Nearly anybody who has competed in or trained for a marathon has probably encountered a peculiar and terrifying feeling. Twenty miles into the race, you are feeling great, and it feels as if you are destined to hit your goal time. Then all of a sudden something goes terribly wrong. With the drop of a hat, suddenly it feels as if your muscles are no longer functional, your thoughts become blurry, and the mere process of finishing the race seems like an insurmountable task. This feeling, commonly known as “bonking” in the running world, is actually a well understood physiological phenomenon, and fortunately, it is preventable too.
What actually happens?
To better comprehend why bonking occurs, and how it can be prevented, it is important to have an understanding of how our bodies store energy. Glycogen is the primary source of energy used in aerobic exercise. Glycogen is a complex carbohydrate stored primarily in our muscles and liver, which consists of many glucose molecules (a type of simples sugar) linked together. When we exercise, our bodies gradually cleave away the glucose molecules found in glycogen and release them into our bloodstream. This gives us a steady source of energy which allows us to keep exercising.
Glycogen to run about 20 miles
Although everybody is different, in general our bodies store roughly enough glycogen to run about 20 miles. Once we have depleted all of the glycogen from our muscles and liver, then our bodies have to run on fat and protein. As it turns out, our bodies have a much more difficult time utilizing fat and protein for endurance exercise, hence we are left with the feeling of bonking.
So what is the solution to this? Is it simply a matter of training more?
The truth of the matter is, no matter how much we train, it is difficult to drastically alter the amount of glycogen that our bodies can store. Some forms of training can help increase the efficiency in which we utilize fats, but the ultimate solution to the problem lies in proper fueling.
It is essential to consume calories during the race
During a marathon, unlike a half-marathon or a 10k, it is essential to consume calories during the race. Our bodies stores enough glycogen to run about 20 miles, and burn roughly 100 calories per mile, which means it is advisable to consume roughly 600 calories during the course of a marathon.
What is the best way to consume these calories?
As it turns out, the best source is generally simple carbohydrates found in the form of grains, fruits, or sports drinks. While it is generally not advisable to consume large amounts of sugar during sedentary activities, during a marathon, most of the negative aspects of consuming sugary foods or drinks are negated. This is because the sugar is immediately utilized by our exercising bodies, and in many ways it mimics our body’s own process of breaking glycogen down into glucose.
A common mistake in fueling during a marathon is waiting until it is too late.
If you wait until you bonk to start consuming calories, you will be burdened by the task of stuffing yourself at every aid station. Instead it is much better to consume small amounts of sports drink or food throughout the course of the race. A common thing to do is to drink one cup of sports drink and one cup of water from each aid station. This will not only provide you with the fuel to prevent bonking, but also with sufficient amounts of electrolytes and water to keep you hydrated. And once the race is over, don’t forget to eat your protein. Your muscles will need it.
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