Stability of the K4b2 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; peak 42.1 +/- 2.6ml center dot min(-1) center dot kg(-1)). Following a 10min rest, participants completed three discontinuous incremental exercise tests on a treadmill while walking (4, 5 and 6km center dot h(-1)) and running (8, 10, 12, 14 and 16km center dot h(-1), or until volitional exhaustion). Participants completed 3min of exercise at each speed, followed by a 3min recovery after each stage above 10km center dot 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 () and were not different when measured by K4b(2) or K4b(2)DEL. There was no difference in between OP and K4b(2) tests (P=0.19, mean difference= 38ml center dot min(-1) and limits of agreement (LOA) = 208 to -285) although K4b(2)DEL overestimated (P=0.05, mean difference= 84ml center dot min(-1) and LOA = 302 to -469). These data suggest that a drift in measurement accuracy appears to cause the K4b(2) to overestimate in tests lasting longer than 1 h.