Another reason why exercise is beneficial: it stimulates the heart to make new muscle cells, both under normal conditions and after a heart attack.

A new study done finds that mice made to do aerobic exercise made over four and a half times the number of new heart muscle cells than those that did not.

In addition, after experiencing a heart attack, mice with treadmill access still ran five kilometers a day, voluntarily. Compared to their sedentary counterparts, the exercising mice showed an increase in the area of heart tissue where new muscle cells were made.