Figure 1. Experimental protocols.

A, protocol 1, exercise. Subjects performed six 5 min bouts of constant-load exercise at 30% (109 ± 8 w), 60% (218 ± 18 w), 70% (253 ± 20 w), 80% (290 ± 24 w), 90% (319 ± 26 w) and 100% (359 ± 29 w) of maximal work rate. Between 30 and 80%, they cycled at 100 W for 10 min, but after exercise at 80% and 90%, they rested for 60 min. Vertical arrows indicate when haemodynamic measurements were made (during the final minute of exercise). Ventilatory variables were recorded continuously. B, protocol 2, isocapnic, resting hyperpnoea. Two hours after completion of protocol 1, subjects performed 5 bouts of isocapnic hyperpnoea at the same minute ventilation values recorded during protocol 1 at rest and during exercise at 60, 80, 90 and 100% of maximal work rate. Vertical arrows indicate when haemodynamic measurements were made (during the final minute of hyperpnoea). Ventilatory variables were recorded continuously.