Hydration During Exercise: The Endurance Athlete's Guide

Why hydration matters

Water is one of the most important parts of your exercise fuelling plan. It helps to:

• Regulate your body temperature
• Transport nutrients around your body
• Support healthy cell function
• Release energy during exercise

However, many athletes struggle to judge how much fluid they should drink.

A common approach is to replace fluid at the same rate that it is lost through sweat. Although this may sound sensible, the body cannot absorb fluid as quickly as it can lose it.

The key principle to remember is:

Your body cannot absorb fluid at the same rate that it loses fluid.

During exercise, the average athlete may lose around one litre of fluid per hour. Fluid losses can be even higher in very hot or humid conditions.

However, trying to replace every drop of sweat can lead to excessive fluid intake.

You do not need to replace every drop of fluid

You can complete exercise with a fluid-related body-weight loss of up to 2% without experiencing a decline in performance or negative health effects.

Instead of trying to replace all the fluid you lose, focus on drinking an amount that your body can comfortably process.

Research suggests that an average fluid intake of approximately 590–740 ml per hour is suitable for most athletes.

Why drinking too much can be dangerous

The goal of hydration is similar to the goal of calorie intake during exercise: consume enough to support performance without taking in more than your body can process.

Research by Dr Tim Noakes, based on ten years of data collected from approximately 10,000 ultrarunners, found that most endurance athletes can efficiently absorb around 475–710 ml of fluid per hour.

Drinking more than this does not necessarily improve performance. In fact, excessive fluid intake can have serious consequences.

Drinking too much can dilute the sodium in your blood. When blood sodium levels become too low, performance can quickly decline.

In severe cases, excessive fluid intake can overwhelm the body's electrolyte balance. This may lead to water intoxication or dilutional hyponatraemia, a potentially fatal condition.

Our recommendations

To reduce the risk of performance and health problems caused by low blood sodium, your fluid intake during exercise should generally remain within the following guidelines:

• Average-sized athletes or moderate temperatures: 590–740 ml per hour
• Lighter athletes or cooler temperatures: 475–530 ml per hour
• Heavier athletes or hotter temperatures: Up to 830 ml per hour

These amounts may vary depending on your body weight, exercise intensity and weather conditions.

The bottom line

For most athletes, drinking approximately 590–740 ml of fluid per hour will support effective hydration during exercise.

The exact amount should be adjusted according to your body weight, exercise intensity and environmental conditions.

Drinking the right amount can help you:

• Maintain performance
• Reduce fatigue
• Avoid bloating
• Lower the risk of cramping
• Feel better before, during and after exercise

Remember: successful hydration is not about replacing every drop of sweat. It is about drinking an amount your body can safely and effectively absorb.