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Background: This study examined the effectiveness of a 12-month activity tracker-based intervention on activity behavior among recent retirees (Enhancing physical ACTivity and healthy aging among recent REtirees [REACT]) in subgroups based on body mass index. Methods: REACT trial randomized 231 participants (mean age 65.2) into intervention and control groups. Main outcomes were accelerometer-measured moderate-to-vigorous (MVPA) and light physical activity (LPA) and sedentary time (SED) measured at baseline and 3-, 6-, and 12-month follow-ups. As a post hoc analysis, the intervention effect was examined among participants with normal weight (n = 77), overweight (n = 89), and obesity (n = 61). Results: An intervention effect was observed among participants with obesity in LPA (time × group P = .045) mirrored by a similar, albeit nonsignificant, effect in SED (P = .067), but not in MVPA (P = .92). A transient increase of 41 minutes per day (95% confidence interval, 14 to 68) in LPA was observed at 6 months among the intervention group, with a concomitant decrease of 42 minutes per day (−72 to −12) in SED. However, these changes were not maintained at 12 months. No between-group differences in changes over time were observed among participants with normal or overweight. Conclusions: Activity trackers may be particularly suitable for promoting changes in LPA and SED among older adults with obesity. However, their long-term effectiveness might be limited.

Retirement poses opportunities and challenges for maintaining and adopting physically active habits, which may have major implications for health and functional ability in later life. Qualitative studies suggest that a broad range of meanings of physical activity should be considered when promoting physical activity among retirees. The current study utilized the Physical Activity Relationship (PAR) approach to examine the importance of meanings attributed to physical activity and their associations with physical activity over time. A total of 230 recently retired participants (65.2 years old, 83% women) responded to a 54-item inventory assessing the importance of meanings attributed to physical activity at baseline. Eight meaning dimensions were identified through exploratory factor analysis. Differences in their importance across gender and occupational background were examined using t-tests and ANOVA. Associations between meaning dimensions and self-reported and accelerometer-measured physical activity over 12 months were examined with general linear models. Dimensions defined as Physical Fitness, Positive Mood, and Belonging were positively associated with changes in self-reported and accelerometer-measured physical activity. Additionally, the importance of several meaning dimensions varied across occupational background. In conclusion, physical activity promotion among retirees should focus on physical fitness, positive mood, and social belonging. Furthermore, meanings attributed to physical activity may vary across occupational backgrounds.