Restrictions in systemic and locomotor skeletal muscle perfusion, oxygen supply and V̇O2 during high-intensity whole-body exercise in humans

Abstract

Perfusion to exercising skeletal muscle is regulated to match O2 delivery to the O2 demand, but this regulation might be compromised during or approaching maximal whole-body exercise as muscle blood flow for a given work rate is blunted. Whether muscle perfusion is restricted when there is an extreme metabolic stimulus to vasodilate during supramaximal exercise remains unknown. To examine the regulatory limits of systemic and muscle perfusion in exercising humans, we measured systemic and leg haemodynamics, O2 transport, and V̇O2 estimated non-locomotor tissue perfusion during constant load supramaximal cycling (498 ± 16 W; 110% of peak power; mean ± S.E.M.) in addition to both incremental cycling and knee-extensor exercise to exhaustion in 13 trained males. During supramaximal cycling, cardiac output (Q̇), leg blood flow (LBF), and systemic and leg O2 delivery and V̇O2 reached peak values after 60-90 s and thereafter levelled off at values similar to or ∼6% (P < 0.05) below maximal cycling, while upper body blood flow remained unchanged (∼5.5 l min-1). In contrast, Q̇ and LBF increased linearly until exhaustion during one-legged knee-extensor exercise accompanying increases in non-locomotor tissue blood flow to ∼12 l min-1. At exhaustion during cycling compared to knee-extensor exercise, Q̇, LBF, leg vascular conductance, leg O2 delivery and leg V̇O2 for a given power were reduced by 32-47% (P < 0.05). In conclusion, locomotor skeletal muscle perfusion is restricted during maximal and supramaximal whole-body exercise in association with a plateau in Q̇ and limb vascular conductance. These observations suggest that limits of cardiac function and muscle vasoconstriction underlie the inability of the circulatory system to meet the increasing metabolic demand of skeletal muscles and other tissues during whole-body exercise. © Journal compilation © 2008 The Physiological Society.