Excess venous return immediately after brief contraction of human calf muscles.

Venous return immediately after brief contraction of human calf muscles was measured. The subject extended his ankle joint in the range of 20 degrees for one second against loads of 10, 20, 30, and 40% of the maximum voluntary contraction in the ankle extensors. Venous return was determined by the difference between the increase in calf volume with (calf blood flow: CBF) and without (maximum inflow rate: MIR) thigh venous occlusion immediately after muscle relaxation. CBF and MIR progressively increased with the loads, and CBF was significantly greater than MIR. The level of venous return was correlated with the increase in the load. Transient increase in venous return was not associated with muscle pumping. Excess venous return should counteract arterial inflow and contribute to maintenance of equilibrium of the transmural pressure between muscle tissue and the capillaries.