Introduction: The aim of this study was to describe maximal fat oxidation (MFO) rates in an athletic population.
Methods: In total, 1121 athletes (933 males, 188 females), from a variety of sports and competitive level, undertook a graded exercise test on a treadmill in a fasted state (≥ 5 h fasted). Rates of fat oxidation were determined using indirect calorimetry.
Results: Average MFO was 0.59 ± 0.18 g∙min-1, ranging from 0.17 – 1.27 g∙min-1. Maximal rates occurred at an average exercise intensity of 49.3 ± 14.8% VO2max, ranging from 22.6 - 88.8% VO2max. In absolute terms, male athletes had significantly higher MFO compared to females (0.61 and 0.50 g∙min-1 respectively, P < 0.001). Expressed relative to fat free mass (FFM), MFO were higher in the females compared to males (MFO/FFM: 11.0 and 10.0 mg∙kg∙FFM-1∙min-1 respectively, P < 0.001). Soccer players had the highest MFO/FFM (10.8 mg∙kg∙FFM-1∙min-1), ranging from 4.1 – 20.5 mg∙kg∙FFM-1∙min-1, whereas, American Football players displayed the lowest rates of MFO/FFM (9.2 mg∙kg∙FFM-1∙min-1). In all athletes, and when separated by sport, large individual variations in MFO rates were observed. Significant positive correlations were found between MFO (g∙min-1) and the following variables: FFM, VO2max, FATMAX (the exercise intensity at which the MFO was observed), percent body fat (%BF) and duration of fasting. When taken together these variables account for 47% of the variation in MFO.
Conclusion: MFO and FATMAX vary significantly between athletes participating in different sports but also in the same sport. Although variance in MFO can be explained to some extent by body composition and fitness status, more than 50% of the variance is not explained by these variables and remains unaccounted for.
Med Sci Sports Exerc. 49(1):133-140.