Recovery from endurance exercise
Muscle glycogen is the predominant fuel for energy during exercise, and the ability to rapidly replenish glycogen stores during recovery is important for athletes. This is particularly true for athletes undergoing long exercise bouts or multiple daily workouts.
The best strategy to promote muscle glycogen resynthesis during the initial few hours after exercise is to ingest a high amount of carbohydrate at frequent intervals.
Provided that carbohydrates are consumed at a rate of about 1.2 gram per kilogram of body weight per hour (0.5 g/lb/h), in 15 to 30 minute intervals, most evidence suggests that protein added to a recovery drink will not further enhance the rate of muscle glycogen resynthesis. (5Burke LM et al. (2004). Carbohydrates and fat for training and recovery. J Sports Sci 22:15-30.
Protein consumed after exercise does assist in the repair and synthesis of muscle proteins, and as such, is vital to the recovery process.
For example, protein added to a carbohydrate/fat supplement increased leg muscle protein accretion during recovery from cycling exercise, as opposed to net losses in muscle protein when just carbohydrate and fat were ingested. (6Levenhagen DK et al. (2002) Postexercise protein intake enhances whole-body and leg protein accretion in humans. Med Sci Sports Exerc. 34:828-837.)
Does protein added to sports drink during exercise improve performance?
Two studies recently reported that consuming a protein and carbohydrate beverage during exercise increased performance as compared to carbohydrate alone. ( Ivy JL et al. (2003). Effect of a carbohydrate-protein supplement on endurance performance during exercise of varying intensity. Int J Sports Nutr Exerc Metab. 13:382-395; Saunders MJ et al. (2004). Effects of a carbohydrate-protein beverage on cycling endurance and muscle damage. Med Sci Sports Exerc. 36:1233-1238.)
Both studies measured exercise time to fatigue in trained cyclists using a randomized double-blind repeated measures design. In each experiment, subjects ingested a 7.75 percent carbohydrate solution on one occasion and a drink that contained 7.75 percent carbohydrate plus an additional 1.94 percent protein (about 4 g of protein per 8-oz serving) on another occasion.
In the first study, subjects cycled at 85 percent peak VO2max immediately after performing three hours of standardized cycle exercise. Results showed that the subjects:
- Rode 36 percent longer when ingesting the carbohydrate solution as compared to the placebo.
- Rode 55 percent longer when ingesting the carbohydrate + protein solution compared to placebo, and this was also significantly longer than the carbohydrate trial.