Blood Flow in the Calf Muscle of Man during Heavy Rhythmic Exercise

Abstract 133 Xenon clearance was recorded during maximal vasodilatation in the calf muscles of trained subjects during rest and during heavy rhythmic exercise (contraction about 0.3 sec, relaxation about 0.7 sec) when the subject was tilted from a supine to a “leg down” position. The k‐value for the wash‐out curve, divided by the mean arterial blood pressure at heart level (MABP), was considered to reflect the relative levels of maximal flow in the two experimental situations. While a shift to “leg down” position during post‐exercise hyperemia did not significantly increase flow through the fully dilated muscle vessels, indicating that they were already maximally distended, the same shift during rhythmic exercise raised the average value of k/MABP approximately 60 per cent above control. This observation is in all probability explained by a marked lowering of mean venous pressure by the “muscle pump” in the dependent legs, despite the huge flow during the heavy rhythmic exercise. This would result in a considerable gain in local perfusion pressure and hence in maximal flow capacity.