Adaptive treadmill control can be manipulated to increase propulsive impulse while maintaining walking speed

Adaptive treadmills (ATM) designed to promote increased propulsion may be an effective tool for gait training since propulsion is often impaired post-stroke. Our lab developed a novel ATM controller that adjusts belt speed via real-time changes in step length, propulsive impulse, and position. This study modified the relative importance of propulsion to step length in the controller to determine the effect of increased propulsive feedback gain on measures of propulsion and walking speed. Twenty-two participants completed five trials at their self-selected speed, each with a unique ATM controller. Walking speed, peak AGRF and PGRF, and AGRF, PGRF, and net impulse were compared between the modifications using one-way repeated measures ANOVAs at a significance level of 0.05. Participants chose similar walking speeds across all conditions (all p > 0.2730). There were no significant differences in peak AGRF (p = 0.1956) or PGRF (p = 0.5159) between conditions. AGRF impulse significantly increased as the gain on the propulsive impulse term was increased relative to the gain on step length (p < 0.0001) while PGRF and net impulse were similar across all conditions (p = 0.5487). Increasing the propulsive impulse gain essentially alters the treadmill environment by providing a controlled amount of resistance to increases in propulsive forces. Our findings demonstrate that the ATM can be modified to promote increased propulsive impulse while maintaining a consistent walking speed. Since increasing propulsion is a common goal of post-stroke gait training, these ATM modifications may improve the efficacy of the ATM for gait rehabilitation.

Adaptive treadmill walking encourages persistent propulsion

BACKGROUND

Adaptive treadmills allow real-time changes in walking speed by responding to changes in step length, propulsion, or position on the treadmill. The stride-to-stride variability, or persistence, of stride time during overground, fixed-speed, and adaptive treadmill walking has been studied, but persistence of propulsion during adaptive treadmill walking remains unknown. Because increased propulsion is often a goal of post-stroke rehabilitation, knowledge of the stride-to-stride variability may aid rehabilitation protocol design.

RESEARCH QUESTION

How do spatiotemporal and propulsive gait variables vary from stride to stride during adaptive treadmill walking, and how do they compare to fixed-speed treadmill walking?

METHODS

Eighteen young healthy subjects walked on an instrumented split-belt treadmill in the adaptive and fixed-speed modes for 10 minutes at their comfortable speed. Kinetic data was collected from the treadmill. Detrended fluctuation analysis was applied to the time series data. Shapiro-Wilk tests assessed normality and one-way repeated measures ANOVAs compared between adaptive, fixed-speed, and randomly shuffled conditions at a Bonferroni-corrected significance level of 0.0055.

RESULTS

Stride time, stride length, step length, and braking impulse were persistent (α > 0.5) in the adaptive and fixed-speed conditions. Adaptive and fixed-speed were different from each other. Stride speed was persistent in the adaptive condition and anti-persistent (α < 0.5) in the fixed-speed condition. Peak propulsive force, peak braking force, and propulsive impulse were persistent in the adaptive condition but not the fixed-speed condition (α ≈ 0.5). Net impulse was non-persistent in the adaptive and fixed-speed conditions. All variables were non-persistent in the shuffled condition.

SIGNIFICANCE

During adaptive treadmill walking, increases in propulsive force and impulse persist for multiple strides. Persistence was stronger on the adaptive treadmill, where increased propulsion translates into increased walking speed. For post-stroke gait rehabilitation where increasing propulsion and speed are goals, the stronger persistence of adaptive treadmill walking may be beneficial.