Role of the Skeletal Muscle Pump in Exercise Onset Hyperemia in the Human Forearm

Abstract

Blood flow to active skeletal muscle increases with the first contraction, but the mechanism responsible for this exercise onset hyperemia is unknown. We tested the hypothesis that the muscle pump is necessary for onset hyperemia. Blood pressure and brachial artery blood flow velocity (Doppler ultrasound) were measured in 6 young males in three different trials, each performed with the arm at heart level (HL) and with the arm hanging below heart level (BH) in the dependent position, perpendicular to the floor : 1) a single dynamic handgrip contraction (20% MVC) (HG), 2) following a 10‐minute arm occlusion combined with a 2‐minute isometric handgrip (from 7:30 to 9:30 of the occlusion period) to induce maximal vasodilation in the forearm (OC), and 3) arm occlusion and handgrip followed by a dynamic handgrip performed 5 seconds after cuff release (OC+HG). HG elicited an increase in forearm conductance that was not different between arm positions (247±77 vs 308±35%). OC elicited a large increase in conductance that was not different between arm positions (0.100±0.010 vs. 0.101±0.008 units). OC+HG (.093±0.008 at heart level and 0.086±0.010 units below heart level) did not cause a greater increase in conductance than either the OC trial or the pre‐handgrip value in the OC+HG trial. These data suggest that the muscle pump does not play an important role in immediate exercise hyperemia in the forearm.