Abstract
Background: Prior work indicates that 50–75% of individuals post-hemiparetic stroke have upper-extremity weakness and, in turn, inaccurately judge the relative torques that their arms generate during a bimanual task. Recent findings also reveal that these individuals judge the relative torques their arms generate differently depending on whether they reference their paretic vs. non-paretic arm.Objective: Our goal was to determine whether individuals with hemiparetic stroke inaccurately matched torques between arms, regardless of the arm that they referenced.Methods: Fifteen participants with hemiparetic stroke and 10 right-hand dominant controls matched torques between arms. Participants performed this task with their right arm referencing their left arm, and vice versa. Participants generated (1) 5 Nm and (2) 25% of their reference elbow's maximum voluntary torque (MVT) in flexion and extension using their reference arm while receiving audiovisual feedback. Then, participants matched the reference torque using their opposite arm without receiving feedback on their matching performance.Results: Participants with stroke had greater magnitudes of error in matching torques than controls when referencing their paretic arm (p < 0.050), yet not when referencing their non-paretic arm (p > 0.050). The mean magnitude of error when participants with stroke referenced their paretic and non-paretic arm and controls referenced their dominant and non-dominant arm to generate 5 Nm in flexion was 9.4, 2.6, 4.2, and 2.5 Nm, respectively, and in extension was 5.3, 2.8, 2.5, and 2.3 Nm, respectively. However, when the torques generated at each arm were normalized by the corresponding MVT, no differences were found in matching errors regardless of the arm participants referenced (p > 0.050).Conclusions: Results demonstrate the importance of the arm referenced, i.e., paretic vs. non-paretic, on how accurately individuals post-hemiparetic stroke judge their torques during a bimanual task. Results also indicate that individuals with hemiparetic stroke judge torques primarily based on their perceived effort. Finally, findings support the notion that training individuals post-hemiparetic stroke to accurately perceive their self-generated torques, with a focus of their non-paretic arm in relation to their paretic arm, may lead to an improved ability to perform bimanual activities of daily living.
Highlights
Judging the relative torques that one generates with their arm(s) can make it difficult to perform bimanual activities of daily living, such as carrying a tray, pushing a grocery cart, and caring for an infant [1, 2]
Data were collected from fifteen participants with hemiparetic stroke and ten participants without neurological impairments
The main findings of this work are that the participants with hemiparetic stroke: (i) had magnitudes of error similar to controls when referencing their non-paretic arm; (ii) had magnitudes of error greater than controls when referencing their paretic arm; and (iii) had similar results to controls, regardless of the arm referenced, when the torque that they generated at each arm was normalized by its corresponding maximum voluntary torque (MVT)
Summary
Judging the relative torques that one generates with their arm(s) can make it difficult to perform bimanual activities of daily living, such as carrying a tray, pushing a grocery cart, and caring for an infant [1, 2]. Based on findings from such assessments, the current understanding is that individuals perceive their self-generated torques by combining peripheral and central information [1, 15, 20,21,22,23,24,25,26]. Central information arises from an individual’s perceived effort, or the extent to which an individual perceives that their arm muscles are being driven in relation to the maximum. The general understanding is that: (i) perceived effort information generated in the cortex is weighed more heavily than sensory information arising from the periphery [2] and (ii) matching errors occur because individuals do not adapt their perceived effort at their affected limb to its weakened state. Prior work indicates that 50–75% of individuals post-hemiparetic stroke have upper-extremity weakness and, in turn, inaccurately judge the relative torques that their arms generate during a bimanual task. Recent findings reveal that these individuals judge the relative torques their arms generate differently depending on whether they reference their paretic vs. non-paretic arm
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