The effect of rhythmically performed muscle contractions on blood flow through muscles was investigated in the calf of cat. During a series of contractions, which had led to maximal dilatation of the resistance vessels, a considerable lowering of the pressure in a small vein from the contracting muscles could be demonstrated between contractions, despite the huge inflow. An optimal effect was obtained when the muscle nerve was stimulated with a short (200–300 msec) impulse train once per sec, a pattern mimicking that during running. Rhythmic contractions of this type led to a characteristic blood flow pattern through the muscles. Arterial inflow to the muscle vascular bed occurred only in between contractions, whereas nearly all the venous outflow from the muscles occurred during the contractions.
The venous pressure reduction occurring between contractions implies a gain in effective perfusion pressure and a corresponding augmentation in blood flow through the muscles. Such an effect was found to be considerable in dependent limbs. Here average blood flow through the rhythmically contracting calf muscles could be as great as, or even greater than, the “free” flow in the immediate post-exercise period. This effect of the “muscle pump” may be of great importance also in the dependent limbs of man.