Muscular cramps are a common and painful phenomenon that, while frustrating when experienced, are easy to correct and prevent. All cramps are caused by a deficit of Adenosine Triphosphate (ATP.) ATP is the molecule found in the cells that is responsible for carrying energy. ATP does not store energy, as glycogen (carbohydrates) and fats do, but rather breaks down existing energy stores to transfer to energy immediately.
While not every obstacle is controllable, when it comes to fueling, being aware of what can cause digestive issues, how to prevent them and how to work through a particular issue when it arises could prevent a DNF. When exercising for an extended period of time and especially when running in an ultra-distance race the body starts to divert the blood that usually aids in digestion to the cardiovascular system. The lack of resources going to digestion causes the body to lose appetite or even reject food through vomiting or indigestion. Confusing the body before the race begins can lead to issues in fueling as the day goes on.