Figure 1. Schematic illustration of the individual and the concurrent activation of the exercise pressor reflex (EPR) and the chemoreflex (CR) during exercise.

Each of the two experimental sessions (Control and Fentanyl) included 3 conditions (Normoxia, Normocapnic Hypoxia, and Normoxic Hypercapnia). This design resulted in 6 bouts during which single-leg knee-extension exercise was performed at a constant workload. The straight arrows indicate the comparisons utilized to estimate the cardiovascular effects of activation of the EPR (), activation of the CR (), and co-activation of the EPR and CR ().