Developing physical Activity and Sedentary behaviour thresholds for the Secondary prevention of Heart disease...

The dose-response relationship between physical activity and sedentary behaviour (SB) with mortality in people with coronary heart disease (CHD) is unclear. The aim was to identify moderate-to-vigorous physical activity (MVPA) and SB thresholds for mortality risk.

This prospective cohort study comprised Australian participants aged ≥ 45 years with self-reported CHD (2006-2020). Self-reported MVPA (min/wk) and SB (hr/day) were the exposures. Cardiac and all-cause mortality were the main outcomes. Survival regression trees identified MVPA and SB thresholds influencing mortality survival rate. Cox regression models and the C-statistic were used to examine the thresholds, comparing them to public health guidelines.

The cohort included 40,156 participants (mean (SD) age, 70.3(10.3) years; 15,278 females (38%)). During a median follow-up of 11.1 (IQR,6.2-14.4) years, 2,497 cardiac and 12,240 all-cause deaths were recorded. The threshold for MVPA and all-cause and cardiac mortality was ≥ 146 min/wk and ≥ 96 min/wk, respectively. For SB, the threshold for mortality was < 5-6 h/day. Sex-specific differences in thresholds for MVPA and SB were found. All MVPA and SB thresholds had equivalent associated risk reductions and predictive abilities for cardiac and all-cause mortality to the public health guidelines.

The newly identified thresholds suggest that the public health physical activity guidelines are suitable for reducing risks of all-cause mortality in people with CHD. For reducing risks of cardiac mortality, the threshold is suggested to be much lower. The SB suggested thresholds for reducing risks of mortality are 5-6 h/day. Further research is required to explore these thresholds and sex-specific differences.