Limited Benefit of Fat_max-Test to Derive Training Prescriptions

Abstract

The intensity that elicits maximal fat oxidation (Fat_max) is recommended for training fat metabolism. However, it remains unclear whether Fat_max leads to the highest fat oxidation rates during prolonged exercise. It was hypothesized that there are no differences in fat oxidation rates among 3 different exercise intensities. Therefore, fat metabolism was compared among 1-h constant load tests at Fat_max, a higher and a lower intensity. A cohort of 16 male cyclists (28±6 yrs, BMI: 22.5±1.2 kg/m²; n=8 with maximal oxygen uptake [VO_2max] of 50–60 ml/min/kg [ET]; n=8 with VO_2max>60 ml/min/kg [HET]) completed a maximal incremental cycling test, a submaximal incremental Fat_max-test and, thereafter, three 1-h constant-load tests in randomized order at Fat_max, one exercise stage below (LOW) and one above (HIGH). LOW, Fat_max and HIGH were performed at 52±13, 60±13 and 70±12% VO_2max. Heart rate and blood lactate were significantly different (p<0.001). However, the fat oxidation rate showed no difference (p=0.61). This was also true within each subgroup (ET: p=0.69, HET p=0.61). In conclusion, the fat oxidation rate of endurance trained cyclists shows no difference between 1-h constant load exercise bouts at about 50–70% VO_2max. The precision and necessity of Fat_max-tests for controlling the training of fat oxidation are therefore debatable.

Key words

fat metabolism - fat oxidation - indirect calorimetry - intensity - cycling - training

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