Validation of the COSMED K4 b² portable metabolic system

The purpose of this investigation was to assess the accuracy of the COSMED K4 b² portable metabolic measurement system against the criterion Douglas bag (DB) method. During cycle ergometry on consecutive days, oxygen consumption (V̇O₂), carbon dioxide production (V̇CO₂), minute ventilation (V_E), and respiratory exchange ratio (R) were measured at rest and during power outputs of 50, 100, 150, 200, and 250W. No significant differences (P>0.05) were observed in V̇O₂ between the K4 b² and DB at rest and at 250W. Though the K4 b² values were significantly higher (P<0.05) than DB values at 50, 100, 150, and 200W, the magnitude of these differences was small (0.088, 0.092, 0.096, and 0.088 L×min^-1, respectively). V̇CO₂ and V̇_E values from the K4 b² were significantly lower than the DB at 200 and 250W, while no significant differences were observed from rest through 150W. The slight overestimation of V̇O₂ (50-200W) combined with the underestimation of V̇CO₂ (200 and 250W) by the K4 b² resulted in significantly lower R values at every stage. These findings suggest the COSMED K4 b² portable metabolic measurement system is acceptable for measuring oxygen uptake over a fairly wide range of exercise intensities.