Getting a taste of the Marathon des Sables heat

Thousands of miles from the Moroccan desert, TR's Paul Halford yesterday found out what it's like to run in 40C heat

Porsche Human Performance Centre heat chamber

by Paul Halford |

Right now hundreds of crazy runners are experiencing arguably the toughest race on earth, the Marathon des Sables in Morocco.

The six-day 251km ultra takes place in the desert across dunes and similarly trying terrain with competitors having to carry nearly everything required for their trip. Last year's event was particularly brutal as participants had to cope with temperatures of up to 56C as well as a stomach bug that was going around camp.

So it was appropriate that yesterday I went along to Silverstone race circuit to be able to experience the merest smidgin of what 900-plus runners are going through. I ran for half an hour on a treadmill in the heat chamber at the Porsche Human Performance Centre with the temperature turned up to 40C.

Why Silverstone? It was there that scientists originally started working with motorsport professionals who would have to be ready to face extreme temperatures in the cockpit in some of the hottest countries on earth. Although this still accounts for much of the lab's use, endurance athletes are increasingly benefitting from the expertise available.

For example, around a dozen British competitors in this year's MdS were helped there in their preparation. Not only did they receive advice from staff at Precision Fuel & Hydration but they were able to acclimatise in the heat chamber.

We met, via Zoom, Pierre Meslet, a French runner who was ninth in last year's challenging event. He told us how that position was far higher than he expected and, listening to him talk about the precision with which he prepared, it's not difficult to see why. For example, Precision Fuel & Hydration had analysed his sweat to see how much salty it is and, thus, how much he would need by way of electrolytes. Preparation is key for an event like that.

The sweat (particularly salty in my case, I was told) was still dripping from me as we heard about his exploits as moments earlier I had taken part in my heat chamber session. I had been able to garner some small idea of what he went through. Initially, as part of the trial, I had run on a treadmill at around 18C at a normal easy training pace. That enabled lead sports scientist Jack Wilson to see how my body was reacting to the heat.

Precision Hydration sweat analysis
Expelling 1617mg of sodium per litre of sweat – categorised as 'very salty'

Although the experience was perhaps not as brutal as I feared, it showed just how much time is a factor when it comes to exercising in the heat. I have always thought I performed quite well in hot races but 30 minutes in the chamber was enough to make me doubt that. After five minutes, my heart rate was actually lower than it had been at the same stage of the cool trial. After 10 minutes, it was just 7bpm higher. However, my heart rate kept rising - and so did my core body temperature.

A fellow journalist had earlier been pulled out as a precaution after just 25 minutes due to reaching the cut-off of 39.2C body temperature. I was not too far behind as I completed the 30 minutes just as my body reached that temperature. My heart rate ended up 25bpm higher than after 30 minutes running at 18C. I was running at an "easy" pace yet my heart rate was only about 5bpm below my usual speed session value.

It was a real eye-opener. If this happened after 30 minutes, how would I cope in something like the MdS, where you are running for hours at a time, where there is no chance of immediate shelter, even if you stop running? However, preparation counts for a lot. Acclimation in a heat chamber would work wonders in the weeks beforehand, especially for northern Europeans who have not had chance to experience recent high temperatures before a race in March. If you aware of the signs of severe hyperthermia, you can pace yourself accordingly. A thorough hydration strategy is also key. That is where advice from Precision Fuel & Hydration comes in.

Indeed, Jack gave me plenty of reassurance that my data did not mean I would be suited to the MdS. Darn it - that's that excuse out of the window!

In a future issue of Trail Running, we'll put Paul's data into action. How does knowing how much you sweat and how salty it is help you in training and in races?

Just so you know, whilst we may receive a commission or other compensation from the links on this website, we never allow this to influence product selections - read why you should trust us