Is the 'Runner's Wall' a Real Thing?

From the WebMD Archives

By Tom DiChiara

The Rumor: If you run too fast or too far, you'll 'hit the wall'

Every runner dreads "hitting the wall" (aka "bonking") -- reaching that point in a race or training run where your legs pump battery acid, your breathing becomes labored, your pace slows to a crawl and the thought of taking another step seems like the worst idea in the world. Some insist they've crashed into this wall in the middle of a 10K. Others believe it's simply a self-imposed mental barrier that can be overcome with a little grit and positive thinking. So, which group is right?

The Verdict: Hitting the wall is a real thing, but only when you're running long distances

"The runner's wall is very real," says exercise physiologist and upwave review-board member Daniel Zeman, M.S. "But you don't hit a wall in a 5K or a 10K. It has to be a situation where you expend more than 2,000 calories or run for durations of longer than two hours."

According to Zeman, most people hit that 2,000-calorie benchmark -- and thus the proverbial wall -- somewhere around the 20- or 22-mile mark of a marathon, which is why the last six miles of the 26.2-mile race are often referred to as "the second half."

Why is that the point where so many crash and burn? It's a simple case of supply and demand. Your body demands glycogen, which is a long chain of sugars (aka carbohydrates) stored in your muscles and liver, to provide the fuel for running. The human body, however, can only store so much glycogen (say, 20 miles' worth). When the supply runs out, the body starts burning fat for energy instead -- which is kind of like trying to power the Back to the Future DeLorean with butter instead of plutonium.

So how does anyone finish a marathon without bonking? That would be with the proper combination of smart pacing, stellar hydration and a process known as carb-loading -- three things that are extremely manageable for the average runner.


The pacing part is pretty intuitive. "If you go out too fast, you're going to hit the wall because you're going to blow through your carbs," says Zeman. The best plan of action is to start conservatively and gradually work up to your goal pace. Hydration is also fairly straightforward. Zeman recommends drinking plenty of fluids in the days leading up to the race, and making a point to imbibe water or a sports drink at the fluid stations along the course. This will ensure that you don't become dehydrated, which causes your core temperature to rise and your fitness to decline.

The final component, carb-loading, is the most crucial for building up those glycogen stores to a level where they can get you to 26.2 miles instead of 20 or 22. As the name suggests, the process involves maintaining a healthy, carbohydrate-rich diet in the three or four days leading up to the race, while simultaneously cutting back on your mileage. Consuming sports drinks and supplements such as energy gels at key points during the race can help replenish your glycogen levels as they ebb. (Just be sure you've practiced with them in training!)

WebMD Feature from Turner Broadcasting System
© Turner Broadcasting System, Inc.


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