Peak Fat Oxidation is not Independently Related to Ironman Performance in Women

The aim of the present study was to investigate if peak fat oxidation rate (PFO) is related to Ironman performance in female athletes. Thirty-six female Ironman athletes (age: 34±1 yrs, [21-45 yrs.] SEM [Range]) with a BMI of 22.1±2.0 kg/m² [18.8-28.4 kg/m²], a body fat percentage of 24.8±1.0% [9.0-37.0%] and a V̇O₂peak of 53.0±1.3 ml/min/kg [36.5-70.5 ml/min/kg] were tested in the laboratory prior to the Ironman Copenhagen 2017. Race time ranged from 9:17:07 to 15:23:48 with mean race time being 11:57:26 h:min:s (717 min). By simple linear regression analyses we found associations between race time and P FO (r²=0.22, p<0.005), V̇O₂peak (r²=0.65, p<0.0001) and the relative exercise intensity eliciting PFO (Fatmax) (r²=0.35, p=0.0001). Furthermore, associations were found between race time and body fat percentage (r²=0.44, p<0.0001) and age (r²=0.16, p<0.05). By means of multiple regression analysis, V̇O₂peak was the only statistically significant variable explaining 64% of the variation in race time (adj. r²=0.64, p<0.005). In conclusion, these results demonstrate that PFO is not independently related to Ironman performance in a heterogeneous group of female athletes. Interestingly, V̇O₂peak alone was able to predict 64% of the variation in Ironman race times.