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

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.