BACKGROUND: People with multiple sclerosis (MS) often experience fatigue, which is aggravated by inactivity. Identifying mediators of changes in physical activity (PA) and fatigue self-management (FSM) behaviors could optimize future interventions that reduce the impact of MS fatigue. PURPOSE: To examine the effects of telephone-delivered interventions on social cognitive theory constructs and test whether these constructs mediated secondary outcomes of PA and FSM behaviors. METHODS: Participants with MS (n = 208; mean age 52.1; female 84.6%) were randomized into contact-control intervention (CC), PA-only intervention, and PA plus FSM intervention. Step count (Actigraphy) and FSM behaviors as well as self-efficacy, outcome expectations, and goal setting for PA and FSM were measured at baseline, post-test (12 weeks), and follow-up (24 weeks). Path analyses using bias-corrected bootstrapped 95% confidence intervals (CI) determined whether constructs at post-test mediated behaviors at follow-up when adjusting for baseline measures. RESULTS: Path analysis indicated that PA-only (beta 0.50, p < 0.001) and PA plus FSM interventions (beta 0.42, p < 0.010) had an effect on goal setting for PA, and that PA plus FSM intervention had an effect on self-efficacy for FSM (beta 0.48, p = 0.011) and outcome expectations for FSM (beta 0.42, p = 0.029). Goal setting for PA at post-test mediated the effects of PA-only (beta 159.45, CI 5.399 to 371.996) and PA plus FSM interventions (beta 133.17, CI 3.104 to 355.349) on step count at follow-up. Outcome expectations for FSM at post-test mediated the effects of PA plus FSM intervention on FSM behaviors at follow-up (beta 0.02, CI 0.001 to 0.058). CONCLUSIONS: Goal setting for PA and outcome expectations for FSM may be important constructs to target in telephone-delivered interventions designed to reduce the impact of MS fatigue.

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