Diurnal variation of fat oxidation rate and energy expenditure in an acute bout of endurance exercise by young healthy males.

BACKGROUND

Few studies have reported that circadian rhythm affects fat oxidation (FOx) during exercise. Time-of-day causing greater FOx and energy expenditure (EE) during exercise would be beneficial in the prevention of physical inactivity-related health disorders such as metabolic syndrome. The study aims to compare EE and FOx rate after an endurance exercise session done in the morning and late-afternoon hours by apparently healthy young male participants.

MATERIAL AND METHODS

The present crossover quasi-experimental study involved 10 moderately active but physically untrained male participants of age 18-25 years with normal body mass index. Participants did a steady-state exercise on a motorized treadmill for 30 minutes at a moderate-intensity (50 ± 2% of their heart rate reserve) on two separate occasions at 9:00-10:00 and 15:00-16:00. A similar meal followed by 2 hours of fasting was done before each trial session. During the last 2 minutes of the exercise session, the respiratory gas analysis estimated volume of oxygen (VO) and volume of carbon dioxide (VCO) consumed in L/min. Indirect calorimetry equations assessed FOx (mg/min), EE (Kcal/min) and respiratory exchange ratio (RER). Data of one participant were removed to adjust for extreme chronotype. Paired -test was applied, and ≤ 0.05 was considered significant.

RESULTS

Morning versus late-afternoon variations in FOx (269 ± 110 vs 290 ± 110, = 0.016), RER (0.86 ± 0.05 vs 0.85 ± 0.05, = 0.040), EE (5.454 ± 0.987 vs 5.494 ± 0.959, = 0.079) and VO2 (1.104 ± 0.201 vs 1.113 ± 0.196, = 0.035) were present after adjustment for chronotype.

CONCLUSION

In an acute bout of endurance, exercise done by young and healthy male individuals, FOx was significantly higher, while EE tends to be higher in late-afternoon than in the morning.