Impaired force control and muscle activation during isometric contractions in people with multiple sclerosis

Motor impairments affect up to 80% of people living with multiple sclerosis (MS) and are often asymmetrical, resulting in self-reports of more- and less-affected legs. The purpose of our study was to examine asymmetries in the neural control of force applied by lower leg muscles in people with MS. Eighteen people with MS and 17 healthy controls performed two types of submaximal isometric contractions with dorsiflexors and plantar flexors. The outcomes included measures of force control and electromyographic (EMG) activity of lower-leg muscles. Force control was worse in people with MS compared with healthy controls (p ≤ 0.003), regardless of the limb assessed or the task performed. They also had greater agonist EMG activity during plantar flexion (p ≤ 0.042), and greater antagonist activity and coactivation levels during dorsiflexion (p < 0.001). No meaningful differences in performance or muscle activity were observed between limbs. The main result was that the MS group exhibited differences in force control of the dorsiflexors and plantar flexors, with no asymmetry between the more- and less-affected legs. The findings are expected to provide new information about mobility limitations and guide targeted rehabilitation approaches.