High-intensity exercise performance is not impaired by low intramuscular glycogen

The purpose of this study was to evaluate the effects of glycogen availability on short-term, high-intensity exercise performance. Eight males completed performance evaluation tasks (PET) consisting of maximum isokinetic strength and endurance, isometric strength, and electrically evoked force of the leg extensors, twice during each of two conditions. On day 1 (D1) of the control condition (C) subjects performed the PET, followed by strenuous exercise designed to deplete glycogen stores of the leg extensors. After consuming a mixed diet for 48h (days 2 and 3) they performed the PET again on day 4 (D4). The experimental condition (E) was identical to C, except that a strictly controlled low carbohydrate diet was consumed during Days 2 and 3. Biopsies from the vastus lateralis before the PET on D4 confirmed differences between conditions in intramuscular glycogen (426 +/- 43 vs 153 +/- 60 mmol glucose units.kg-1 d.w. for C and E respectively, P less than 0.001). Results obtained from the PET were not different between conditions on D4, nor within conditions when D1 and D4 were compared. Resting blood glucose, hematological variables indicative of hydration and acid-base status, and post PET blood lactate were similar for all trials. It is concluded that short-term, high-intensity exercise performance of glycogen depleted leg extensors is not impaired.