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 K4b(2) portable metabolic analyser in ten active males (age 31 ± 11 years; [Formula: see text] 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 K4b(2) calibrated immediately before the test (K4b(2)), or a K4b(2) calibrated 1 h before the test (K4b(2)DEL). Compared to the OP, carbon dioxide production ([Formula: see text]) and [Formula: see text] were not different when measured by K4b(2) or K4b(2)DEL. There was no difference in [Formula: see text] between OP and K4b(2) tests (P = 0.19, mean difference = 38 ml · min(-1) and limits of agreement (LOA) = 208 to -285) although K4b(2)DEL overestimated [Formula: see text] (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 K4b(2) to overestimate [Formula: see text] in tests lasting longer than 1 h.