Post hemiparetic stroke an individual may face difficulty performing bimanual tasks due to an asymmetry in their arms' strengths. Here, we determined whether participants with a strength asymmetry were impaired bi-directionally when matching torques between arms (i.e., paretic arm matches non-paretic arm, non-paretic arm matches paretic arm). Six participants with chronic hemiparetic stroke and four participants without neurological impairments partook in this study. First, we identified the maximum voluntary torque that participants could generate about each elbow joint (τ). Then, we determined how accurately and precisely participants could match, bidirectionally, submaximal isometric flexion torques (0.25 · τ) between arms. Results demonstrate that task directionality impacted the ability of our participants with stroke who had a strength asymmetry to match torques between arms; specifically, participants were unimpaired matching to a referenced non-paretic arm yet impaired in the opposite direction. Additionally, results reveal that the degree to which participants overshot the target torque when matching with their non-paretic arm could be predicted based on their strength asymmetry (R = 0.67). We propose that individuals with stroke may avoid torque matching impairments during bimanual tasks by matching their paretic arm to their non-paretic arm.

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.