A comparison of leg blood flow (Panel A, Q̇M), muscle oxygen uptake (Panel B, V̇MO2), the arterial-venous O2 content difference (Panel C, CaO2 - CvO2), muscle oxygen delivery (Panel D, Q̇MO2), and arterial oxygen saturation (Panel E, SaO2) assessed during graded knee-extensor exercise in patients with chronic obstructive pulmonary disease (COPD) (n = 8) and control subjects (n = 8). Data are presented as mean ± SEM. * significantly different from control subjects at peak work rates. † significantly different y-intercept from control subjects.