ABSTRACT: Oxygen transport to working skeletal muscles is challenged during whole-body exercise. In general, arm-cranking exercise elicits a maximal oxygen uptake (V˙O2max) corresponding to approximately 70% of the value reached during leg exercise. However, in arm-trained subjects such as rowers, cross-country skiers, and swimmers, the arm V˙O2max approaches or surpasses the leg value. Despite this similarity between arm and leg V˙O2max, when arm exercise is added to leg exercise, V˙O2max is not markedly elevated, which suggests a central or cardiac limitation. In fact, when intense arm exercise is added to leg exercise, leg blood flow at a given work rate is approximately 10% less than during leg exercise alone. Similarly, when intense leg exercise is added to arm exercise, arm blood flow and muscle oxygenation are reduced by approximately 10%. Such reductions in regional blood flow are mainly attributed to peripheral vasoconstriction induced by the arterial baroreflex to support the prevailing blood pressure. This putative mechanism is also demonstrated when the ability to increase cardiac output is compromised; during exercise, the prevailing blood pressure is established primarily by an increase in cardiac output, but if the contribution of the cardiac output is not sufficient to maintain the preset blood pressure, the arterial baroreflex increases peripheral resistance by augmenting sympathetic activity and restricting blood flow to working skeletal muscles.
1The Copenhagen Muscle Research Center, Department of Anesthesia, Rigshospitalet, University of Copenhagen, DENMARK; and 2School of Sport and Education, Brunel University, UNITED KINGDOM
Address for correspondence: Stefanos Volianitis, Ph.D., School of Sport and Education, Brunel University, Uxbridge, Middlesex UB8 3PH United Kingdom; E-mail: Stefanos.Volianitis@brunel.ac.uk.
Submitted for publication December 2005.
Accepted for publication February 2006.