Lyan J.M. Blikman, Jetty van Meeteren, Dimitris Rizopoulos, Vincent de Groot, Heleen Beckerman, Henk J. Stam, Johannes B.J Bussmann
Rehabilitation Medicine, Erasmus MC, 3000 CA Rotterdam, The Netherlands. E-mail: l.blikman@erasmusmc.nl
DOI: 10.2340/16501977-2375

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.

Fatigue affects many people with multiple sclerosis and is associated with daily functioning. There are several subtypes of fatigue and physical behaviour, although this is often not recognized in the literature. Therefore, we studied the associations between subtypes of fatigue and physical behaviour in a large group of fatigued persons with multiple sclerosis. Fatigue was divided into subjective, physical, cognitive and psychological dimensions, and physical behaviour was divided into the dimensions amount of activity, intensity of activity, day pattern, and distribution of activities. The results showed that physical behaviour dimensions, the distribution dimension excepted, were associated only with the physical dimension of fatigue, and not with other fatigue dimensions or total fatigue scores. The results of this exploratory study highlight the importance of more detailed assessment of both fatigue and physical behaviour in multiple sclerosis.