Intensity modifies the association between continuous bouts of physical activity and risk of mortality: A prospective UK Biobank cohort analysis

Recent evidence suggests continuous bouts of physical activity (PA) are associated with longevity. We hypothesized the risk of mortality would be lower when the most active minutes of the day were in a continuous bout. PA was assessed using accelerometery in UK Biobank participants. The intensity of the most active continuous (MXCONT) and accumulated (MX) X min of the day, and their ratio (MXRATIO = MXCONT/MX), were determined. MXRATIO indicates how the most active minutes of the day are accumulated, ranging from a single continuous bout through to sporadic accumulation spread across the day. Durations (X) considered ranged from 1 to 20 min. The outcome was mortality. In total, 94,541 participants (56.5% female) were included. Over a median (interquartile range) follow-up of 6.9 (6.3, 7.4) years, 2649 (2.8%) deaths occurred. Intensity moderated the association between how the most active minutes of the day were accumulated and mortality risk, expressed relative to sporadically accumulated moderate PA. If the most active minutes were of moderate intensity, the risk of mortality was halved for continuous compared to sporadic accumulation, irrespective of duration; if the most active minutes were of vigorous intensity, a continuous bout was associated with the lowest risk for durations under 5 min (e.g., 3 min: hazard ratio (HR) = 0.27, (95%confidence interval (95%CI): 0.21-0.34)), while sporadic accumulation was associated with the lowest risk for durations beyond 5 mins (HR = 0.11, (95%CI: 0.08-0.15) for the most active 20 min). Optimal PA patterns for reducing mortality differ by intensity and duration. For moderate-intensity PA, a lower mortality risk may be optimized by prioritizing continuous PA for up to 20 min. However, for vigorous-intensity PA, multiple short bouts (<5 min) may be optimal. This suggests tailored PA recommendations may enhance longevity benefits.