Preexercise Carbohydrate Feeding and High-Intensity Exercise Capacity: Effects of Timing of Intake and Carbohydrate Concentration

The present study aimed to investigate the influence of timing of pre-exercise carbohydrate feeding (Part A), and carbohydrate concentration (Part B), on short-duration high-intensity exercise capacity. In Part A, seventeen males, and in Part B ten males, performed a peak power output (PPO) test, two familiarisation trials at 90% of PPO, and 4 (for Part A) or 3 (for Part B) experimental trials involving exercise capacity tests at 90% PPO. In Part A, the 4 trials were conducted following ingestion of a 6.4% carbohydrate/electrolyte sports drink ingested 30 (C30) or 120 (C120) minutes before exercise, or a flavour-matched placebo administered either 30 (P30) or 120 (P120) minutes before exercise. In Part B, the 3 trials were performed 30 minutes after ingestion of 0%, 2% or 12% carbohydrate solutions. All trials were performed in a double blind cross-over design following and overnight fast. Dietary intake and activity in the two days before trials was recorded and replicated on each visit. Glucose, lactate, heart rate and mood/arousal were recorded at intervals during the trials. In Part A, C30 produced the greatest exercise capacity (mean±SD; 9.0±1.9 min, P<0.01) compared with all other trials (7.7±1.5 min P30, 8.0±1.7 min P120, 7.9±1.9 min C120). In Part B, exercise capacity (min) following ingestion of the 2% solution (9.2±2.1) compared with 0% (8.2±0.7) and 12% (8.0±1.3) solutions approached significance (p=0.09). This study provides new evidence to suggest that timing of carbohydrate intake is important in short duration high-intensity exercise tasks, but a concentration effect requires further exploration