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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.
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).
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.
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).
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.
The authors are with the Dept. of Kinesiology, James Madison University, Harrisonburg, VA 22807.