Synchronization of Exercise Timings Relative to Glycemic Control - A Systematic Review

Background: Diabetes mellitus is a chronic metabolic disorder characterized by impaired glucose regulation. Exercise is a key non-pharmacological strategy to improve insulin sensitivity and metabolic control. Emerging evidence indicates that the timing of exercise, especially in the afternoon, may optimize glycemic outcomes. Objective: To analyze the effect of exercise timing on glycemic markers in individuals with metabolic diseases like diabetes. Methodology: For this review, two authors performed literature searches in numerous databases. For quality assessment Modified Downs and Black Checklist has been used.  After a comprehensive analysis, seven studies met the inclusion criteria. Results: Afternoon timing results had favorable outcomes, showing a decline in their glucose parameters. Unlike morning timing also showed considerable results in a decrease of glycemic factors. Studies reported statistically significant findings in favor of afternoon exercise. For example, Savikj et al. (2018) reported reduced blood glucose levels based on CGM in the afternoon group (6.1 ± 0.4 mmol/l) compared to the morning group (6.6 ± 0.4 mmol/l; p < 0.05). Mancilla et al. (2020) showed a decline in fasting plasma glucose in the afternoon group (−0.3 ± 1.0 mmol/l) versus an increase in the morning group (+0.5 ± 0.8 mmol/l), with a significant intergroup difference (p = 0.02). VO₂ max improvements were significant in both groups with p-values of 0.003 (morning) and 0.001 (afternoon). Additionally, Gomez et al. (2015) found that hypoglycemic events were significantly lower following morning exercise sessions compared to afternoon (p < 0.001). Conclusion: Afternoon timing plays a pivotal role in reducing the glycemic parameters. Future research endeavors should focus on incorporating larger sample sizes, and more randomized control trials should be conducted on the female population Keywords: Circadian Rhythm; Diabetes; Exercise Timing; Muscle Clocks; Morning Exercise; Afternoon Exercise