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13. 3. 2012.

Glucose and glycogen in activity

Glucose and glycogen supplies

Average male that weighs 75kg has around 1800 calories of carbohydrates stored in liver, muscles and blood in approximately following amounts:

Muscle glycogen – 1400 calories
Glycogen in liver – 320 calories
Glucose in blood – 80 calories
TOTAL – 1800 calories

These amounts of carbohydrates influents training lasting. If the supplies are decreased too much, it comes to the “wall” – you feel yourself too exhausted and you wish to quit. Comparing to 1800 stored carbohydrates calories, average slim male of 75kg has also 60,000 – 100,000 calories  stored in fat – enough to run hundreds of miles! But, unfortunately, that fat cannot be used effectively like fuel because muscles need some amount of carbohydrates; carbohydrates are limiting factor in endurance sports.
During low intense activities, for example walking, muscle burn mostly fat. At light to moderate training(jogging) stored fat gives 50-60 percent of fuel. If you train hard, for example sprinting, compete or any other way train intensively, you mostly rely on glycogen supplies.
Biochemical changes that show during training influent the amount of glycogen that can be stored in muscles. Good trained muscles develop the ability of storing 20-50% glycogen more than non-trained. It increases endurance capacity and it is one of the reasons why racers beginners simply cannot eat carbohydrates and run like pro marathon runners.

Muscular glycogen on 100g of muscles:
Non- trained muscle – 13g
Trained muscle – 32g
After carbohydrate load – 35-40g


While miss of glycogen in muscles leads us to the “wall”, miss of glycogen in liver causes “snapping”. Liver glycogen goes into blood to maintain normal sugar level in blood needed for brain functioning. In despite of adequate glycogen amount in muscles, athlete can feel noncoordinance, dizzy, impossibility to concentrate and weakness because liver cannot release sufficient amount of sugar in blood.
Muscles and brain needs glucose for energy. What is not seen at the first look is that muscles can store glucose and burn fats, and brain cannot neither of these two. That means that food has to be consumed immediate before hard activity to enable sufficient sugar level in blood, or brain will not function optimally. Athletes with low amount of sugar in blood train weakly because weakly fed brain limits muscle work and mental energy.
Any food, especially cereals before heavy activity will lead to brain charging and carbohydrates loading, so your brain will be enabled enough energy to handle sports activity on higher level. 

"Sports nutrition", Nancy Clark

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