Control of hyperpnoea and pulmonary gas exchange during prolonged exercise: The role of group III/IV muscle afferent feedback

It remains unclear whether feedback from group III/IV muscle afferents is of continuous significance for regulating the pulmonary response during prolonged (>5 min), steady‐state exercise. To elucidate the influence of these sensory neurons on hyperpnoea, gas exchange efficiency, arterial oxygenation and acid–base balance during prolonged locomotor exercise, 13 healthy participants (4 females; 21 (3) years, V̇O2max${{\dot{V}}_{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}$: 46 (8) ml/kg/min) performed consecutive constant‐load cycling bouts at ∼50% (20 min), ∼75% (20 min) and ∼100% (5 min) of V̇O2max${{\dot{V}}_{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}$ with intact (CTRL) and pharmacologically attenuated (lumbar intrathecal fentanyl; FENT) group III/IV muscle afferent feedback from the legs. Pulmonary responses were continuously recorded and arterial blood (radial catheter) periodically collected throughout the exercise. Pulmonary gas exchange efficiency was evaluated using the alveolar‐arterial PO2${{P}_{{{\mathrm{O}}}_{\mathrm{2}}}$ difference (A−aDO2${\mathrm{A - a}}{{D}_{{{\mathrm{O}}}_{\mathrm{2}}}$). There were no differences in any of the variables of interest between conditions before the start of the exercise. Pulmonary ventilation was up to 20% lower across all intensities during FENT compared to CTRL exercise (P