After all that winter training, dark evenings in the cold and wet, it is great to be enjoying these balmy summer days, warm, pleasant runs under clear blue skies. And it’s great that we don’t have to endure the hammer-like heat of the tropics.

Except of course we do – sometimes. Temperatures in the upper twenties and thirties are becoming ever more common and we may find ourselves joining the Parisians and getting temperatures in the forties.

These temperatures present our bodies with a problem! Normal body temperature is between 36 and 37 and varies from person to person and from hour to hour. If it rises too much, above 40.5, we are in danger. Fortunately, we have sophisticated body systems to keep it within acceptable limits.

We are all familiar with the basics of the system for keeping us cool. Exercise, get hot, start to sweat, which keeps us cool. We also know that as we sweat, we lose water, start to dehydrate and will eventually run out of sweat and begin to overheat. This is heat stroke, which can seriously damage or even kill us.

The great thing about training in this country is we can choose not to train on very hot days and avoid such dangers. We know that it will probably be cold and wet again shortly.

Unfortunately, we can’t choose our race days so sometimes we will probably be racing in Arizona like conditions.

Temperature Regulation

Our body’s temperature regulation system is very sophisticated. We lose heat through three routes; breathing, convection/radiation through the skin and sweating (evaporation). Sweat actually makes the smallest contribution. The bulk of the work is done by blood flowing through capillaries in the skin being cooled by the air around us.

As we get hotter the body diverts more blood to the skin reducing the amount going to the muscles. This reduces the amount of oxygen available to the muscles which then start to use the anaerobic fuel systems which are less efficient and use more fuel. As a result, we begin to fatigue more quickly in high temperatures.

As our core temperature rises we begin to sweat to gain the additional incremental benefit of evaporation cooling. This means we begin to dehydrate. This results in blood thickening and a reduction in blood volume. Thicker blood means the heart has to work harder to push it around the body. As that happens the body diverts further blood to the heart muscle and the system becomes less efficient at cooling us.

Along with the water in our sweat, we also lose essential minerals (salts). As well as affecting our physical performance a loss of about 2% of our body weight through sweat affects us mentally; mood, concentration, memory and cognitive ability are impacted.

In most cases the body “self-limits” our performance forcing us to cut down the rate at which we are working to prevent the system from failing but we do have the ability to override the self-limiting process. This makes sense; if you are being pursued by a lion slowing down to avoid overheating is not a good idea.

The problem comes when we override it and continue to do so in pursuit of running longer and faster for fun – did I really say “for fun”. When we do that the system can run away, ultimately produce more heat as it attempts to cool us. When that happens we have reached the point when heatstroke can kill us.

Training for heat

The good news is that we can take advantage of hot days to get our bodies to adapt to running in high temperatures. Professional athletes going to a competition in a hot climate will aim to acclimatise for weeks if not months; we don’t have that luxury so we should take advantage of those really hot days.

Just as normal training provokes muscle developments, so training in high temperatures encourages the body to develop more capillaries in the skin and trains them to relax, getting more blood through the skin making the process more efficient. As the skin becomes a more efficient radiator less blood has to be diverted from the muscles allowing them to operate more aerobically and conserving energy.

Because the process is more efficient we don’t have to rely on sweat to cool us which means we conserve the water, and therefore the salts.

To produce these adaptations, we don’t have to run ourselves ragged in high temperatures. Even a small amount will begin to stimulate those changes – so get out and enjoy training on those hot days.

Training safely and efficiently

Whether training or racing, you want to be safe and efficient.

Being safe involves guarding against the danger of heatstroke and being able to react to it should it occur.

Training efficiently is about training in a way that makes the best use of your time.


A few simple precautions are really all that is needed, but do read the note at the end of this section:

  • You must start out adequately hydrated. This does not mean swallowing huge quantities of water just before you start (this can cause a condition called hyponatremia which itself is dangerous). Simply make sure you are properly hydrated, the best way to do this is to check your urine colour. Dark yellow=dehydration present! Transparent = good levels of hydration.
  • It also makes sense to have access to water, but if you are out for less than about an hour, you shouldn’t need to drink providing you started out properly hydrated.
  • If you are going to be out longer, you should take water with you, once again laced with suitable salts.
  • Start drinking this early in small quantities.
  • If you are taking water with you, buy a belt that holds a bottle. Running with one of those strange hand-held bottles aren’t good for maintaining posture.
  • Start cool – don’t sunbath and then go for a run – best start from an air-conditioned room or car.
  • Wear loose-fitting clothing – preferably white – and consider a cap or visor
  • Keep the intensity low, you are out to get the body to adapt, not break records.
  • Where possible run in the shade – In the sun the temperature can effectively be 10 – 15 degrees higher than the actual air temperature
  • Run with a buddy if possible, at the very least let somebody know your route and expected time of return.

Efficient training

A session in the heat is designed to help you acclimatise. It is not designed to improve speed, endurance or anything else.

The biggest threat to your performance is an interruption to your training. We lose fitness faster than we can gain it. For that reason, we should finish a heat adaptation session ready to repeat it the following day

Make sure you start out properly fuelled. You will burn more calories in the heat and you will be using your glycogen stores.

If you are out for more than an hour take some top-up food with you. In normal conditions, your glycogen stores will last you about two hours but you will deplete them faster in the heat.

Keep the intensity of the session low. The benefit of any training session is limited by the speed at which the body can make the adaptations it is designed to produce. Doing more than the body can respond to is counter-productive and acclimatisation changes take place more slowly than normal training adaptations.

Refuel and rehydrate properly after the training session. Drink small quantities frequently until your urine returns to an acceptable colour. Eat a protein and carb-rich snack (about 20 grams of protein) within about 20 minutes of finishing.