Partial weight support differentially affects corticomotor excitability across muscles of the upper limb

Abstract

Partial weight support may hold promise as a therapeutic adjuvant during rehabilitation after stroke by providing a permissive environment for reducing the expression of abnormal muscle synergies that cause upper limb impairment. We explored the neurophysiological effects of upper limb weight support in 13 healthy young adults by measuring motor‐evoked potentials (MEPs) from transcranial magnetic stimulation (TMS) of primary motor cortex and electromyography from anterior deltoid (AD), biceps brachii (BB), extensor carpi radialis (ECR), and first dorsal interosseous (FDI). Five levels of weight support, varying from none to full, were provided to the arm using a commercial device (Saebo Mobile Arm Support). For each level of support, stimulus–response (SR) curves were derived from MEPs across a range of TMS intensities. Weight support affected background EMG activity in each of the four muscles examined (P <0.0001 for each muscle). Tonic background activity was primarily reduced in the AD. Weight support had a differential effect on the size of MEPs across muscles. After curve fitting, the SR plateau for ECR increased at the lowest support level (P =0.004). For FDI, the SR plateau increased at the highest support level (P =0.0003). These results indicate that weight support of the proximal upper limb modulates corticomotor excitability across the forearm and hand. The findings support a model of integrated control of the upper limb and may inform the use of weight support in clinical settings.

Human arm weight compensation in rehabilitation robotics: efficacy of three distinct methods

“…Therefore, many rehabilitation robots with arm weight compensation functions have been developed. The common robot types that provide system-dependent arm weight compensation can be divided in gantry-based robots [8][9][10], passive exoskeletons [11,12], actuated exoskeletons [4,11,13,14], and actuated end-effector robots [5,6,[15][16][17][18].…”

“…Arm weight compensation should be provided in any pose without restricting or hindering any possible degree of freedom. However, most endeffector robots can restrict the user's freedom of movement while providing arm weight compensation due to mechanical limitations and missing human joint angle information, e.g., [5,6,[15][16][17][18].…”

“…However, several papers have investigated the efficacy of arm weight compensation through additional electromyography (EMG) measurements of relevant muscles [29][30][31][32][33]. For example, arm weight compensation decreased EMG activity during static holding [32] and reaching tasks [29][30][31], and the transfer of this effect to stroke patients was also shown [29]. However, static holding was performed in only one pose [32], not over the whole workspace to analyze pose-dependent effects of arm weight compensation.…”

“…For example, arm weight compensation decreased EMG activity during static holding [32] and reaching tasks [29][30][31], and the transfer of this effect to stroke patients was also shown [29]. However, static holding was performed in only one pose [32], not over the whole workspace to analyze pose-dependent effects of arm weight compensation. Furthermore, previous EMG signal analyses have mainly focused on individual muscle evaluations [29][30][31] instead of a combined evaluation of all relevant muscles with respect to their passive reference measurements as a score.…”

The Present and Future of Robotic Technology in Rehabilitation

“…The upper limb exoskeleton robots offer: (1) assist-as-needed force fields to keep the upper limb within the desired path of motion, referred to as path-assistance, to promote higher movement accuracy, and (2) adjustable weight support to eliminate the effect of gravity, both of which can potentially assist with motor learning after a stroke. It has been shown that elimination of gravity using partial weight support can reduce abnormal motor synergies in the upper limb after stroke and improve range of motion and function [45–47]. Studies have also shown that subjects exhibit higher movement accuracy along the desired path with assist-as-needed force fields [43].…”