Carbohydrate-protein (CHO+Pro) beverages reportedly improve endurance and indices of muscle disruption, but it is unclear whether these effects are related to total energy intake or specific effects of protein.

Purpose: The authors examined effects of CHO+Pro on time to exhaustion and markers of muscle disruption compared with placebo (PLA) and carbohydrate beverages matched for carbohydrate (CHO) and total calories (CHO+CHO).

Methods: Eleven male cyclists completed 4 rides to exhaustion at 75% VO2peak. Participants consumed 250 ml of PLA, CHO (7.75%), CHO+CHO (9.69%), or CHO+Pro (7.75%/1.94%) every 15 min until fatigue, in a double-blind design.

Results: Time to exhaustion was significantly longer (p<.05) in CHO+Pro (126.2+/-25.4 min) and CHO+CHO (121.3+/-36.8) than PLA (107.1+/-30.3). CHO (117.5+/-24.2) and PLA were not significantly different. Similarly, CHO+Pro was not significantly different from CHO and CHO+CHO. Postexercise plasma creatine kinase was lower after CHO+Pro (197.2+/-149.2 IU/L) than PLA (407.4+/-391.3), CHO (373.2+/-416.6), and CHO+CHO (412.3+/-410.2). Postexercise serum myoglobin was lower in CHO+Pro (47.0+/-27.4 ng/mL) than all other treatments (168.8+/-217.3, 82.6+/-71.3, and 72.0+/-75.8). Postexercise leg extensions at 70% 1RM were significantly greater 24 hr after CHO+Pro (11.3+/-4.1) than PLA (8.8+/-3.7), CHO (9.7+/-4.3), and CHO+CHO (9.5+/-3.6).

Conclusion: These findings suggest that at least some of the reported improvements in endurance with CHO+Pro beverages might be related to caloric differences between treatments. Postexercise improvements in markers of muscle disruption with CHO+Pro ingestion appear to be independent of carbohydrate and caloric content and were elicited with beverages consumed only during exercise.