1. Fluids are imperative to run in these weather conditions. Ensuring proper hydration can keep nutrients traveling through the blood stream easier and reduce muscle fatigue. (Although his muscles will still be tired.)
2. Food is also imperative. Most of us don't eat "normal" nutrition while running, but at these distances, high energy foods will further produce energy. His preparatory runs have included eating during the runs to train the body to split resources between digestion and running. Otherwise the necessary nutrients will never enter the blood and abdominal pain (or even nausea) would interfere with the run.
3. Proper shoegear is also an important task. This would not be the appropriate time to try barefoot running, as he will be running through deserts, over mountains and on surfaces that are extremely unfogiving to the human foot. He therefore will be utilizing multiple shoes for this process, thus the shoe sponsor Hoka One One.
4. Proper equipment is also being utilized from running clothes to resources utilized to carry his nutrition options with him.
5. A support team is also imperative for this type of trek. When I went the measily distance of 50 miles (walking) as a 12 year-old, our support team were cars coming with food and fluids every couple hours. I don't know the full extent of his support team, but they are there.
So now when you make your plans to run any distance, you can determine to a lesser extent from these important items how to run safely and smart.