Figure 1. Timeline and experimental protocol.

A, overall experimental protocol; subjects' non-dominant arm was instrumented with a brachial catheter and a deep venous catheter. Phentolamine and propranolol were administered intra-arterially to block α- and β-adrenoceptors, respectively, before the experimental trials. Twenty minutes of rest separated each trial. After both normoxic and hypoxic trials were performed in the control (saline) condition, l-NMMA and ketorolac (KET) were administered intra-arterially to block NO and PG synthesis, respectively. Normoxic and hypoxic trials were repeated under the blockade condition (shaded boxes). The order of the normoxic and hypoxic trials was counter-balanced. B, normoxic trial timeline; baseline measurements were made for 3 min, followed by 5 min of 20% MVC rhythmic handgrip exercise. C, hypoxic trial timeline; baseline measurements were made for 3 min, oxygen saturations were then lowered to ∼85% (within first 2 min) and maintained for duration of trial. After 3 min of steady-state hypoxia, subjects performed 5 min of 20% MVC rhythmic handgrip exercise.