Whether you are an amateur or professional athlete - anyone who is active in sport should make sure they have sufficient fluid and energy intake. Sports drinks play a key role in this. But not every drink is the same. The terms hypotonic, isotonic and hypertonic describe the concentration of dissolved particles contained in the drink compared to blood plasma - with sometimes significant effects on fluid absorption in the body.
What do hypotonic, isotonic and hypertonic mean?
Type of drink | Osmolarity (particle concentration) | Absorption rate | When is it suitable? |
Hypotonic | Less than blood plasma | Very fast | Before or during short periods of exercise |
Isotonic | Approximately the same as blood plasma | Fast | During prolonged exercise |
Hypertonic | Higher than blood plasma | Slow | After sport for regeneration |
Hypotonic sports drinks
What is it?
A hypotonic drink contains fewer dissolved particles (e.g. sugar, electrolytes) than blood. This means it is absorbed into the blood particularly quickly - ideal for rapid rehydration.
When to use?
Before exercise to replenish fluid stores
During short periods of exercise when little or no energy intake is required
In the heat to quickly replenish fluids
Advantages:
Fast fluid absorption
Low stomach load
Ideal for endurance and heat loads
Caution:
Often contains few carbohydrates, therefore does not provide sufficient energy during long periods of exertion.
Isotonic sports drinks
What is it?
An isotonic drink has a similar particle concentration to blood. Water, salts and carbohydrates are absorbed efficiently - ideal during prolonged, intensive exercise.
When to use it?
During sport (from approx. 60 minutes of exercise)
During endurance competitions or long training sessions
When fluid and energy are needed at the same time
Advantages:
Good balance between water and energy intake
Fast-acting
Promotes endurance performance
Caution:
Contains more sugar than hypotonic drinks - not ideal for pure fluid requirements without energy needs.
Hypertonic sports drinks
What is it?
Hypertonic drinks contain more dissolved particles than the blood, e.g. in the form of sugar (often in soft drinks, fruit juices or energy drinks). The body must first draw water from the tissues to balance the osmolarity - which delays absorption.
When to use?
After sport, to replenish glycogen stores
As a regeneration drink in combination with protein
For very long periods of exercise in combination with isotonic drinks
Advantages:
High energy content
Supports regeneration and replenishment of carbohydrate stores
Caution:
Delayed water absorption
Can cause stomach problems if consumed directly during intense exercise
Not suitablefor rapid rehydration
Conclusion: The right drink at the right time
The choice of the right sports drink depends heavily on the time, the duration of the exercise and the goal. Here is a brief guide:
Goal | Recommended drink |
Fast hydration | Hypotonic |
Energy + fluid | Isotonic |
Regeneration | Hypertonic |
The right sports drink supports performance, prevents dehydration and promotes recovery after sport. If you want to mix your own, you should make sure you have a balanced mix of water, electrolytes and carbohydrates - depending on your needs.
Source:
Raschke, C., Ruf, S. 2022. Sport und Ernährung: Wissenschaftlich basierte Empfehlungen, Tipps und
Ernährungspläne für die Praxis (5. Auflage). Thieme