Journal Title (Medline/Pubmed accepted abbreviation): J. Sports Sci.
Page numbers: 361-369
doi (if applicable): 10.1080/02640414.2012.735370
Background: Carbohydrates aid in performance during continuous exercise. Recently, it has been shown that consumption of 0.2 g of protein per kg body weight per hour can further improve endurance performance by delaying fatigue, improving the efficiency of converting food to energy, improving the insulin response, and other mechanisms.
Hypothesis: A carbohydrate-protein beverage will enhance performance over a carbohydrate-only beverage on a self-paced, multiple-sprint exercise session.
Experimental Design: randomized, double-blind, cross-over design
Subjects: A total of 9 male athletes involved in university team sports, age 23.4 ± 1.8 y
8% carbohydrate beverage (maltodextrin and dextrose)
6% carbohydrate beverage plus 2% protein (whey protein isolate)
Participants consumed 5 mL/kg body weight before the start of the study and then 2.5 mL/kg body weight at periods of rest during the study. The beverages contained the same amount of energy (kcal). Total consumption was 70.2 ± 11.1 g/hr in the carbohydrate condition and 52.7 ± 8.4 g/hr carbohydrate plus 17.6 ± 2.8 g/hr protein in the carbohydrate-protein condition.
The participants completed three testing sessions separated by about 1 week. Each session involved modified Loughborough Intermittent Shuttle Tests (LIST) which consisted of legs of walking, jogging, cruising, and sprinting as dictated by an audio recording (60 min), then self-paced shuttle runs (30 min). At the first session, the participants were familiarized with the procedures, assessed for maximum oxygen capacity (VO2max), and assessed for average speed. For sessions 2 and 3, they arrived at the laboratory after an overnight fast. They consumed the first dose of one of the two treatment beverages, and donned a global positioning system (GPS) to record speed and a heart rate monitor. After a 15-min warm up, they began the LIST test. There were 6 multi-stage intervals of sprinting, and beverages were consumed in between legs (in addition to the first dose, at 15, 30, 45, 60, and 75 min). Body weight was measured before and after the session from which fluid loss was calculated. Gut fullness was inquired about throughout the protocol. Blood and urine were collected before the test, at 60 min, and at the end.
- When consuming the carbohydrate-protein beverage, participants ran 2.5 ± 1.4% faster and completed 2.7 ± 2.5% more distance compared to the carbohydrate trial. These results suggest that the addition of protein to a sports beverage provides a “likely moderate” benefit for speed and “very likely moderate” benefit for distance, respectively.
- Average speed during each leg did not differ statistically except for the last leg. During the last 15 min leg (self-paced), average speed was faster with the carbohydrate-protein beverage compared to the carbohydrate-only beverage. The difference in speed between the first leg and the sixth leg was significant in the carbohydrate trial but not the trial with carbohydrates and protein.
- Both beverages provided adequate hydration to the athletes.
- The beverage did not affect heart rate or feelings of gut fullness.
- Ratings of perceived exertion did not differ between conditions even though intensity was slightly greater with the carbohydrate-protein beverage.
- Blood glucose and insulin concentrations were similar between conditions. Blood urea concentrations increased, albeit still within the normal clinical range, at 60 min in the carbohydrate-protein trial only. This is expected since urea is a product of amino acid metabolism.
Key practice applications: The carbohydrate-protein beverage improved cruising and sprinting speed compared to carbohydrate-only beverage.