Glycogen Depletion: Tips On How To Avoid 'Hitting The Wall'


There is one phenomena that terrifies marathoners more than any other: "bonking." It typically occurs around mile 20 in a marathon when the runner begins to feel as if he has had a lead apron thrown over his entire body. Everything begins to tighten up and the finish line which once seemed so obtainable begins to slip ever further beyond the grasp of the runner. At this point, often the best one can hope for is a long, slow trudge into the finish. Curiously, bonking is not a universal experience for all marathoners. Some runners feel tired at the end of races, but never completely hit the wall. So why is it that some runners bonk marathon after marathon and what can they do to prevent it?

Let's begin by discussing what happens when one bonks. The phenomena is caused when a runner goes into a state of glycogen depletion. Glycogen is the carbohydrate that endurance athletes burn most easily, especially when working at a high aerobic level. Once all of one's glycogen has been burned, the body must resort to burning fat to use for energy. The problem with using fat as an energy source is that it burns less efficiently than glycogen. So, when attempting an intense aerobic workout, your body performs less effectively when using fat for energy than it does glycogen. If you are interested in the science behind this, here is a leading study done by Benjamin Rapoport that discusses in depth glycogen levels in marathoners.

Now to discuss the ways to avoid bonking.

First, different methods work for different athletes when attempting to deal with glycogen depletion. Understanding your own body is imperative. In general, the most important factor to prevent bonking is maintaining a proper nutrition plan. In the days leading up to a marathon, make sure you are eating plenty of carbohydrates.

Many of us have heard the term "carbo-loading," but I find that this term leads people down a road of poor eating habits. Instead of eating 6 lbs. of pasta the night before a race, I recommend being nutritionally conscious the whole week leading up to the race. Add sweet potatoes to a meal or two. Have a quinoa dish one night. Maybe breakfast on some oatmeal and a banana instead of rushing out the door every morning.

Be conscious that you are eating carbs, but you don't have to over-do it. On the morning of the race, I recommend having a breakfast of easily digestible carbs such as toast with jelly and a banana. Even if you get an upset stomach from nerves, it is important to have something in your system on race day. Finally, during the race make sure that you take nutrition early and often to prevent glycogen depletion later. There are many good forms of race-day nutrition such as gu's, gummies, bars and fruit. So, practice nutrition intake during long runs and find what works best for you.

There are some runners, though, that no matter what they do nutritionally they still bonk in the late stages of every marathon. For those runners, there is a training method called "Glycogen Depletion Training" that basically teaches your body to burn fat more efficiently, so when your body runs out of glycogen it can still perform.

If you are interested in this method, I recommend pursuing it very carefully. To train in a glycogen depleted state, a runner does a run in the morning without taking in any carbohydrates since dinner the night before. Basically, he induces a small bonk, and teaches his body to continue performing in that state. If you are considering attempting this, it is recommended that you never do long or quality runs in a glycogen depleted state, because that would lead to a less effective aerobic workout (thus negating any positive effects received from the training).

Only short-to-medium distance runs should be done in a state of glycogen depletion. Once again, this method need not be employed by every marathoner, only those struggling to avoid bonking at the end of every marathon.

At the end of the day, the greatest way to avoid bonking and have a good marathon experience is to train properly, eat well, listen to your body and not go out too fast. That is a simple piece of advice and if every runner abided by it, there would be a lot more smiles in the last mile of every marathon. 

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