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 (∼95% V̇O2max) 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 ∼70% V̇O2max + 6 × 1-min at 125% V̇O2max 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.