A Simple Method to Quantify the V˙O2 Mean Response Time of Ramp-Incremental Exercise

Abstract

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. 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; 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). Results 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. 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 V˙O2 data with power output during ramp-incremental exercise.

Influence of type 2 diabetes on muscle deoxygenation during ramp incremental cycle exercise

“…The rate of change V O2 relative to PO during ramp incremental exercise reflects the capacity of aerobic metabolism to adjust to the non-steady state conditions incurred during a ramp incremental protocol. Initially, the mean response time (MRT) of ramp incremental exercise was estimated using the approach recently described by Iannetta et al (2019). Briefly, we determined the average steady-state V O2 corresponding to three separate bouts of moderateintensity constant-power outputs (performed on a separate visit), and we then compared the ramp-derived power output associated with that V O2 to the constant-power output that elicited that V O2 (Iannetta et al, 2019).…”

“…Initially, the mean response time (MRT) of ramp incremental exercise was estimated using the approach recently described by Iannetta et al (2019). Briefly, we determined the average steady-state V O2 corresponding to three separate bouts of moderateintensity constant-power outputs (performed on a separate visit), and we then compared the ramp-derived power output associated with that V O2 to the constant-power output that elicited that V O2 (Iannetta et al, 2019). The difference between these power outputs was converted to the time to retrieve the time-interval corresponding to MRT.…”

Establishing the V̇o2 versus constant-work-rate relationship from ramp-incremental exercise: simple strategies for an unsolved problem

“…4 and 13). For 30 W/min ramp protocols, we have recently shown that the MRT is best calculated by measuring the steady-state V O 2 during a 6-min bout of moderate exercise performed before ramp exercise, which, projected on the ramp V O 2 -to-work rate relationship, provides an accurate estimate of time (s or W) by which to "left shift" the V O 2 data (19). Given that G in the moderate domain should be greater in response to slower ramp protocols (22,40,44), it is hypothesized that the difference in seconds between the ramp and constant-work-rate V O 2 (i.e., the MRT) would be reduced progressively from faster to slower ramp protocols, necessitating less of a correction to achieve the same work rate at LT across different ramp slopes.…”

Constant Load Exercise at Gas Exchange Threshold is Accompanied by a Distinct Elevation in Blood Lactate Level

“…Therefore, when the work rate at the GET VO 2 is taken as the GET work rate, it may result in overestimation of the GET work rate because the work rate is, in a sense, ahead of VO 2 . However, there is no currently widely used or standard way to correct for this, although a quantitative way to correct for this has been reported and seems promising [32]. Therefore, our GET-level FL-exercise protocol, which is not corrected for this, may well be overestimating the individual "true" GET level CL-Ex.…”

“…It is known that for a stepwise initiation of CL-exercise, there is a delay in the increase of VO 2 , which is known as the mean response time. This delay in the response to VO 2 increases with exercise intensity [32,33]. Therefore, when the work rate at the GET VO 2 is taken as the GET work rate, it may result in overestimation of the GET work rate because the work rate is, in a sense, ahead of VO 2 .…”