Having recently completed my first official ‘mini ultra’ 50km marathon, one of the most common queries I received was about when I was going to do my carb loading, so I thought I would put forward my opinion on this concept!
Carbohydrates are stored in the body, and unlike fat, storage space is limited. Our muscles are the primary storage site, however our liver has a small capacity to draw upon for various functions. Upon requirement of energy, stored carbohydrate (in the form of glycogen) is converted into glucose and utilised as fuel.
Now, the body uses two primary fuel sources – carbohydrates and fats. For rapid production of energy, carbohydrates provide the bulk of the fuel. This occurs predominantly during high intensity exercise. At low and moderate intensities, fats contribute a greater proportion of fuel as the process for breakdown is more complex and requires oxygen. At any given time the body is using a mix of these two sources but the contribution of each is dependant upon what we are doing.
The average human body can hold somewhere between 1600-2400 calories of energy from glycogen.