Differential benefits of 12-week morning vs. evening aerobic exercise on sleep and cardiometabolic health: a randomized controlled trial

Modern life and rising stress have contributed to increased sleep disorders and metabolic and cardiovascular diseases. While exercise is known to be an important health intervention, the optimal timing for its effectiveness remains uncertain. This study aims to investigate the effects of a 12-week timed exercise program on sleep, lipid profiles, and vascular function. Fifty-eight sedentary males were divided into three groups: morning exercise (ME) at 6–8 a.m., evening exercise (EE) at 6–8 p.m., and control group (CON) without exercise. The 12-week intervention involved moderate-intensity aerobic exercise (≥ 150 min/week). Sleep was assessed using the Munich ChronoType Questionnaire (MCTQ) and Dim Light Melatonin Onset (DLMO). Metabolic indicators were assessed through body composition and blood biochemical tests. Ultrasound imaging was performed to evaluate hemodynamics at the common carotid artery. Both exercise groups reduced body fat after 12-week exercises, with ME showing significant reductions as early as week 4. Total cholesterol and triglycerides in ME also decreased. Shortened sleep latency was observed in both exercise groups, with DLMO and sleep advanced in ME. Although both exercise groups showed decreased stiffness and increased wall shear stress, EE demonstrated greater enhancements in blood flow rate, center-line velocity, carotid artery dilation and lowering systolic blood pressure. A 12-week aerobic exercise significantly improves physical health in sedentary adults. Morning exercise (6–8 a.m.) is particularly effective for rapid body fat reduction, lowering plasma cholesterol and triglycerides, and advancing sleep-wake cycle. Evening exercise (6–8 p.m.) is more effective for enhancing vascular function. Trial registration: Chinese Clinical Trial Registry, ChiCTR2400094208, 18/12/2024.