Rising energetic cost of walking predicts gait speed decline with aging

Background: Slow gait is a robust biomarker of health and a predictor of functional decline and death in older adults, yet factors contributing to the decline in gait speed with aging are not well understood. Previous research suggests that the energetic cost of walking at preferred speed is inversely associated with gait speed, but whether individuals with a rising energetic cost of walking experience a steeper rate of gait speed decline has not been investigated. Methods: In participants of the Baltimore Longitudinal Study of Aging, the energetic cost of overground walking at preferred speed (mL/kg/m) was assessed between 2007 and 2014 using a portable indirect calorimeter. The longitudinal association between the energetic cost of walking and usual gait speed over 6 meters (m/s) was assessed with multivariate linear regression models, and the risk of slow gait (<1.0 m/s) was analyzed using Cox proportional hazards models. Results: The study population consisted of 457 participants aged 40 and older who contributed 1, 121 person-visits to the analysis. In fully adjusted models, increases in the energetic cost of walking predicted the rate of gait speed decline in those older than 65 years (β=-0.008 m/s, p <.001). Moreover, those with a higher energetic cost of walking (>0.17 mL/kg/m) had a 57%greater risk of developing slow gait compared with a normal energetic cost of walking (≤0.17 mL/kg/m; adjusted hazard ratio=1.57, 95%confidence interval: 1.01-2.46). Conclusions: These findings suggest that strategies to maintain walking efficiency hold significant implications for maintaining mobility in late life. Efforts to curb threats to walking efficiency should focus on therapies to treat gait and balance impairments, and reduce clinical disease burden.