Effects of Belt Accelerations During Push-Off on Propulsion Mechanics in Individuals Post-Stroke.

Stroke often causes hemiparesis, affecting balance and walking ability. Propulsion, a major subtask of walking, has two components: trailing limb posture and propulsive force generated by plantarflexor muscles. Our group previously developed a method to challenge propulsion by accelerating the belt supporting the trailing limb during push off. In this study, we test the efficacy of a similar paradigm in 34 post-stroke individuals, and compare the effects of posterior belt accelerations applied to both legs (symmetric condition), and only to the paretic leg (asymmetric condition). We hypothesized that the two conditions would elicit changes in propulsion mechanics during and after exposure. Results indicate that belt accelerations induced measurable effects in paretic propulsion mechanics during exposure, and some of these effects persisted over a 1-3 minute post-exposure session conducted at self-selected speed. Specifically, by the end of the exposure session, participants increased their paretic TLA by $7.2~\pm~0.9$ %, and their plantarflexor muscle activation by $6.6 \pm 2.2$ % in the soleus and $7.8~\pm~2.3$ % in the lateral gastrocnemius, compared to their baseline. Changes in propulsion mechanics led to a small but statistically significant (0.024 m/s or $3.4 \pm 1.4$ %) post-exposure increase in self-selected walking speed. Effects were primarily induced on metrics of propulsion mechanics of the leg directly exposed to belt acceleration; therefore, differential effects as a function of acceleration condition were only observed for the non-paretic leg. A responder analysis indicated that individuals with greater impairment exhibited larger relative changes in plantarflexor muscle activation after exposure.