Oxygen cost of ventilation and its effect on the VO 2 plateau

Evidence of significant oxygen requirements for ventilation during moderate to intense exercise prompted the investigation into whether the oxygen cost of ventilation effects the presence of the VO 2 plateau. The purpose was to compare whole-body VO 2 (wb-VO 2) to locomotor-muscle VO 2 VO 2LOC; calculated by subtracting the VO 2 of the muscles used to ventilate during exercise (VO 2RM) from wb-VO 2 during maximal exercise for the presence of the VO 2-plateau. Twenty-two subjects performed a VO 2max test on a cycle ergometer to determine the range of V E for each subject. On a separate occasion, the VO 2RM was measured at nine different V E using isocapnic hyperpnea trails. Maximal VO 2RM equaled 18.1±4.4% of wb-VO 2max. VO 2RM increased exponentially with increasing V E. The increase in wb-VO 2 during maximal exercise was greater than that for wb-VO 2 when compared to VO 2LOC (p < 0.05), and therefore the incidence of a VO 2 plateau was greater for VO 2LOC (15 of 22 subjects) when compared to wb-VO 2 (1 of 22 subjects, p < 0.05). The VO 2RM significantly reduces the wb-VO 2 slope during maximal exercise, and can be accurately predicted based on the regression equation {VO 2RM (mL/min) = 346.9 0.007614 x VE (L/min)}. The data indicate that the use of wb-VO 2 to model and understand body and muscle energetics during exercise can be questioned. Correcting wb-VO 2 for the VO 2RM provides a more valid representation of the oxygen uptake kinetics of the exercising muscles