The Value of Exercise

The Value of Exercise

THE VALUE OF EXERCISE

by Arturo Rolla, MD

(FROM THE EDITOR: We recently encountered the following exchange,
on one of the Internet's many diabetes discussion lists. We thought it worth
sharing. Arturo Rolla, MD, the author, is an endocrinologist at Harvard Medical
School.)
Q: I have heard many times that exercise helps to lower insulin
resistance. My question: Is it a fleeting or a cumulative effect? In other words:
If I exercise today, will it help me for some time after the exercise; or does
only an active person who exercises everyday benefit from exercise?
A: Exercise has many different effects. Just on carbohydrate
metabolism there is an acute decrease in insulin resistance with increased uptake
of glucose in the muscles, therefore the BGs decrease.
If the exercise is prolonged and you use up all the glycogen
in your muscle (muscle glycogen depletion) the muscles continue to take up glucose
for hours after you stopped exercising. That's why it is not unusual to get
hypoglycemia from exercise at night!
If you exercise on a regular basis you decrease the fat mass
and specially the abdominal fat (the worst). The decrease in (abdominal) fat
tends to improve insulin resistance, most likely by decreasing the levels of
circulating Free Fatty Acids. So, prolonged exercising has a prolonged or more
permanent effect on insulin resistance.
There is also a possibility that well trained muscle fibers
(more and larger) by themselves may be more sensitive to insulin, but that has
not been shown clearly--as far as I know.