By Kim Petersen
The summer is upon us!
It is a wonderful time with barbecues, trips to the beach, and a lot of sun.
However, there is still one particular aspect that might make us long for colder times – the running!
Running in the heat can often be a painful and utterly frustrating experience.
You probably know the feeling:
The legs feel like lead, the head is about to boil over, and you just want to lay on the beach with a cold beer or coke.
In this article, you will get 5 efficient tips to meet the challenges of running in the heat.
The article comprises the following sections. You can click on any of the headlines to jump to that particular section.
Why is it so hard to run in the heat?
First and foremost, let us consider why it is so hard for the body to run in the heat, and whether it affects runners differently?
When you are running, you produce a lot of heat on top of the energy you produce to propel yourself forward.
Only about 20% of your total energy production will be used to push you forward, while the remaining 80% will be transformed into heat.
When we are producing heat, our body temperature will rise. This is problematic as the body can only function within a narrow temperature interval.
The body can maintain physical activity until it reaches a body temperature of about 39-40 degrees, according to two scientific analyses made on triathletes. Despite this, higher temperature tolerance has been discovered when it comes to trained endurance athletes.
In order to avoid any overheating, we need to reduce the body heat we produce.
The body has various mechanisms to perform this task, but I will not dwell on them in this article. This is because these mechanisms are practically made inefficient by hot and humid weather.
Therefore, to reach an efficient cooling of the body, we need to actively help support the body’s natural cooling mechanisms.
I will now focus on the actions you can take to best help support your body’s natural cooling system!
5 efficient and simple tips for you
You can either use all 5 tips or just one or two for a noticeable effect.
The most important tip, however, is the first one.
Tip #1: Slow down your running pace
When you slow down the pace, you will produce less heat. As a result, you will not have to rely as much on your body’s cooling mechanisms.
The degree to which you should slow down is a hard question as it depends on several things.
One of the factors with the greatest influence on your ability to maintain a steady-state in the heat is your weight.
People with a lighter weight have a more beneficial relationship between their heat production and the ability to lose heat.
A heavier runner will BOTH produce more heat and lose more heat, compared to a lightweight runner.
Moreover, even from a slower running pace, the heavier runner’s heat production will start to exceed the body’s ability to lose heat.
Consequently, in hot and humid conditions, heavier runners have a greater physiological disadvantage, compared to lighter runners.
Illustration of 4 runners with different weight and their respective heat production and loss of heat at a different running pace. Credit: Lore of Running by Tim Noakes
Notice the points of intersection for the 4 runners (i.e. where the two lines meet). It is at this point (i.e. the running pace) that the body no longer is able to lose the extra heat that is being produced. And as mentioned, this will happen at a much slower running pace for heavier runners, compared to lighter runners.
It is hard to provide you with specific guidelines, but here is a general recommendation.
Start by running with a pace that is 15-20 seconds slower per km, compared to your usual pace on your regular runs. If you feel comfortable with this, then feel free to increase the tempo.
Doing interval training in the heat is possible
Compared to your regular runs, it is much easier to keep the pace during interval training.
This is even though the production of heat is much greater for interval training, compared to your regular runs where you maintain a steady state.
This can be explained by how the rests between each interval allow your body to lose some of the excess heat.
Instead of standing still during your rests, try jogging around. You will instantly feel how much harder it is to keep up the tempo for the intervals!
So, I would recommend stationary rest when it is very hot.
For some runners, it can be hard to actively slow down from the tempo they are used to.
If you are one of them, I would recommend running without a watch or other measuring device and only let your body guide you for your run.
Nevertheless, this is the most important tip I can give you:
Without slowing down the pace and accepting that you cannot run as fast as you normally do under normal conditions, the other tips will not be able to make an impact!
Tip #2: Adapt your body to running in the heat
If you have read other articles about running in the heat, then you might have already read the general advice of running after 7 pm and before 9 am to avoid the worst heat.
If this is not possible every time you are going for a run, then you need to teach your body to adapt to hot weather conditions.
You can only do this by running in the heat. However, you need to run with a lower intensity and shorter durations, compared to what you normally do. But after a short while, you should be able to run like you normally do, even though it is hot outside.
The recommended duration of training in hot weather is between 30 and 100 min., according to Shapiro and his research group.
The period should be between 10-14 days in order to acclimatise the body to the high temperatures.
After 14 days to a month, you should be able to notice an improvement in your ability to tolerate the heat.
You can start by running at around 70-75% of your capacity in the first week, 80-90% in the following week, and 90-100% in week 3.
After this, your body should have adapted to the heat, and you can start hoping the summer will continue!
Tip #3: Cool your body down before running
Various studies conducted on both people and animals show that if you cool down your body and the active muscles right before going on a run, you will improve your ability to run in the heat.
This is probably because it will take longer for the body to reach the critical 39-40 degrees when it has been cooled down.
Conversely, it is not recommended to lay out in the sun or be outdoors before running in the heat.
When your body temperature is too high before going for a run, you will reach the critical temperatures much quicker.
It might be a problem if, for instance, you are a labourer working outdoors in the heat and then wish to go for a run straight after work.
You can cool down the body and the active muscles with ice bags and cold towels before the run.
Another option is to stay in a cool room before your training session.
An ice-cold bath will probably also help if you are used to that sort of thing!
Tip #4: Get something cold for your head, neck, and legs
Marvin and his colleagues discovered that the time it takes to reach exhaustion at 75% maximal oxygen uptake was improved by 50% in conditions of moderate heat when the test subjects cooled down their faces with cold water.
The hypothesis behind this strategy is that the cooling of the brain and blood to the brain “tells” the brain that there is no danger oncoming!
Incidentally, a study from 2009 conducted by Ely shows that if the skin temperature stays relatively cold, the runners were able to maintain their running pace over an 8 km distance. This is even though the core body temperature reached the otherwise critical 40 degrees!
This study confirms the results of an earlier study from 1987.
In this study, the researchers found that the effect of cooling the skin works like a so-called contraction reflex, which helps increase the blood flow to the heart. So, NOT any cooling of the body temperature.
Cooling the body during a run – this is how you do it best
It is obviously challenging to cool your body.
The water you may carry with you in a hydration belt or water bottle will quickly turn warm and become pointless.
Therefore, it can be a good idea to freeze the bottles for your hydration belts the night before and take them out of the freezer before your run.
After about 15-20 minutes, the ice should have thawed, and you will have cold water for the head and the neck.
Another trick is to invest in a lightweight running cap, damp it with water, and then freeze it.
Then, when you are going for your run, the freezing cap will slowly melt, and you will get a continuous stream of water for the head and neck.
Remember to take off the cap when you no longer feel the cooling effect, as it will otherwise have the opposite effect!
Also, it is a good idea to run past water stations, if you have the possibility of doing so.
Tip #5: Do not overdrink in the heat
You have heard it a hundred times before:
”Remember to drink plenty of water in hot weather, otherwise you will dehydrate.”
This statement is naturally true because when the temperatures rise, you will sweat more and lose more fluid.
This loss of fluid has a couple of unfortunate side effects.
For instance, your body temperature and heart rate will start to rise, and the blood flow to your skin and active muscles will decrease.
Finally, the heart’s ability to pump the blood around in the body deteriorates.
The question then is; if it is important to drink before and during your run, how much should you drink?
It is not necessary to recover 100% of your loss of fluids.
In a study conducted on female long-distance runners from 2001, the researchers discovered something interesting.
The runners were able to sustain their performance on a 30 km running test by only recovering 68% and 73% of their loss of liquid under weather conditions of 17 and 25 degrees, respectively.
Similarly, Daries and his team of researchers discovered that there was no difference in the performance of 8 male long-distance runners in hot weather with varying fluid intake. The fluid intake was more than double (0,4 L vs. 0,9 L) for one of the running tests – and this did not affect the performance.
Therefore, there is no evidence to suggest that you should recover 100% of the fluid you lose by sweating.
On the contrary, Daries and his researchers found that two out of eight runners did not complete the test because of stomach problems due to the large amounts of fluid intake!
My point is simply to show you that it is important to drink before and during your training.
However, there is no need to develop a hysterical relationship to your fluid intake.
If you are out running for more than 1 hour, then make sure to drink water periodically to ensure a healthy gastric emptying time.
For example, 130-150ml every 15-20 min. and perhaps mix it with energy drinks containing electrolytes.
I would normally recommend a fluid intake between 400-700ml every hour. In hot weather, it should be closer to 700ml.
Even more tips for running in the heat
Naturally, there is an array of various tips and tricks for running in the heat, which I will give you here.
- Try running the flat running routes in order to distribute the heat production evenly. Hill running will make the heat production skyrocket, which you want to avoid.
- If there is some wind, it would be an advantage to start with tailwind and finish with headwind. This way you will enjoy the wind when you need it the most.
- Running in the forest or paths with shades will make a difference in avoiding the sun’s rays and provide you with a temperature difference of 2-3 degrees, which you will be able to feel the effects of.
- Remember to drink plenty of liquid after the run. If you are slightly dehydrated, you will have trouble sleeping in the heat, which consequently leads to poor recovery.
With my warmest wishes, I hope you enjoy your training session – and please do remember a breathable sunscreen!
Ad libitum fluid intakes and thermoregulatory responses of female distance runners in three environments.
Cheuvront SN1, Haymes EM.
J Sports Sci. 2001 Nov;19(11):845-54.
Effect of fluid intake volume on 2-h running performances in a 25 degrees C environment.
Daries HN1, Noakes TD, Dennis SC.
Med Sci Sports Exerc. 2000 Oct;32(10):1783-9.
Evidence against a 40 degrees C core temperature threshold for fatigue in humans.
Ely BR1, Ely MR, Cheuvront SN, Kenefick RW, Degroot DW, Montain SJ.
J Appl Physiol (1985). 2009 Nov;107(5):1519-25. Epub 2009 Aug 27.
Lore of Running by Tim Noakes
Oxford University Press, 4.udgave, 2001
Acclimatization strategies--preparing for exercise in the heat.
Shapiro Y1, Moran D, Epstein Y.
Int J Sports Med. 1998 Jun;19 Suppl 2:S161-3.
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