Effects of acute carbohydrate supplementation during sessions of high-intensity intermittent exercise

The present study evaluated the acute effects of carbohydrate supplementation on heart rate (HR), rate of perceived exertion (RPE), metabolic and hormonal responses during and after sessions of high-intensity intermittent running exercise. Fifteen endurance runners (26 +/- 5 years, 64.5 +/- 4.9 kg) performed two sessions of intermittent exercise under carbohydrate (CHO) and placebo (PLA) ingestion. The sessions consisted of 12 x 800 m separated by intervals of 1 min 30 s at a mean velocity corresponding to the previously performed 3-km time trial. Both the CHO and PLA sessions were concluded within similar to 28 min. Blood glucose was significantly elevated in both sessions (123.9 similar to 13.2 mg dl(-1) on CHO and 147.2 +/- 16.3 mg dl(-1) on PLA) and mean blood lactate was significantly higher in the CHO (11.4 +/- 4.9 mmol l(-1)) than in the PLA condition (8.4 +/- 5.1 mmol l(-1)) (P < 0.05). The metabolic stress induced by the exercise model used was confirmed by the elevated HR (similar to 182 bpm) and RPE (similar to 18 on the 15-point Borg scale) for both conditions. No significant differences in plasma insulin, cortisol or free fatty acids were observed during exercise between the two trials. During the recovery period, free fatty acid and insulin concentrations were significantly lower in the CHO trial. Supplementation with CHO resulted in higher lactate associated with lipolytic suppression, but did not attenuate the cortisol, RPE or HR responses.