How does smoking affect the muscular system?

The main effect of smoking on the muscular system is from what chemicals the blood is carrying, versus carrying oxygen (O2) molecules. If hemoglobin on red blood cells is carrying less O2, then the muscles do not have enough O2 to do the work needed at the cellular level. As a secondary effect, if the person is short of breath from smoking, they are less likely to be active. So muscles become flabby, adding to the amount of work on the muscles and on the body. With less O2, it is harder to exercise and to walk, thus creating a viscous cycle in which muscles don't get worked, the smoking limits respirations, thus getting less O2, and the muscles continue to get flabby.