Mechanisms of Physical Activity Behavior Change in an Incentive-Based Intervention: Mediation Analysis

Objective: The physical activity loyalty (PAL) scheme was a cluster randomized controlled trial of a 6-month complex intervention targeting workplace physical activity. Financial incentives were incorporated in an evidence-based behavior change program, including self-regulation techniques. This article examines short-term (<6 months) and long-term (>= 6 months) mediation effects on physical activity. Method: Participants included 853 adults (457 intervention, 396 control). Physical activity was objectively assessed using pedometers at baseline and at 6 and 12 months. Hypothesized short-term mediators (e.g., self-efficacy, intentions) were assessed at baseline and 4 weeks. Hypothesized long-term mediators (e.g., habit, intrinsic motivation) were assessed at baseline and 6 months. Mediation models employed the structural equation modeling product-of-coefficients approach. Results: Intervention participants experienced significant decreases in 6-month pedometer steps/day versus controls (b = -336, p = .02), which were partially mitigated by positive indirect effects through 6-month integrated regulation (ab = 94.7, 95% CI [18.7, 204.4]), intrinsic motivation (ab = 59.0, 95% CI [3.09, 154.5]), and habit (ab = 198.7, 95% CI [84.3, 369.9]). There were no between-groups differences in 12-month pedometer steps/day but positive indirect effects through 6-month integrated regulation (ab = 128.0, 95% CI [27.3, 313.2]), planning (ab = 115.0, 95% CI [3.71, 285.5]), and habit (ab = 153.3, 95% CI [39.3, 333.1]). Conclusions: Most examined mediators were nonsignificant, and mediation analyses did not explain decreases in physical activity for interventions versus controls. Results show that, contrary to self-determination theory hypotheses, intrinsic motivation is not necessarily adversely impacted if financial incentives are embedded in a complex intervention.