Maintaining carbohydrate availability is a key challenge in multi-stage races

A major challenge in multi-day races such as cycling's Grand Tours and the Marathon des Sables is maintaining adequate carbohydrate availability. This is because we quickly deplete carbohydrate stores during exercise and our carbohydrate storage capacity is limited. Additionally, when carbohydrate stores are low, we find it difficult to maintain training intensity at race pace. The storage form of carbohydrates in humans is glycogen, which is mainly found in the muscles and liver. It is believed that the maximum amount of glycogen an athlete can store is less than 3500 kcal of energy. This is not enough for a full day of racing. It is therefore very important that the glycogen stores in the body are filled to the maximum and remain as full as possible by consuming carbohydrates during activity.

Glucose-fructose mixtures

Muscle glycogen recovery depends primarily on the amount of carbohydrate consumed. That's why the sports nutrition guidelines for recovery after training or competition say that for quick refueling, athletes should look to consume 1.0 to 1.2 grams of carbohydrates per kilogram of body mass per hour in the first four hours after training. When it comes to the types of carbohydrates to consume, it seems to be very important which carbohydrates you consume. Since muscle glycogen replenishment appears to be independent of whether the carbohydrate source is glucose-based or glucose-fructose mixtures, liver glycogen is different. This can only be filled up with fructose. The availability of liver glycogen is very important for the ability to maintain high intensity for a long period of time. The recovery of liver glycogen is accelerated by carbohydrates containing fructose.

Compared to muscle glycogen, liver glycogen metabolism appears to be more sensitive to the type of carbohydrates consumed. The increased recovery of liver glycogen stores when fructose and glucose are taken together is typically twice as fast as with glucose alone, even when the total amount of carbohydrates is identical.

Fructose-glucose mixtures during recovery improve subsequent physical performance

In a recent study, a group of runners completed two strenuous runs four hours apart. During the four-hour recovery period, runners were provided with carbohydrate drinks that contained either glucose-based carbohydrates (maltodextrin) or maltodextrin-fructose mixtures. After taking the maltodextrin-fructose mixtures, the athletes were able to run approximately 30% longer compared to taking equivalent amounts of glucose-based carbohydrates alone.

Another recent study compared two groups of cyclists. They first did very intensive exercise and then after training they ate either maltodextrin-fructose mixtures or just glucose-based (maltodextrin) carbohydrates for four hours. Maltodextrin-fructose improved endurance performance by about 20%, suggesting that fructose-containing carbohydrates during athletes' recovery periods can improve their performance the next day.