Multidomain changes in clinical outcomes after 12 weeks of resistance-based exercise training in healthy older adults: a four‑domain framework for identifying non‑responders.

PURPOSE: To characterise multidomain changes observed over 12 weeks among healthy older adults participating in a supervised resistance-based exercise programme. BACKGROUND: Resistance-based exercise improves physical performance in older adults, yet clinical evaluation often relies on isolated outcome measures and overlooks multidimensional changes. We investigated multidomain changes following a 12‑week supervised exercise training programme in healthy older adults using a reduced, clinically interpretable four‑domain framework and a Multidomain Quality Outcome Index (MQOidx) to characterise overall responsiveness. METHODS: A total of 126 healthy older adults (age: 67.7  ±  5.3 years; 62.7% women) completed a 12-week training programme. A comprehensive battery of assessments was categorised in four clinically interpretable domains: 'body composition', 'muscle capacity', 'functional performance', and 'pain & HRQoL'. Changes were expressed as z‑standardised factor scores and standardised mean differences (SMD). Multidomain responders were classified based on their MQOidx change (≥  + .33 SMD). RESULTS: Values in the 'functional performance' domain improved substantially (SMD  =  .67 ± .57), leading to overall improvement (MQOidx SMD  =  .30 ± .56). Values in the 'muscle capacity' domain remained stable, while those in 'body composition' showed a slight negative shift. Changes in the 'Pain & HRQoL' domain were heterogeneous. Forty-six percent of participants met responder criteria. Non‑responders were characterised by worsening of values in the 'pain & HRQoL' domain and small deteriorations in the 'muscle capacity' and 'body composition' domains, while still exhibiting measurable improvements in 'functional performance'. Baseline characteristics showed the strongest associations with 'muscle capacity' and 'functional performance', whereas associations with change were limited and primarily involved 'pain & HRQoL' and the composite index (MQOidx). CONCLUSIONS: Early-phase change in these four domains appears asynchronous. The use of a multidomain evaluation framework reveals this heterogeneity and may facilitate the early identification of diverging response trajectories. Baseline characteristics showed stronger associations with baseline domain status than with short-term changes. PROMs showed limited mean short-term change but contributed to identifying divergent outcome trajectories. As this was a single-arm study without a control group, the observed changes cannot be attributed to the intervention alone. Further studies are needed to assess external validity and longer-term stability. TRIAL REGISTRATION NUMBER: NCT05053282 (22.09.2021).