Illustrating the value of cohort studies in PA epidemiology

Introduction: Randomised controlled trials are accepted as a ‘gold standard’ approach in physical activity (PA) epidemiology. While they are suited to investigating the efficacy of treatment approaches at specific life stages, cohort studies are crucial for answering questions about the patterns of PA and associated health outcomes across the lifespan, in the ‘real world’.
Purpose: To present two examples of how data from a large cohort study of women have challenged conventional thinking about the behavioural epidemiology of physical activity in women.
Methods: Narrative review of findings from the Australian Longitudinal Study on Women’s Health (ALSWH), which has included repeated measures of self-reported PA for >25 years.
Results: ALSWH researchers have published >100 papers on changes in PA across the lifespan, dose-response relationships between PA and health outcomes, interactions of PA with other health behaviours (including sitting time and weight), and relationships between PA and health service use and costs. In this presentation we highlight two examples which challenge conventional thinking in PA epidemiology:
1) PA does not decline at a fixed rate across the adult lifespan in women, and trajectories of physical activity reflect life stages and key events in women’s lives, possibly more so than socio-economic and physical environment factors.
2) Although habitual physical activity confers a benefit of 14-16 years of additional healthy life for women, the rate of functional decline in older age is remarkably similar in active and inactive women, and vigorous PA does not necessarily mean greater benefits at this later life stage.
Conclusions. Cohort studies provide data which are imperative to understanding relationships between PA and health, which cannot always be demonstrated in RCTs.
Practical implications: Cohort studies should not be regarded as ‘second class’ contributors to PA epidemiology.
Funding: The ALSWH is funded by the Australian Government Department of Health.