At 30K you felt great. But now your legs are suddenly heavy, your mind foggy and you feel like you’re falling apart. You may be “hitting the wall.”

tired woman runner taking a rest after running hard on city road

Ask anyone training for a marathon what they fear most about running 42.2K and most will likely say “the wall.”

RELATED: Half and Marathon Training Plans by Canadian Running

The infamous and dreaded marathon wall refers to a point late in the race when one experiences a sudden onset of overwhelming fatigue and loss of energy. Some runners also experience dizziness, confusion and emotional disturbance (think depression and despair). While most often referring to the marathon distance, hitting the wall is sometimes applied to shorter races such as the half, but this is most often caused by poor pacing (i.e. going out too fast). Hitting the wall is also called “bonking.”

Many agree that this sensation happens when the body is depleted of glycogen. Glycogen is a complex carbohydrate structure that is used to store energy in the liver and muscles. During aerobic exercise, glycogen is broken down into glucose which is the preferred and predominant fuel for high-intensity and endurance activity.

Once the body uses up its available glycogen stores, it must then transition to using fats for energy. Compared to carbohydrates (glycogen), fats exist in near endless supply in the body, but are not nearly as efficient for producing energy.

RELATED: Fueling for performance: Carbo-loading dos and don’ts

The average (untrained) person can store about 1,500kcal worth of carbs which is enough energy for about 24 kilometres of running. But endurance training—regular long runs and more mileage—in addition to carbo-loading can significantly increase the body’s ability to store additional glycogen.

A well-trained and carbo-loaded athlete can in theory have enough glycogen to last the entire 42.2K of a marathon and thus avoid hitting the wall altogether. Taking in additional carbsvia energy drinks, gels and chewsduring the race will also help achieve this. In addition to carbo-loading, athletes should aim to ingest 30-60 grams of carbs for every hour of endurance exercise.


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