Oxygen cost of ventilation during incremental exercise to VO2 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 VO2 plateau at maximal exercise. The purposes of this study were to: - (i) use isocapnic hyperpnoea trials to determine the oxygen cost of ventilation (VO2VENT) across a range of ventilation (VE); - (ii) determine the mean VO2VENT at maximal exercise expressed as a percentage of whole-body VO2 max, and; - (iii) determine if a plateau in VO2 is more evident when the VO2VENT is subtracted from whole-body VO2 at maximal exercise. Methods: A total of 21 subjects performed a VO2 max test on the cycle ergometer to determine the range of VE for each subject. From the initial VO2 max test, nine VE values across the range of VE were selected for each subject and the oxygen cost of each was measured. Results - The mean maximal VO2VENT equalled 8.8 ± 3.3% of VO2 max and ranged from 5.0% to 17.6%. VO2VENT increased exponentially with increasing VE, but there was considerable subject variability in the oxygen cost per litre of VE as VE increased. Subtracting the VO2VENT from whole-body VO2 at maximal exercise increased the detection of a plateau in VO2 at VO2 max. Conclusions - The data of the present study indicate that the VO2VENT is a significant portion of VO2 max and may be a limiting factor of maximal exercise performance in some subjects.