Increasing and maintaining physical activity in later life: a target trial emulation of daily living problems or death across three ageing cohorts

Abstract Background Maintaining independence and survival are central goals of healthy ageing. For older adults who have been less active, the association of increasing and maintaining physical activity with subsequent daily living problems or death has implications for health promotion and programme planning. Methods We emulated sequential, visit-defined target trials using longitudinal cohorts from the USA, Europe and South Korea. Participants were aged 65 years or older, previously less active and independent in five basic activities of daily living (ADLs). We compared increased activity frequency maintained at the first follow-up with persistently lower frequency. Overlap weighting and inverse-probability adjustment for adherence and outcome observation estimated cumulative risks over two subsequent visits, generally about four years. Post hoc analyses examined baseline prognosis and hypothetical programme coverage. Results The analysis included 19204 participants contributing 43754 eligible trial entries. Risk ratios for an ADL problem or death were 0.776 (95% confidence interval 0.728–0.827) in the US cohort, 0.764 (0.672–0.868) in the European cohort and 0.725 (0.643–0.816) in the South Korean cohort (all P < 0.001). Absolute risk differences were − 7.08, − 8.15 and − 4.89 percentage points, respectively. Mortality contributed substantially to these differences; evidence for ADL problems alone was less consistent. Larger absolute differences at higher baseline risk remained supported after multiplicity adjustment in the US cohort. Risk priority did not clearly outperform age priority in any cohort. With 50% programme reach and 50% strategy achievement among those reached, modelled reductions relative to the natural activity course were approximately 9–11 events per 1000 eligible entries. Conclusions Increasing and maintaining activity frequency was associated with lower risk of daily living problems or death across three ageing cohorts, with the clearest common signal concerning survival. These findings support evaluating sustained activity support within healthy ageing programmes, with attention to programme reach and successful strategy achievement.