Glycogen

Replenishing Glycogen

The primary fuel sources for moderate- to high-intensity exercise are glycogen stored in the muscles and liver and glucose carried to working muscles through the blood. Both glycogen and glucose are products of carbohydrate breakdown, and for this reason they are often referred to collectively as “carbohydrate fuel”.

Blood glucose is available in much more limited amounts than muscle and liver glycogen, but it can be replenished much more rapidly. It takes many hours to replenish glycogen through carbohydrate consumption, while it takes only about 20 minutes for the sugars consumed in a sports drink to pass through the stomach and become broken down into glucose in the bloodstream.

Consuming carbohydrate during exercise is essential for prolonging endurance. While an athlete cannot consume enough carbohydrate to completely halt the use of glycogen for energy, he or she can consume enough to slow its depletion significantly. Research has shown that most athletes can ingest carbohydrate at a maximum rate of 1.2 grams per minute without suffering gastrointestinal distress. But athletes can burn glycogen at more than three times this rate while exercising at near anaerobic threshold intensity. Hence, the longer an athlete exercises, the more glycogen-depleted he or she will be afterwards despite efforts to consume as much carbohydrate as possible during the workout or competition.

After exercise, the sooner the athlete begins to replenish muscle glycogen by consuming carbohydrate, the better. This is because, following exercise, the muscle cells are much more receptive to insulin, the hormone responsible for transporting glucose through the bloodstream to the liver and muscles, where it can be stored as glycogen. The body can synthesize glycogen two to three times as fast during the first two hours after exercise than it can at other times.

How much carbohydrate is needed? As a general guideline, athletes should try to consume about one gram of carbohydrate per pound of bodyweight during the first two hours of exercise. Most or all of this carbohydrate should be high-glycemic, because high-glycemic carbohydrates stimulated greater insulin release and are therefore delivered to the muscles and liver more quickly than their low-glycemic counterparts. Examples of high-glycemic carbohydrate food sources are bagels, baked potatoes, bread, Cornflakes, and raisins.

To stimulate even greater insulin release, athletes should consume about one gram of protein for every four grams of carbohydrate they consume in the two hours following exercise. For example, a 160-lb. athlete would want to consume approximately 160 grams of carbohydrate and 40 grams of protein in the first two hours after exercise. Eating more than this amount of protein will have the opposite effect, impeding glycogen replenishment by slowing gastric emptying, as will eating more than a very small amount of fat or fiber.

Most athletes are not particularly hunger right after a workout or competition. For this reason, the most practical way to kick-start glycogen replenishment following exercise is by drinking a sports drink containing carbohydrate and protein in a 4:1 ratio. In recent tests, a sports drink featuring this 4:1 ratio (Endurox R4) increased insulin levels in athletes 70% more after a workout than a conventional sports drink that contained no protein. It also increased endurance by 55% in the next workout.


Source:
Powering Muscle