Why Marathon Runners Hit the Wall
Marathon runners hit the wall because their bodies run out of glycogen stores, which are the main source of energy during long-distance running.
It's often said that hitting the wall proves a runner is out of shape — in fact, even a well-trained runner can reach it by starting too fast or not taking in enough carbohydrate for the effort.
Understanding why runners hit the wall helps athletes plan their nutrition and pacing to avoid sudden exhaustion and improve endurance during marathons.
It's like a car running out of gas; when runners use up their stored energy, they get really tired and slow down a lot.
Knowing how endurance fuel works can help runners make safer choices about training, pacing, and eating before long runs. It also explains why a plan that feels fine early in a marathon may become much harder later on.
Imagine a runner who can comfortably use 10 energy units each mile but starts a marathon using 12; the extra demand steadily drains the body's quickest fuel. If the runner takes in no carbohydrate, the supply eventually becomes low, so the body leans more on slower-to-access fat and the pace falls sharply. Starting more gently and taking planned carbohydrate could delay that drop, even though it cannot make the body's energy supply unlimited.
The body uses more than glycogen
As glycogen gets low, the body can use fat for energy too, but it cannot turn fat into quick running fuel as easily.
Pacing saves energy
Starting at a pace that feels manageable helps runners avoid burning through their stored energy too quickly.
Fueling can happen during a run
Many runners eat or drink carbohydrates during long races to top up their available energy before they feel completely drained.