14 Sep 2007
Just as carbohydrate provides basic usable form of energy in the body (glucose), so does fat. This usable form of energy in the body is called Free Fatty Acids (FFA).
Fats taken through the diet are first digested to produce fatty acids. After the fatty acids are absorbed they are converted to triglycerides. Triglycerides are the stored form of FFA. Stores of triglycerides are found in the adipose(fat) tissue and in the skeletal muscles.
Early in the exercise the blood fatty acid concentration falls as the muscle begins to draw on the available fatty acids. But, if the exercise continues for more than a few minutes the hormone epinephrine is called into play. Epinephrine signals the fay cells to break apart their stored triglycerides and to liberate more fatty acids into the blood. After about 20 minutes of exercise the blood fatty acid concentration rises and surpasses the normal resiting concentration.
It is during this phase of sustained, sub maximal exercise-beyond 20 minutes- that the fat cells begin to shrink in size as they empty their lipid stores.