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Let’s talk about running. Specifically, running a long way in a hot environment.

From an evolutionary perspective humans are exceptionally well designed to disperse heat from their bodies. We cool ourselves in a fundamentally different way to other mammals - when other animals pant, we sweat. Panting cools animals by bringing air at environmental temperature into the lungs, which is then heated as it passes through the respiratory system, and expelled at a hotter temperature than it arrived to the body at.

The human cooling system on the other hand works mainly by pumping hot blood to the surface of your skin, and this blood is then filtered to become a protein-free, hypotonic plasma filtrate (that’s just blood with the red blood cells, proteins and (most) the salt taken out). This then moves out of your body through your sweat glands and is seen by you as sweat. As sweat evaporates it cools you down.

The human method of cooling has a number of advantages for exercising in hot environments, primarily it allows humans to shed a huge amount of heat into an environment that is already very hot, such as sub-saharan Africa. In short this affords humans a unique ability to exercise in the heat. Also, due to the fact it is such an efficient cooling system, it allows us to exercise for a longer amount of time than many other animals.

In much the same way that athletes train their heart and muscles, the sweating system is can be adapted - there is a whole system working here within the human body that is very trainable, but predominantly ignored by athletes. By exercising “hot” - either in a warm environment or by wearing a jumper & hat - your sweat response changes. Sweat glands become larger and better at re-absorbing the salt in your sweat, while your brain starts your sweat response at a lower body temperature. When trained both of these adaptations make exercise in the heat easier.

What this means for you as an athlete, sports scientist or coach is that you have just been introduced (or reminded if you already knew this stuff) to a physiological variable just as important as any other measure, such as body fat or resting heart rate. Now you know how all about sweat that you can now specifically tailor your training to when necessary. In the lead up to a match / race / competition that you know will be hot it’s smart to change your training accordingly.

From a personal level I saw the importance of this during the Leeds Half Marathon 2016, which was run on a very hot day in May. Generally speaking British runners are not very well adapted to the heat and this can be seen by comparing the finishing times in the 2016 race to the 2015 and 2017 results. If you look at the average finishing time for the top 50 runners you can see that the 2016 race was significantly slower than the years before and after it.


Average Finishing Time (first 50) 1:18:57 1:21:00 1:19:51

(The top 5 finishers each year were removed from this since they are very well adapted to the heat so unnaffected by the hot conditions)


On a more anecdotal note I was able to see this in the way other people looked out on the course. Having done lots of “hot” training in the lead up to the race I had a very good sweat response, but most of the runners had been training in the spring, in Yorkshire so were not well adapted to the heat. In the last 15 minutes, when the sun was hottest, I was noticed I was consistently passing lots of other runners,  many of whom I knew would have beaten me on a cool day. An added benefit to having good thermoregulation was that I didn’t require a long recovery time after finishing. In fact within a few minutes of crossing the line I had met a friend in a pub close to the finish line! So, the lesson here is clear; by specifically training your sudomotor system in order to create a more severe thermoregulatory response you can get to the pub earlier - although this probably does mean the first round’s on you...