Following endurance training stroke volume both at rest, and during exercise, increases. After undergoing a training program, more blood returns to the heart, and therefore more blood enters the left ventricle. This increases the stretch on the ventricle wall, and as a result, the left ventricular wall contracts more forcefully. With further training, the cardiac muscle also hypertrophies, which increases the contraction even more. As a result, more blood is forced out of the left ventricle with each contraction. These changes combine to increase the stroke volume.