Objective assessment of neuromuscular fatigue in patients with multiple sclerosis

Abstract

Background: Patients with multiple sclerosis (MS) often experience fatigue. It is not clear how to document the neuromuscular fatigue using a standard procedure with a defined cut-off score. To be able to interpret the score correctly, one has to know the reliability of the indices and the error of measurement. Objective: To determine objectively and subjectively the occurrence of neuromuscular fatigue in multiple sclerosis patients while performing a hand grip exercise protocol. Secondly, to investigate the psychometric properties of the hand grip force and fatigue indices. Methods: Twenty patients with multiple sclerosis and 20 age and sex-matched healthy controls were studied on three test days, using isometric grip force tests. Participants had to perform exercises by hand grip contractions. Important outcome measures were maximal strength, fatigue indices and subjective experience of fatigue, recorded at maximal five test moments per day. The grip force was measured by a hand held e-link dynamometer. The arm function was assessed by questionnaires (Neurological Fatigue Index for Multiple Sclerosis, Modified Fatigue Impact Scale) and clinical tests (Motricity Index, Modified Ashworth Scale, Box and Block Test). Results: The maximal grip force in the hand which performed the exercises decreased significantly over time in both the healthy controls and patients with multiple sclerosis with similar magnitude. However, the patients with multiple sclerosis showed more neuromuscular fatigue during a sustained f