The roles of motivational interviewing and self-efficacy on outcomes and cost-effectiveness of a community-based exercise intervention for inactive middle-older aged adults.

Increasing physical activity (PA) among inactive middle-older aged adults in rural communities is challenging. This study investigates the efficacy of a PA intervention supporting inactive adults in rural/semirural communities. Inactive participants enrolled on either a single signposting session (n =427) or a multisession pathway combining signposting with motivational interviewing (MI; n = 478). Pre-post outcomes data assessed activity levels (International Physical Activity Questionnaire-Short Form; Single Item Sport England Measure), self-efficacy (New General Self-Efficacy scale [NGSE]) and well-being (five-item World Health Organization Well-Being Index [WHO-5]). Measures were repeated at longitudinal time points (26, 52 weeks) for the MI pathway. Outcomes were contrasted with results from an unmatched comparison group receiving treatment as usual (TAU). Cost-utility (quality-adjusted life years [QALY]-incremental cost-effectiveness ratio) and return on investment (NHS-ROI; QALY-ROI) were estimated for short (5 years), medium (10 years) and long (25 years) time horizons. Both pathways significantly increased participants' PA. The MI pathway resulted in significantly greater increases in PA than signposting-only and TAU. Improvements in psychological outcomes (NGSE; WHO-5) were significantly greater in the MI pathway than TAU. Longitudinal results indicated MI pathway participants sustained increases in light-intensity PA at 52 weeks (p < 0.001;  = 0.16). Regression analyses found baseline self-efficacy predicted increased PA at 52 weeks, while baseline well-being did not. The relationship between self-efficacy and PA increased successively across time points. However, magnitude of participants' increased self-efficacy did not predict PA at any time point. Both pathways were cost-effective and cost -saving for participants aged ≥61 years from the short time horizon, with the MI pathway having greater ROI estimates. Overall, MI increased efficacy of a signposting PA intervention and was cost-saving for older adults.