155-j : INTAKE OF GLUCOSE AND FRUCTOSE DOES NOT IMPROVE RECOVERY GLYCOGEN STORES

Taking different types of carbohydrates after intensive exercise does not lead to a better and faster recovery of glycogen stores. Researchers of the University of Maastricht found this in a study of 14 well-trained cyclists.

GLYCOGEN

During intense exercise athletes use mainly glycogen stores as fuel in the muscles. If this stock is exhausted, performance deteriorates significantly. By taking in enough carbohydrates athletes can replenish their glycogen stock. The authors state that the body can absorb a maximum amount of glucose from 1.2 to 1.5 g of carbohydrate per kg of body weight per hour. Larger amounts of glucose does not lead to a greater or faster absorption, probably because the transport systems in the intestine are then saturated. The take up of glucose in combination with fructose during exercise sometimes appears to lead to an improved performance, probably because fructose can be absorbed via other mechanisms than glucose. In this study researchers have investigated if a combination of glucose and fructose may cause an accelerated recovery of the glycogen content in the muscle.

GLUCOSE AND FRUCTOSE

The 14 well-trained cyclists who participated in this study were on average 28 years old. They started with 3 times the same protocol, in alternating sequence and always between them for at least a week. The athletes had to make an exhaustive cycling effort in which they alternated two minutes at 90% and 2 minutes at 50% of their maximum capacity (Wmax). If they were no longer able to sustain this, the intensity of the heavy blocks was reduced to 80% and then to 70% of their Wmax. A muscle biopsy was taken immediately after exercise, blood was taken and questions answered about any gastrointestinal complaints.

Next, they were given a drink containing carbohydrates (1.5 g / kg body weight of carbohydrate per hour) for 5 hours every 30 minutes.

The beverages consisted of:
1.5 g / kg of glucose,
1.2 g / kg of glucose with 0.3 g / kg of fructose or
0.9 g / kg of glucose 0.6 g / kg of sucrose per hour.

Every 30 minutes blood was collected and muscle biopsies were taken again after 2 and after 5 hours. The analyses showed that the glycogen concentration was decreased after exercise to an average of 288 mmol / kg, while in well-trained athletes prior to exercise this value was between 500 and 600 mmol / kg. In addition, the researchers found that three different carbohydrate combinations had not resulted in any difference in muscle glycogen concentration during or after the recovery period. However, the cyclists reported more stomach problems when they had only been given glucose.

(fig. 1) Glucose enters the bloodstream
(fig. 2) Fructose metabolized in liver

CONCLUSION

The ingestion of a combination of fructose and glucose does not lead to a faster or better recovery of the energy reserves in the muscle after exhaustive effort. Cyclists seem to suffer less from stomach problems if they also take fructose in addition to glucose during a recovery period in which they take in the maximum amount of carbohydrates.