Hydration: How Much Should You Drink During Exercise?

Hydration

As the weather starts to warm up again, it’s time to ditch the winter thermals and start re-focusing on your hydration needs during exercise. With so many drink options available and mixed messages about how much and when to drink during exercise, this article will look at the ‘who, why, what, when and how’ of hydration.

Who?

Hydration needs are highly individualised due to variations in sweat rates between people, or even for the same person exercising in different conditions. Sweat rate is influenced by a number of factors including:

  • Body size – larger body sizes tend to sweat more
  • Fitness level – fitter athletes generally start to sweat earlier
  • Genetics – some people naturally sweat more than others
  • Temperature – hot and humid conditions increase sweat rates
  • Wind – air flow over the skin improves body cooling and reduces sweat rates
  • Exercise intensity – as intensity increases, so does sweat rate.

So, while there is no ‘one size fits all’ approach when it comes to replacing fluid losses from sweat, being aware of your own hydration needs before, during, and after exercise is an important consideration for all active people.

Why?

During exercise, fluid is critical for maintaining blood volume, regulating body temperature, and for muscle contraction. Sweating is the body’s way of maintaining core temperature while exercising but the loss of body fluid that occurs can result in dehydration (eg. if fluid intake is suboptimal). Generally, the body has a good capacity to tolerate low to moderate levels of dehydration; however, as levels of dehydration rise, performance can be impaired through:

  • Increased heart rate
  • Increased perception of effort
  • Increased fatigue
  • Impaired cognitive performance (e.g. skill and coordination)
  • Gastrointestinal issues, such as nausea
  • Increased risk of heat illness

What?

With so many drink options now available, deciding which fluid best suits your needs can be tricky. When choosing the best drink for you it’s a good idea to consider:

  • The duration and intensity of your session
  • Whether there is a need to replace carbohydrate and electrolytes during the session
  • Individual preferences (e.g. flavour preferences, gastrointestinal comfort)

Unlike plain water, dairy options and sports drinks contain carbohydrate and sodium (salt). When used appropriately, carbohydrate can have positive effects on performance, especially during moderate and high intensity exercise. Sodium is an important electrolyte that aids hydration by helping the absorption of water through the gut and assisting the body to ‘hold on to fluid’ more effectively (e.g. reduce urine output).

When?

The optimal amount and timing of drinks will depend on your individual sweat rate and exercise conditions (e.g. hot vs. cold weather, easy ride vs. racing, etc).  An Accredited Sports Dietitian can work with you to develop an individual hydration plan but as a general strategy:

  • Begin exercise well hydrated
  • Follow a hydration plan based on your individual needs while exercising
  • Rehydrate after you finish exercising as you are unlikely (and it’s not necessary) to replace 100% of fluid losses during exercise

Keep in mind that there is no performance advantage to starting an exercise session over-hydrated and it is actually more likely to result in negative side effects. Being too aggressive with your hydration can lead to interrupted sleep the night before, bloating and gastrointestinal upset, and the frequent need to urinate during exercise. It is important not to drink beyond your needs while exercising, as this can result in a condition known as hyponatremia (a medical issue where sodium levels in the blood become too dilute, most commonly seen in endurance or ultra endurance races where large volumes of low electrolyte fluids are consumed beyond participants’ needs).

How?

Hopefully you now have a better understanding of hydration needs and realise that there is no ‘one size fits all’ approach when it comes to drinking during exercise. Here’s a quick summary of tips for optimising your hydration plan:

  • Aim for pale yellow urine over the day – it’s a good sign that you’re appropriately hydrated
  • Avoid high levels of dehydration – this can impair performance and increase risk of heat illness
  • The best drink choice is different for different sessions – consider the duration and intensity of the session, the need to replace carbohydrate and/or electrolytes and individual preferences
  • Individualise your hydration plan and the timing of drinks during exercise – this will depend on your sweat rate, environmental conditions and practicality
  • More is not better – there is no performance benefit to being over-hydrated and it will increase your risk of negative side effects

For a tailored approach to your individual circumstances, seek the advice of an Accredited Sports Dietitian.