Cardiorespiratory fitness and cognitive processing speed in multiple sclerosis: The possible roles of psychological symptoms

Abstract

BackgroundAerobic exercise training may improve cognitive performance among persons with multiple sclerosis (MS). This is largely based on evidence that cardiorespiratory fitness (as a cross-sectional surrogate for aerobic exercise training) is associated with cognitive processing speed. There may be a set of “other” variables (i.e., psychological symptoms) that influences the association between cardiorespiratory fitness and cognitive processing speed in MS, and such factors should be accounted for when designing optimized exercise rehabilitation interventions. MethodsThe primary objective of the present study involved examining psychological symptoms of anxiety, depression, pain, and fatigue as possible mediators, moderators, or confounders of the association between cardiorespiratory fitness and cognitive processing speed. Sixty-two persons across the MS disability spectrum completed anxiety, depression, pain, and fatigue questionnaires; underwent Symbol Digit Modalities Test administration; as well as two separate incremental exercise tests to exhaustion for measurement of psychological symptoms, cognitive processing speed, and cardiorespiratory fitness, respectively. ResultsDepressive symptoms, pain, and fatigue were significantly and jointly associated with cardiorespiratory fitness and cognitive processing speed (p < .05) based on bivariate correlation analyses. Despite those associations, hierarchical linear regression, bivariate correlation, and partial correlation analyses indicated that those psychological symptoms were not mediators, moderators, or confounders of the cardiorespiratory fitness/cognitive processing speed relationship, respectively. ConclusionThe present pattern of results suggests that aerobic exercise training (via improving cardiorespiratory fitness) might improve cognitive processing speed independent of the influence of depression, pain, and fatigue. Such results further suggest that having elevated depressive symptoms or severe MS-related fatigue might not affect aerobic exercise training-related changes in cognitive processing speed, and that psychological symptoms might not distort the association between aerobic exercise training and changes in cognitive processing speed.