LAUSR

Objective: The Lifestyle-integrated Functional Exercise (LiFE) intervention has been shown to promote physical activity in fall-prone older adults. However, the underlying mechanisms of how LiFE functions remain unclear. This study compares the effects of the individual and group-based LiFE formats on psychological determinants of behavior change derived from the health action process approach, habit formation theory, and self-determination theory. Methods: Secondary analysis on basis of the randomized, non-inferiority LiFE-is-LiFE trial were performed. Questionnaire data on psychological determinants were obtained from older adults (M = 78.8 years, range 70–95) who took part in either the individual (n = 156) or the group-based (n = 153) LiFE intervention. Measurement points varied from three to six times, and from baseline (T1) up to a 12-month follow-up (T6). A generalized linear mixed model was specified for each determinant. Results: Both LiFE and gLiFE participants reported lower levels of motivational determinants at T6. LiFE participants showed significantly higher values of action planning and coping planning at T6. Participants in both formats showed increased levels of action control at T6, whereas participants’ habit strength decreased post-intervention but then stabilized over time. LiFE participants showed higher levels of autonomy, competence, and relatedness throughout the study, but levels of intrinsic motivation did not differ between formats and from T1 to T6. Conclusion: In both formats, but especially in the individual LiFE, the behavior change techniques used affected volitional rather than motivational or general determinants of behavior change. Habit strength as an important indicator of the sustainability of the LiFE exercises stabilized over time, indicating that participants, at least partly, sustained their formed habits long-term.