155-k: GLYCOGEN STOCK RECOVERY DEPENDS ON TYPE OF SUGAR

Athletes who have to perform again within a few hours in an exhaustive effort, are better off to drink water with table sugar than water with glucose. In that case the energy stocks in the liver recovers more quickly. For the restoration of the energy supply in the muscles it does not matter what type of sugar athletes drink.

During intense exercise sugars, known as carbohydrates, are the main source of energy. There exist different types of sugars, mostly built up from glucose and / or fructose molecules. Athletes take carbs in the form of for example a drink or an energy bar. The body itself also has a stock of sugar called glycogen stores. This glycogen is divided between the liver and the muscles and contains enough energy for about one hour of intensive exercise.

When glycogen stores become depleted, the athlete must switch to another energy source or take carbohydrates. Since switching to another energy source will result in a deterioration of performance, most exercisers choose to take carbohydrates during training or competition.

Not only during but also after exercise is it important to replenish glycogen stores quickly, especially when there is again a training or competition on the program within a few hours. But what kind of sugars provides the fastest recovery?

Glucose
Sucrose
Fructose

SUCROSE OR GLUCOSE

For the restoration of glycogen in the liver as quickly as possible, an athlete can best take sucrose. Sucrose is also known as table sugar and consists  partly of glucose and a portion of fructose. For the restoration of glycogen in the muscles sucrose and glucose (dextrose) work as well. This according to research by sports scientists from England and the Netherlands.
The researchers found this difference after fifteen highly trained cyclists did a maximal depletion test. After the test they gave one group glucose dissolved in water and the other group sucrose dissolved in water.  Of these, the cyclists were given in both cases 1.5 grams per kilogram of body weight per hour. It was then up to 5 hours after the depletion test, with analysis techniques which make use of magnetic resonance imaging (MRI and MRS), investigated how the glycogen stores in the liver and the muscles were recovered.

Although the concentration of glycogen in the muscles equally increased after ingestion of glucose or sucrose, the energy supply in the liver was found to increase more by the sucrose. As a result, the overall increase in glycogen in the liver was 15-20 grams larger. This is enough energy to cycle about four minutes at 75% of maximum power

ADVICE

Athletes who have multiple (long-term) competitions or workouts in one day, would do well to take sucrose instead of glucose. Probably it does not matter which carbs they take if the races or the workouts are on two different days. During the night there is enough time for a complete recovery of both energy stores in the muscles and in the liver. For athletes who do not fully deplete their energy reserves during the competition it  makes no difference what type of sugar they use, like for example for rowers and gymnasts.

A number of investigators have previously shown that it makes no difference for the recovery of the glycogen reserves in the muscles when athletes in addition eat glucose and also fructose. A combination of both (such as sucrose), therefore, turns out to be better for the recovery of glycogen stores in the liver.

Finally, it was found that the cyclists had fewer stomach problems when they had taken sucrose. This is probably because the small intestine for the absorption of sucrose demands different types of transport proteins, so that less water is disposed and the absorption proceeds more rapidly. Especially with the ingestion of large amounts of sugars this allows for less abdominal discomfort