Originally Posted by
Roody
The second study was all about exercise. Older people on a high carb diet, who could eat as much as they wanted, lost weight and had better sugar metabolism, whether they exercised or not. But exercise increased a type of sugar used for energy by muscle cells (glycogen). Exercise also "decreased glycogen synthase activity", but I don't know what that means.
This is actually very interesting and a key component to why glucose tolerance is the same in the people who exercised and the people who did not.
Glycogen synthase is used to convert glucose into glycogen. It would seem that the more energy you use the more that would need to be replaced, therefore there should have been an increase in glycogen synthase.
But because the muscle has more glycogen stored in it it has decreased ability to uptake glucose because there is less room for it, thus not as much glucose can be taken up by the muscle.
They took muscle samples after an overnight fast, not after any activity, so since the exercised group had more glycogen stored there would be less need to uptake glucose from the blood. Plus the measurement of synthase was taken 3 days after the last exercise session. Because the tank is full you can't put more gas into it without it spilling over.
I would imagine that after exercising synthase activity would increase, thus decreasing glucose intolerance at that time. So it appears that they are saying that exercise will not decrease glucose intolerance globally, but it will increase glucose uptake after exercise.
They also looked at synthase activity only in the muscles. What effect would there be if you included the liver? and does exercise increase the amount of glycogen that the liver can store?