Determination of maximal fat oxidation for prescribing exercise in healthy sedentary subjects

PURPOSE: Physical activity is recommended as a component of weight management. Exercise intensity has been showed to be one of the most important factors in determining substrate utilization. Purpose of our study was to determine the level at which physical exercise elicits maximal fat oxidation. METHODS: Fifteen healthy sedentary subjects, 8 men and 7 women, mean age 53 (range 37 – 71), BMI 26,6  1,33 performed an incremental exercise test to exhaustion on treadmill, using Bruce protocol. Breath-by-breath measurements of VO2 (ml/Kg/min) were detected throughout exercise and FAT rate (mg/Kg/min) was determined using indirect calorimetry (Cosmed, Quark CPET). The data is shown as mean values ± standard error of the mean. For the statistical analysis of the data, linear regression analysis was used. RESULTS: The average VO2max was 28,63±2,03 ml/Kg/min (men 30,91±3,27; women 26,03±2,08 ml/Kg/min). FATmax of 7,19±0,77 mg/Kg/min (men 0,80±1,22; women 6,26±0,84 mg/Kg/min) was reached at VO2 of 18,23±1,28 ml/Kg/min (men 18,85±2,03; women 17,51±1,59 ml/Kg/min) and it was located at 64±2,05 %VO2max (men 61±2,06; women 68±4,96 %VO2max). A positive linear correlation between FATmax and VO2 at FATmax (r=0,85, p<0,0001) has been found. CONCLUSIONS: Our data demonstrate that in healthy sedentary subjects the maximal fat oxidation rate was located at 64 %VO2max (range of intensity 55-75 %VO2max). In addition, our result showed that women utilize fat acid substrate on a wider range of exercise intensity (55-80 %VO2max) than men (55-67 %VO2max), suggesting that this difference must be taken into account when prescribing exercise for weight management in healthy sedentary subjects.