HYPO, ISO, HYPER
Nowadays the sports drinks, as presented in this article, can be divided into three categories: hypotonic, isotonic, and hypertonic. Let’s look closer at each of the drink type.
Hypotonic drinks – are drinks which have lower osmolality* than the inner environment of human body. Osmolality is defined by the presence of osmotically active particles, like ions, glucose, and other derivates of sugar. Hypotonic drinks have low contents of these particles thanks to which they are quickly absorbed into the organism. In practice, it means that hypotonic drinks quickly replenish lost fluids (in sports the fluids are lost mainly by sweating). However, they don’t contain much of glucose or other types of sugar. In other words they don’t function as a quick supply of energy. Its major function is quick rehydration without supplying any further energy input. These drinks can be consumed all day long. These days the hypotonic drinks are the most popular sports drinks.
Isotonic drinks – are drinks which have the same osmolality as the inner environment of human body and are absorbed slower than hypotonic drinks. Isotonic drinks contain more glucose or other sugar derivates and as such they provide replenishing of not only water but also an energy. In the past the isotonic drinks were considered the best sports drinks because they are very similar to the blood plasma in its structure. Later on it has been proven that the amount of salt in sweat is lower than the amount of salt in plasma. That means that when drinking isotonic drinks the amount of replenished salt does not match the amount of salt sweated out. The amount of salt in plasma does not become balanced but slightly (and unnecessarily) increased. This is the main reason the isotonic drinks are not recommended as the ideal option for fluid intake before and during a performance. They should be the smallest part of fluids intake in athlete’s nutrition. Isotonic drinks can serve well to replenish fluids and energy in a specific time after performance.
Hypertonic drinks – are drinks with higher osmolality than the inner environment of human body. Hence they are unsuitable for quick replenishing of fluids. They can be used after performances to replenish the lost energy.
Nowadays there is a wide range of these drinks available on the market. The better news is that anyone can make a simple sport drink at home:
Hypotonic drink – mix 100 ml of 100% orange juice, 1 litre of water and a pinch of salt (approx. 1g)
Isotonic – mix 200 ml of 100% orange juice, 1 litre of water and a pinch of salt (approx. 1g)
Hypertonic – mix 400 ml of 100% orange juice, 1 litre of water and a pinch of salt (approx. 1g)
* What is osmosis? Brief and clear definition including animations can be found here.