Maximal Fat Oxidation by Heart Rate Variability in Physically Active Subjects

Introduction: the objective of this study is to identify the intensity of the maximal fat oxidation point (Fatmax) and its relationship to the first heart rate variability threshold (HRVT1). Subjects and methods. 23 subjects (10 M; 13 W), BMI 24.3 ± 3.1 kg/m2, age 32 ± 10 years, physically active (≥ 600 METS minute-week), performed an incremental step test on a cycloergometer. V · O2, V · CO2, HRV and fat oxidation were recorded for each stage. Measurements of central tendency, mean contrast, correlation coefficient and Bland-Altman plot analysis were used for the statistical analysis. Results. The values for Fatmax vs. HRVT1 were 48.7 ± 7.1 vs. 55.4 ± 9.2 %V · O2peak, 68 ± 34 vs. 84 ± 39 Watts, 112 ± 14 vs. 125 ± 11 bpm and 1.25 ± .49 vs. 1.41 ± .54 L · min-1; all intensities presented significant differences (p < .01) and correlations higher than .8 were identified for W and V · O2. The SD1 value in Fatmax was 5.56 ± 2.8 ms. Fatmax was at 84.2; 90.5 and 90.5% of the load in W, HR and V · O2peak of HRVT1, respectively. The value of 84.2% HRVT1 and SD1 = 5.56 in intensity of watts did not present significant differences (p > .05), correlations higher than .8, a bias of ≈3W and a good level of agreement with the values of Fatmax. Conclusion: there is correlation between HRVT1 and Fatmax in the V ·
O2 and Watts variables. The watts load of Fatmax can be identified using this relationship.