How our body reacts to heat while running

The summer has been hot this year, and running in high temperatures isn’t easy. If you are not used to the heat, your heart begins to pound much earlier than it should, sweat covers your eyes, your mouth dries up and you are constantly thirsty. It is because of these unpleasant sensations that we try to run either at sunrise or after sunset, or even on a treadmill in an air-conditioned sports club. However, there are ways to avoid all of this and get the most out of your run and enjoy it.

Lawrence Armstrong, a heat researcher at the University of Connecticut, says the human body is surprisingly easy to adapt to heat, much more easily than to cold or altitude.

In a January 2015 article in Comprehensive Physiology, Daniel Lieberman makes the following assumption about our adaptation to heat. Perhaps this is a consequence of the fact that our ancestors hunted in the African savannah at noon, when all the most dangerous predators rested in the shade. Since then, people have dispersed all over the world, and even if we live in northern latitudes, heat tolerance is still preserved in our genes, and at the right time the body will remember this.

This does not mean that you can just take it and go out into the sunshine for a run, and the body will adjust itself. Despite the fact that we were born to run in the heat, some people still don’t adapt so well to these conditions. That is why it is worth following certain rules that will help you, even if you belong to the second type of people.

10-15 ° C
Most runners don’t see it as warmth, and if they were just walking, they would be perfectly right. However, even this low temperature will affect you during a long race.

In 2007, in a Medicine & Science in Sports & Exercise article, a team led by physiologist Matthew Ely studied the performance of elite marathon runners and those close to their level in temperatures ranging from 4 to 8 ° C. What they found was surprising: even at temperatures of 10-15 ° C, performance declined slightly, which was comparable to about a 1-2-minute slowdown for two out of ten elite athletes. For a three-hour run in men, the deceleration was 4–8 minutes. A recent poll by the French National Institute of Sport and Physical Education of nearly 2 million marathon runners found that the optimum temperature for male professionals is around 5 ° C.

There are several reasons for this. First, in such studies, the temperature is measured only at the start. This means that a race that starts at 15 ° C can end at 21 ° C.

Physiologically, training in heat sets off a cascade of responses that begin with the fact that not all of our muscles are working effectively. In fact, about 80% of the energy generated by our muscles comes out of the body as … heat. In cold weather, it keeps us warm, but when we start exercising, the body has to get rid of this heat, and one such way is by sweating. This is very important as our blood carries excess heat to the skin, through which it exits to the surface.

But our body is very large, there are also many muscles, and here the blood must not only deliver excess heat to the skin, but also provide our muscles with the oxygen they need to work. And in this battle, muscles always lose. Even the lightest sweating is a sign that your muscles are already receiving less oxygen and their efficiency is decreasing.

16-21 ° C
This temperature range is considered by many to be not so optimal for running. The Run SMART Project calculator calculated that at 20 ° C, running 10 kilometres would degrade 1.7% (slightly more than 6 seconds per mile). For marathon runners, this will be a 1-4 minute slowdown.

However, some people find it easier and better to run in hot weather than in cold weather. Your body begins to adapt to an elevated temperature as soon as you start running in hot weather. Within a week, your blood plasma volume begins to expand. This can increase your weight by 0.5-1 kilograms, but it gives you extra fluid and the ability to sweat without dehydration. It also allows you to continue to cool the body intensely, while not particularly reducing blood flow to the muscles.

Next adaptation: we start to sweat during exercise much earlier and more profusely than in cooler temperatures. In this way, our body learns to anticipate the subsequent rise in temperature and takes proactive measures.

Sweat becomes less salty as the body works to store sodium. Your heart rate gradually slows down at each level of effort – this allows your heart to fully perform each beat and pump more blood. This is called stroke volume, with which the heart draws more blood, not only for muscle work, but also for increased body cooling.

Moreover, even your perception of heat changes, that is, the temperature from the category “everything, I’m dying” turns into simply “hot”.

These changes take place within 14 days after the start of training in the heat. But you should not rush and you need to start gradually, otherwise you really risk overheating.

22-26 ° C
At this temperature, elite marathon runners lose 3 minutes, and the rest – as much as 20 minutes, while women perform better than men. Perhaps this is due to the fact that women are usually smaller than men and their ratio “body weight-surface” is more optimal, as a result of which heat removal into the environment is more efficient.

The same goes for men. During the Olympic Games in Atlanta, South African runner Joshua Tughwane, who weighed only 45 kilograms, won the men’s marathon at 23 ° C and 90% relative humidity. The silver medalist from South Korea Lee Bong Joo weighed 56 kilograms.

Results are not only influenced by the correlation between heat and body size for marathon runners. In laboratory experiments conducted shortly before the Athens Olympic Games in 2004, physiologist Tim Noack observed two groups of men who ran 8 kilometers on treadmills. In one group, the weight of men did not exceed 50 kilograms, in the other the average weight was 59 kilograms. In cool temperature conditions, the results of these groups were almost equal, but once the indoor temperature rose to 35 ° C, the lighter athletes were faster by about 45 seconds per mile than their larger counterparts. That is, the larger you are, the more you will be exposed to heat. Based on this, you need to learn how to properly adjust your pace to weather conditions.

27–32 ° C
At this temperature, extra sweating goes from an advantage to a problem. When sweat pours out in streams, you lose more water than heat. You also begin to run at the limit of the capabilities of not only your body, but also physics: there are simply conditions under which it no longer matters how profusely you sweat, since the sweat simply does not have time to evaporate to keep up with that amount of heat, which you are generating. The only way out of this situation is to slow down the pace, so if you want to get satisfactory results at high temperatures, you will need to put in much more effort during training, gradually increasing the pace.

32 ° C and above
And here the real heat already begins! The key to running in these conditions is to think carefully about anything that can in any way affect your performance, be it your pace or the choice of clothing. You have to do a good job of hydration by developing a specific drinking plan, and not forget about isotonic. It is also worth teaching yourself to drink more fluids. Your limit will not exceed 1 liter per hour, but most people are not used to drinking so much fluids in such short periods of time.

Even if you decide to go for a light jog of 5 kilometers, which you usually do not take water with you, and the weather forecast shows 27 ° C, it is better to take a small bottle of water with you.

Another interesting adaptation option is to start going to the sauna. Especially if you decide to take part in a competition in some tropical country with a hot and humid climate. To train elite athletes, special cameras are used, which simulate the weather conditions of the place where the competition takes place. But ordinary people do not have this opportunity, so our way out in this case is to visit the sauna at least two weeks before the start of the race.

Memo for running in the heat

  1. Remember: even if you think it is cool outside, your body still heats up, part of the blood volume goes to provide cooling, and your muscles begin to work less efficiently, not receiving their portion of oxygen. On short runs, this can be ignored, but it is worth considering this factor during long runs, as changes in pace will become noticeable.
  2. Try not to avoid exercising in hot weather. Let your body adapt to these conditions. Your system will become more efficient in a fairly short time (the time to adapt to heat – 10-14 days), as it learns to anticipate temperature increases and adapts to new conditions.
  3. When temperatures and humidity rise, it is best to slow down. Your productivity will continue to be at a high level even though the speed is slowed down.
  4. If you are going to compete in the heat, do not train in the last two days before the race and make sure that you do not overexert your body.
  5. Properly restore your water reserves, using for this not only water, but also isotonics, which will replenish the supply of important minerals that leave your body with sweat. If you have a long run, it is a good idea to have a drinking schedule, set a timer, and drink every time the alarm sounds.

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6 thoughts on “How our body reacts to heat while running

  1. Well done and very interesting how we adapt and how long it takes to do such. I often marveled at how people could do road work in the middle of summer in Florida heat when I visited there. Makes sense reading this post !

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