Accuracy of Individuals Post-hemiparetic Stroke in Matching Torques Between Arms Depends on the Arm Referenced

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.

Individuals With Hemiparetic Stroke Accurately Match Torques They Generate About Each Elbow Joint

“…In our study, participants with stroke had varying degrees of hemiparesis, represented by the strength asymmetry index ranging from 0.18 to 1.25. Nonetheless, our participants with hemiparetic stroke, when matching torques within a single arm, had magnitudes of errors considerably less than those in our group's previous studies in which individuals with stroke were requested to match torques between arms (e.g., van der Helm et al, 2017; Gurari et al, 2019). For comparison, in this study, when matching a fixed torque of 5 Nm within a single arm, torque-matching errors reached upwards of 7.9 Nm at the paretic arm of our participants with stroke and 6.8 Nm at the dominant arm of controls.…”

“…The methods presented here were designed to resemble the methods used in our assessment of torque perception during a between-arms task so that we could interpret our results in light of those findings (van der Helm et al, 2017; Gurari et al, 2019). As such, we refer the reader to these previous publications for further information relevant to the design of this study.…”

“…Previous research, using between-arms protocols, suggests that individuals with hemiparetic stroke perceive a reference torque about their elbow based mainly on the effort required to produce the torque (Bertrand et al, 2004; Mercier et al, 2004; Lodha et al, 2012; Yen and Li, 2015; van der Helm et al, 2017). Our earlier work revealed errors in matching torques between arms to the extent that an individual with hemiparetic stroke perceived their self-generated torque at their paretic arm as being seven times greater than at their non-paretic arm (Gurari et al, 2019). The deficit observed in a between-arms task could arise due to deficits within the paretic arm itself.…”

Accuracy of older adults in judging self-generated elbow torques during multi-joint isometric tasks

“…Furthermore, future work aims to address how accurately individuals with hemiparetic stroke perceive their self-generated torques during a multi-DOF, multi-joint isometric task. Current literature indicates that individuals with hemiparetic stroke have altered accuracy in estimating forces generated 5,[51][52][53] and are challenged with controlling independent joint movements due to abnormal muscle coactivation patterns in the paretic upper limb [54][55][56][57][58] . Therefore, future work will address the effect of changes in motor commands on the accuracy of judging self-generated torques during a multi-DOF, multi-joint task in individuals post-hemiparetic stroke.…”

“…Activities of daily living often require coordinated production of torques in multiple degrees-of-freedom (DOFs) across multiple joints at the upper-extremity. Even so, our understanding of how torques are perceived is largely limited to tasks requiring activation about one joint in a single DOF, or at the fingers 2 – 5 . As such, there is a need to understand an individual’s perception of torques during tasks that are more complicated and generalizable to the real-world.…”