To study the effects of different exercise intensity performed at different exercise times on lipid metabolism response during prolonged exercise. Nine young men performed endurance exercise at different exercise intensities (60%VO₂max or Fatmax) in the morning (9 am to 10 am) or evening (5 pm to 6 pm); blood samples were collected before exercise and immediately and one and two hours after exercise completion. Expired gas was analyzed from the start of exercise until two hours after exercise completion. There were no significant changes in catecholamine (adrenaline and noradrenaline) and free fatty acid levels between morning and evening trials for each endurance exercise intensity. However, the morning and evening trials both exhibited significantly higher lipid oxidation at Fatmax than that at 60%VO₂max. These results suggest that exercise at Fatmax offers greater lipid oxidation than that at 60%VO₂max, regardless of exercise timing.

• It is important to consider exercise intensity when evaluating lipid oxidation.

• Few studies have investigated the effects of the intensity of exercise on lipid oxidation in the morning and evening.

• Fat_max exhibited greater total lipid oxidation compared to that of 60%VO_2max when energy expenditure was equated, but time of day did not affect lipid oxidation in prolonged exercise.