You run, cycle, or string together sports sessions, and you're wondering what to drink during exercise. Isotonic, hypotonic, hypertonic - these slightly technical words hide a simple idea: not every drink affects your body in the same way. We'll explain everything without jargon, so you can finally know which one to choose based on your session and the day's weather.
What a drink's tonicity really means
Tonicity is simply the concentration of sugars and minerals in a drink compared with that of your blood. The more concentrated a drink is, the longer your body takes to absorb it. This concept determines how quickly the liquid passes through your system, and therefore when you should use it.
Many athletes choose their drink solely based on taste or habit, without really knowing what they are providing their bodies. Yet understanding tonicity helps avoid two common mistakes: drinking something too sugary for a short outing, and drinking something too diluted for a long effort that genuinely requires energy.
Hypotonic drink: the lightest option
A hypotonic drink is less concentrated than blood. It passes through the body very quickly and hydrates rapidly, without providing much energy. It is the ideal choice in very hot weather or for short efforts, when the main risk is dehydration rather than running out of fuel.
Isotonic drink: the perfect balance
An isotonic drink has a concentration close to that of blood. It hydrates and provides energy at the same time, without slowing digestion. It is the go-to option for long, moderate efforts such as a run lasting more than an hour, a bike ride, or an intense fitness session on a hot day.
Hypertonic drink: reserved for very intense efforts
A hypertonic drink is more concentrated than blood. It provides a lot of energy but slows fluid absorption and can cause digestive heaviness if it is not well tolerated. It is mainly suitable for very long, very intense efforts, or for recovery immediately after a competition, when the need for energy exceeds the immediate need for hydration.
To put these three categories into the broader context of hydration drinks, our electrolyte drink guide compares what each one really provides.
How to choose based on your activity
Running and sports lasting less than an hour
For a short session, a hypotonic drink or even water is more than enough. Your body has not yet depleted its energy stores, so the main goal is to replace what you lose through sweating and maintain a good electrolyte balance.
Trail running, long-distance cycling, and prolonged efforts
As soon as the effort lasts more than an hour, an isotonic drink becomes much more relevant. It provides water, carbohydrates, and minerals to help you go the distance without a sudden drop in energy or digestive discomfort.
High heat and heatwaves
When temperatures rise, hydration takes priority over energy. A light drink rich in minerals but low in sugar helps your body absorb fluids more quickly and replace the salt lost through sweating.
For running in particular, the guidelines vary greatly depending on the distance. We explain them in detail in our guide on how much to drink based on your distance.
What about electrolytes?
Whatever tonicity you choose, electrolytes remain the real focus. Sodium, potassium, and magnesium are the minerals you lose the most through sweating, and they are what allow your muscles and nervous system to function properly during exercise.
The role of potassium, magnesium, and sodium
Sodium helps your body retain water and prevent cramps. Potassium contributes to muscle contraction and recovery. Magnesium plays a role in energy production and helps your muscles relax properly after exercise. That is exactly why Buddy electrolytes combine these three minerals in a simple, no-added-sugar formula designed to support any type of effort.
So, which one should you choose?
Just remember this. For a short effort or in hot weather, focus on light hydration. For a long, moderate effort, an isotonic drink offers the best balance between energy and absorption. Hypertonic drinks should be reserved for very intense efforts or immediate recovery. When in doubt, hydration that is rich in electrolytes and low in sugar remains the safest choice for the vast majority of athletes.
If you want to try making one yourself, a homemade version takes five minutes to prepare. We give you the proportions in our homemade electrolyte drink recipe.
Before, during, after: the right hydration routine
Choosing the right tonicity is important, but timing matters just as much. Your body does not have the same needs before you start, during exercise, or once the session is over.
Before exercise
In the two hours before a session, it is best to drink regularly and in small amounts rather than consuming a large volume all at once. Mineral-rich water or a slightly hypotonic drink allows you to start with good hydration reserves without creating that feeling of a full stomach.
During exercise
This is when your choice of tonicity really makes a difference. Drink small, regular sips rather than waiting until you feel thirsty - a signal that appears when your body is already short of water. For a session lasting more than an hour, aiming for around one hundred and fifty to two hundred milliliters every twenty minutes is a good starting point, adjusted according to the heat and how much you sweat.
After exercise
Recovery is the time to replenish the mineral stores lost through sweat. A drink rich in sodium, potassium, and magnesium helps your muscles recover faster and limits next-day soreness. This is often where electrolytes make all the difference between a slow recovery and truly getting back into shape.
When you already manage your energy with gels or bars, a sugar-free formula is enough to replace mineral losses. That is the approach behind our electrolyte powder, which can be dosed according to the heat; its levels are compared with those of other brands on drinkscore.info.
FAQ: your questions about sports drinks
What is the real difference between an isotonic drink and a hypotonic drink?
The difference lies in the concentration of sugars and minerals. A hypotonic drink is more diluted and hydrates faster, while an isotonic drink has a concentration close to that of blood and provides more energy while still being well absorbed.
When should you really drink a hypertonic drink?
A hypertonic drink is useful for very long, very intense efforts, such as an ultramarathon, or immediately after a competition to quickly replenish energy stores. Outside these situations, it is not necessarily needed.
Can you make an isotonic drink yourself at home?
Yes, you can mix water, a little salt, fruit juice, and sometimes honey to approach an isotonic concentration. However, achieving the precise dosage is difficult to reproduce, which is why many athletes prefer formulas that are already balanced.
Do isotonic drinks cause weight gain?
An isotonic drink contains sugar, but in an amount intended to be used during exercise, when your body burns it directly. The risk of weight gain mainly comes from consuming it outside any sporting context.
Which drink should you choose for a simple sports session lasting less than an hour?
For a short session, water is often enough. If you sweat heavily or the session takes place in very hot weather, a drink rich in electrolytes and low in sugar will help you recover better without overloading your body.
