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With hot weather upon us all around the country, it's time to talk about hydration and controlling our body heat. Keeping your fluids up is important all year round, but it becomes even more important during Summer, when our bodies struggle to keep their core temperature within safe levels and we can find it hard to replace what we lose.

Let's start off with a few technicalities, then get into what they mean for you.

• The salts (electrolytes) in sports drinks help:

  • Fluid empty from the stomach and re-hydrate you quicker

  • Encourage your kidneys to retain more water, reducing dehydration

  • Keep you thirsty so you continue drinking

• The sugars:

  • Are the right type to not cause stomach upsets that some sugars could

  • Maintain energy levels without making you too full

  • Are in the right concentration (4-6%) to deliver good amounts of energy without slowing water absorption

There are other benefits for endurance athletes, but as you can see we have plenty to gain by including sports drinks in our race day hydration regimen. Look at the nutritional information label on your drink, if it lists carbohydrate content as being more than about 8g per 100ml it may not be the best, try another one. If you prefer to mix your own sports drink from the powder, always follow the instructions closely, that way you'll get the optimal mixture.

Q: How do I keep cool?

A: We have several natural methods of removing excess heat. Unfortunately, most of these become ineffective during really hot weather. There is one mechanism of heat removal that retains its effectiveness during hot weather, evaporation. As you know, even this isn't all that good if the air is humid².

To overcome the problems in really hot weather, we can try a couple of things:

• Get cool water onto your skin. It doesn't matter whether it's from a spray bottle, a wet towel or any other method you can think of. As long as the water is cooler than the sweat on your skin and the moisture in the air, it will help. As soon as that water warms up, replace it.

• While your skin is moist, get some air flowing over it. This will help with evaporation and convection of heat away from your skin. Moving air is particularly important in humid conditions.

• Don't get dehydrated! Even though sweating is less effective in humid conditions, it's still very important and may be your only way of removing heat when it's hot. For details on how much to drink, see the practical recommendations below.

Q: Why do we need to keep cool and hydrated?

A: Our bodies function through countless chemical reactions that are happening all the time without us being aware of it. We need reactions to control our movement, deliver energy to the muscles that need it, remove waste products like carbon dioxide from our blood and many, many more. If these processes are affected, so is our performance. When we become too hot, some of the things that help all of this happen as quickly and efficiently as possible (enzymes) stop working, or in extreme conditions may get damaged permanently.

On top of that, when you become dehydrated, your blood becomes thicker. That makes it harder for your heart to deliver blood to your muscles, therefore you will recover more slowly between races. Dehydration has also been shown to impair your ability to think, leading to a greater chance of mistakes, potentially meaning more injuries².

Practical Recommendations

The goal of drinking during exercise is to prevent excessive dehydration, defined as a loss of more than 2% of pre-exercise body weight¹ . To do this, it's important to know how much to drink and how often. Given some of the things mentioned earlier, Exercise Scientists generally recommend drinking 250ml (about 1 glass) of fluid every 15 minutes when exercising in the heat. Regular drinks of this size are better than huge amounts in one go. Colder drinks (about 5°C) also make a slight difference by increasing the speed of hydration, but it's not significant enough to worry about, just go with whatever you prefer.

Try having sports drinks sometimes and plain water sometimes. I suggest making every second drink plain water. However, don't dilute a sports drink like some people recommend. For the reasons explained earlier, this makes the sports drink less effective.

Start working on hydration well before you begin exercising. That is, start drinking as soon as you get up, and keep drinking from then on. You don't necessarily have to drink as much to begin with, but get to the full amount once you reach the track.

Do everything you can to stay cool, remove unnecessary clothing - such as race jerseys - between races, stay in the shade, keep the cool water up to your skin and fan some air over your face if possible. Most of all, rest while you can, don't go running around and creating extra heat while you could be cooling off.

In summary:

• Start hydrating before you get to the track
• 250ml per 15 minutes
• Alternate between sports drinks and water
• Keep cool any way you can
• Don't forget to re-hydrate at the end of the meeting (1.5L for every kilogram of weight lost)

If you ever find yourself feeling unwell on a hot race day, go and see the first aid team. They know the signs of heat illnesses and how to treat them.

1. Sawka, M., Burke, L., Eichner, E.,  Maughan, R., Montain, S., & Stachenfeld, N. (2007) American College of Sports Medicine Position Stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2),377-390.

2. Armstrong, L., Casa, D., Millard-Stafford, M., Moran, D., Pyne, S., & Roberts, W. (2007). American College of Sports Medicine Position Stand: Exertional heat illness during training and competition. Medicine & Science in Sports & Exercise, 39(3), 556-572.

Matt Vickers

BA Exercise Science

Exercise Physiologist

As seen in XBR December 07