Abstract

BackgroundPeople with multiple sclerosis (MS) are encouraged to engage in exercise programs but an increased experience of fatigue may impede sustained participation in training sessions. A high number of movements is, however, needed for obtaining optimal improvements after rehabilitation.MethodsThis cross-sectional study investigated whether people with MS show abnormal fatigability during a robot-mediated upper limb movement trial. Sixteen people with MS and sixteen healthy controls performed five times three minutes of repetitive shoulder anteflexion movements. Movement performance, maximal strength, subjective upper limb fatigue and surface electromyography (median frequency and root mean square of the amplitude of the electromyography (EMG) signal of the anterior deltoid) were recorded during or in-between these exercises. After fifteen minutes of rest, one extra movement bout was performed to investigate how rest influences performance.ResultsA fifteen minutes upper limb movement protocol increased the perceived upper limb fatigue and induced muscle fatigue, given a decline in maximal anteflexion strength and changes of both the amplitude and the median frequency of EMG the anterior deltoid. In contrast, performance during the 3 minutes of anteflexion movements did not decline. There was no relation between changes in subjective fatigue and the changes in the amplitude and the median frequency of the anterior deltoid muscle, however, there was a correlation between the changes in subjective fatigue and changes in strength in people with MS. People with MS with upper limb weakness report more fatigue due to the repetitive movements, than people with MS with normal upper limb strength, who are comparable to healthy controls. The weak group could, however, keep up performance during the 15 minutes of repetitive movements.Discussion and ConclusionAlbeit a protocol of repetitive shoulder anteflexion movements did not elicit a performance decline, fatigue feelings clearly increased in both healthy controls and people with MS, with the largest increase in people with MS with upper limb weakness. Objective fatigability was present in both groups with a decline in the muscle strength and increase of muscle fatigue, shown by changes in the EMG parameters. However, although weak people with multiple sclerosis experienced more fatigue, the objective signs of fatigability were less obvious in weak people with MS, perhaps because this subgroup has central limiting factors, which influence performance from the start of the movements.

Highlights

  • Multiple sclerosis (MS) is a chronic auto-immune disease, causing sensory as well as motor problems, such as muscle weakness, tremor and spasticity leading to limitations in walking and functional mobility, and upper limb dysfunction [1,2].People with MS (PwMS) benefit from resistance and endurance training which was shown to improve muscle strength, physical fitness, functional mobility and quality of life [3]

  • There was no relation between changes in subjective fatigue and the changes in the amplitude and the median frequency of the anterior deltoid muscle, there was a correlation between the changes in subjective fatigue and changes in strength in people with MS

  • Weak people with multiple sclerosis experienced more fatigue, the objective signs of fatigability were less obvious in weak people with MS, perhaps because this subgroup has central limiting factors, which influence performance from the start of the movements

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Summary

Introduction

People with MS (PwMS) benefit from resistance and endurance training which was shown to improve muscle strength, physical fitness, functional mobility and quality of life [3]. Pilot studies have already showed the benefits of repetitive arm training by the use of robotic therapy, both in stroke patients and in PwMS [6,7,8] It is, seen that PwMS need to limit their exercise duration due to excessive fatigue when performing repeated muscle exercises. Surface electromyography (sEMG) has been used to detect objective signs of muscle fatigue, underlying fatigability [12] Both frequency and amplitude parameters are indicative for muscle fatigue [13]. A high number of movements is, needed for obtaining optimal improvements after rehabilitation

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