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

Abstract.

The purpose of this study was to compare the test-retest reliability of oxygen uptake ($\dot V{\rm O}_{\rm 2}$ ) kinetics with carbon dioxide output($\dot V{\rm CO}_{\rm 2}$ ) 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 $\dot V{\rm O}_{\rm 2}$ kinetics or $\dot V{\rm CO}_{\rm 2}$ kinetics. Static gain of $\dot V{\rm O}_{\rm 2}$ 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 $\dot V{\rm CO}_{\rm 2}$ kinetics displayed increased variability in comparison to $\dot V{\rm O}_{\rm 2}$ kinetics at each frequency of amplitude ratio and phase shift. Systematic bias ranged between 0% and 4%, except at frequency 10 mHz of $\dot V{\rm CO}_{\rm 2}$ kinetics phase shift which showed a 10% bias for slower $\dot V{\rm O}_{\rm 2}$ kinetics in test 2. It is possible that the increased variability of $\dot V{\rm CO}_{\rm 2}$ kinetics compared to $\dot V{\rm O}_{\rm 2}$ kinetics might be attributable to a lower signal to noise ratio in$\dot V{\rm CO}_{\rm 2}$ kinetics, variations in ventilation or the storage mechanisms of CO₂. The lower variability of $\dot V{\rm O}_{\rm 2}$ kinetics compared with $\dot V{\rm CO}_{\rm 2}$ kinetics suggests that the PRBS test of $\dot V{\rm O}_{\rm 2}$ kinetics has the greater potential for further development as an indicator of aerobic fitness.