Carbohydrates are the bodies equivalent of petrol for cars. Without them we don't run properly. There are two types of
carbohydrates, simple and complex, which relates to the number of molecules in their make up. Simple carbohydrates are basically
sugars (glucose and sucrose being two of the commonest), whilst starches make up a lot of the complex carbohydrates.
An index, called the Glycemic Index, has been devised to give us information about how sugary foods are. It is useful as the
higher the index the greater the fluctuations in the bloods glucose and insulin levels, which can lead to a condition called
hypoglycemia, which is where our blood sugar is very low and we feel very lethargic.
Basically, to avoid this, highly sugary foods shouldn't be consumed between about an hour and 30 minutes before exercise.
Nutritionists also prefer complex carbohydrates because they are better at storing vitamins, minerals and fibre, hence why you
may have heard the term that sugars are empty calories.
Carbohydrates are stored in the body in the form of glycogen, both in the liver (which is used primarily for brain function) and
in muscles. The muscle glycogen is what is used to power us around our runs. It is the depletion of this fuel (about 1500-2000 calories)
which results in "hitting the wall" in a marathon as the body then needs to find other fuels with which to power us. It is the reason
why marathon runners need to take on more than just water in a race.
Trained muscles can store more glycogen than untrained ones, part of the reason why trained athletes are better.
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