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Hydration and performance

April 06 2022 6 min read

Kevin Currell is Head of Performance Nutrition, at the English Institute of Sports and is also Lead Performance Nutritionist for British Athletics and GB Short Track. We spoke to Kevin about hydration and its effects on performance.

The amount of water in your body could be anywhere from 50% to 75% and this is in constant flux and change. Exercise adds to this, so when you start to workout, blood is diverted to the muscles and to the surface of the skin. When your muscles contract, the breakdown of energy leads to a production of heat, and this needs to be dissipated or your core body temperature will continue to rise. As this heat is produced in the muscles, it is transferred to the blood and then through the circulation to the skin where it can escape into the air. To help this heat escape effectively the body starts to sweat, which produces a film of water on our skin. When this evaporates it has a cooling effect and is one of the main mechanisms by which our body regulates temperature.


The exact effect on hydration on exercise performance is a controversial area of sports nutrition, with many conflicting bits of evidence. There are grand statements, such as, ‘for every 1% increase in dehydration, there is a 10% decrease in performance’ right through to the other extreme of ‘hydration status has no effect on performance whatsoever.’

The reality is likely to be somewhere in between the two and is also very individual. This makes absolute sense, as walk into any gym and you’ll be able to observe the individual variation in sweat rates. One person can be jogging away on the treadmill and only have a light sheen of sweat, whereas the next can look like they‘ve poured a bucket of water over their head! So how can you make sure you are in the best state to perform? Here are three great tips:

  1. Make sure you start the exercise session in a hydrated state
    There’s no point in starting a training session dehydrated. It will only increase your perception of effort and make things seem harder. Simply monitor your urine colour and output. If your urine looks like lemonade you are likely to be hydrated, if it looks like apple juice then consider drinking more water.
    Don’t worry about it too much – you certainly don’t need to take one of those hand held bottles on a 5 km run!
  3. POST EXERCISE If you want to be really accurate with this one, then weigh yourself before and after exercise. For every 1kg you lose, make sure you consume 1.5L of fluid after exercise and before you exercise again or go to bed. Make sure the drink contains some sort of electrolyte to help keep the water in your body rather than passing straight through you.