Skeletal muscle pump

Arterial blood pumping

Between muscle relaxations, intramuscular pressure transiently returns to a level below the venous blood pressure. This allows blood from the capillary system to refill the veins until the next contraction. It is postulated that this change in pressure may be great enough to draw blood from the arterial side to the venous side. It is hypothesized that this pressure drop during rhythmic contraction actually increases blood flow through the muscle, and may be responsible for a portion of the increase in muscle blood flow immediately at the onset of activity. This explanation is attractive, because it would explain the readily observable tight coupling between muscle contraction and a rapid increase in muscle blood flow. However, recent evidence has emerged that cast doubts on this theory. Experiments have shown that a strong muscle contraction can occur without a corresponding increase in skeletal muscle blood flow. Given the proposed manner of action of the muscle pump to increase arterial blood flow, it would seem impossible for a muscle contraction and skeletal muscle hyperemia to be uncoupled. Another experiment recently was only able to find evidence that vasodilation, not the skeletal muscle pump, was responsible for maintaining proper pressure and blood return. This might have to do with the lack of rigorous physiological tests thus far used to be able to prove the pump.

Experiments have shown the use of passive leg exercises, where only vasodilation was used, was responsible for increased blood return.