Choice of Arm Use in Stroke Survivors is Largely Driven by the Energetic Cost of the Movement

Abstract

Background. The decision of which arm to use to achieve a goal depends on energetic costs and performance abilities of each arm. Following a stroke, there is a reduction in the use of the more-impaired arm. Is it because the energetic costs of the more-impaired arm are increased, or because its use dictates a lower chance of success? Objective. We sought to elucidate the impact of energetic cost and task success on the arm choice of stroke survivors. Methods. Thirteen chronic stroke survivors and thirteen neurologically-intact subjects participated in an experiment where they reached towards visual targets in a virtual-reality environment. Energetic cost of reaching with their less-used arm (nondominant/more-impaired) was adjusted by amplifying the range of motion, while task accuracy requirement was independently modulated by changing target size. Results. Reducing the energic cost of reaching increased the use of the less-used arms in both groups, but by a greater amount in the stroke survivors. In contrast, lowering task accuracy requirement altered arm choice similarly in the two groups. The time spent in decision-making (reaction time) reflected different impacts of energetic cost and task success on the arm choice of the two groups. Conversely, velocity changes were similar between the groups. Conclusions. The impact of energetic cost on arm choice of stroke survivors is greater than neurologically-intact subjects. Thus, the reduction in the use of the impaired arm following stroke may be primarily due to a subjective increase in the effort it takes to use that arm.