Effects of Movement Context on Reach-Grasp-Lift Motion and Grip Force after Stroke

Loss of upper extremity function after stroke is a significant problem resulting in enormous personal, societal, and economic costs. Neurophysiological discoveries over several decades have revealed great potential for use-dependent neural adaptation, and have revitalized the search for training strategies that optimize recovery. Although task-specific repetitive practice is recognized as a key stimulus to promote upper extremity function after stroke, choices of what to practice and how to practice remain challenging and poorly guided by evidence. This research was inspired by evidence in healthy individuals, that movement can be altered by characteristics of the task and the environment, together referred to as the movement context. The purpose of this research was to determine whether motor performance of the paretic upper extremity is affected by two specific movement context variations: 1) preferred speed versus fast, and 2) unilateral versus bilateral. Using electromagnetic motion tracking and pressure sensor quantification of grip force, we assessed upper extremity task performance in people with post-stroke hemiparesis. To evaluate effects of movement speed, we compared paretic-limb performance of a reach-grasp-lift task at a self-selected preferred speed to the same task performed as fast as possible. People with hemiparesis were able to move faster than their preferred speed, and when they did, movement quality was better. Reach paths were straighter, finger movements were more efficient, and the fingers opened wider. To evaluate effects of the bilateral movement context, we compared paretic-limb performance of a reach-grasp-lift-release task unilaterally versus bilaterally. We found no immediate improvement in the bilateral context. We further explored effects of the bilateral movement context by measuring maximal and submaximal grip force capacity using grip dynamometers. Unlike healthy controls and unlike the non-paretic side, the paretic side of people with hemiparesis produced more maximal force in the bilateral condition. In a submaximal task, however, the bilateral condition did not enhance the paretic side\u27s contribution. These results suggest that emphasizing speed during post-stroke rehabilitation may be worthwhile, that the bilateral movement context has little immediate impact on task performance, and that the paretic limb may benefit from the bilateral condition only at high force levels