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Running Hot

The weather forecast says ‘Hot, Hot, Hot’.
Today is race day and over the last couple of weeks the weather has been warm, yet in an effort to be ‘sensible’ and to be able to run at your usual training speeds you’ve simply avoided the heat and missed training.  Is this the right thing to have done?
Often, runners fear the heat and just avoid training at all and then rock up to their target race, lacking any sort of ‘heat training’ and therefore acclimatisation.

So what can we do?

How We Keep Cool
Our bodies are constantly adapting to keep our core temperature at roughly 37°C.  As we run we burn fuel for energy and 80% of that energy is returned eventually as heat.  Add to that a warm sunny day and the risk of hyperthermia increases. So in order to keep things cool the core moves blood to the surface of the skin to dissipate heat to the environment. As we do this our sweat glands produce sweat to cool the skin.  As a result of this added demand, our heart rate increases for the same running pace on a warmer day.
As you get hotter you are increasing the stress on your body and there are three important factors that we need to understand as endurance runners.

How is Performance Is Affected?
Muscular endurance is most definitely affected on hot days as the ability to maintain muscular contractions greatly reduces. This is not helped as hyperthermia shifts energy production from an aerobic to a more anaerobic form which means that the bodies stores of glycogen are used up much more quickly.
‘Circulatory Strain’ is also experienced as the amount of blood volume available to your running muscles is greatly decreased as it is being used to keep you cool.
The one we always talk about of course is dehydration. We know there is a critical point at which too much water and salt loss has a degrading effect on performance, let alone putting you in danger of serious illness or in a worst case – a life threatening situation.
High humidity on top of warm sunshine also causes problems, as this slows the rate of cooling sweat evaporation from the skin.

Heat Acclimatisation through Sensible Training
The best and most effective way to acclimatise to heat is actually to plan to train on hot days. Yet we should be sensible.
Some folk will be predisposed to adapting to running in heat.  Others will not.
The first thing to do is to cut back on both duration and intensity during your period of acclimatisation. As it will take around 14 days of training in the heat to experience acclimatisation; therefore you should plan your training load to get back to normal through this time frame.  Training to heart rate has shown to be a very good way of aiding adaptation, as more heart beats will be required to push blood to the skin so to stay within your known ‘zones’ you will be forced to slow down.  As you adapt you will speed back up again.  Many report that Zone 2* (L2) is a great way to get the adaptation process started.
So cut back, take your time and give your body a chance to adapt.
If you are not yet acclimatised and wish to continue with speed or high intensity training then go for the cooler parts of the day, either early morning or late evening.  Also avoiding the ‘Black-Top’ and heading for the trails is no bad thing. Tarmac absorbs much heat and you can definitely tell when running on it.

If you know you are going to train on a hot day then clearly it is sensible to drink more fluids. Little and often through the day is better than leaving it to the last minute to down a half litre of water. Some people will benefit by increasing their salt intake, either through their normal diet or by taking a salt tab such as High Five Zero. This will have more relevance if you are running a longer endurance event than a short 5km run.
So what should you do? Well it is more about trial and error. Many find the unquenchable thirst is solved by taking a drink of water with a salt tab added or a sports electrolyte drink that also contains some carbohydrate. Others who are heading out for a longer run of two hours or more on a hot day sip a High Five Zero through the couple of hours prior to their training session and this works just fine.  Others will prefer to take this on board as they run, instead of or in addition to.
The science appears to be mixed as to whether plain water or a sports drink are better and again I would suggest it is down to personal preference through trial and error. Some have found that a 50-50 mix of water and orange juice with a teaspoon of salt will work just fine.
Generally, it is agreed that sipping your drink whilst running, little and often, works just great. Work around 125ml every twenty minutes or so and see how you get on whilst you are running at Zone 2* heart rate – you can always adjust the amount and timing later. Always remember to start this early, as leaving it until you are thirsty – is leaving it too late. Conditions and your own personal preference will dictate exactly how you adopt this strategy.
It is also important to remember that just because you are seeing a good adaption to training in the heat it does not mean you can get away with drinking less water – this is just not the case. You will still sweat more.

Fine yarns definitely dry quicker and the general rule has been that loose fitting open knit clothing keeps you cooler, allowing air to move against your skin, so aiding the cooling process. Likewise open mesh garments more easily allow evaporation of sweat from the skin to take place.
Some runners are finding that close fitting garments that move the sweat away from the skin are more beneficial as evaporation takes place from the garment. Again it’s all personal preference.
Light colours that reflect heat and sunlight are definitely better than blacks and navy blues by a significant margin.

Race Day or Training Warm Up – Is It Still Necessary?
Yes, is the short answer.
That said, I always advise runners to cut back on the duration and the intensity as you do not want to raise core temperatures too much immediately prior to training or a race. Limb and joint mobilisation whilst walking in the shade can definitely take place which followed by a cool shower (not freezing cold) can then help to lower the core temperature once again before heavy exertion and therefore delaying a rise in core temperatures. Again, not something for everyone or always practical even.
Keep the running to a minimum, but some is still a good idea, as you raise the heart rate slightly and you get your cooling system active.

Racing (and Training Hard)
We’ve heard it all before, yet it still holds true. Slow down and keep the fluid intake going, having experimented with what you feel to be the correct approach in training.
Also, give yourself a fighting chance and find races that take place in the early morning or late evening and if you are particularly prone to the heat then find another race.

So there you have it, taking a sensible approach to your training and racing during hot weather periods can reap many benefits as you become more adapted to the processes your body undertakes to keep you cool. Yes, some experimentation is in order and thinking about your clothing is also sensible. Then there is what to do if you become too hot and head into heat exhaustion, let alone which sun cream to use that avoids blocking your pores and so reducing sweating – all of which are another topic in themselves.
The key is simple, summer is coming and if you are planning a race when the conditions could be ‘Hot, Hot, Hot’ then some serious thinking time about your training planning and hydration strategy will most likely not be wasted time.

  • Plan for the warm weather and schedule your training accordingly.
  • Train to heart rate, even if the speed is lower than normal, your body is working just as hard to keep you moving and cool.
  • To help you adapt to warmer weather, try running at a cooler part of the day, slowly increasing the time you may spend in the hotter part of the day (although still best to avoid the hottest part).
  • Reduce your normal running time on especially hot days. A normal 90 minute run could be trimmed down to an hour.
  • Split your run in half. Run half your normal time in the early morning and the second half later in the evening, both when it is cooler.
  • Think about the best clothing to wear, that suits you.
  • Develop a hydration strategy that works for you – this could include a plan for longer runs that includes bottle drops on route.
  • Drink early in your run, never wait until you are thirsty.

*Note: Zone 2 or L2 running is just out of breath and talking is still comfortable in sentences.

About Run Stu

Accelerate Performance and Healthy Run Coaching, Heart rate, Periodisation, Strength & Stability. Business owner @accelerateuk Coach to #TeamAccelerate The open road, fell, moorland and high places. Sunny days, days the wind blows and rain is horizontal - 'You're Alive!' Twitter and Instagram: @RunStuCoach

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