Stroke impairs the control of isometric forces and muscle activations in the ipsilesional arm

Laura Pellegrino,Maura Casadio,Psiche Giannoni,Lucio Marinelli,Martina Coscia

doi:10.1038/s41598-021-96329-0

Abstract

Stroke often impairs the control of the contralesional arm, thus most survivors rely on the ipsilesional arm to perform daily living activities that require an efficient control of movements and forces. Whereas the ipsilesional arm is often called ‘unaffected’ or ‘unimpaired’, several studies suggested that during dynamic tasks its kinematics and joint torques are altered. Is stroke also affecting the ability of the ipsilesional arm to produce isometric force, as when pushing or pulling a handle? Here, we address this question by analyzing behavioral performance and muscles’ activity when subjects applied an isometric force of 10 N in eight coplanar directions. We found that stroke affected the ability to apply well-controlled isometric forces with the ipsilesional arm, although to a minor extent compared to the contralesional arm. The spinal maps, the analysis of single muscle activities and the organization of muscle synergies highlighted that this effect was mainly associated with abnormal activity of proximal muscles with respect to matched controls, especially when pushing or pulling in lateral directions.

Highlights

Stroke often impairs the control of the contralesional arm, most survivors rely on the ipsilesional arm to perform daily living activities that require an efficient control of movements and forces
Subjects performed the tasks with both arms: stroke subjects always started with their contralesional arm, and their matched controls started with the same arm
The description in terms of spinal maps related to the generation of isometric forces in the upper limbs of both controls and stroke subjects; 3

Summary

Introduction

Stroke often impairs the control of the contralesional arm, most survivors rely on the ipsilesional arm to perform daily living activities that require an efficient control of movements and forces. The spinal maps, the analysis of single muscle activities and the organization of muscle synergies highlighted that this effect was mainly associated with abnormal activity of proximal muscles with respect to matched controls, especially when pushing or pulling in lateral directions Living activities such as opening a door, writing with a pencil, manipulating common objects, require efficient control of upper limb movements, and of contact forces. As a first step toward this goal, we investigated a pure force control task, eliminating confounds due to motion and dynamics effects, and we focused on a reaching task in isometric conditions[18,19] In this context, Roh and colleagues[19] proposed an isometric protocol to match task variables across control and stroke-impaired subjects and investigated muscle synergies. They examined the spatial activation patterns of elbow and shoulder muscles

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