The effect of timing of physical exercise on glycemia: a systematic review and meta-analysis of human intervention studies

Abstract Aim Physical exercise (PE) may be important for glucose metabolism. Therefore, this systematic review and meta-analysis aims to investigate the effect of PE performed in the morning versus afternoon or evening on glycemia parameters in human intervention studies. Methods MEDLINE and Embase.com were searched until February 2023 for intervention studies in the general adult population, examining the effect the timing of PE on glycemia parameters after one or multiple bouts of exercise. Results were meta-analysed using a random-effects models where appropriate or were described using qualitative synthesis. Results 55,569 publications were screened for a series of reviews, of which 20 studies (680 participants) were included in this review. In studies including one bout of PE ( n = 12), glucose levels measured directly after PE were 0.26 mmol/L (95%CI -0.18;0.70, I 2 = 81%, n = 3) higher after morning PE, compared to afternoon PE. Studies including repeated PE for 1–12 weeks ( n = 8), showed that fasting glucose was 0.25mmol/L (95%CI 0.02;0.47, I 2 = 32%, n = 7) higher in morning PE, compared to afternoon/evening PE. Other outcomes (e.g. 24 h mean glucose, HOMA-IR) could not be meta-analyzed and were assessed qualitatively, showing no associations or results in line with the results above. Only time in range (TIR) and hypoglycemic events tended to favor morning PE. Conclusion This review suggests that fasting glucose may be higher following morning PE, compared with afternoon or evening PE in long-term studies. Evidence on glucose directly after PE in acute studies and other glycemic outcomes remains limited and inconclusive. The included studies were generally small, heterogeneous in design and interventions, and often did not account for important factors such as nutritional intake and chronotype. Therefore, well-designed, adequately powered trials that account for lifestyle factors and assess clinically relevant outcomes are needed to clarify these associations. Trial registration This review is part of a larger search ‘The effect of altering timing of physical activity, sleep and energy intake on glycemia and Type 2 Diabetes risk in humans’, of which the protocol was registered in the PROSPERO database on November 27 th , 2021 under number: CRD42021287828.