Effect of a 1-hour single bout of moderate-intensity exercise on fat oxidation kinetics

The present study aimed to examine the effects of a prior 1-hour continuous exercise bout (CONT) at an intensity (Fatmax) that elicits the maximal fat oxidation (MFO) on the fat oxidation kinetics during a subsequent submaximal incremental test (IncrC). Twenty moderately trained subjects (9 men and 11 women) performed a graded test on a treadmill (Incr), with 3-minute stages and 1-km·h−1 increments. Fat oxidation was measured using indirect calorimetry and plotted as a function of exercise intensity. A mathematical model (SIN) including 3 independent variables (dilatation, symmetry, and translation) was used to characterize the shape of fat oxidation kinetics and to determine Fatmax and MFO. On a second visit, the subjects performed CONT at Fatmax followed by IncrC. After CONT performed at 57% ± 3% (means ± SE) maximal oxygen uptake (V̇o2max), the respiratory exchange ratio during IncrC was lower at every stage compared with Incr (P < .05). Fatmax (56.4% ± 2.3% vs 51.5% ± 2.4% V̇o2max, P = .013), MFO (0.50 ± 0.03 vs 0.40 ± 0.03 g·min−1, P < .001), and fat oxidation rates from 35% to 70% V̇o2max (P < .05) were significantly greater during IncrC compared with Incr. However, dilatation and translation were not significantly different (P > .05), whereas symmetry tended to be greater in IncrC (P = .096). This study showed that the prior 1-hour continuous moderate-intensity exercise bout increased Fatmax, MFO, and fat oxidation rates over a wide range of intensities during the postexercise incremental test. Moreover, the shape of the postexercise fat oxidation kinetics tended to have a rightward asymmetry.