Mediators of Physical Activity Adherence: Results from an Action Control Intervention in Couples.

Background: Behavior change interventions targeting self-regulation skills have generally shown promising effects. However, the psychological working mechanisms remain poorly understood.

Purpose: We examined theory-based mediators of a randomized controlled trial in couples targeting action control (i.e., continuously monitoring and evaluating an ongoing behavior). Self-reported action control was tested as the main mediating mechanism of physical activity adherence, and in addition self-efficacy and received social support from the partner.

Methods: Overweight individuals (N = 121) and their heterosexual partners were randomly allocated to an intervention (information + action control text messages) or a control group (information only). Across a period of 28 days, participants reported on action control, self-efficacy, and received support in end-of-day diaries, and wore triaxial accelerometers to assess stable between-person differences in mediators and the outcome adherence to recommended daily activity levels (≥30 min of moderate activity in bouts of at least 10 min).

Results: On average, participants in the intervention group showed higher physical activity adherence levels and higher action control, self-efficacy, and received support compared to participants in the control group. Action control and received support emerged as mediating mechanisms, explaining 19.7 and 24.6% of the total intervention effect, respectively, in separate analyses, and 13.9 and 22.2% when analyzed simultaneously. No evidence emerged for self-efficacy as mediator.

Conclusions: Action control and received support partly explain the effects of an action control intervention on physical activity adherence levels. Continued research is needed to better understand what drives intervention effects to guide innovative and effective health promotion.

Trial Registration Number: (controlled-trials.com ISRCTN15705531).