Oxygen cost of ventilation during incremental exercise to VO 2 max

Objective:  Evidence of significant oxygen requirements for ventilation during exercise (exercise hyperpnoea) prompted the investigation into whether the oxygen cost of ventilation affects the presence of a whole‐body VO 2 plateau at maximal exercise. The purposes of this study were to: (i) use isocapnic hyperpnoea trials to determine the oxygen cost of ventilation (VO 2VENT ) across a range of ventilation (V E ); (ii) determine the mean VO 2VENT at maximal exercise expressed as a percentage of whole‐body VO 2 max; and (iii) determine if a plateau in VO 2 is more evident when the VO 2VENT is subtracted from whole‐body VO 2 at maximal exercise. Methods:  A total of 21 subjects performed a VO 2 max test on the cycle ergometer to determine the range of V E for each subject. From the initial VO 2 max test, nine V E values across the range of V E were selected for each subject and the oxygen cost of each was measured. Results:  The mean maximal VO 2VENT equalled 8.8 ± 3.3% of VO 2 max and ranged from 5.0% to 17.6%. VO 2VENT increased exponentially with increasing V E , but there was considerable subject variability in the oxygen cost per litre of V E as V E increased. Subtracting the VO 2VENT from whole‐body VO 2 at maximal exercise increased the detection of a plateau in VO 2 at VO 2 max. Conclusions:  The data of the present study indicate that the VO 2VENT is a significant portion of VO 2 max and may be a limiting factor of maximal exercise performance in some subjects.