Relation Between Blood Flow and Contraction Force in Active Skeletal Muscle

Abstract

The relationships between blood flow and contraction force in intermittently contracting eat skeletal muscle during alterations of flow by various procedures were studied. When flow only to the active gastrocuemiussoleus was measured, mechanical reduction in perfusion pressure, sympathetic chain stimulation and intra-arterial norepinephrine and epinephrine infusion were found to have esscritially identical effects in producing reduction in muscle force proportionate to that in blood flow. When flow in the whole leg musculature was measured while either the gastrocnemius-soleus or the quadriceps was active, varying results were obtained with these procedures which could be ascribed to differenees in response of vessels in active and resting muscles. During the carotid sinus reflex some vasoconstrictor activity occurred in active muscle. On the assumption that the maximal, muscle force is an index of the nutritional component of the flow, it may be inferred that, in general, those procedures in which total flow was restricted produced no alteration in distribution of nutritional and non-nutritional flow within the active muscle. Blood flow and muscle force were generally unaffected by concomitant stimulation in the hypothalamus of the sympathetic vasodilator system. An increase in flow and force occasionally was observed whien these were at low levels, or when a rise in arterial pressure occurred. The sympathetic vasodilator system produces no alteration in distibution of flow and would seem to play no role in the maintenance of blood flow and performance of normal active muscle. A fundamental difference appears to exist in the responses of the vasculature of resting and active skeletal muscle; this difference is related to the interplay of specialized effects of the vasomotor innervations and the action of vasodilator metabolites.