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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY
1Department of Physical Education, University of Las Palmas de Gran Canaria, Canary Islands, Spain; 2The Copenhagen Muscle Research Center, Rigshospitalet, Copenhagen, Denmark; Departments of 3Physiology-Pharmacology and 4Cardiology, Karolinska Institute, Stockholm; and 5Department of Sport and Health Sciences, University College of Physical Education and Sports, Stockholm, Sweden
Submitted 6 December 2004 ; accepted in final form 13 May 2005
To determine whether conditions for O2 utilization and O2 off-loading from the hemoglobin are different in exercising arms and legs, six cross-country skiers participated in this study. Femoral and subclavian vein blood flow and gases were determined during skiing on a treadmill at 
76% maximal O2 uptake (
O2 max) and at O2 max with different techniques: diagonal stride (combined arm and leg exercise), double poling (predominantly arm exercise), and leg skiing (predominantly leg exercise). The percentage of O2 extraction was always higher for the legs than for the arms. At maximal exercise (diagonal stride), the corresponding mean values were 93 and 85% (n = 3; P < 0.05). During exercise, mean arm O2 extraction correlated with the PO2 value that causes hemoglobin to be 50% saturated (P50: r = 0.93, P < 0.05), but for a given value of P50, O2 extraction was always higher in the legs than in the arms. Mean capillary muscle O2 conductance of the arm during double poling was 14.5 (SD 2.6) ml·min–1·mmHg–1, and mean capillary PO2 was 47.7 (SD 2.6) mmHg. Corresponding values for the legs during maximal exercise were 48.3 (SD 13.0) ml·min–1·mmHg–1 and 33.8 (SD 2.6) mmHg, respectively. Because conditions for O2 off-loading from the hemoglobin are similar in leg and arm muscles, the observed differences in maximal arm and leg O2 extraction should be attributed to other factors, such as a higher heterogeneity in blood flow distribution, shorter mean transit time, smaller diffusing area, and larger diffusing distance, in arms than in legs.
diffusing capacity; fatigue; oxygen extraction; performance; training
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