IMPACT OF ANKLE MUSCLE STRENGTH AND VOLUNTARY ACTIVATION ON WALKING PERFORMANCE IN MULTIPLE SCLEROSIS

Walking impairment in multiple sclerosis (MS) is often attributed to muscle weakness; however, the contribution of neural activation deficits and interlimb asymmetry remains unclear. This study aimed to investigate the relationships between ankle muscle strength, rapid force production, voluntary activation, and walking performance in individuals with MS. Sixty participants with MS (mean Expanded Disability Status Scale score 3.3) performed maximal voluntary ankle dorsiflexion and plantar flexion contractions with simultaneous electromyography, enabling the assessment of maximal force, rate of force development (RFD), and voluntary activation based on electromyographic measures of muscle activity. Measures were analysed separately for the most and less affected leg and related to functional performance assessed by walking performance (Six-Minute Walk Test) and stair climbing (Nine-Step Stair Ascent). In the most affected leg, walking performance and stair climbing showed moderate-to-strong associations with dorsiflexion RFD at early time intervals (50–100 ms), maximal force, and voluntary activation measures, whereas the associations were consistently weaker in the less affected leg. Early-phase RFD demonstrated stronger relationships with functional performance than maximal force alone, indicating a prominent role of impaired neural drive. In contrast, plantar flexion measurements exhibited more modest and symmetrical associations across limbs. These findings suggest that functional limitations in MS are closely linked to asymmetric deficits in the rapid neural activation of ankle muscles, particularly dorsiflexors, rather than generalized muscle weakness. The results highlight the importance of targeting neural activation and rapid force production in rehabilitation strategies aimed at improving walking and stair-climbing performance in individuals with MS.