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 (