Effect of pre-exercise carbohydrate availability on fat oxidation and energy expenditure after a high-intensity exercise

The aim of this study was to test the hypothesis that reduced pre-exercise carbohydrate (CHO) availability potentiates fat oxidation after an exhaustive high-intensity exercise bout. Eight physically active men underwent a high-intensity exercise (similar to 95%. (V) over dotO(2max)) until exhaustion under low or high pre-exercise CHO availability. The protocol to manipulate pre-exercise CHO availability consisted of a 90-min cycling bout at similar to 70%. (V) over dotO(2max)+ 6 x 1-min at 125%. (V) over dotO(2max) with 1-min rest, followed by 48 h under a low-(10% CHO, low-CHO availability) or high-CHO diet (80% CHO, high-CHO availability). Time to exhaustion was shorter and energy expenditure (EE) lower during the high-intensity exercise in low-compared to high-CHO availability (8.6 +/- 0.8 and 11.4 +/- 1.6 min, and 499 +/- 209 and 677 +/- 343 kJ, respectively, P<0.05). Post-exercise EE was similar between low- and high-CHO availability (425 +/- 147 and 348 +/- 54 kJ, respectively, P>0.05), but post-exercise fat oxidation was significantly higher (P<0.05) in low- (7,830 +/- 1,864 mg) than in high-CHO availability (6,264 +/- 1,763 mg). The total EE (i.e., exercise EE plus post-exercise EE) was similar between low-and high-CHO availability (924 +/- 264 and 1,026 +/- 340 kJ, respectively, P>0.05). These results suggest that a single bout of high-intensity exercise performed under low-CHO availability increased post-exercise fat oxidation, and even with shorter exercise duration, both post-exercise EE and total EE were not impaired.