Maximal Fat Oxidation is Related to Performance in an Ironman Triathlon

The aim of the present study was to investigate the relationship between maximal fat oxidation rate (MFO) measured during a progressive exercise test on a cycle ergometer and ultra-endurance performance. 61 male ironman athletes (age: 35 +/- 1 yrs. [23-47 yrs.], with a BMI of 23.6 +/- 0.3kg/m (2) [20.0-30.1kg/m (2) ], a body fat percentage of 16.7 +/- 0.7% [8.4-30.7%] and a VO (2) peak of 58.7 +/- 0.7ml/min/kg [43.9-72.5ml/min/kg] SEM [Range]) were tested in the laboratory between 25 and 4 days prior to the ultra-endurance event, 2016 Ironman Copenhagen. Simple bivariate analyses revealed significant negative correlations between race time and MFO (r (2) =0.12, p<0.005) and VO (2) peak (r (2) =0.45, p<0.0001) and a positive correlation between race time and body fat percentage (r (2) =0.27, p<0.0001). MFO and VO (2) peak were not correlated. When the significant variables from the bivariate regression analyses were entered into the multiple regression models, VO (2) peak and MFO together explained 50% of the variation observed in race time among the 61 Ironman athletes (adj R (2) =0.50, p<0.001). These results suggests that maximal fat oxidation rate exert an independent influence on ultra-endurance performance (>9h). Furthermore, we demonstrate that 50% of the variation in Ironman triathlon race time can be explained by peak oxygen uptake and maximal fat oxidation.