Background
Long-term causal evidence comparing different physical activity patterns and mortality outcomes is needed. Using observational data to emulate an RCT, this study compared different physical activity patterns over 15 years in relation to mortality from all causes, cardiovascular disease (CVD) and cancer in mid-aged Australian women.

Methods
We used the target trial emulation framework to emulate an RCT using data from 11,169 women in the Australian Longitudinal Study on Women’s Health (ALSWH; 1946−51 cohort). We compared two emulated interventions against consistent non-adherence (control) to WHO moderate-to-vigorous physical activity (MVPA) recommendations during the 15-year ‘exposure period’: (1) consistent adherence to recommendations (at least 150 min/week) over 15 years; and (2) starting to meet the recommendations at age 55, 60, or 65 years. Mortality outcomes that occurred between surveys 4−9 (women were 53−58 to 68−73 years), were ascertained from Australian death registries. Analyses were adjusted for sociodemographic and health variables using marginal structural models under the assumptions of conditional exchangeability, positivity, consistency, and no interference.

Results
Comparing consistent adherence to MVPA recommendations with consistent non-adherence, there was evidence (Bayes factor [BF] = 5.71) for a protective effect for all-cause mortality (risk ratio [RR]: 0.50, 99.5% CI [0.27, 0.94]; risk difference [RD]: −5.2%, 99.5% CI [−10.5%, 0.1%]). Findings for CVD (BF = 2.05; RR: 0.50, 99.5% CI [0.19, 1.30]; RD: −2.1%, 99.5% CI [−5.3%, 1.1%]) and cancer mortality (BF = 2.26; RR: 0.35, 99.5% CI [0.10, 1.17]; RD: −3.3%, 99.5% CI [−8.4%, 1.9%]) were more uncertain and less conclusive, as were those for an effect of starting to meet MVPA recommendations in the mid-fifties on mortality outcomes.

Conclusions
Based on findings from this target trial emulation, women should be encouraged to meet physical activity recommendations throughout mid-age to derive mortality benefits.