Relationship Between Training Status and Maximal Fat Oxidation Rate

This study aimed to compare maximal fat oxidation rate parameters between moderate- and low-performance runners. Eighteen runners performed an incremental treadmill test to estimate individual maximal fat oxidation rate (Fat_max) based on gases measures and a 10,000-m run on a track. The subjects were then divided into a low and moderate performance group using two different criteria: 10,000-m time and VO₂max values. When groups were divided using 10,000-m time, there was no significant difference in Fat_max (0.41 ± 0.16 and 0.27 ± 0.12 g.min^-1, p = 0.07) or in the exercise intensity that elicited Fat_max (59.9 ± 16.5 and 68.7 ± 10.3 % O₂max, p = 0.23) between the moderate and low performance groups, respectively (p > 0.05). When groups were divided using VO₂max values, Fat_max was significantly lower in the low VO₂max group than in the high VO₂max group (0. 29 ± 0.10 and 0.47 ± 0.17 g.min^-1, respectively, p < 0.05) but the intensity that elicited Fat_max did not differ between groups (64.4 ± 14.9 and 61.6 ± 15.4 %VO₂max). Fat_max or %VO₂max that elicited Fat_max was not associated with 10,000 m time. The only variable associated with 10,000-m running performance was %VO₂max used during the run (p < 0.01). In conclusion, the criteria used for the division of groups according to training status might influence the identification of differences in Fat_max or in the intensity that elicits Fat_max.

Key points

• The results of the present study suggest that the criteria used to categorize aerobic training status of subjects can influence the magnitude of differences in Fat_max.
• The Fat_max is similar between groups with similar 10,000-m running performance.
• The 10,000-m running performance seems to be associated with an increased ability to oxidize carbohydrate.

Key words: fat oxidation, running performance, indirect calorimetry