Response Heterogeneity With Exercise Training and Physical Activity Interventions Among Persons With Multiple Sclerosis

Abstract

Multiple sclerosis (MS) is a heterogeneous disease, both in its pathology and symptomology. This poses a challenge for the medical management and rehabilitation of MS; however, physical activity and exercise training are rehabilitation approaches that have demonstrated beneficial effects on many of the burdensome consequences of MS such as mobility impairment and fatigue. Given the heterogeneous course of MS, it is possible that outcomes of physical activity and exercise training interventions demonstrate heterogeneity both in the magnitude and pattern of change, but there has been little focus on response heterogeneity with these interventions among persons with MS. In this narrative review, a search of the existing literature was performed to identify studies that reported individual participant data, which was used to describe the variability in the response to physical activity and exercise training interventions among persons with MS. Inter-individual variability seemingly occurs across outcomes and modalities, which underscores the consideration of factors that might influence response heterogeneity. Factors related to MS disease characteristics, nervous system damage, and the degree of MS-related disability might influence individual responsiveness. Large-scale studies that permit the examination of heterogeneity and its predictors will inform future research on the area of physical activity and exercise training in MS, and lead to the development of individually tailored rehabilitation approaches that will more effectively elicit change.

Keywords: exercise training; multiple sclerosis; physical activity; response heterogeneity.

Figure 1.

Inter-individual variability of the change in physical activity as measured by the Godin Leisure-Time Exercise Questionnaire in response to an internet-based physical activity intervention. Each black bar represents the change in physical activity of an individual participant and the gray bar represents the average change of the group. *represents a significant difference (p < 0.01) compared with the pretrial value.

Figure 2.

Inter-individual variability of the VO_2peak response with aerobic exercise training in persons with MS. (A) The individual change in VO_2peak after 8–10 weeks of standardized aerobic exercise training with arm ergometry, rowing, or cycle ergometry. (B) The individual change in VO_2peak after 4-weeks of standardized arm ergometry training. Each black bar represents the change in VO_2peak of an individual participant and the gray bar represents the average change of the group. *represents a significant difference (p < 0.05) compared to the change in the control group. VO_2peak = peak oxygen consumption.

Figure 3.

Inter-individual variability of the change in 6MWT distance with aerobic exercise training in persons with MS. (A) The individual change in 6MWT distance after 8–10 weeks of standardized aerobic exercise training with arm ergometry, rowing, or cycle ergometry. (B) The individual change in 6MWT distance after 12-weeks of standardized treadmill training. Each black bar represents the change in 6MWT distance of an individual participant and the gray bar represents the average change of the group. *represents a significant difference (p < 0.05) compared to the change in the control group. 6MWT = Six Minute Walk Test.

Figure 4.

Inter-individual variability of the change in knee extensor strength (A) and knee flexion strength (B) after 12-weeks of progressive resistance exercise training. Each black bar represents the change in strength of an individual participant and the gray bar represents the average change of the group. *represents a significant difference (p < 0.05) compared to the change in the control group. KE MVC = knee extensor maximal voluntary contraction; AI = angular impulse; KF = knee flexors.

Figure 5.

Inter-individual variability of the change in functional mobility after 12-weeks of progressive resistance exercise training. Each black bar represents the change in score of an individual participant and the gray bar represents the average change of the group. *represents a significant difference (p < 0.05) compared to the change in the control group.

Figure 6.

Inter-individual variability of the change in fatigue (A) and depressive symptoms (B) after 12-weeks of progressive resistance exercise training. Each black bar represents the change score of an individual participant and the gray bar represents the average change of the group. *represents a significant difference (p < 0.05) compared to the change in the control group. FSS = Fatigue Severity Scale; MDI = Major Depression Inventory.

Figure 7.

MS-specific phenotypic factors that possibly influence response heterogeneity with exercise training and physical activity interventions. Relationships between the three core factors (CNS damage, MS burden, and MS characteristics) create additional factors that also need to be accounted for when considering individual responsiveness.