Key facts: hydration

How to keep hydrated during a race


Although relatively well understood by triathletes, hydration before, during and after exercise becomes significantly more important as race distances increase.


Athletes can lose up to 1-2 litres of sweat per hour during moderate to high intensity exercise, and if fluid is not replaced then this can lead to dehydration.

Dehydration is typically described as fluid loss greater than 2% body mass, so for example 1.4kg in a 70kg athlete. 

It has various implications for both health and performance, including increased body temperature, increased heart rate and increased glycogen (carbohydrate) usage at the muscles. 

This combination can lead to the exercise being perceived as more difficult even whilst working at the same intensity, meaning that you have to work harder to maintain the same speed and power output, leading to early fatigue and increased race times. 

The importance of electrolytes

Sweating is a great mechanism for regulating body temperature and cooling the body down, but if sweat rates supersede the rate at which fluid is replaced then this can lead to dehydration. 

Sweat consists of fluid (from the blood plasma) and electrolytes (including sodium, potassium, magnesium, chloride and calcium), both of which are important for the body’s optimal functioning. 

Of the electrolytes lost, sodium has the greatest importance for exercise performance. Sodium is required for regulating fluid balance, assisting in controlling blood pressure, and for the normal functioning of muscles and nerves. 

Many triathletes often hydrate using only water, but if sweat rates are high (losing fluid and electrolytes) then this can lead to diluted plasma sodium concentration. 

As a consequence, cognitive performance including concentration, decision-making and accuracy can be reduced, which are key elements during a triathlon. 

The ideal strategy for fluid replacement

Fluid intake varies depending on exercise, environmental temperature, sweat rates and thirst, but by consuming fluids containing electrolytes you can partially replace those lost through sweat. 

Consuming around 500ml of fluid with a pre-race meal two to four hours before the start line, then an additional 250-500ml in the lead up to the event, can help ensure optimal hydration on the start line.

During an event, the primary aim is prevent dehydration, which typically means taking on around 500-1000ml per hour. Thirst, environmental temperature and sweat rates will indicate if more or less is required. 

A carbohydrate and electrolyte blend is often great for this time, as it can contribute towards fluid intake and fuelling. Alternatively if carbohydrate intake is achieved through gels and bars or other food sources, then a purely electrolyte drink is ideal.  

Following exercise, the aim is to replace fluid lost through sweat; this should be at a rate of 1.5l for every 1kg lost, and requires assessing body weight before and after exercise.  

Fluid should be consumed gradually during the hours after exercise to avoid gastrointestinal discomfort.  


Jill Leckey is Senior Sports Nutritionist for Science in Sport (SiS)