Physical Fitness, Cognitive Function, and Disability Status in Multiple Sclerosis

Background: Cognitive impairment is a highly prevalent, poorly managed, and disabling consequence of multiple sclerosis (MS). Exercise training that improves physical fitness (i.e., aerobic capacity and muscular strength) represents a promising approach for managing cognitive impairment in persons with MS based on the gerontology literature. To date, there is limited evidence that physical fitness is associated with multiple domains of cognitive dysfunction (e.g., impaired cognitive processing speed, verbal/visual memory) across the disability spectrum in persons with MS. This is a precursory step before designing and testing exercise training interventions for improving cognitive function in MS.

Objectives: We examined the associations among aerobic capacity, lower limb muscle strength, and cognitive functions in persons with mild, moderate, and severe disability.

Methods: The sample included 63 persons with mild (n=21), moderate (n=21), and severe (n=21) MS disability based on a neurological examination for deriving EDSS scores. The participants underwent neuropsychological assessments of cognitive processing speed (i.e., Symbol Digit Modalities Test (SDMT)), verbal memory (i.e., California Verbal Learning Test-2 (CVLT-2)), and visual memory (i.e., Brief Visuospatial Memory Test-Revised (BVMT-R)). All participants further underwent testing for measuring aerobic capacity (i.e., peak oxygen consumption) on a recumbent stepper (NuStep) and muscular strength (i.e., peak torque of knee flexors and extensors) on an isokinetic dynamometer (Biodex).  

Results: There were significant group differences in cognitive and fitness outcomes among persons with mild, moderate, and severe disability. SDMT scores, but not CVLT-2 or BVMT-R scores, were associated with aerobic capacity and muscular strength in the overall sample (r’s = .41 - .49). SDMT scores were associated with aerobic capacity (r = .55), but not muscular strength (r’s = .33 - .40) in persons with mild disability, and this association was attenuated, but remained statistically significant after controlling for age as a covariate (pr = .41). SDMT scores were not associated with aerobic capacity or muscular strength in persons with moderate (r’s = .04 - .06) or severe disability (r’s = .08 - .14).

Conclusions: These results indicate that disability status is a moderator of the association between aerobic capacity and cognitive processing speed, but not a moderator of physical fitness and memory outcomes. This supports aerobic exercise training for improving cognitive processing speed in persons with mild MS, and further suggests that aerobic and resistance exercise training might not have as large an effect on cognitive function in persons with moderate and severe MS disability.