Abstract

Background: The role of the perception of breathing effort in the regulation of performance of maximal exercise remains unclear.

Aims: To determine whether the perceived effort of ventilation is altered through substituting a less dense gas for normal ambient air and whether this substitution affects performance of maximal incremental exercise in trained athletes.

Methods: Eight highly trained cyclists (mean SD) maximal oxygen consumption (VO₂max) = 69.9 (7.9) (mlO₂/kg/min) performed two randomised maximal tests in a hyperbaric chamber breathing ambient air composed of either 35% O₂/65% N₂ (nitrox) or 35% O₂/65% He (heliox). A ramp protocol was used in which power output was incremented at 0.5 W/s. The trials were separated by at least 48 h. The perceived effort of breathing was obtained via Borg Category Ratio Scales at 3-min intervals and at fatigue. Oxygen consumption (VO₂) and minute ventilation (V_E) were monitored continuously.

Results: Breathing heliox did not change the sensation of dyspnoea: there were no differences between trials for the Borg scales at any time point. Exercise performance was not different between the nitrox and heliox trials (peak power output = 451 (58) and 453 (56) W), nor was VO₂max (4.96 (0.61) and 4.88 (0.65) l/min) or maximal V_E (157 (24) and 163 (22) l/min). Between-trial variability in peak power output was less than either VO₂max or maximal V_E.

Conclusion: Breathing a less dense gas does not improve maximal performance of exercise or reduce the perception of breathing effort in highly trained athletes, although an attenuated submaximal tidal volume and V_E with a concomitant reduction in VO₂ suggests an improved gas exchange and reduced O₂ cost of ventilation when breathing heliox.