Cardiovascular and metabolic responses to static contraction in man

Abstract

There is substantial controversy regarding muscle blood flow and its regulation during static exercises. Major issues include (1) the relationship between developed force and muscle blood flow, (2) the ability of metabolic vasodilation to overcome neurally mediated vasoconstriction, (3) the time course and magnitude of hyperaemic flow following static exercise and (4) blood flow to the contralateral inactive limb. At rest, 15, 25 and 50% maximal voluntary contractions (MVC) femoral venous flow in four healthy young men (LBF; mean±1 SD) was 0.4 ± 0.3, 1.76 ± 0.65, 0.90 ± 0.32 and 1.06 ± 0.59 l min^-1, and mean arterial pressures (MAP) were 104±13, 140±14, 160 ± 17 and 161 ± 11 mmHg. Thus, LBF does not increase proportionally with increasing levels of MVC, despite increased arterial pressure. Further, during both 25 and 50% MVC, which were held to exhaustion, an elevated limb vascular resistance was encountered towards the end of contraction, which suggests that neurally mediated vasoconstrictor activity overrides local vasodilation. Femoral venous effluent documented perfusion of active muscle during contractions of 15 and 25% MVC, but less so at 50% MVC. Immediately in recovery LBF reached levels of 3–3.5 l min^-1, which corresponded to 150 ml 100 g^-1 min^-1. When both O₂ uptake and lactate release during the contractions and in recovery were taken into account, a close correlation between rate of energy turnover and exerted force was found. When MAP was raised by static contraction of the opposite quadriceps, LBF in the inactive leg increased momentarily. Within 1 min vascular resistance became elevated and the blood flow became reduced.