Abstract
OBJECTIVES: This study examined the malleability of a tripartite cluster of purported mechanistic variables targeted in a 4-week intervention program designed to improve adults' engagement in physical activity. The targeted cluster of purported mechanisms consisted of negative views of aging (NVOA), self-efficacy beliefs, and behavioral intentions. METHODS: A randomized single-blind control group design was used to implement the AgingPLUS program in a sample of middle-aged and older adults (N = 335; Mage = 60.1 years; SDage = 8.3 years; age range 45-75 years). RESULTS: Using an intention-to-treat approach and analyses of covariance adjusting for participants' baseline scores, findings showed significant improvements in the purported mechanistic variables both at the immediate (Week 4) and delayed posttest (Week 8) in the treatment group but not in the control group. These improvements were for the most part maintained until 8-month postrandomization, although to a smaller extent. Specifically, participants in the AgingPLUS group showed significant improvements in NVOA, self-efficacy beliefs, and behavioral intentions compared to the Health Education control group. Standardized effect sizes for statistically significant effects were variable and ranged from small (d = -0.23) to large (d = 0.80). Effect sizes showed some decay of the intervention at the 8-month posttest. DISCUSSION: Taken together, the findings supported the efficacy of the AgingPLUS program and showed that variables representing the purported mechanisms of the intervention were significantly moved in a positive direction. In doing so, the AgingPLUS program met a major requirement of the experimental medicine approach to behavior change interventions. CLINICAL TRIALS REGISTRATION NUMBER: NCT0329948.