Step-to-step transition cost during gait increases with age in a healthy population

1. Introduction
Muscle strength declines with age and this is accompanied by changes in gait mechanics. A typical change that has been observed is the distal to proximal redistribution of joint work, from a dominancy of ankle work to hip joint work [1]. This redistribution might result in an increase in the external work performed on the center of mass (CoM) for the step-to-step transition in walking and concomitant increase in energy cost of walking [2].

2. Research question
In this study we investigated the changes in external mechanical work during step-to-step transition and single support of walking over the lifespan. It was hypothesized that, as a result from the distal-to-proximal redistribution of joint work, push off work in the trailing leg work would decrease and leading leg collision work during the step-to-step transition would increase with age, while single support work would increase with age.

3. Methods
Seventy-four healthy adults, uniformly distributed over the age range between 18 and 79 yr, walked on a dual belt instrumented treadmill with a split belt protocol of which the two tight belt baseline speeds (0.7 and 1.4 m/s) were analyzed for the purpose of this study. External mechanical work on the CoM was calculated separately for the single support (SS) and step-to-step (S2S) transition phases [3]. Linear regression analyses were performed to investigate the effect of age on external mechanical work during step-to-step and single support phases.

4. Results
Positive push off work during step-to-step transition decreased with age (1.4 m s−1: −0.102 J/year p = .05, .7 m s−1 -0.088 J/year p = .007), while negative collision work increased with age (1.4 m s−1: −0.191 J/year p < .001, .7 m s−1: −0.052 J/year p = .007). Concurrently, single support work increased with age (1.4 m s−1: +0.286 J/year p ​< ​.001, .7 m ​s−1: +0.113 J/year p ​= ​.007)