A Mathematical Model to Describe Fat Oxidation Kinetics during Graded Exercise

CHENEVIERE, X., D. MALATESTA, E. M. PETERS, and F. BORRANI. A Mathematical Model to Describe Fat Oxidation Kinetics during Graded Exercise. Med. Sci. Sports Exerc., Vol. 41, No. 8, pp. 1615-1625, 2009. Purpose: The purpose of this study was to develop a mathematical model (sine model, SIN) to describe fiat oxidation kinetics as a function of the relative exercise intensity [% of maximal Oxygen uptake (%(V) over dotO(2max))] during graded exercise and to determine the exercise intensity (Fat(max)) that elicits maximal fat oxidation (MFO) and the intensity at which the fat oxidation becomes negligible (Fat(min)). This model included three independent variables (dilatation. symmetry. and translation) that incorporated primary expected modulations of the curve because of training level or body composition. Methods: Thirty-two healthy volunteers (17 women and 15 men) performed a graded exercise test on a cycle ergometer, with 3-min stages and 20-W increments. Substrate oxidation rates were determined using indirect calorimetry. SIN was compared with measured values (MV) and with other methods currently used [i.e., the RER method (MRER) and third polynomial curves (P3)]. Results: There was no significant difference in the fitting accuracy between SIN and P3 (P = 0.157), whereas MRER was less precise than SIN (P < 0.001). Fat(max) (44 +/- 10% (V) over dotO(2max)) and MFO (0.37 +/- 0.16 g.min(-1)) determined using SIN were significantly correlated with MV, P3, and MRER (P < 0.001). The variable of dilatation was correlated with Fat(max), Fat(min), and MFO (r = 0.79, r = 0.67. and r = 0.60, respectively, P < 0.001). Conclusions: The SIN model presents the same precision as other methods currently used in the determination of Fat(max) and MFO but in addition allows calculation of Fat(min). Moreover, the three independent variables are directly related to the main expected modulations of the fat oxidation curve. SIN, therefore, seems to be an appropriate tool in analyzing fat oxidation kinetics obtained during graded exercise.