The spectre of "The Wall" is dreaded by marathon runners. But what exactly is the Wall?
I will now quote from my write-up of my first marathon in 1990. The piece can be seen in full at www.briansacks.co.uk
The Wall occurs at the 18 to 20 mile point and essentially happens when the body has used up all its energy. It is then that one realises that the Wall is not just for others, it's for you too! I quickly realised that although I felt fine from the waist up, my legs had nothing left to give. I had a distinct feeling that if I pushed it at all, I would collapse there and then. So I decided that I would "switch off" from the Race – I said to myself "I've done my 20 mile race; now I'm doing tomorrow's 6 mile slow jog but I'm doing it a day early".
What is going on biologically?
Your muscles can store around 1500 kilocalories of ready energy in the form of glycogen. Each mile you run uses up 100 kilocalories of energy. That would indicate that you would "hit the wall" at 15 miles. But the picture isn't that bad because you can also metabolise fat at a rate that would allow you to walk at four miles per hour. These combined sources of energy make for the later point of hitting the Wall. Once you've hit the Wall, you are down to just metabolising fat, and it isn't fun.
I have indicated above how I adjusted to the Wall when I was completely surprised by it on my first marathon. I will discuss further strategies next week.