How much water do you need when you exercise?

When you’re exercising, you lose fluids through evaporation via sweat and through breathing.

So, how much water does your body need? The best way to measure your water needs is by how your body feels.

About 70% of your body is made up of water; it’s important for every chemical reaction in the body. You need about two to three litres of water a day to transport nutrients. This will help with digestion; remove waste and toxins and also support brain function for energy, mood and concentration.

We lose water and body salts (sodium and chloride) through urine too and when it evaporates as sweat.

The National Academy of Medicine recommends that women get 2.7 litres of water per day and men get 3.7 litres. About 20% of that should come from foods. This may sound like a lot, but remember – it depends on your activity-levels, weight, health and many other factors.

How much fluids can you drink during a workout?

According to the Korey Stringer Institute at the University of Connecticut, the best way to know how much fluid to drink during exercise is to calculate your sweat rate to assess how much fluid you lose during activity. Then, you can calculate how much you need to drink.

  1.  Before the workout, make sure you’re hydrated (light-coloured urine). Dehydration will affect normal sweat rate.
  2. Step on the scale nude to weigh yourself before the workout.
  3. Exercise for one hour.
  4. During the one-hour workout, don’t drink any fluids as this will affect sweat rate. If you drink water, weigh the water before and after the workout to determine the difference.
  5. After the workout, take another nude body weight and calculate the difference between pre- and post-exercise.  If water is consumed during exercise, subtract the water weight from the post-exercise weight.
  6.  A person’s sweat rate is the amount of fluid they should aim to replace during exercise. If you are a heavy sweater, you may be able to drink everything they lose during the workout. You may not recover all your lost fluids until after a workout.
  7.  In the same breath, don’t allow yourself to become thirsty. If you’re thirsty, you’re already dehydrated.
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Don’t overdrink either; this can lead to hyponatremia; when sodium levels in the body are depleted to dangerous levels. It can result in confusion, lack of coordination and can, in some cases, be fatal.

Early signs of dehydration include:

  • Thirst.
  • Increased body temperature.
  • Early onset of fatigue in exercise.
  • Faster heart rate and breathing than expected.
  • Decreased exercise capacity.

Late signs of dehydration include:

  • Dizziness.
  • Difficult breathing.
  • Weakness.

Work out your water needs

The more active you are, the more water you will need. In a nutshell: start your workout with a full tank, and then replenish your fluids based on your pre- and post-workout weight.

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