StartReact increases the probability of muscle activity and distance in severe/moderate stroke survivors during two-dimensional reaching task

StartReact elicits faster, larger, and more appropriate muscle activation in stroke survivors but has been only cursorily studied to date during multi-jointed reaching. Our objective was to evaluate StartReact on unrestricted, two-dimensional point-to-point reaching tasks post-stroke. Data from 23 individuals with stroke were collected during point-to-point reaching. Voluntary and StartReact trials were compared between mild, severe/moderate, and the unimpaired arm. StartReact showed an increase in probability of muscle activity, larger muscle activity amplitude, and faster muscle activity onset. Despite changes in muscle activity, metrics of movement (distance, final error, linear deviation) were not different between StartReact and Voluntary trials except in severe/moderate stroke who had larger reaching distances during StartReact. While StartReact impacted many metrics of muscle activity, the most profound effect was on the probability of muscle activity increasing 34% compared to voluntary which allowed severe/moderate subjects to increase reaching distance but did not translate to decrease in final error suggesting that the additional movement was not always directed towards the appropriate target. These results indicate that SR has the capacity to activate paralyzed muscle in severe/moderate patients, but future studies are needed to explore the possible use of SR in the rehabilitation.