Maximal Fat Oxidation During Exercise in Trained Men

Abstract

Fat oxidation increases from low to moderate exercise intensities and decreases from moderate to high exercise intensities. Recently, a protocol has been developed to determine the exercise intensity, which elicits maximal fat oxidation rates (Fat_max). The main aim of the present study was to establish the reliability of the estimation of Fat_max using this protocol (n = 10). An additional aim was to determine Fat_max in a large group of endurance-trained individuals (n = 55). For the assessment of reliability, subjects performed three graded exercise tests to exhaustion on a cycle ergometer. Tests were performed after an overnight fast and diet and exercise regime on the day before all tests were similar. Fifty-five male subjects performed the graded exercise test on one occasion. The typical error (root mean square error and CV) for Fat_max and Fat_min was 0.23 and 0.33 l O₂ × min^-1 and 9.6 and 9.4 % respectively. Maximal fat oxidation rates of 0.52 ± 0.15 g × min^-1 were reached at 62.5 ± 9.8 % V·O₂max, while Fat_min was located at 86.1 ± 6.8 % V·O₂max. When the subjects were divided in two groups according to their V·O₂max, the large spread in Fat_max and maximal fat oxidation rates remained present. The CV of the estimation of Fat_max and Fat_min is 9.0 - 9.5 %. In the present study the average intensity of maximal fat oxidation was located at 63 % V·O₂max. Even within a homogenous group of subjects, there was a relatively large inter-individual variation in Fat_max and the rate of maximal fat oxidation.

Key words

Reproducibility - typical error - cycling - indirect calorimetry - exercise intensity

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