The impact of physical activity and exercise timing on metabolic health among individuals at high risk of type 2 diabetes.

The timing of physical activity and exercise has been suggested to play a role in metabolic health. This narrative review synthesises current evidence on the impact of habitual physical activity and exercise timing on glucose homeostasis and insulin sensitivity, blood lipids and body composition among individuals with overweight, obesity and impaired glucose homeostasis. To this end, we reviewed evidence from both observational and experimental studies. Overall, current evidence on physical activity/exercise timing and metabolic health is inconsistent, with several studies reporting no significant time-dependent differences, and other studies suggesting more favourable glucose-related outcomes and improved insulin sensitivity and lipid profiles when physical activity/exercise is performed later in the day. Body composition outcomes appear to be largely independent of exercise timing. The interpretation of the current evidence is limited by the small number of studies, heterogenous study designs and variability in exercise modalities and durations. We identify important gaps in knowledge, particularly regarding sex-specific responses, the role of chronotype and the real-world feasibility of timing-based exercise recommendations. While engaging in physical activity or exercise at any time of day is more beneficial than remaining inactive, further studies are warranted to clarify the optimal timing for metabolic health in individuals at risk of type 2 diabetes.