Figure 1. Experimental protocol.

Subjects completed each of the 14 days consecutively. Familiarization (Day 1) consisted of pulmonary function testing, anthropometric measurements, and a practice HVR. On the pre-and post-intermittent hypoxia (IH) trials (Days 2 and 14) subjects were instrumented for collection of muscle sympathetic nerve activity, and cardiovascular and ventilatory parameters. During the hypoxic intervention (Days 3–13) subjects breathed a hypoxic inspirate such that oxyhaemoglobin saturation was maintained at 80% and end-tidal carbon dioxide was kept at baseline levels.