The Role of Stability and Metabolic Cost in Gait Adaptation

Abstract

The purpose of this dissertation was to identify the role and importance of mediolateral stability and energetic cost in continuous gait adaptation and to distinguish the differential roles of metabolic and mechanical costs during gait adaptation. In Aim 1, an exploratory investigation of the rates of adaptation of step lengths, the mediolateral margin of stability, mechanical work rates, and metabolic rate was conducted. Seventeen neurotypical younger adults walked for 20 minutes on a split-belt treadmill with the belts moving at 1.5 and 0.5 m/s (a 3:1 speed ratio). Mediolateral stability adapted within the first minute of gait adaptation, while metabolic rate and mechanical work rate by the legs adapted more gradually. This difference in adaptation rates supports the hypothesis that optimizing stability occurs first, and optimizing energetic cost occurs later during gait adaptation. In Aim 2, the metabolic cost of walking was experimentally manipulated by having participants adapt their gait while walking downhill. Sixteen neurotypical younger adults adapted their gait over 20 minutes while walking level (0-degree grade) and over 20 minutes while walking downhill (4-degree grade). We evaluated the effect of reduced metabolic cost on the timescales of adaptation of mediolateral stability, metabolic rate, mechanical work rate, and step length during continuous gait adaptation. During downhill gait adaptation, neurotypical younger adults had a lower metabolic rate and took less advantage of the external work provided by the treadmill. They also did not adapt step lengths to the same extent. The reduced metabolic demand of walking downhill, leading to lower metabolic rates during downhill adaptation, may have reduced the need to adjust gait behavior and take advantage of the external work. This suggests that metabolic rate is a primary driving mechanism during gait adaptation and that people will alter gait behavior until they reach a “good enough” optimum between a low metabolic rate and a familiar movement pattern. Future work should determine whether the roles of mediolateral stability and energetic cost are similar in clinical populations as in young adults. Understanding the roles of mediolateral stability and energetic cost in clinical populations and how they may differ from a neurotypical young population will help to inform gait rehabilitation.