The test-retest reliability of gas exchange kinetics in humans using a pseudo random binary sequence exercise test

The purpose of this study was to compare the test-retest reliability of oxygen uptake ( ) kinetics with carbon dioxide output( ) kinetics using a pseudo random binary sequence (PRBS) exercise test. A reliable test of gas exchange kinetics would have the potential of being applied as a sports fitness test. Ten healthy male subjects agreed to participate in the study and all subjects completed two identical PRBS exercise tests (test 1 and test 2), separated by a 30 min period of inactivity. Three consecutive 300 s PRBS cycles were completed in each test with 20 s exercise intensity changes between 25 and 85 W using an electrically braked cycle ergometer. Fourier analysis was computed for frequencies 3.3, 6.7 and 10 mHz. Statistical analysis by two-way ANOVA with repeated measures did not reveal significant differences between test 1 and test 2 for either kinetics or kinetics. Static gain of for test 1 [9.11 (SD 0.59) ml·min^–1·W^–1] and test 2 [9.23 (SD 0.64) ml·min^–1·W^–1] did not differ significantly between tests. The 95% limits of agreement for kinetics displayed increased variability in comparison to kinetics at each frequency of amplitude ratio and phase shift. Systematic bias ranged between 0% and 4%, except at frequency 10 mHz of kinetics phase shift which showed a 10% bias for slower kinetics in test 2. It is possible that the increased variability of kinetics compared to kinetics might be attributable to a lower signal to noise ratio in kinetics, variations in ventilation or the storage mechanisms of CO₂. The lower variability of kinetics compared with kinetics suggests that the PRBS test of kinetics has the greater potential for further development as an indicator of aerobic fitness. Electronic Publication