One of the most reliable and inexpensive ways to increase exercise performance and recovery is carbohydrate supplementation. Studies have found that ingestion of carbohydrates before and during exercise reliably increases exercise performance, especially for exercise over 30-45 minutes in duration. In addition to reducing fatigue, use of carbohydrates during exercise will speed the rate of recovery after exercise by inhibiting proteolysis, especially if protein intake is adequate. This article will discuss how carbohydrates increase performance, the types of carbohydrates that can be used, and the ideal dosing strategy for increased performance.
Mechanism of action
During exercise, glycogen and plasma glucose are both major sources of energy. Carbohydrate ingestion keeps blood glucose levels high, providing a steady source of energy for working muscles. This also aids in the preservation of muscle glycogen, prolonging the time it takes for glycogen stores to become depleted. Carbohydrates may additionally improve exercise performance by having a positive effect on the central nervous system.
Types of simple carbohydrates
Dextrose: Dextrose, or d-glucose, is also known as corn sugar. It is 70-80% as sweet as sucrose (table sugar).Dextrose is absorbed and utilized quickly, providing a rapid energy source.
Maltodextrin: Maltodextrin refers to dextrose polymers of varying lengths. Unlike dextrose, maltodextrin is not very sweet. Although technically a complex carbohydrate, maltodextrin results in a glycemic response similar to that of dextrose. Dextrose is less expensive, sweeter, and mixes more easily.
Fructose: Fructose is the sugar that gives fruit its sweet taste. It is lower on the glycemic index than dextrose, being absorbed more slowly in the intestine and then metabolized in the liver.
Most studies on carbohydrates and exercise have used maltodextrin, dextrose, or a combination of the two. One concern that is brought up is that ingestion of these carbohydrates will cause rebound hypoglycemia, and thus decrease exercise performance. This can be solved by ingesting the carbohydrates before, and at regular intervals during exercise – in fact, it has been found that carbohydrate ingestion before and during exercise has an additive benefit compared to just one or the other. Fructose and other low GI sources of carbohydrates are inferior, although the difference is small. Low GI carbohydrates lead to more complaints of gastrointestinal discomfort, and are also absorbed more slowly, limiting muscle glucose availability.
During intense exercise, the amount of glucose being used can exceed the maximal rate of absorption, so it is important to consume a large amount of carbohydrates for maximal effectiveness. However, if too much is consumed, gastrointestinal discomfort may follow. The literature indicates that amounts over 1.5 g per minute will definitely not improve fuel utilization, with little likely benefit beyond 1.0-1.1 g per minute. It is also important that the solution be diluted enough for optimal absorption – in the realm of 20-40 g of carbohydrates per 16 oz. Based on this information, my carbohydrate recommendations for maximum exercise performance are as follows:
For strength training or exercise of short duration (30-60 minutes):
2-3 tbsp dextrose (20-30 g) in 12-24 oz. water 15-30 minutes before exercise
3-5 tbsp dextrose (30-50 g) in 16-32 oz. water taken throughout exercise
For endurance exercise:
3 tbsp dextrose (30 g) in 24 oz. water 15-30 minutes before exercise
3 tbsp dextrose (30 g) in 16 oz. water at the beginning of exercise and every 30 minutes (note that it is also essential to ensure adequate sodium intake when consuming this much fluid)
Note that these are for maximal performance only, and recommendations depend on circumstances. A person trying to limit caloric intake, for example, would want to consume less. Also, one may want to reduce carbohydrate intake accordingly if consuming protein during exercise.