Trajectories of Leg Strength and Gait Speed among Sedentary Older Adults: Longitudinal Pattern of Dose Response

Abstract

Background. Current theory about how an older adult's leg strength influences walking speed is based primarily on nonlinear patterns of association observed in cross-sectional data. Compared with adults with normal or high levels of leg muscle strength, weak older adults are thought to have a greater capacity for functional change in response to changes in lower extremity strength. Longitudinal data, however, have not been applied to study this putative pattern of dose response. Methods. Three repeated measures of leg strength, gait speed, and covariates were evaluated in a cohort of 134 sedentary, community-dwelling male and female participants (aged >64 years) of a randomized exercise intervention. Empirical Bayes methods were used to evaluate the association between trajectories of strength and gait speed during the course of the study. Results. We observed a potentially clinically important, positive linear association between strength change and gait speed change. Each additional unit increase in the monthly rate of strength change increased the rate of gait speed change by 0.29 meters/minute/month (95% CI [confidence interval] = 0.03, 0.55 m/min/mo). Absolute change in walking velocity due to strength changes in the cohort ranged from a gain of approximately 15 m/min to a loss of approximately 13 m/min over the 9-month period (changes of -18% to +20% relative to a normal walking speed of 72 m/min). Conclusions. In this cohort, change in functional walking speed depended more on the rate of strength change observed than on the amount of muscle weakness present at baseline. These results have important implications for screening and intervention programs designed to change functional walking ability among sedentary older adults.