Calf muscle pumping activity
Blood circulating to the end of the foot is returned to the heart by a vein.
Veins have valves that open and close during muscle contraction and relaxation and carry blood to the heart.
Muscles may vibrate (shake) by running or having an impact. The person's body unconsciously controls the wasteful movements and vibrations and exerts the force to hold them down. In sports, this can lead to loss of stamina and poor performance.