Above all, a sports drink should be well tolerated and serve the purpose that water losses due to sweating during training can be quickly compensated. For this, the intestine must be able to process the drink quickly and the nutrients must also pass quickly into the blood (= osmolarity or osmotic concentration). Depending on the situation, there must also be a supply of energy and electrolytes. But above all, good taste is very important to ensure that you drink safely enough.
Temperature of sports drinks
Drinks are particularly well tolerated if they have a temperature between 12 and 20 degrees. Cool drinks are usually better drunk than warm ones, although lukewarm drinks reach the small intestine fastest via the stomach. At low outside temperatures, the drink should be lukewarm, as cold drinks (<5°C) additionally remove heat from the body.
Absorption speed of the drink
The particle density, gastric emptying rate and absorption rate in the small intestine determine the absorption rate of liquids. A maximum of 500 to 800 ml per hour can be released from the stomach into the small intestine. Water and beverages with a low carbohydrate concentration leave the stomach quickly, higher concentrated beverages such as fruit juices reach the intestines more slowly. In the intestine, too, the composition is decisive for the absorption speed: water is passively absorbed – this process is relatively slow. In the presence of sodium and glucose, active transport mechanisms are used and the liquid reaches the blood from the intestine about 3 to 4 times faster than with water. Sodium promotes the binding of fluid in the body.
Osmolarity of sports drinks
Sports drinks are mixed with minerals and carbohydrates, whereby their concentration is optimised for rapid absorption by the body. Most sports drinks are therefore isotonic, i.e. they have the same osmotic pressure (number of dissolved parts corresponds to about 300-320 mosmol/l) as blood. Hypotonic (lower osmotic pressure) or hypertonic (higher osmotic pressure) drinks enter the blood more slowly.
Comparison of isotonic, hypotonic and hypertonic drinks
Isotonic drinks have an osmolarity of 280 to 330 mosmol per litre. Isotonic drinks include fruit juice spritzers, special sports drinks and alcohol-free beer. They are absorbed most quickly by the body. As they provide carbohydrates, they are recommended for hard physical work and sports.
Hypotonic drinks have an osmolarity of less than 300 mosmol per liter. Hypotonic drinks are water and mineral water. Liquid absorption is slower here than in isotonic drinks because hypotonic drinks have readily available carbohydrates. They are well suited for fast rehydration as they are already completely absorbed in the small intestine.
Hypertonic beverages, such as juices or juice drinks, have an osmolarity of more than 325 mosmol per liter. Hypertonic drinks must first be diluted in the small intestine, which delays the absorption of fluids and only stops in the large intestine. These drinks are highly concentrated, rich in sugar and calories and are therefore unsuitable as thirst quenchers and sports drinks.
Recommendations for fluid intake
One should always start the training or a competition with sufficiently filled liquid reservoirs. Especially for endurance activities it is important to start to drink before the onset of thirst. It is best to drink slowly and at regular intervals – about 0.2 litres every 20 minutes would be ideal.
Suitable sports drinks after exercise
Drinks for the time after sports should be rich in magnesium, potassium and carbohydrates. Fruit juices (pure or with mineral water in a ratio of 1:1, possibly with the addition of melting flakes), milk mix drinks and slightly sweetened tea drinks are particularly suitable.