Force acquisition frequency is less impaired compared to grip strength or hand dexterity in individuals with chronic stroke.

Abstract

Despite numerous studies that show force regulation is impaired after stroke, two recent studies suggest that the ability to regulate submaximal, isometric grip forces may remain substantially intact. Here we asked how this aspect of hand motor control, measured for both a power grip and pinch grip, compares to two other key aspects of hand function-grip strength and dexterity. For 20 individuals with a range of hand impairment levels in the chronic phase of stroke (Age: 62 ± 16.0years, Time post stroke: 958.3 ± 966.5days, Sex: 19M 1F) we quantified the average rate of target acquisition for force targets in the range of 3 to 30% maximum voluntary contraction as participants used the two different grips to squeeze a force sensor to control a cursor on a screen. The same force sensor was used to assess subject grip strength for the two grips, while dexterity was assessed using the Box and Blocks Test (BBT), and the Nine Hole Peg Test (NHPT) for both the paretic and non-paretic hand. On average, the relative rate of force acquisition of the paretic hand using a power grip was 74.0 ± 18.6 SD % of the non-paretic hand, a value significantly higher than the 48.6 ± 25.6 SD% for grip strength (paired t test, p < .005) or the 41.4 ± 29.1 SD % (p < .005) and 23.3 ± 30.1 SD % (p < .005) for the BBT and NHPT, respectively. Results were similar for the lateral pinch grip, suggesting similar thumb force tracking performance. Grip force tracking, measured as rate of force acquisition, is less impaired after stroke than hand strength or dexterity, a finding with implications for the neural mechanisms of stroke and the design of assistive technologies.