Physical behaviour is weakly associated with physical fatigue in persons with multiple sclerosis-related fatigue

Background: Fatigue affects 80% of persons with multiple sclerosis and is associated with daily physical functioning. Both fatigue and physical behaviour are multidimensional concepts. Objective: To study the association between the dimensions of physical behaviour and multiple sclerosis- related fatigue. Methods: Cross-sectional analysis of 212 persons with multiple sclerosis. Participants were severely fatigued, with a Fatigue Severity Scale median (interquartile range): 5.4 (4.8-5.9) and were minimally to moderately neurologically impaired, based on the Expanded Disability Status Scale: 2.5 (2.0-3.5), 73% had relapsing-remitting multiple sclerosis. Fatigue was measured by questionnaires (i.e. Checklist Individual Strength, Modified Fatigue Impact Scale), and the dimensions subjective, physical, cognitive and psychological fatigue were distinguished. Physical behaviour was measured using an Actigraph GT3X+, and outcomes were categorized into the dimensions of activity amount, activity intensity, day pattern, and distribution of activities. Results: The physical behaviour dimensions were significantly associated with only the physical fatigue dimension (omnibus F-test: 3.96; df1 = 4, df2 = 207; p = 0.004). Additional analysis showed that the amount of activity (unstandardized beta coefficient (β) = -0.16; 95% confidence interval (CI) -0.27 to -0.04; p = 0.007), activity intensity (β = -0.18; 95% CI -0.31 to -0.06; p = 0.004) and day pattern of activity (β = -0.17; 95% CI, -0.28 to -0.06; p = 0.002) were the physical behaviour dimensions that were significantly associated with physical fatigue. Conclusion: Physical behaviour is weakly associated with physical fatigue and is not associated with other dimensions of fatigue.