Peter Res, Zhenping Ding, Matthew O. Witzman, Robert C. Sprague, IV and John L. Ivy
Exercise Physiology and Metabolism Laboratory, Department of Kinesiology and Health Education, The University of Texas, Austin, TX.
Increasing the plasma glucose and insulin concentrations during prolonged variable
intensity exercise by supplementing with carbohydrate has been found to spare muscle
glycogen and increase aerobic endurance. It has also been found that the addition of
protein to a carbohydrate supplement will enhance the insulin response of a carbohydrate
supplement. The purpose of the present study was to compare the effects of a carbohydrate
and a carbohydrate-protein supplement on aerobic endurance performance.
Methods. Ten trained cyclists exercised on 3 separate occasions at intensities that varied between 45 and 75% VO2max for 3 h and then at 85% VO2max until fatigued. Supplements (200 ml) were provided every 20 min and consisted of placebo (CON), an 8% carbohydrate solution (CHO) and an 8% carbohydrate-2% protein solution (CHO- PRO). Treatments were administered using a double-blind randomized design.
Results. CHO supplementation significantly increased time to exhaustion (CHO 19.2±4.1 min vs. CON 10.9±3.4 min), while the addition of protein enhanced the effect of the CHO supplement (CHO-PRO 25.3±4.3 min, p < 0.05). Blood glucose and plasma insulin levels were elevated above CON during CHO and CHO-PRO supplementation. There were no differences in rates of fat or carbohydrate oxidation during CHO and CHO-PRO supplementation, although both of these supplements increased reliance on carbohydrate as a substrate.
Conclusions. In summary, we found that the addition of protein to a carbohydrate supplement in a 4 to 1 ratio enhanced aerobic endurance performance by 24% above that which occurred with carbohydrate alone. The results suggest that the addition of protein to a carbohydrate supplement is of benefit to the endurance athlete.