Fuel
Resources During Exercise
1-10 seconds
At the very start of exercise, the muscles use free fatty
acids floating in the bloodstream. This is an especially important
energy source for quick demand by muscles as in a competitive
speed sport.
5-10 minutes
Muscles use intramuscular glycogen (stored carbohydrate),
which is metabolized to glucose and becomes the source of
energy
As the muscle glycogen is depleted (number
of minutes differs in people, with athletes having larger
stores of muscle glycogen) and then glucose released from
the liver becomes the source to fuel muscles. This is called
hepatic glycogenolysis.
20-30+ minutes
Muscles are using the glucose from the liver and free fatty
acids which come from triglycerides from fat stored in adipose
tissue (fat)
As the time of exercise is
extended, breakdown of protein and fat rather than carbohydrate
produces a higher level of free fatty acids and low levels
of glucose to be used as source of fuel for muscles.
This is called gluconeogenesis.
