In-Depth Analyses of the Effects of a Diet and Resistance Exercise Intervention in Older Adults: Who Benefits Most From ProMuscle in Practice?

Background: The ProMuscle in Practice intervention, comprising resistance exercise and an increased protein intake, was effective in improving muscle strength, lean body mass, and physical functioning in older adults aged 65 years and older (N = 168). However, a heterogeneous response to such interventions is common. Therefore, we explored the differences in responsiveness to the intervention in subgroups based on demographic characteristics and mobility-impairing disorders. Method: Multiple regression analyses were performed to study mean changes between baseline and 12 weeks on the Short Physical Performance Battery, chair rise test, lean body mass, knee extension strength, leg press strength, and leg extension strength. The interaction term Treatment × Subgroup was included to study differences in effects between subgroups. Subgroups comprised age (≤75 vs >75 years), sex (men vs women), presence of frailty, presence of sarcopenia, and presence of osteoarthritis. Results: A significant interaction effect including age was found on lean body mass (β = −0.8; 95% CI: −1.5, −0.2), favoring participants aged 75 years and younger. A significant interaction effect including sex was found on leg press strength (β = 15.5; 95% CI: 0.6, 30.3), favoring women. Participants with or without frailty, sarcopenia, or osteoarthritis responded equally to the intervention in terms of absolute effects. Conclusions: Participants aged 75 years and younger and women benefited to a great extent from the intervention, as they improved significantly on nearly every outcome. Effects in participants with and without a mobility-impairing disorder were comparable, indicating that the intervention is suitable for both groups.