Fitness and cognitive processing speed in persons with multiple sclerosis

Background: Cognitive impairment is prevalent, disabling, and poorly managed in persons with MS. To date, two studies have identified aerobic capacity as a correlate of cognition in MS, but there has yet to be an investigation of multiple domains of fitness as correlates of cognition in this population. Such an examination is important for identifying the appropriate modes of exercise training for possibly improving cognition. Objective: This study examined the relationships among aerobic capacity, muscle strength, and balance with cognitive function in persons with MS. Methods: 31 persons with MS and 31 controls matched by age, height, weight, and sex completed two neuropsychological measures of cognitive processing speed (PASAT and SDMT). Participants underwent an incremental exercise test to exhaustion on a cycle ergometer as a measure of aerobic capacity; three maximal isometric extensions and one maximal isometric flexion with each knee on an isokinetic dynamometer at three different joint angles as a measure of muscular strength; and stood on a force platform without shoes for 30 seconds with eyes open to measure postural sway. Results: Independent samples t-tests indicated that MS and control groups differed in PASAT score (t = −2.13, p = .04), SDMT score (t = −2.69, p = .01), aerobic capacity (t = −2.99, p < .01), and balance (t = 4.06, p < .01), but not in muscular strength. Cognitive processing speed was significantly associated with aerobic capacity (r = .43 and .44) and balance (r= −.52 and −.52), but not muscular strength in the overall and MS samples, respectively. Lastly, hierarchical regression analysis indicated that aerobic capacity (β = .27) and balance (β = −.40) accounted for differences in cognitive processing speed between MS and control groups. Conclusions: Aerobic capacity and balance, but not muscular strength, are associated with cognitive processing speed in persons with MS, suggesting that aerobic exercise and balance training are avenues for possibly improving cognitive impairment in this population