Should physical activity intervention efforts take a whole population, high-risk, or middle road strategy?

Purpose: This study was designed to compare theoretical strategies for changing physical activity (PA) in terms of their potential to reduce the incidence of chronic conditions in midage women: (1) whole population: +30 minutes/week in all, (2) high-risk: +60 minutes/week in the lowest 25% of the PA distribution, and (3) middle road: shift all those not meeting guidelines to a level commensurate with meeting guidelines. Methods: 10,854 participants (50-55 years in 2001) in the Australian Longitudinal Study of Women's Health completed mail surveys in 2001, 2004, 2007, and 2010. PA was calculated as MET·minutes/week spent in walking, moderate and vigorous PA in the previous week. Incidence rates per 1000 person-years for diabetes, heart disease, hypertension, cancer, and depression were calculated for the actual distribution and after modeled shifts in PA. Results: The incidence rates were 10.6 for diabetes, 7.0 for heart disease, 30.7 for hypertension, 8.0 for cancer, and 28.4 for depression. Greater reductions in incidence were found for the middle road strategy than for the whole population and high-risk strategies, with reductions ranging from -6.3% for cancer to -12.3% for diabetes. Discussion: This theoretical modeling showed that a middle road strategy to increasing PA was superior to the whole population and high-risk strategies, in terms of reducing incidence rates of chronic conditions in middle-aged women.