A MODERATE GLYCEMIC MEAL BEFORE ENDURANCE EXERCISE CAN ENHANCE PERFORMANCE

The purpose of this study was to determine whether presweetened breakf ast cereals with various fiber contents and a moderate glycemic index optimize glucose availability and improve endurance exercise performan ce. Six recreationally active women ate 75 g of available carbohydrate in the form of breakfast cereals: sweetened whole-grain rolled oats ( SRO, 7 g of dietary fiber) or sweetened whole-oat flour (SOF, 3 g of d ietary fiber) and 300 ml of water or water alone (Con). The meals were provided 45 min before semirecumbent cycle ergometer exercise to exha ustion at 60% of peak O-2 consumption ((V) over bar O-2peak). Diet and physical activity were controlled by having the subjects reside in th e General Clinical Research Center for 2 days before each trial. Blood samples were drawn fi om an antecubital vein for glucose, free fatty acid (FFA), glycerol, insulin, epinephrine, and norepinephrine determi nation. Breath samples were obtained at 15-min intervals after meal in gestion and at 30-min intervals during exercise. Muscle glycogen conce ntration was determined from biopsies taken from the vastus lateralis muscle before the meal and immediately after exercise. Plasma FFA conc entrations were lower (P < 0.05) during the SRO and SOF trials for the first 60 and 90 min of exercise, respectively, than during the Con tr ial. Respiratory exchange ratios were higher (P < 0.05) at 90 and 120 min of exercise for the SRO and SOF trials, respectively, than for the Con trial. At exhaustion, glucose, insulin. FFA, glycerol, epinephrin e, and norepinephrine concentrations, respiratory exchange ratio, and muscle glycogen use in the vastus lateralis muscle were similar for al l trials. Exercise time to exhaustion was 16% longer (P < 0.05) during the SRO than during the Con trial: 266.5 +/- 13 and 225.1 +/- 8 min, respectively. There was no difference in exercise time for the SOF (25 0.8 +/- 12) and Con trials. We conclude that eating a meal with a high dietary fiber content and moderate glycemic index 45 min before prolo nged moderately intense exercise significantly enhances exercise capac ity.