Perfusion to exercising skeletal muscle is regulated to match O(2) delivery to the O(2) 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, O(2) transport, and , and 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 (Q), leg blood flow (LBF), and systemic and leg O(2) delivery and reached peak values after 60-90 s and thereafter levelled off at values similar to or approximately 6% (P
J Physiol. 586(10): 2621-2635.