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. Furthermore, 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. Nine 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, a 7.75% carbohydrate solution, and a 7.75% carbohydrate / 1.94% protein solution. Treatments were administered using a double-blind randomized design. Carbohydrate supplementation significantly increased time to exhaustion (carbohydrate 19.7 ± 4.6 min vs. placebo 12.7 ± 3.1 min), while the addition of protein enhanced the effect of the carbohydrate supplement (carbohydrate-protein 26.9 ± 4.5 min, p < .05). Blood glucose and plasma insulin levels were elevated above placebo during carbohydrate and carbohydrate-protein supplementation, but no differences were found between the carbohydrate and carbohydrate-protein treatments. In summary, we found that the addition of protein to a carbohydrate supplement enhanced aerobic endurance performance above that which occurred with carbohydrate alone, but the reason for this improvement in performance was not evident.
John L. Ivy, Peter T. Res, Robert C. Sprague and Matthew O. Widzer
John L. Ivy, Lynne Kammer, Zhenping Ding, Bei Wang, Jeffrey R. Bernard, Yi-Hung Liao and Jungyun Hwang
Not all athletic competitions lend themselves to supplementation during the actual event, underscoring the importance of preexercise supplementation to extend endurance and improve exercise performance. Energy drinks are composed of ingredients that have been found to increase endurance and improve physical performance.
The purpose of the study was to investigate the effects of a commercially available energy drink, ingested before exercise, on endurance performance.
The study was a double-blind, randomized, crossover design. After a 12-hr fast, 6 male and 6 female trained cyclists (mean age 27.3 ± 1.7 yr, mass 68.9 ± 3.2 kg, and VO2 54.9 ± 2.3 ml · kg–1 · min–1) consumed 500 ml of either flavored placebo or Red Bull Energy Drink (ED; 2.0 g taurine, 1.2 g glucuronolactone, 160 mg caffeine, 54 g carbohydrate, 40 mg niacin, 10 mg pantothenic acid, 10 mg vitamin B6, and 10 μg vitamin B12) 40 min before a simulated cycling time trial. Performance was measured as time to complete a standardized amount of work equal to 1 hr of cycling at 70% Wmax.
Performance improved with ED compared with placebo (3,690 ± 64 s vs. 3,874 ± 93 s, p < .01), but there was no difference in rating of perceived exertion between treatments. β-Endorphin levels increased during exercise, with the increase for ED approaching significance over placebo (p = .10). Substrate utilization, as measured by open-circuit spirometry, did not differ between treatments.
These results demonstrate that consuming a commercially available ED before exercise can improve endurance performance and that this improvement might be in part the result of increased effort without a concomitant increase in perceived exertion.