The effect of a structured running exercise intervention on non-exercise physical activity and sedentary behaviour in persons with mild Multiple Sclerosis and healthy controls

Background Exercise interventions fail to increase objective physical activity (PA) in persons with Multiple Sclerosis (PwMS), while they self-report higher exercise participation. This suggests that PwMS change their non-exercise PA (NEPA). We aimed to explore NEPA changes of PwMS and healthy controls (HC), and whether these constrain exercise adaptations. Methods Twenty-nine mildly-disabled PwMS and 26 HC completed a 10-month home-based running program. A non-randomised controlled study design was used. The primary outcome was time in different NEPA intensities (light intensity PA [LIPA] and moderate-to-vigorous intensity PA [MVPA]) and in sedentary behaviour ([SB]; total and uninterrupted SB) at baseline (T1), after 5 (T2) and 10 (T3) months of exercise. Data were averaged over days with and without exercise sessions (EX and NONEX days). Secondary outcomes included patient-reported and physical exercise adaptations (fatigue, walking mobility, blood pressure, body composition and cardiorespiratory fitness). Results A significant reduction in non-exercise MVPA was observed from T1 to T2 (− 113 ± 31 min/week, p < 0.01) and from T1 to T3 (− 95 ± 26 min/week, p < 0.01) in PwMS, which approximately matched the weekly exercise duration at those time points. PwMS also increased their uninterrupted SB on NONEX days compared to EX days (+ 0.7 ± 0.3 h, p < 0.01). There were no changes in MVPA or SB of HC (group × time effect MVPA: p < 0.05; group × EX day effect uninterrupted SB: p < 0.01). Secondary outcomes improved similarly in both groups and were not associated with NEPA/SB changes. Conclusions In contrast to HC, PwMS significantly changed their NEPA and the pattern in which they accumulated SB in response to structured exercise. This might be a necessary behavioural compensation in order to adhere to the exercise intervention and did not constrain patient-reported and physical outcomes. Future research is warranted to unravel the underlying causes and to investigate the effects on other exercise adaptations, such as cardiometabolic health. Trial registration The present study was registered (December 10, 2019) at clinicaltrials.gov as NCT04191772