Lack of exercise and lack of physical activity make the problem worse. The calf muscle pump refers to the collection of veins located deep inside the leg and that are supported by powerful muscles that help push blood back up to the heart. This muscle group is helped by the veins themselves with 1-way valves that prevent blood from flowing backward. A well-functioning calf muscle pump is important to healthy leg veins. When veins are stretched or unhealthy, or the calf muscle pump is not working well, it can lead to ambulatory venous hypertension, or high blood pressure, in the veins. This high pressure hurts blood flow and nutrition to the skin and, if not corrected, leads to skin breakdown.