Influence of Morning and Afternoon Exercise on Body Composition and Metabolic Health

Introduction: Exercise, a non-pharmacological intervention, is widely recognized for its beneficial effects on metabolic health. However, the different effects of morning and afternoon exercise on various metabolic indicators remain unclear. Therefore, this study aimed to systematically evaluate and analyze the effect of exercise at various times on body composition, glucose metabolism, and lipid metabolism. Methods: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, this study conducted a literature search in electronic databases including PubMed, Embase, and Web of Science. The studies included exercise regimens in the morning, afternoon, or morning and evening and analyzed body weight, body mass index, fat mass, fasting blood glucose, hemoglobin A1c (HbA1c), insulin, or triglycerides. The risk of bias was assessed using the Cochrane tool (Rob2), and publication bias was assessed using funnel plots and Egger tests. Results: Thirteen long-term and five acute studies were analyzed (n = 658 participants). Morning training was more effective in reducing body fat (mean deviation [MD] -0.39, 95% confidence interval [CI] -0.66 to -0.13, ), waist circumference (MD -0.53, 95% CI -1.06 to -0.00, I ² = 31%, p = 0.05), and HbA1c (MD -0.11, 95% CI -0.19 to -0.03, I ² = 0%, p = 0.009), whereas afternoon training was better in lowering fasting blood glucose (MD 0.13, 95% CI 0.01 to 0.24, I ² = 0%, p = 0.03) and triglycerides (MD 0.1, 95% CI 0.02 to 0.18, I ² = 41%, p = 0.02). Conclusion: Both morning and afternoon training are beneficial for metabolic health; however, their effects differ. Morning training was more likely to reduce body fat, waist circumference, and HbA1c, whereas afternoon exercise was more likely to reduce fasting blood glucose and triglycerides. Incorporating exercise timing into clinical guidelines could enhance the effectiveness of lifestyle interventions for metabolic disorders.