Key result
Morning aerobic exercise reduces carbohydrate oxidation and lowers respiratory exchange ratio versus afternoon exercise.
Why the study?
The time-of-day effect of exercise on physiological cardiorespiratory and metabolic responses in humans remains less clear.
Does morning aerobic exercise alter cardiorespiratory and metabolic responses compared to afternoon exercise in healthy young adults?
Population
30 healthy young adults (15 men, 15 women) aged 20.9 ± 1.5 years
Comparison
Morning aerobic exercise before 9 am vs afternoon aerobic exercise after 3 pm
Design
Randomized crossover trial
Follow-up
30 minutes per exercise session
Authors
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Morning exercise may favor fat oxidation in healthy adults; leaves open whether timing or chronotype matching improves cardiometabolic outcomes.
RCT (n=30)
randomized
Does morning aerobic exercise alter cardiorespiratory and metabolic responses compared to afternoon exercise in healthy young adults?
Absolute Event Rate: 0.92% vs 0.941%
p-value: p=< 0.05
Morning aerobic exercise may be more effective in mobilizing fat as an energy source compared with afternoon exercise, and exercising heart rate varies significantly by individual chronotype.
Kang et al. (2025) conducted an RCT in Healthy adults (n=30). Morning aerobic exercise (before 9 am) vs. Afternoon aerobic exercise (after 3 pm) was evaluated on Respiratory exchange ratio (RER) (p=< 0.05). Morning aerobic exercise yielded a lower respiratory exchange ratio (0.920 vs 0.941) and carbohydrate oxidation rate (27.83 vs 30.65 mg/kg/min) than afternoon exercise (p<0.05).
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