Increases in the incremental exercise mean response time across the steady state domain: Implications for exercise testing & prescription

We hypothesized that slowed oxygen uptake (VO2) kinetics for exercise transitions to higher power outputs (PO) within the steady state (SS) domain would increase the mean response time (MRT) with increasing exercise intensity during incremental exercise. Fifteen highly trained cyclists (mean ± standard deviation [SD]; age (39 ± 6) years [yr]; and VO2 peak = (61 ± 9) mL/kg/min performed a maximal, ramp incremental cycling test and on separate days, four 6-min bouts of cycling at 30%, 45%, 65% & 75% of their incremental peak PO (Wpeak). SS trial data were used to calculate the MRT and verified by mono-exponential and linear curve fitting. When the ramp protocol attained the value from SS, the PO, in Watts (W), was converted to time (min) based on the ramp function W to quantify the incremental MRT (iMRT). Slope analyses for the VO2 responses of the SS versus incremental exercise data below the gas exchange threshold (GET) revealed a significant difference (p = 0.003; 0.437 ± 0.08 vs. 0.382 ± 0.05 L⋅min−1). There was a significant difference between the 45% Wpeak steady state VO2 (ssVO2) (3.08 ± 0.30 L⋅min−1, respectively), and 30% Wpeak ssVO2 (2.26 ± 0.24) (p < 0.0001; 3.61 ± 0.80 vs. 2.20 ± 0.39 L⋅min−1) and between the iMRT for 45% and 30% Wpeak ssVO2 values (50.58 ± 36.85 s vs. 32.20 ± 43.28 s). These data indicate there is no single iMRT, which is consistent with slowed VO2 kinetics and an increasing VO2 deficit for higher exercise intensities within the SS domain.