During ramp-incremental exercise, the mean response time (MRT) of oxygen uptake (V˙O2) represents the time delay for changes in muscle V˙O2 to be reflected at the level of the mouth and is generally calculated by linear (MRTLIN) and monoexponential (τ′) fitting of V˙O2 data. However, these methods yield MRT values that are highly variable from test-to-test.
Therefore, we examined the validity and the reproducibility of a novel method to calculate the MRT.
On two occasions, 12 healthy men (age, 30 ± 10 yr; V˙O2max: 4.14 ± 0.47 L·min−1, 53.5 ± 7.3 mL·kg−1·min−1) performed a ramp-incremental cycling test (30 W·min−1) that was preceded by a step transition to 100 W. The ramp power output corresponding to the steady-state V˙O2 at 100 W was determined and the difference between that power output and 100 W was converted to time to quantify the MRT (MRTSS).
The values of MRTLIN, τ′, 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.
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 V˙O2 data with power output during ramp-incremental exercise.
1Faculty of Kinesiology, University of Calgary, Calgary, Alberta, CANADA; and
2Department of Medicine, University Health Network, Toronto, Ontario, CANADA
Address for correspondence: Juan M. Murias, Ph.D., Faculty of Kinesiology, University of Calgary, KNB 434, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4; E-mail: firstname.lastname@example.org.
Submitted for publication September 2018.
Accepted for publication December 18, 2018.