Metabolic costs of walking and arm reaching in persons with mild multiple sclerosis

Movement slowness is a common and disruptive symptom of multiple sclerosis (MS). A potential cause is that individuals with MS slow down to conserve energy as a behavioral adjustment to heightened metabolic costs of movement. To investigate this prospect, we measured the metabolic costs of both walking and seated arm reaching at five speeds in persons with mild MS (pwMS; n = 13; 46.0 ± 7.7yrs) and sex- and age-matched controls (HCs; n = 13; 45.8 ± 7.8yrs). Notably, the cohort of pwMS was highly mobile and no individuals required a cane or aid when walking. We found that the net metabolic power of walking was approximately 20% higher for pwMS across all speeds (p = 0.0185). In contrast, we found no differences in the gross costs of reaching between pwMS and HCs (p = 0.492). Collectively, our results suggest that abnormal slowness of movement in MS – particularly reaching – is not the consequence of heightened effort costs alone. Our findings are consistent with the possibility that demyelination of reward regions of the central nervous system in MS disrupt the dopamine-mediated impetus to move more quickly and thereby prompt slower movements. NEW & NOTEWORTHY Individuals with multiple sclerosis (MS) often move more slowly than those without the disease. A possible cause is that movements in MS are more energetically expensive and slowing is an adaptation to conserve metabolic resources. Here, we find that while walking is more costly for persons with MS, arm reaching movements are not. These results bring into question the driving force of movement slowness in MS and implicate other motor-related networks contributing to slowing.