Peak muscle perfusion and oxygen uptake in humans: importance of precise estimates of muscle mass

The knee extensor exercise model was specifically developed to enable in vi vo estimates of peak muscle blood flow and O-2 uptake in humans. The origin al finding, using thermodilution measurements to measure blood flow in rela tion to muscle mass IF. Andersen and B. Saltin. J. Physiol. (Lond.) 366: 23 3-249, 1985], was questioned, however, as the measurements were two- to thr eefold higher than those previously obtained with the Xe-133 clearance and the plethysmography technique. As thermodilution measurements have now been confirmed by other methods and independent research groups, we aimed to ad dress the impact of muscle mass estimates on the peak values of muscle perf usion and O-2 uptake. In the present study, knee extensor volume was determ ined from multiple measurements with computer tomography along the full len gth of the muscle. In nine healthy humans, quadriceps muscle volume was 2.3 6 +/- 0.17 (range 1.31-3.27) liters, corresponding to 2.48 +/- 0.18 (range 1.37-3.43) kg. Anthropometry overestimated the muscle volume by similar to 21-46%, depending on whether quadriceps muscle length was estimated fi om t he patella to either the pubic bone, inguinal ligament, or spina iliaca ant erior superior. One-legged, dynamic knee extensor exercise up to peak effor t of 67 +/- 7 (range 55-100) W rendered peak values for leg blood flow (the rmodilution) of 5.99 +/- 0.66 (range 4.15-9.52) l/min and leg O-2 uptake of 856 +/- 109 (range 590-1,521) ml/min. Muscle perfusion and O-2 uptake reac hed peak values of 246 +/- 24 (range 149-373) and 35.2 +/- 3.7 (range 22.6- 59.6) ml.min(-1).100 g muscle(-1), respectively. These peak values are simi lar to 19-33% larger than those attained by applying anthropometric muscle mass estimates. In conclusion, the present findings emphasize that peak per fusion and O-2 uptake in human skeletal muscle may be up to similar to 30% higher than previous anthropometric-based estimates that use equivalent tec hniques for blood flow measurements.