Increased Exertion Variability is Linked to Disruptions in Effort Assessment in Multiple Sclerosis.

Accurate assessment of exertion is crucial for determining whether to continue or rest during physical activity. Individuals with multiple sclerosis (MS) often report fatigue and motor impairments, yet the mechanisms underlying their assessments of effortful exertion remain poorly understood. Recent work with healthy individuals suggests that motor variability can distort judgments of effort; however, this relationship has not been explored in individuals with MS. In this study, we investigated how variability in physical exertion affects effort assessment in individuals with MS compared to healthy participants. We had participants exert varying levels of physical effort and retrospectively assess the effort they exerted. Individuals with MS exhibited increased exertion variability and tended to overreport their levels of exertion compared to healthy participants. Increased exertion variability was associated with less accurate effort assessment, and this effect was more pronounced in individuals with more advanced MS. 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 efforts feel particularly costly to those individuals living with MS and identifying a promising target for treatment and rehabilitation.