Background Despite a large evidence base and increasing number of physical activity interventions, rates of physical inactivity and associated chronic diseases are rapidly increasing globally. It is an imperative time to examine if new intervention trials have contributed novel evidence to the field. The purpose of this overview of systematic reviews is to investigate the evolution of evidence for physical activity promotion interventions over time through the analysis of changes in effect sizes for physical activity (PA) and cardiorespiratory fitness (CR) outcome measures.

Methods The search process was conducted in two stages. In the first phase, the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, CINAHL, PsycINFO and Web of Science were searched for systematic reviews that examined the effects of interventions targeted at increasing physical activity within individuals, and included randomised controlled trials. In the second phase, primary studies included within the eligible systematic reviews were pooled. Interventions aiming to increase physical activity in healthy adults at the individual level, assessed through randomised controlled trials, were included. A cumulative meta-analysis was performed separately for interventions with PA and CR outcome measurements.

Results When assessed through cumulative meta-analysis, the totality of the evidence demonstrates that intervention effectiveness has not changed very much over the past fifteen years and that further trials are unlikely to overturn the positive and stabilised findings. The analyses indicate that the effect size for interventions became precise and stable in 2001 after the conduct of 12 physical activity (PA) and 11 cardiorespiratory (CR) outcome trials. In the time following the attainment of these thresholds of stability and precision, 70 further full scale RCTs (59 for PA and 11 for CR outcomes) have been conducted.

Conclusion Substantial evidence exists demonstrating that physical activity interventions can modify individual behaviour. However, there is limited evidence of advancements in intervention effectiveness. Given the stability and sufficiency of the evidence base, researchers are urged to shift focus towards the optimisation and scaling-up of interventions across populations.