Isotonic, hypotonic and hypertonic drinks: What you need to know

Isotonic, hypotonic and hypertonic drinks: What you need to know

Do you know how much water we should take in order to maintain a proper water balance? Thanks to sports drinks, we can hydrate ourselves at the right time according to the weather and exercise conditions

Physical exercise and Hydration

In an exercise or physical activity, starting from a moderate intensity, and above all of a long duration, special attention is paid to hydration.

Therefore, the amount of fluid that an athlete needs to provide to his body before, during and after sporting activity will depend on these factors, and by taking them into account, it will be possible to guarantee that adequate performance is maintained, as well as to avoid possible health problems.

Water hydration

If we do a strenuous physical activity, we should have a bottle of water next to us

Other factors that are also relevant when planning the strategy for optimal hydration will be:

  • Air temperature
  • Ambient humidity level
  • Altitude
  • Our own physiology

In spite of all of them, determining exactly how much water, in individual terms, is needed every day is quite complicated

Hydrate sports drinks

However, through the following recommendations, a good starting script can be established

How much water should you drink each day?

If you train regularly, you’ll probably need to bring in between 0.5 and 1 ounce for every pound of weight. Now in measures for which we do not know the previous ones, it would be to drink for each kg of body weight between 32 – 65ml of water.

Example: if I weigh 80kg, I will need to drink between 2.5 and 5.2 litres of water a day

Now, this quantity does not have to come exclusively from water, but all the food can be counted, since these foods have water

Correct hydration of the sportsman: drink water but also…isotonic drinks

Most people who play sports on a regular basis tend to pay little attention to hydration. They do not drink enough water, but not at the right time. Especially after heavy training, few people replenish their water:

  • Loss of glycogen,
  • of electrolytes, and,
  • vitamins with isotonic drinks.

During vigorous physical activity, 1.5 to 3.5 litres of liquid are lost per hour through sweat. In addition, during intense training and sports competitions, water loss can delay the sensation of thirst and so the sportsperson can stop drinking without having completed his or her optimal level of hydration.

With a loss of body fluids of 1.5 to 2 litres the thirst mechanism starts to be activated and this level of water loss already has a rather serious impact on temperature control

Run hydration sports drinks

Therefore, you should never wait until you are thirsty to drink water, but plan your hydration according to the type and duration of your physical activity to avoid dehydration.

Dehydration is very easy and happens quickly, it is very important for sportsmen and women to control our water loss during exercise

Characteristic signs of dehydration

  • Headache.
  • Dizziness.
  • Muscle cramps.
  • Lack of energy.
  • Fatigue.
  • Irritability.

Characteristic signs of dehydration

Dehydration can happen to you at the second that you get “lost”… Avoid being late by applying this advice

How much should you drink for exercise?

Before exercise

  • Drink 2 to 3 glasses of water within two hours before training
  • Weigh yourself just before you start training

During the exercise

  • Drink a glass of water (200-250ml approx.) every 15 minutes

After exercise

  • Weigh yourself immediately after training
  • Drink 2-3 glasses of water for every pound lost during exercise. (1 pound = 2,2kg)

How much water should you drink during endurance exercise?

If you train or are doing a moderate to high intensity type of activity for more than 90 minutes, you should not only drink water, but also replenish electrolytes.

Water during endurance exercise

In the same way, if you want to keep up the same intensity, it will also be necessary to restore the glycogen stores, which can be quite depleted while you are doing the sport

The most recommended advice is to take a sports drink, which is specially prepared to combat these two symptoms, the replenishment of energy by providing a carbohydrate that is easy to digest and absorb, and at the same time a mineral complex that allows optimal hydration and promotes electrolyte recovery

What are Electrolytes?

It is a scientific term used to describe a compound that ionises when dissolved in suitable ionising solutions. An electrolyte refers to the fact that the substance is electrically charged, and moves from its negative electrode (cathode) to its positive electrode (anode).

Electrolytes are particles that help to regulate the balance of the body’s fluids


As an example, within the body, fluids such as blood, plasma, and interstitial fluid (fluid between cells) are like seawater, and have a high concentration of sodium chloride (NaCl)

The electrolytes in NaCl are
  • Sodium Ion (Na+, cation) and Chloride Ion (Cl-, anion)
  • As for your body, the main electrolytes are Sodium (Na+), Potassium (K+), Chloride (Cl-), Calcium (Ca2+), Magnesium (Mg2+), Bicarbonate (HCO3-), Phosphate (PO42-), Sulphate (SO42-)

Electrolytes are important because they enable cells (especially nerves, heart and muscle) to maintain tensions across their cell membranes, and to transport electrical impulses (nerve impulses, muscle contractions) across themselves and other cells.

The kidneys are responsible for maintaining the concentration of electrolytes in the bloodstream, despite changes in the body. Sweat expels electrolytes and minerals such as magnesium, calcium, zinc, iron… and even vitamins, from our body.

If we do a physical activity, there is an alteration of these electrolytes, especially sodium and potassium, which need to be replaced.

Optimal hydration

Therefore, sports drinks emphasize this fact, and provide the necessary ingredients for optimal replenishment

Importance of Electrolytes and Muscle Contraction

Sports Drinks

From everything we have seen so far, an athlete must stay hydrated. During training, the body temperature rises, and we break out in a sweat, which allows the body to stay cool, but can cause you to lose water and with it carry over sodium and sugars, which are necessary for peak performance and maintaining health.

Sports drinks not only replenish water and electrolytes, they also help the body absorb the fluid and include carbohydrates and other nutrients that help the body recover. Replenishing carbohydrates is essential as they provide energy for the muscle and help the body maintain an adequate concentration of glucose in the blood.

Although there are several types of sports drinks, they are not all the same or perform the same function:

Isotonic Drinks

Must provide between 6-8g of glucose per 100ml. They have the same balance of nutrients, such as sugars and electrolytes, that are normally found in the body. They also have a higher caloric intake. With this type of characteristic, the drink will pass to the intestine where it will be absorbed, and will reach the blood quickly, without difficulty. In a hot environment, and with intense exercise, or even if you sweat a lot, this isotonic drink will help to replace liquids, electrolytes and energy.

It will help delay fatigue (thanks to hydration and glucose), and avoid the dreaded cramps caused by the decompensation of electrolytes

Hypotonic drinks

These drinks have a lower balance of carbohydrates and electrolytes than those present in the body, but higher amounts of sugars and potassium. They are absorbed fairly quickly, and are ideal for the most “pushing” moment of the training or event, as they act as an energy “shot”, leading to an extra increase in performance.

They are recommended during physical exercise

Hypertonic drinks

These are the drinks that concentrate the greatest amount of dissolved substances, including water, carbohydrates and electrolytes (sodium, potassium, phosphorus and chlorine). It is said that their concentration of solutes is higher than that of plasma, and therefore, after their ingestion, the body releases water to dilute the liquid ingested, to bring it to an isotonic state (same balance as plasma). These drinks are not recommended for locations or situations where there is a high temperature, or if the sportsperson sweats too much. Therefore, they should be used when the loss of sweat is not excessive, when water replacement is not so necessary, and when the loss of nutrients, which in this case will be energy, is in the form of carbohydrates. If the activity is carried out at low temperatures they are the best option.

Never use them in marathons, where high temperatures are reached, if during the summer time

Where to buy Sports Drinks

You can Buy Sports Drinks at


  • Exercise and Fluid Replacement, ACSM Position Stand, American College Of Sports Medicine, Medicine and Science In Sports & Exercise, 2007

Related Entries

Review Types of drinks

Isotonic - 100%

Hypotonic - 100%

Hypertonic - 100%

Considerations - 100%


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About Javier Colomer
Javier Colomer
"Knowledge Makes Stronger", Javier Colomer's motto, sets out his clearest statement of intentions expressing his knowledge and fitness experience.
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