Timing of supervised exercise and cardiometabolic risk markers in adults: A systematic review and meta-analysis of randomized controlled trials

Objectives Regular exercise improves cardiometabolic health; however, the magnitude of its benefits may vary by time of day. To evaluate whether the timing of supervised exercise training is associated with differences in cardiometabolic outcomes in adults. Study design Systematic review and meta-analysis of randomized controlled trials. Methods PubMed, EMBASE, Cochrane Library, Web of Science, and Scopus were searches from inception to March 2026. Randomized controlled trials (RCTs) of ≥2 weeks comparing supervised exercise performed at different times of day in adults and reporting cardiometabolic outcomes were eligible. Mean difference (MD) with 95% confidence intervals (CIs) were pooled using random-effects models with restricted maximum likelihood estimation. Knapp–Hartung and leave-one-out sensitivity analyses, exploratory subgroup analyses, and GRADE assessment were performed. Results Twelve RCTs (n = 879) were included. Later-day exercise was associated with a small reduction in fasting blood glucose compared with earlier exercise (MD = 0.16 mmol/L, 95% CI 0.03 to 0.29; I 2 = 0.0%). This finding remained statistically significant with Knapp–Hartung adjustment. No clear timing-related differences were observed for HbA1c, fasting insulin, HOMA-IR, blood lipids, systolic or diastolic blood pressure, BMI, or fat mass. Systolic blood pressure showed substantial heterogeneity ( I 2 = 72.5%). Certainty of evidence ranged from very low to moderate across outcomes. Conclusions Later-day exercise was associated with a small reduction in fasting blood glucose, but current evidence does not support a consistent advantage of a specific exercise time for other cardiometabolic outcomes. Larger, well-standardized RCTs are needed before specific exercise-timing recommendations can be made.