Limitations to vasodilatory capacity and V̇o2 max in trained human skeletal muscle

To further explore the limitations to maximal O2 consumption (Vo2 max) in exercise-trained skeletal muscle, six cyclists performed graded knee-extensor exercise to maximum work rate (WRmax) in hypoxia (12% O2), hyperoxia (100% O2), and hyperoxia + femoral arterial infusion of adenosine (ADO) at 80% WRmax. Arterial and venous blood sampling and thermodilution blood flow measurements allowed the determination of muscle O2 delivery and O2 consumption. At WRmax, O2 delivery rose progressively from hypoxia (1.0 ± 0.04 l/min) to hyperoxia (1.20 ± 0.09 l/min) and hyperoxia + ADO (1.33 ± 0.05 l/min). Leg Vo2 max varied with O2 availability (0.81 ± 0.05 and 0.97 ± 0.07 l/min in hypoxia and hyperoxia, respectively) but did not improve with ADO-mediated vasodilation (0.80 ± 0.09 l/min in hyperoxia + ADO). Although a vasodilatory reserve in the maximally working quadriceps muscle group may have been evidenced by increased leg vascular conductance after ADO infusion beyond that observed in hyperoxia (increased blood...