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Hydration - Understand the basics

Q. Why is fluid replacement so important and what is the best fluid to drink during exercise?
A. Unless fluid losses are replaced during exercise, an athlete will become dehydrated. Dehydration impairs performance by causing the following:  

  • increased heart rate

  • impaired heat regulation

  • increased perceived exertion (i.e. exercise feels harder than usual and the athlete fatigues earlier)

  • reduced mental function

  • reduced skill level

  • stomach upset


All levels of dehydration impair performance and the magnitude increases as the degree of dehydration increases. In order to minimise dehydration, athletes need to drink enough during exercise to match their sweat losses. Sweat loss can be determined by weighing athletes before and after exercise. Each kilogram of weight loss indicates 1 litre of fluid loss. Adding the amount of fluid consumed during the exercise session, gives total fluid loss for the session. For example, if an athlete finishes an exercise session 1 kg lighter and has consumed 1 litre of fluid during the session, total sweat loss equals 2 litres. Once an athlete's average sweat loss is known, a plan can be prepared to enable the athlete to match sweat losses in subsequent exercise sessions.

Ideally fluids consumed during exercise, should meet the following criteria:

  • have a palatable flavour to encourage greater fluid intake

  • contain 6-8% carbohydrate

  • contain electrolytes such as sodium and potassium

  • be non-carbonated