of the predicted frequency. Walking at the preferred and pre dicted frequencies resulted in minimal metabolic costs and maximal sta bility of the head and joint actions. Mechanical energy conservation w as constant across conditions. The head was more stable than the joint s. The joints appeared to be in service of the head in maintaining a s table trajectory. The major findings of this study suggest a complemen tary relationship between energetic (physiological) and stability cons traints in the adoption of a preferred frequency of walking. Multiple subsystems may be involved in constraining observed macroscopic behavi or in intact biological systems. The approach and results of the study imply that a useful tack in understanding how dynamical control struc tures arise is to study the potential criteria that serve to act as co nstraints on skilled movement patterns in unimpaired and impaired popu lations.