Figure 1. Study timeline.

Following insertion of the brachial artery catheter, subjects rested quietly for 30–45 min and then either exercise or vasodilator infusion began (randomized). Endothelium-dependent and endothelium-independent vasodilatation was determined in random order utilizing local infusions of acetylcholine (Ach) and sodium nitroprusside (SNP), respectively. During the graded handgrip (HG) exercise trials, participants exercised for 4 min each at 5, 15 and 25% of their maximal voluntary contraction (MVC). The last 30 s of haemodynamics for baseline within a given trial, vasodilator infusion and each exercise workload was used to determine steady-state levels for each variable. Following the completion of control trials, phentolamine and propranolol were administered via the catheter and continuously infused to eliminate local sympathetic vasoconstriction, and the trials were repeated in random order.