Since the exercising dependent leg displaces blood toward the heart, against a potential gradient, it must perform useful circulatory work. We studied the peripheral circulation in healthy, sedentary males by measuring calf circumference (using mercury-in-Silastic strain gages), muscle pump ejection velocity (using a transcutaneous Doppler flowmeter), intrathoracic and intra-abdominal pressures (through catheters in the esophagus and rectum) and power of the leg muscle pump (product of blood flow and the upstream-downstream venous pressure difference). Measurements of pressure, flow velocity, and volume changes in the dependent venous beds of healthy young men demonstrated that during running in place, (1) the abdominal contraction necessary to fix the pelvis raised inferior caval pressure and impeded venous outflow from the legs, but that, (2) the leg muscles themselves were capable of effectively pumping blood past this functional obstruction. By doing so, these peripheral pumps contributed more than 30% of the energy required to circulate blood during running.

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