The wall is a term used to describe an event which happens to many marathon runners when they have crossed a point in the race where they have no more glycogen reserves. Glycogen is the substance stored in the muscles and liver which is the muscles primary fuel. Glycogen is derived from carbohydrates in our diet.

At this point the body has run out of fuel and swaps over to begin using your fat reserves as a fuel source. This takes a small period of time and the resultant lack of fuel will affect an athlete’s performance.

When you "hit the wall" your body feels suddenly very weak and you are unable to run at your normal pace. Many people feel unsteady on their feet and light-headed.

The solution to the wall is firstly to train your body to accept the change from glycogen to fat by running a number of long training runs into that zone. The second is to take carbohydrate gels or drinks during the race to keep your glycogen stores topped up.