Page 35 - 2009 AMA Summer

CARBS AND PEAK PERFORMANCE
Author of ‘Moveable Feasts’ Amy-Jane Beer talks hill food, facts and myths.
Your body is an engine, and you want it to perform at its best, you must give it the right fuel. For any short term physical challenge like a big mountain day, this means carbohydrates.
The amount of energy stores in carb-rich foods is astounding. A morsel of sliced white bread the size of a first class stamp contains approximately one kcal. Burned in a super efficient stove, this would be enough to boil 10 millilitres of ice cold water. Two full slices will boil a kettleful. Weight for weight, table sugar contains about four times the energy of dynamite – there’s enough in a small chocolate bar to blast you over a kilometre into the air, if it could be harnessed efficiently enough. Fortunately the only way to do this is to eat the thing then walk up a mountain or climb lots of stairs. With this much energy available in carbs, it’s hardly surprising that for most liv- ing organisms, they are the fuel of choice.
If you don’t eat carbs, your body has to obtain them from other sources, such as reserves of glycogen, fats or even, in extreme
cases, by breaking down
muscle tissue. Not only is this a
very inefficient way of getting fuel to your cells, it’ll make you feel lousy. Trendy low carb diets mess with your internal chemistry, big time.
Glucose
Whatever type of carbohydrate you ingest, there is only one form that the body actually makes use of, and that is the simple sugar glucose. All other useable forms of carbohy- drate are first converted into glucose before being used to fuel your essential body pro- cesses. Some sports drinks boast ‘glucose polymers’ - these are sugars made up of several linked glucose molecules – they pack a big punch in terms of energy but are less sweet and thus easier to take when exercis- ing. Other simple sugars, such as fructose (fruit sugar) are useful sources of energy but because they have to be converted to glu- cose first they don’t ‘burn’ as fast.
Glycogen
When your body encounters a surplus of glucose, it converts some of it to a compound called glycogen. Glycogen is stored in your muscles and liver so that when you start working hard, there is a ready store of fuel right there. An average 70kg man has about 1700
kilocalories of fuel stored as glycogen in his body before beginning exercise. Of this, about 82% is in his muscles, 15% is in his liver and the remaining 3% is circulating in his blood. It can be mobilised quite easily once the muscles start working and will allow him to perform steady exercise such as running, biking or walking uphill, for about 90 minutes. When glycogen runs out, you’ll experience the unpleasant phe- nomenon known as ‘Hitting the Wall.’
Hitting the Wall
Even a fit individual will find themselves flag- ging after about an hour and a half of stren- uous exercise. This is the time it takes for reserves of glycogen stored in the muscles to begin to run out. If the muscles are to carry on working, they must find another source of fuel. This is what our muscle pro- tein and fat reserves are for – in a normal healthy individual, these will be enough to keep things ticking over, but because pro- tein and fat cannot be mobilised as quickly as glycogen, performance will be reduced. If the athlete continues to push hard without taking on more carbs, he or she will soon reach the point where the demand for fuel from the muscle cells simply cannot be met. The result it the sort of jelly-legged helpless- ness that became familiar to participants and spectators at endurance events such as marathons in the 1980s. It’s not so com- mon now – marathon runners suffer in plen- ty of other ways, but with the aid of energy
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