Comparing a recommendation for self-paced versus moderate intensity physical activity for midlife adults: Rationale and design.

Current U.S. guidelines recommend that adults obtain 150 min per week of moderate intensity physical activity (PA), 75 min of vigorous intensity PA, or some equivalent combination. However, less than half of U.S. adults reach this goal, with the proportion even smaller among adults with overweight or obesity. Moreover, regular PA declines after age 45-50. Previous research suggests a shift in national guidelines to emphasize PA of a self-selected intensity (i.e., self-paced), instead of prescribed moderate intensity PA, may result in better adherence to PA programs, particularly among midlife adults with overweight or obesity. The present paper presents the protocol for a field-based RCT testing the hypothesis that adherence to PA programs is improved when PA is explicitly recommended to be self-paced rather than prescribed at moderate intensity among midlife (ages 50-64) adults (N = 240) with overweight or obesity. All participants receive a 12-month intervention designed to help them overcome barriers to regular PA and are randomly assigned to either self-paced or prescribed moderate intensity PA. The primary outcome is total volume of PA (minutes by intensity) as measured by accelerometry. Secondary outcomes include self-reported min/week of PA and changes in bodyweight. Additionally, using ecological momentary assessment, we examine putative mediators of treatment effects. We hypothesize self-paced PA will lead to a more positive affective response to PA, more perceived autonomy, and lower perceived exertion during PA, and thus greater increases in PA behavior. Findings will have direct implications for PA intensity recommendations among midlife adults with overweight or obesity.