A Simple Method to Quantify the VO2 Mean Response Time of Ramp-Incremental Exercise

During ramp-incremental exercise, the mean response time (MRT) of oxygen uptake (VO2) represents the time delay for changes in muscle VO2 to be reflected at the level of the mouth and is generally calculated by linear (MRTLIN) and monoexponential (tau ') fitting of VO2 data. However, these methods yield MRT values that are highly variable from test-to-test. Purpose Therefore, we examined the validity and the reproducibility of a novel method to calculate the MRT. Methods On two occasions, 12 healthy men (age, 30 +/- 10 yr; VO2max: 4.14 +/- 0.47 L center dot min(-1), 53.5 +/- 7.3 mL center dot kg(-1)center dot min(-1)) performed a ramp-incremental cycling test (30 W center dot min(-1)) that was preceded by a step transition to 100 W. The ramp power output corresponding to the steady-state VO2 at 100 W was determined and the difference between that power output and 100 W was converted to time to quantify the MRT (MRTSS). Results The values of MRTLIN, tau ', and MRTSS were 28 +/- 16 s, 27 +/- 12 s, and 26 +/- 11 s, respectively, which were not different (P > 0.05) from each other. However, compared to the MRT parameters derived from the fitting-based methods, MRTSS had a higher correlation coefficient (R = 0.87) and a smaller coefficient of variation (15% +/- 9%) from test-to-test. Conclusions In conclusion, the novel method proposed in the current study was found to be valid and highly reproducible in a test-retest design. Therefore, we advocate the use of this approach when a precise and accurate determination of the MRT is needed to properly align the VO2 data with power output during ramp-incremental exercise.