1. The effect of carbohydrate (CHO) ingestion on muscle glycogen utilization during exercise was examined on seven male subjects completing two 60 min treadmill runs at 70% maximum oxygen uptake (VO2,max), 1 week apart. On each occasion the subjects consumed either water or a 5.5% CHO-electrolyte solution immediately before and during exercise. Muscle samples were obtained from the vastus lateralis by needle biopsy before and immediately after exercise. Venous blood samples were also collected from an ante-cubital vein at rest and at 10, 20, 40 and 60 min into the run. 2. Higher blood glucose concentrations (P < 0.01) were observed throughout the run during the CHO trial compared with the water trial. Serum insulin concentration was only higher after 20 min of exercise (P < 0.01). 3. A 28% reduction in mixed glycogen utilization was observed as a result of CHO ingestion when compared with water ingestion (108.7 +/- 16.3 vs. 150.9 +/- 19.9 mmol (kg dry matter)-1, respectively; P < 0.01). 4. The ingestion of the CHO solution resulted in sparing of glycogen in type I (slow twitch) fibres only (38 +/- 7% degradation of glycogen as opposed to 66 +/- 3% during the water trial; P = 0.01).
