The aim of this study was to compare respiratory measures taken simultaneously using the Cosmed K4b2 and Cortex Metamax II portable metabolic systems. 10 trained male cyclists performed a graded exercise cycle test to exhaustion (40w.3 min - 1) under standardized conditions. The measured respiratory variables were significantly correlated between both devices: r=0.97 and 0.98 (n=10, p<0.01) for oxygen uptake ( VO2) and ventilation (VE), respectively. Further Bland and Altman plots revealed a good level of agreement for measures of VO2 expressed in mL.min - 1 [- 670 to 486] (mean bias of - 91.7, i. e., - 3.1%) or in mL.min - 1.kg - 1 [- 7.3 to 9.0] (mean bias of 0.85, i. e., 2.3%) and VE [- 23.1 to 18.2] (L.min - 1, mean bias of - 2.4, i. e. - 4.1%). However, poor agreement was found for measures of carbon dioxide (VCO2, mL.min - 1) [- 280 to 1 394] (mean bias of 671 i.e., 20.3%). VCO2 at maximal exercise intensity was also significantly (p<0.01) greater in the Cortex compared to the Cosmed system. The higher measured CO2 concentrations led to significantly (p<0.01) higher calculated respiratory exchange ratio (RER) values with the Cortex device. In conclusion, there was satisfactory agreement between the Cosmed K4b2 and Cortex Metamax II systems for most respiratory measures; however there was a poor level of agreement between VCO2 and calculated RER measurements between the 2 systems.
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