While this summer hasn’t exactly been sun-drenched it is always worth thinking about whether we’re properly hydrated before, during and after training. In this article we focus specifically on how to measure your water loss during exercise.

The Water In Equals Water Out Concept

Hydration is an all-day affair - we’re using fluids to cool the engine that is the human body, as well as being an important part of many of the chemical and biological reactions that occur in the body. You don’t even have to be awake to lose fluids with up to 1 kg in weight lost mostly through sweat while sleeping on a warm night.

In terms of keeping hydrated a good general rule of thumb is to consume fluids at a rate to match our losses. Water In should equal Water Out.

For example we should sip water through-out the day if we are working in an office, while increasing the rate of consumption when exercising to somewhere north of 500 ml an hour depending on intensity and temperature.

How To Measure Water Out

So how do we work out how much water to drink when exercising? How much Water In do we need to replace the lost Water Out?

Try this simple test.

Step 1. Weight yourself before exercise - naked is best (honestly).

Step 2. Exercise while drinking your normal quantity of water or energy drinks. Keeping a note of how much you consume including any post exercise recovery drink.

Step 3. Warm down after your session to the point you are no longer sweating.

Step 4: Shower, dry yourself and hit the weighing scales one more time - naked again for consistency.

Step 5: Compare your weight in Step 1 and Step 4

  • SAME: In an ideal world you will be the same weight - or slightly under it - as when you started. This means your _Water In _equals your Water Out.
  • LIGHTER: If you are significantly lighter - 500 g or more - then you should consider increasing your fluid intake during training to bring the gap back to no more than about 300 g. Every 100 g of weight is equivalent to 100 ml of water.
  • HEAVIER: If you are heavier then when you started it is likely that you are over drinking or eating. Throttle back the next time.

Some Things To Remember

  1. This is a very simple test. For example it doesn’t take into account the implications of your bladder filling up during exercise. Caffeine has a mild diuretic effect so some water that would otherwise make its way usefully into your system ends up being flushed into the bladder where it serves no purpose other than to weigh you down!
  2. As we noted at the start of the article hydration is an all-day affair - do manage your water intake across the day. Starting an event or training session dehydrated won’t help your performance, even if you consume enough water during.
  3. While we suggest weighing yourself naked, we make no such recommendation with regards to the exercise itself. We’ll leave that up to you!

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