Time to Read:

  • 5 Minutes

Main Points:

  1. Hydration science
  2. Sweating
  3. Hydration monitoring (before, during & after exercise)
  4. Conclusion

One of the most important aspects of sports nutrition is hydration. We know beyond any doubt that hydration levels are vital to maintain, because even a small dehydration will lead to a significant and immediate drop in athletic output.

The old saying goes that 1% dehydration leads to a 10% drop in performance.

Whether or not this is true is impossible to quantify accurately, but what we can be sure of is that dehydration does negatively affect sporting performance.

At KYMIRA we don’t like to advise based on opinion alone – we review the science and take a measured viewpoint based on the available literature. We’re going to do the same with hydration by answering the question - what does the science say?

Hydration Science

Traditionally hydration guidelines were vague – advice such as ‘drink 8 glasses of water per day’, or ‘drink 2-3 litres per day’ was commonplace. Another one was ‘drink until your urine is clear’. This is all reasonable advice for most people, but it’s not specific enough for athletes. There are too many other factors at play in sport and performance, so we have to clarify as much as we can before we offer solid advice.

We know a couple of things to be absolute…

  1. The rate of sweating almost certainly outstrips the rate of rehydration. This is simply a question of physics – the human body is covered in sweat glands and can sweat well over 2.5L per hour (depending on the size of the individual). The amount at which a person can comfortably consume liquids is around 2 litres per hour.
  2. During sports performance, rehydration rates are slowed because it’s not comfortable to train or compete with a stomach full of liquid. It’s hard to run a marathon when you’re carrying a belly full!

The additional factors to consider are those such as the pre-race hydration strategy, the ambient temperature, the rate of sweating etc. for example, at events taking place in a hot environment the rate of sweating is increased.

Considering those issues, a study from the American College of Sports Medicine suggests a personalised rehydration strategy for athletes, based on fluid loss (determined by weight loss during exercise) electrolyte loss and the need for carbohydrate replenishment post training or competition.

Mineral Loss Via Sweating

Discussing the idea of rehydration is a little over simplistic – it’s not merely fluid we’re looking to replace, it’s electrolytes and minerals too. In this study published in the Journal of the International Society of Sports Nutrition, athletic performance was measured in response to sweating and mineral loss. It was concluded that dehydration and mineral loss has a marked effect on sports performance and physical recovery between bouts of exertion, proving once and for all that it’s not just rehydration that is important, it’s also vital to ensure minerals are replaced.

Any athlete knows that mineral loss leads to cramping during the latter stages of an event, hence the need for isotonic sports drinks. The good news is that electrolytes are easily replaced either with food or drinks so needn’t cause too much concern, but it’s important that athletes don’t simply rely on water to replace electrolytes.

Hydration Monitoring for Amateur Athletes

It’s all well and good us telling you how the pros assess their fluid levels and monitor blood sugars etc, but that’s not realistic for most amateur athletes. Here’s advice from the British Nutrition Foundation on Hydration for Optimum Athletic Performance…

Before Exercise    

  • Drink 500ml of fluid 2 hours before exercising to allow time for any excess to be lost in urine.
  • Drink a further 125-250ml immediately before exercise.
  • Weigh yourself (see After Exercise below).

During Exercise  

  • Drink small amounts regularly, aiming for 125-250ml every 10-20 minutes. You can maintain optimal performance by replacing at least 80% of sweat loss during performance.

After Exercise    

  • You need to consume 150% of the amount of fluid lost during exercise to allow for the fluid that is naturally lost from the body via urine. For example, if you have lost 1L of fluid, you need to drink 1.5L.
  • Calculate your fluid loss by weighing yourself before and after training. 1kg of weight loss resulting from exercise is roughly equivalent to 1L of fluid loss.
  • Weight loss in kilos then needs to be multiplied by 1.5 to calculate the amount of fluid to consume. (This does not need to be consumed all at once, immediately after exercise).
  • Aim for 500ml immediately after training, then consume the remainder at intervals afterwards.

We would also add to this that it’s important to replace electrolytes, whether from an isotonic drink or post-event food. According to the research, this should help maintain and improve performance.

Hydration for Sport – Concluded

The studies show clearly that dehydration is a key factor when it comes to performance decline, so avoiding it as much as possible is vital. We’ve also shown how important it is to replace electrolytes and minerals lost during sweating if we want to maintain performance.

By following the advice from the British Nutrition Foundation, but with added electrolyte replacement strategy you should avoid any problems with dehydration and maintain your performance throughout your training and events.

For more training, nutrition and recovery advice visit our blog.


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