BACKGROUND/OBJECTIVE Barriers and facilitators of exercise maintenance and residual effects of exercise training intervention on physical and cognitive function after the cessation of training are inadequately described in older adults. DESIGN AND SETTING One year after the cessation of a supervised exercise training intervention, a mixed methods approach employed a quantitative phase that assessed body composition and physical and cognitive function and a qualitative phase that explored determinants of exercise maintenance after participation in the intervention. PARTICIPANTS Community-dwelling older Irish adults (aged >65 years) who had completed 12 weeks of supervised exercise training 1 year previously. MEASUREMENTS Fifty-three participants (male/female ratio = 30:23; age = 70.8 +/- 3.9 years) completed the follow-up testing comprising body composition and physical and cognitive function. Semistructured interviews were conducted with 12 participants (male/female ratio = 6:6) using the Theoretical Domains Framework to inform the interview guide. RESULTS At 1 year follow-up, body fat increased (mean = 4.3%; 95% confidence limit = 2.2% to 6.3%), while lean body mass (mean = -0.6%; 95% confidence limit = -1.2% to -0.1%), strength (leg press, mean = -5.6%; 95% confidence limit = -8.3% to -2.8%; chest press, mean = -11.0%; 95% confidence limit = -14.8% to -7.8%), and cognitive function (mean = -3.7%; 95% confidence limit = -5.7% to -1.8%) declined (all P < .05). Interviews revealed key facilitators (social aspects and beliefs about benefits of exercise) and barriers (affordability and general aversion to gyms) to exercise maintenance in this population. CONCLUSION Key barriers and facilitators to exercise maintenance were identified, which will inform the development of future behavior change interventions to support exercise participation and maintenance in older adults to mitigate adverse changes in body composition and physical and cognitive function with advancing age.