Why is hydration important? The effect of dehydration on performance

Our bodies are made up of ~60% water. Water has many roles in the body but when exercising, water is vital to help maintain blood volume and regulate our core temperature. During exercise to help keep us cool, we sweat and lose water through evaporation on our skin. If we do not replace this lost water, we can become dehydrated.

When we become dehydrated (as defined by a body fluid deficit >2% of body mass), blood volume decreases. This makes it more difficult to maintain blood pressure and blood flow. This puts a strain on our cardiovascular system and can make exercise harder than it would normally be when fully hydrated. This can speed up fatigue and impact on performance.

To prevent declines in health and performance, it is recommended to avoid a loss body fluid >2% of body mass especially in hot-humid environments.

Signs and symptoms of dehydration in athletes may include:

  • Thirst
  • Dark urine colour (think apple juice)
  • Daily bodyweight fluctuations > 1%
  • Headaches
  • Increased perception of effort
  • Poor concentration
  • Reduced urine output

More severe signs/ symptoms of dehydration include:

  • Disorientation/ confusion
  • Rapid pulse
  • Collapse/ unconsciousness

How you can monitor daily hydration using WUT model

You can simply and easily monitor daily hydration using the Weight, Urine, Thirst (WUT) model.

Athletes should be able to maintain a stable body Weight when measured first thing in the morning. Day to day bodyweight changes >1% body mass may indicate dehydration.

We all know that when we drink more water, we tend to visit the bathroom more regularly. When we are dehydrated, the opposite can happen, and our Urine can be darker in colour. A smaller volume of urine and darker colour first thing in the morning may indicate dehydration.

Being Thirsty is another indication we have not drunk enough fluid, with many athletes already being dehydrated when symptoms of thirst appear.

Athletes can ask themselves three questions using the WUT model to determine if they are dehydrated.

  1. Am I thirsty?
  2. Is my morning urine dark in colour?
  3. Is my bodyweight this morning noticeably lower than yesterday morning?

If you have answered “yes” to two of these, you are likely dehydrated. If you answered “yes” to all three of these, you are very likely dehydrated and should drink more and reassess your fluid intake with an Accredited Sports Dietitian. 

How much fluid you need to replace post-exercise to fully rehydrate. 

The amount of fluid needed post-exercise to fully rehydrate is 125-150% of your body fluid loss. To work this out, simply weigh yourself before and after your exercise session. A 1 kg loss in body weight roughly equals a 1 L loss of fluid.

For example, if you lost 1 kg, you would need to consume 1.25 – 1.5 L of fluid within the post exercise recovery window to meet your rehydration goals.

What conditions/sports are athletes more likely to become dehydrated in?

The below conditions can increase the likelihood of becoming dehydrated:

  • Athletes performing sustained or vigorous exercise/ competing in warm or hot conditions
  • Athletes training/ competing in humid conditions
  • Athletes training or living at altitude or travelling on flights
  • Athletes who suffer from traveller’s diarrhoea
  • Athletes who fall ill with gastroenteritis or fever

When, how and why would you need to use an electrolyte supplement?

Before, during and after exercise:

For everyday hydration and in the lead up to exercise or competition, water is the preferred choice. An electrolyte supplement or true oral rehydration solution (ORS) that follows the World Health Organisation (WHO) guidelines can be used pre-exercise for more effective hydration if athletes are showing signs and symptoms of dehydration.

Electrolyte supplements can also be used during exercise or competitions > 2 hours duration of moderate to high intensity in the heat to help prevent large losses of body fluid. When added to the fluid volume needed to fully rehydrate post exercise, electrolyte supplements assist the body hold onto more fluid therefore, rehydrating more effectively.

Glucose and salt (sodium within electrolyte supplements help to accelerate rehydration goals compared with plain water. Glucose is required to facilitate the absorption of sodium within the small intestine and sodium assists with retaining more fluid in the body. Together with the right amount of fluid, glucose and sodium are important elements of electrolyte supplements.

If an electrolyte supplement is not available, salty foods that contain carbohydrate (glucose) such as cereal, bread, pretzels, milk and vegemite consumed alongside plain water can be an alternative option.

When looking for an electrolyte supplement, ensure it is HASTA or Informed-Sport certified. This means that athletes can use these electrolyte supplements with the confidence that they are low risk for containing WADA banned substances. Make sure you check the HASTA (www.hasta.org.au and Informed-Sport (www.informed-sport.com) websites to match up the right batch number/s.

Be mindful of electrolyte supplements with additional ingredients (i.e. minerals, caffeine or amino acids). These are typically unnecessary for effective hydration, can be expensive, have potential negative effects on your health and, could be a higher risk of contamination from WADA banned substances.

What is the main difference between an electrolyte supplement and a sports drink?

The main difference between electrolyte supplements and sports drinks are the electrolyte (sodium) and carbohydrate (glucose) content.

Electrolyte supplements can be added to water for effective hydration in sports where excess energy (sugar) is not desirable. Sports may include gymnastics, ballet, diving, boxing, Muay Thai and other weight-category sports.

Sports drinks can be used in sports such as marathons, triathlons and other endurance events where optimal fuelling (carbohydrate) is required in addition to hydration needs as these can contribute to fuel needs before and during exercise and refuelling needs after exercise. For more effective and rapid hydration/ rehydration, electrolyte supplements can be added to sports drinks to boost their sodium content.