The cardiovascular response to exercise with several groups of skeletal muscle implies that work with the legs may reduce arm blood flow. This study followed arm blood flow (Yarm) and oxygenation on the transition from arm cranking (A) to combined arm and leg exercise (A+L). Seven healthy male subjects performed A at approximately 80 % of maximum work rate (Wmax) and A at ~80 % Wmax combined with L at approximately 60 % Wmax. A transition trial to volitional exhaustion was performed where L was added after 2 min of A. The Yarm was determined by constant infusion thermodilution in the axillary vein and changes in biceps muscle oxygenation were measured with near-infrared spectroscopy. During A+L Yarm was lowered by 0.38 +/- 0.06 l min-1 (10.4 +/- 3.3 %, P < 0.05) from 2.96 +/- 1.54 l min-1 during A. Total (HbT) and oxygenated haemoglobin (HbO2) concentrations were also lower. During the transition from A to A+L Yarm decreased by 0.22 +/- 0.03 l min-1 (7.9 +/- 1.8 %, P < 0.05) within 9.6 +/- 0.2 s, while HbT and HbO2 decreased similarly within 30 +/- 2 s. At the same time mean arterial pressure and arm vascular conductance also decreased. The data demonstrate reduction in blood flow to active skeletal muscle during maximal whole body exercise to a degree that arm oxygen uptake and muscle tissue oxygenation are compromised.