Randomized controlled trial of the behavioral intervention for physical activity in multiple sclerosis project: Social cognitive theory variables as mediators.

Background: We recently reported in a phase-III, randomized controlled trial that a behavioral intervention based on social cognitive theory (SCT) and delivered through the Internet using e-learning approaches increased device-measured minutes/day of moderate-to-vigorous physical activity (MVPA) over a 6-month period among persons with multiple sclerosis (MS).

Objective: This planned tertiary outcome paper examined SCT variables as mediators of the behavioral intervention effect on change in device-measured minutes/day of MVPA.

Method: Persons with MS (N = 318) were randomized into behavioral intervention (n = 159) or attention/social contact control (n = 159) conditions. The conditions were administered over a 6-month period via an Internet website and supported with behavioral coaching by persons who were uninvolved in screening, recruitment, random assignment, and outcome assessments. We collected MVPA and SCT data before and after the 6-month period. The data analysis involved linear mixed modeling on MVPA and SCT outcomes followed by latent change score modeling for examining SCT variables as mediators of the intervention effect on change in MVPA.

Results: The linear mixed model indicated statistically significant group by time interactions on device-measured minutes/day of MVPA and scores from SCT measures of exercise self-efficacy, barriers self-efficacy, goal setting, and planning. The effect of the intervention on device-measured minutes/day of MVPA was mediated by the SCT variable of exercise self-efficacy based on the statistical significance of the Wald z-score for the indirect effect in the latent change score model.

Conclusions: This study provides evidence for exercise self-efficacy as a SCT mediator of the behavioral intervention effect on device-measured minutes/day of MVPA in persons with MS.