Drink more if you perspire more

It is important to note that different individuals will have different perspiration rates, depending on fitness and heat acclimatisation status.

A runner who is more heat-acclimatised may need a more aggressive hydration plan, as he is likely to sweat more readily than fellow runners who are less heat adapted.

As such, there is hardly a one-size-fits-all hydration strategy for the replenishment of fluid loss during endurance events.

Follow these steps to implement your personal hydration strategy:

  • Weigh yourself without any clothes before your run (for example 60kg)
  • Head out for your run. Take note of the weather conditions, exercise duration, intensity and exact volume of water drank (e.g. one hour easy run, drank 500ml)
  • After towelling yourself dry, weigh yourself again without any clothes (e.g. 59.5kg)
  • Calculate the difference. In the above example: Amount of weight difference: 60 - 59.5 = 0.5kg Amount of sweat loss: body weight loss + water ingested = 0.5kg + 0.5kg = 1kg or 1 litre

In the above example, the runner has lost one litre of fluid in an hour of easy running, assuming there was no other form of fluid loss (e.g. urination) during the run.

Note that sweat rates may differ according to exercise intensity, duration and weather conditions. So, you should repeat this test under conditions that best mimic your race setting, to estimate your sweat rate and devise a personal hydration plan for your upcoming race accordingly.

You do not need to replace the entire volume of sweat loss during the run or race, as it can be difficult to drink so much when running.

Our body can handle up to 1 to 2 per cent of dehydration and perform just as well, if not better (you carry less weight for your run). However, do remember to replace all the fluid loss after your run or race.

A version of this article appeared in the print edition of The Straits Times on September 16, 2017, with the headline 'Drink more if you perspire more'. Print Edition | Subscribe