Dietary carbohydrate intake and endurance exercise performance of trained female cyclists
1989
O'Keeffe, K.A. | Keith, R.E. | Wilson, G.D. | Blessing, D.L.
Seven highly trained female cyclists (age 22 +/- 5 yr, average +/- SD; wt:60 +/- 5 kg; ht:165 +/- 6 cm; VO2 max: 55 +/- 6 ml/min/kg) rode on a cycle ergometer at 80% VO2 max to fatigue following week-long consumption of isocaloric diets containing low (LCHO), moderate (MCHO) or high carbohydrate (HCHO) content (13%, 54%, 72% of total kcal). Total caloric intake was the normal intake for subjects. Subjects were randomly assigned to dietary treatments with all subjects eventually consuming all diets. Expired air and blood samples were taken before, during, and at the end of each exercise session. Respiratory exchange (R) values and plasma glucose and lactate concentrations were determined. Results indicated that mean exercise time to fatigue increased with increasing dietary carbohydrate content (LCHO:60 +/- 12 min; MCHO:98 +/- 13; HCHO:113 +/- 28). Exercise time on LCHO was significantly shorter (p less than 0.05) compared to MCHO and HCHO. Individually, most subjects rode the longest when consuming 6-7 g CHO/kg body weight (HCHO diet). Mean R values during exercise were significantly greater (p less than 0.05) following HCHO than LCHO or MCHO. There were no differences among groups for mean plasma glucose or lactate concentrations. In the present study, female athletes increased their time to fatigue as the carbohydrate content of their normal diets increased.
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