The reliability of VO₂ kinetics during a 6-minute walking test is influenced by walk speed

[Purpose] This study aimed to investigate the reliability of time constant measurements of oxygen intake at fast and comfortable speeds during a 6-min waling test. [Participants and Methods] The study included 10 healthy young males who walked at 4.5 km/h and 6.0 km/h twice for 6 min each in speed treadmill. Breath-by-breath gas exchange data were continuously measured and used to calculate the time constant of oxygen uptake. The reproducibility and variability of the variables were verified using the limit of agreement, inter-class correlation coefficient, coefficient of variation, and standard error of measurement. [Results] The limit of agreement was -8.5 to 2.3 s and -3.9 to 2.1 s for speeds 4.5 km/h and 6.0 km/h, respectively. The inter-class correlation coefficient, coefficient of variation, and standard error of measurement of the time constant for both speeds were 0.52 and 0.83, 11.2% and 6.4%, and 5.3 s and 1.8 s, respectively. [Conclusion] The results of this study suggested that the cardiopulmonary response, in terms of oxygen uptake, was more consistent during fast walking than during comfortable walking in a 6-min walking test with constant speed.