Stability of the K4b(2) portable metabolic analyser during rest, walking and running

This study investigated the stability of the measurement of respiratory variables during rest, walking and running using the K4b2 portable metabolic analyser in ten active males (age 31 ± 11 years; peak 42.1 ± 2.6 ml · min-1 · kg-1). Following a 10 min rest, participants completed three discontinuous incremental exercise tests on a treadmill while walking (4, 5 and 6 km · h-1) and running (8, 10, 12, 14 and 16 km · h-1, or until volitional exhaustion). Participants completed 3 min of exercise at each speed, followed by a 3 min recovery after each stage above 10 km · h-1. The respiratory variables were measured using either a laboratory-based metabolic cart as a reference method (Oxycon Pro, OP), a K4b2 calibrated immediately before the test (K4b2), or a K4b2 calibrated 1 h before the test (K4b2DEL). Compared to the OP, carbon dioxide production () and were not different when measured by K4b2 or K4b2DEL. There was no difference in between OP and K4b2 tests (P = 0.19, mean difference = 38 ml · min-1 and limits of agreement (LOA) = 208 to -285) although K4b2DEL overestimated (P = 0.05, mean difference = 84 ml · min-1 and LOA = 302 to -469). These data suggest that a drift in measurement accuracy appears to cause the K4b2 to overestimate in tests lasting longer than 1 h.