Carbo Loading

As I prepare for the Phoenix Rock 'n' Roll Marathon this weekend, I need to start carbo loading.  I'd like to review why we need to carbo load, and how to do so properly.

When we run, our bodies need fuel.  The basic sources are carbohydrates, fat, and protein.  Protein is necessary for recovery AFTER exercise, but we use very little of it as fuel DURING exercise.  Likewise, fat is an inefficient fuel source during aerobic exercise.  The most efficient and readily available fuel during aerobic activity is carbohydrates, which our body stores as glycogen in our muscles and liver.

When runners talk about hitting "The Wall," what they are usually experiencing is depleted glycogen stores, and they are now forced to rely on fat and protein catabolism.

To avoid hitting the wall, you want to be able to burn glycogen as the primary fuel during the race.  This is one reason why carbohydrate drinks, gels, and so forth are beneficial during the marathon.  This is also the reason why carbo loading is popular and important.

During the last week of training, your training tapers such that you are burning less and storing more glycogen, simply as a result of decreased mileage.  The final three days or so before the race, you want to "top off" your glycogen stores by consuming approximately 90% of your calories as carbohydrates, approximately 4 grams per pound of body wt (800 grams of carbs for a 200 lb person, for example).

Carbo loading, then, means that carbs are to be emphasized in your diet in the days leading up to the race.  Pasta, rice, potatoes, and breads are favorite choices.  Low fiber fruits such as bananas are good, too.  Carbo loading will also cause you to retain water, so you get the added benefit of hydration leading up to the race.  Don't be surprised if you gain a few pounds during the days of carbo loading.

Carbo loading does NOT mean you should gorge yourself the days before the race.  To do so will leave you feeling sluggish and slow.  Eat about the same number of calories, just shift to carbs (~90%).