Characterization of knee extensor muscles fatigability during isokinetic concentric contractions in patients with multiple sclerosis

Abstract

Increased muscle fatigability has been reported in patients with multiple sclerosis (MS) assessed during sustained isometric contractions however rehabilitation programs and daily life activities often involve concentric contractions. The aim of this study was to characterize knee extensor muscles fatigability in patients with MS during concentric contractions. Thirty-eight patients with MS and 14 healthy persons were included in this study. An isokinetic assessment of knee extensor muscles fatigability was carried out during a fatiguing task of 50 concentric contractions, associated with an electromyographic activity analysis of the rectus femoris, vastus lateralis, biceps femoris and semitendinosus muscles. Patients with MS experienced lower knee extensor muscles fatigability than healthy subjects. When torque was normalized to maximal isometric peak torque, patients with MS and healthy persons had the same level of relative strength at the end of the fatigue protocol (50% of the maximal isometric peak torque). During the fatiguing task neuromuscular efficiency decreased but coactivations of knee flexor muscles remained unchanged. Fatigability is a common complaint in patients with MS but they experienced lower muscle fatigability than healthy persons during maximal concentric contractions, nevertheless they finished fatigue protocol at the same level of relative strength.