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This Article Full Text Full Text (PDF) All Versions of this Article: 586/10/2621    most recent jphysiol.2007.149401v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Mortensen, S. P. Articles by González-Alonso, J. Search for Related Content PubMed PubMed Citation Articles by Mortensen, S. P. Articles by González-Alonso, J. Related Collections Integrative

¹ The Copenhagen Muscle Research Centre, Rigshospitalet, University of Copenhagen, Denmark
² Department of Anaesthesia, Rigshospitalet, Faculty of Health Sciences, University of Copenhagen, Denmark
³ Centre for Sports Medicine and Human Performance, Brunel University, Uxbridge, UK

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 , 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 (), leg blood flow (LBF), and systemic and leg O₂ delivery and 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, 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, , LBF, leg vascular conductance, leg O₂ delivery and leg 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 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.

(Received 5 December 2007; accepted after revision 20 March 2008; first published online 27 March 2008)
Corresponding author J. González-Alonso: Centre for Sports Medicine and Human Performance, Brunel University, Uxbridge, Middlesex UB8 3PH, UK. Email: j.gonzalez-alonso{at}brunel.ac.uk

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