Why is fluid important during exercise?

Water has many important roles in the body and is required to maintain blood volume and regulate body temperature. During exercise the body cools itself by sweating but this ultimately results in a loss of body fluid which, if not replaced, can lead to dehydration. Sweat production (fluid loss) increases with increasing temperature and humidity, as well as with an increase in exercise intensity.

Drinking fluid during exercise is necessary to replace the fluid lost through sweat and the amount of fluid consumed should reflect the amount of fluid lost through sweat. As sweat rates vary between individuals, knowing your unique sweat rate and how much fluid you should be drinking is important. An Accredited Sports Dietitian can help to tailor an individual fluid plan for you.

Dehydration and Performance

As dehydration increases, there is a reduction in physical and mental performance. There is an increase in heart rate and body temperature, and an increased perception of how hard the exercise feels, especially when exercising in the heat. Impaired skill level can also occur, along with mental fatigue that can impact concentration and decision making. Dehydration can also increase the risk of nausea, vomiting, diarrhoea and other gastro-intestinal problems during and after exercise.

Can you drink too much?

In cool weather or when the exercise intensity is low, sweat losses may be small. Drinking more fluid than necessary has the potential to interfere with performance (and can be dangerous to health) in several ways. Over-hydration during exercise is called hyponatraemia (dilute levels of sodium in the bloodstream). Symptoms include headaches, disorientation and in severe cases, coma or death. It is important to note though that this is relatively rare and dehydration is a typically a more common issue for athletes.

Estimating your sweat rate (fluid loss)

Knowing your sweat rate can give you an indication of how much you should be drinking during exercise. Accredited Sports Dietitians routinely measure an athlete’s sweat rate during training and competition in a range of environmental conditions, to provide them with the information required to design an individual fluid plan.

How much fluid and when

The amount and timing of fluid depends on each individual’s needs and the rules and regulations of the sport. Different sports have different challenges and opportunities for hydration. Here are some tips to help you with your fluid goals:

• Always start exercise hydrated to lower the risk of becoming dehydrated during exercise
• Aim for pale-yellow, straw coloured urine as a useful sign of adequate hydration
• Avoid drinking excessive amounts of fluid before and during exercise as this can lead to increased urination and gastrointestinal upset
• You will continue to lose fluids through sweating and urine losses after you finish exercising, so plan to replace 125-150% of this the fluid that you’ve lost during the session over the 4-6 hours after you stop exercising
• Drink fluids in conjunction with your salty recovery snacks (e.g. cereal, bread, vegemite, milk) to help your body rehydrate more effectively

What is the best fluid to drink?

As there are many drink options available, it’s important to determine which fluid is best for you. Plain water can be an effective drink for fluid replacement, especially in low intensity and short duration sports. Sports drink can be useful in during some activities, especially high intensity or endurance sports, as it contains both carbohydrate for fuel and flavour and electrolytes (sodium) to help the body ‘hold on to’ fluid more effectively as well as stimulate thirst.

Fluid needs are highly individualised and there’s no ‘one size fits all’ approach to fluid intake. Work with an Accredited Sports Dietitian to develop a plan for drinking during exercise based on your unique sweat rate to minimise your risk of dehydration-related performance impairments.

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