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Sports Science - Overhydration
Date: 29 Apr, 2009

It is very important to stay hydrated when training, and while it is important to make sure you drink enough fluid, it is also very important to make sure that you dont drink too much.

Overhydration is also known as hyponotremia or water intoxication. It occurs when you drink too much fluid and the sodium (salt) level in your bloodstream becomes diluted. This causes the amount of salt available to body tissue to decrease, and in turn causes problems with heart, muscle and brain function.

The signs of overhydration include:

         Dizziness,

         Nausea

         Apathy 

         Confusion

         Mild swelling in fingers and hands

Many people do not realise that you can overhydrate your body, and the symptoms can be mistaken for those of dehydration, so it is imperative that you monitor your fluid intake during training. Ideally you should know how much fluid you need per session, and make sure you are drinking the amount that you need.

A quick way to test if you are getting enough or too much fluid during a training session is to weigh yourself before and after your session. Your weight should be the same before and after your workout.  If you weigh less after your session, then you havent had enough fluid, and if you weigh more, youve had too much.

Specifically, to work out how much water you should be drinking during similar training sessions, follow the following formula:

For your typical training session, weigh yourself before and after. Work out how much weight you lost during the session. Add this to the amount of water you drank during that session to give your total sweat loss.

Example:

Subject X had a 90 minute training session

  1. Weight before training: 85kg
  2. Weight after training: 84.25kg

Therefore he lost 0.75kg during training (1kg lost is equal to 1000mL of water lost)

Subject X had 450mL of water during is training session

Therefore his total sweat loss was 1.2kg (0.75kg + 0.45kg) = 1200mL

Your total sweat loss for the session is equal to the amount of fluid you should drink for a similar session.

Subject X will need to consume 1200mL of water during similar training and competition sessions, he/she should spread this over the session, for example, drink 200-250mL every 15minutes if possible.

 

To work out percentage of bodyweight lost in that session, take the total sweat loss and divide it by your pre-session weight, then x by 100.

Example:

% of body weight lost = (1.2 kg/85 kg) x100 = 1.4%

 

If you gain weight during the session, then cut back the amount of fluid per session by the amount of weight you have gained. For example, if you gained 300g during a session and drank 1.5L of water, then reduce the amount of water you have to 1.2L (where 1kg = 1000mL of fluid)

1500mL-300mL =1200mL or 1.2L.

Remember, to avoid dehydration or overhydration, keep a track of how much fluid you need per session, and stick to it. If you change your training plan, go through the process again and work out how much fluid you need to drink. If you are exercising for longer than 60 90 minutes, then drink a sports drink as well as or instead of water, as this replaces sodium and carbohydrate in your blood. Make sure you choose an appropriate sports drink that doesnt contain too much sugar read the label to check what you are drinking.  An ideal sports drink would contain at least 4-8% carbohydrate and 500-700mg/L of sodium.

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