Enhanced oxygen extraction and reduced flow heterogeneity in exercising muscle in endurance-trained men

The aim of this study was to investigate the effects of endurance training on skeletal muscle hemodynamics and oxygen consumption. Seven healthy endur ance-trained and seven untrained subjects were studied. Oxygen uptake, bloo d flow, and blood volume were measured in the quadriceps femoris muscle gro up by use of positron emission tomography and [O-15]O-2, [O-15]H2O, and [O- 15]CO during rest and one-legged submaximal intermittent isometric exercise . The oxygen extraction fraction was higher (0.49 +/- 0.14 vs. 0.29 +/- 0.1 2; P = 0.017) and blood transit time longer (0.6 +/- 0.1 vs. 0.4 +/- 0.1 mi n; P = 0.04) in the exercising muscle of the trained compared with the untr ained subjects. The flow heterogeneity by means of relative dispersion was lower for the exercising muscle in the trained (50 +/- 9%) compared with th e untrained subjects (65 +/- 13%, P = 0.025). In conclusion, oxygen extract ion is higher, blood transit time longer, and perfusion more homogeneous in endurance-trained subjects compared with untrained subjects at the same wo rkload. These changes may be associated with improved exercise efficiency i n the endurance-trained subjects.