Experiencing extreme cold was quite horrific at times. I regularly worried about bits of my face, hands and feet falling off. Extreme heat however, presents a whole host of other problems. It's even worse when you are running in direct sunlight for 12 hours a day.

How hot does it get in the Sahara? Well, there are the legendary myths surrounding the MDS of temperatures well into the 50s and even 60s and then what you read about on Wikipedia... 

"The Sahara desert is one of the hottest regions of the world, with a mean temperature generally over 30 °C (86 °F) and the averages high temperatures in summer are over 40 °C (104 °F) and can even soar to more than 46 °C (114.8 °F) and often for over 3 months. Daily variations may also be extreme: a swing from 37.5 to −0.5 °C (100 to 31 °F) has been observed[1] but are rather around 15 °C (27 °F) and 20 °C (36 °F)."

Whilst temperatures as 'low' as 40c might sound quite comforting (they are when you are worrying about 50c), the big factor is that these are temperatures in the shade. The impact of being in the sun can, apparently, raise the temperature by a further 10-15c. Oh crap.

So hot, you can cook an egg...

Yes, literally... this is in fact possible as I learned in this short video of an egg cooking in just 43c in Melbourne. Extreme heat also poses serious risks to humans. The 'Centers for Disease Control and Prevention' considers you should start being concerned when the mercury rises above 32c (90f). Here are the key issues:

• Dehydration: at 32c (90f) in direct sunlight, in low humidity, the human body can lose up to 2 litres every 15 minutes from sweating, exposing you to many more medical issues
• Severe sunburn: This isn't just the redness, blistering, swelling etc. The big impact in a race such as the MDS is that sunburn reduces your ability to release excess heat
• Heat cramps: Can be painful muscle spasms, usually in the legs, but also in the stomach (in a hot race, you may smell the impact... adding to the poor diet and nerves smell!)
• Heat exhaustion: typically involves heavy sweating, feeling weak, fainting, a weak pulse and vomitting
• Heat stroke: This is life threatening... when the body's core temperature gets above 41c (105f), you will typically stop sweating, experience rapid shallow breathing and ultimately find yourself in a situation that can cause brain damage and death in just 10 minutes unless you can be cooled

A simple summary can be found in this video... note that any runner is considered a little stupid considering the risks... Imagine turning up the thermometer another 20c, running for 12 hours and depriving  yourself of water?

Sweating at the limits of possibility

Given we evolved in the hot sun of Africa, our bodies are actually much better adapted to the heat than the cold. Our ability to cope with extreme heat primarily relates to sweating - something I do more than any other human I have ever encountered. Some simple 'sweat tests' I have done in the heat of the Joburg summer suggest I lose up to 5 litres an hour when running hard (a simple calculation of weight before + fluid taken on - weight after). This is truly staggering and presents a real worry... It will be hotter in the desert, I will be carrying a heavier pack, I will be running for a minimum of 5 hours a day and I will only have 12 litres of water per day!

Staying alive in the MDS

This really isn't rocket science, but there is a lot of prep you can do. it is possible to adapt to extreme heat within about 2 weeks. You can very effectively (I am assured) adapt to heat as the body 'learns' to increase blood flow, increase sweating (not sure that is possible for me) and retain more salt. So, my preparation plans are simple 1) Run in the heat of the day and 2) Spend time in the sauna. During the MDS I am going to have to do a number of things to keep cool and keep dehydrated:

1) Ensuring I don't get sun burned (factor 50!)
2) Covering up and protecting my head
3) Keeping my heart rate low and not running too hard in the extreme heat
4) Drinking regularly and not wasting water
5) Taking on large amounts of salt

One thing is for sure. As a pasty white Englishman, this isn't going to be much fun at all!