Increased exertion variability is linked to disruptions in effort assessment in multiple sclerosis.

BACKGROUND: Individuals with multiple sclerosis (MS) often report fatigue and motor impairments, which may affect how accurately they assess physical exertion. Recent work with healthy individuals suggests that motor variability can distort judgments of exertion (i.e. feelings of effort); however, this relationship has not been explored in individuals with MS. OBJECTIVE: To determine how variability in physical exertion affects subjective effort assessment in individuals with MS compared with healthy participants. METHODS: Individuals with MS and age-matched healthy controls exerted varying levels of physical exertion and retrospectively assessed the feelings of effort associated with their exertion. Hierarchical linear models were used to compare motor performance and effort assessment metrics between cohorts. RESULTS: In total, 29 patients with MS and 22 healthy controls were included. Individuals with MS exhibited increased exertion variability compared with healthy participants (β=1.00, 95%CI=[0.32,1.68]). Increased exertion variability was associated with less accurate subjective effort assessment (β=3.16, 95%CI=[1.34,4.98]), and this effect was more pronounced in individuals with more advanced MS (β=1.49, 95%CI=[0.16,∞]).Conclusion:These results suggest a possible mechanism through which motor variability may be associated with inflated perceptions of effort in MS, highlighting a potential account of why exertion feels particularly costly to people living with MS.