NEURAL MECHANISMS CONTRIBUTE TO THE AGE RELATED INCREASE IN METABOLIC COST OF GAIT

Abstract

Aging is associated with biomechanical and physiological changes in several organ systems, including neural changes of voluntary movement. One manifestation of age-related changes in neural control of gait is the increased activation of muscles that are antagonist to the prim movers during the stance phase of gait. Another age-related adaptation is the increased metabolic cost of locomotion. Several studies have attempted to link gait mechanics to the increased cost of transport, but none of the mechanical gait variables accounted for the age-related increase in oxygen uptake. Here we hypothesized that the related increase in metabolic cost during gait is mediated by increased antagonist muscle coactivation. EMG and oxygen consumption data were collected during treadmill walking to determine the levels of antagonist muscle coactivation and metabolic cost. The data revealed that old subjects experienced significantly greater levels of both coactivation and metabolic cost. Old subjects had 4-17% greater levels of metabolic cost of gait than young subjects, and 53-61% greater levels of total antagonist muscle coactivation than young subjects. Regression analyses showed that there was a strong association between the level of antagonist muscle coactivation and metabolic cost of gait, suggesting that neural factors contribute to the age-related metabolic adaptations in gait.