Testing the purported mechanisms of the AgingPLUS intervention: Effects on physical activity outcomes.

Following the experimental medicine approach, Diehl et al. (2023) demonstrated the malleability of negative views of aging (NVOA), self-efficacy beliefs, and exercise intention in middle-aged and older adults who participated in the AgingPLUS intervention program. The present study built on those findings and addressed (a) whether the intervention resulted in significant improvements in physical activity (PA) and (b) whether the purported mechanistic variables were significant mediators of the intervention's effects on PA outcomes. AgingPLUS used a randomized, single-blind control group design to implement the intervention in a sample of 335 adults aged 45-75 years. This study reports findings from 278 participants (M_age = 60.1 years; SD = 8.3 years) for whom PA measures were available at baseline and the delayed posttest at Week 8. Compared to participants in the Health Education control group and compared to baseline, participants in the AgingPLUS program showed significant improvements in accelerometer-assessed PA (e.g., total daily steps walked; total daily minutes of moderate-to-vigorous PA [MVPA]) and self-reported PA (e.g., weekly kcals burned in MVPA; increase in weekly total minutes of MVPA). Findings from bias-corrected bootstrap mediation analyses yielded partial support for the purported mechanisms of the intervention. Specifically, improvements in NVOA mediated the effects of the intervention on several accelerometer-assessed PA outcomes. Furthermore, improvements in NVOA, general, motivational, and volitional self-efficacy beliefs were significant mediators on several self-reported PA outcomes. Overall, findings provided support for small but significant effects of AgingPLUS on PA outcomes and supportive evidence for several of the theoretical mechanisms tested. (PsycInfo Database Record (c) 2025 APA, all rights reserved).