Oxygen cost of ventilation and its effect on the VO2 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 VO2 plateau. The purpose was to compare whole-body VO2 (wb-VO2) to locomotor-muscle VO2 [VO2LOC; calculated by subtracting the VO2 of the muscles used to ventilate during exercise (VO2RM) from wb-VO2] during maximal exercise for the presence of the VO 2-plateau. Twenty-two subjects performed a VO2max test on a cycle ergometer to determine the range of VE for each subject. On a separate occasion, the VO2RM was measured at nine different V E using isocapnic hyperpnea trails. Maximal VO2RM equaled 18.1±4.4% of wb-VO2max. VO2RM increased exponentially with increasing VE. The increase in wb-VO2 during maximal exercise was greater than that for wb-VO2 when compared to VO2LOC (p < 0.05), and therefore the incidence of a VO2 plateau was greater for VO2LOC (15 of 22 subjects) when compared to wb-VO2 (1 of 22 subjects, p < 0.05). The VO 2RM significantly reduces the wb-VO2 slope during maximal exercise, and can be accurately predicted based on the regression equation {VO2RM (mL/min) = 346.9[0.007614 x VE (L/min)]}. The data indicate that the use of wb-VO2 to model and understand body and muscle energetics during exercise can be questioned. Correcting wb-VO 2 for the VO2RM provides a more valid representation of the oxygen uptake kinetics of the exercising muscles.