Correlation Between Heart Rate at Maximal Fat Oxidation and Aerobic Threshold in Healthy Adolescent Boys and Girls

Purpose : To investigate the association between the heart rate (HR) at maximal fat oxidation (MFO) and the HR at the aerobic threshold (AerT) in adolescent boys and girls, and to identify sex differences in the intensity that elicits MFO (Fat max ) as a percentage of HR peak (HR peak ). Methods : Fifty-eight healthy adolescents participated in this study (29 boys and 29 girls). Participants performed a cardiopulmonary exercise test on a cycle ergometer. MFO was calculated using a stoichiometric equation, and the AerT was identified using gas exchange parameters. Results : A strong correlation between HR at Fat max and HR at AerT was found in both boys and girls ( r = .96 and .94, respectively). Fat max as a percentage of HR peak occurred at 61.0% (4.9%) of HR peak and 66.8% (6.9%) of HR peak in adolescent boys and girls ( P = .001, F = 13.6), respectively. MFO was higher in boys compared with girls (324 [150] and 240 [95] mg/min, respectively), and no sex differences were observed in the relative contribution of fat to energy expenditure at Fat max . Conclusions : HR at Fat max and HR at AerT were highly correlated in adolescent boys and girls. Girls obtained Fat max at a higher percentage of HR peak than boys.