Background: Multimorbidity is a common issue in aging societies and is usually associated with dementia in older people. Physical activity (PA) may be a beneficial nonpharmacological strategy for patients with complex health needs. However, insufficient PA is predominant in this population. Thus, there is an evident need to expand the knowledge on potential determinants influencing PA engagement among elderly persons at risk of dementia and multimorbidity.

Methods: We used baseline data from the multicenter, cluster-randomized controlled AgeWell.de study. The main aim was to describe PA engagement and identify potential PA determinants in a sample of community-dwelling Germans aged 60−77 years old with an increased risk of dementia and multimorbidity.

Results: Of the 1030 included participants, approximately half (51.8%) engaged in PA ≥2 times/week for at least 30 min at baseline. We identified self-efficacy (beta = 0.202, (p < 0.001) and BMI (beta = −0.055, (p < 0.001) as potential PA determinants.

Conclusions: The identified determinants, self-efficacy, and BMI are consistent with those reported in the literature. Specific knowledge on PA determinants and stages of change in persons with risk of dementia and multimorbidity might guide the development of effective future prevention measures and health services tailored to this population.

Trial registration: German Clinical Trials Register (reference number: DRKS00013555).