A modified step-ramp-step protocol to prescribe constant-speed exercise in treadmill running

Purpose: This study investigated whether a running-adapted version of the cycling-based "step-ramp-step" (SRS) protocol would improve prediction of $\dot{V}$ O₂ in treadmill exercise compared to the traditional prescriptive approach.

Methods: Fourteen healthy individuals (6 females; 25 ± 6 years; 66.1 ± 12.7 kg) performed a treadmill-based SRS protocol including a ramp-incremental test to task failure followed by two constant-speed bouts within the moderate-(MOD_step-below estimated lactate threshold; θ_LT), and heavy-intensity domains (HVY_step-between θ_LT and respiratory compensation point; RCP). Using the uncorrected $\dot{V}$ O₂-to-speed relationship from the ramp exercise, three constant-speed bouts were performed at 40-50% between: baseline and θ_LT (CSE_MOD); θ_LT and RCP (CSE_HVY); and RCP and peak (CSE_SEV). For CSE_MOD, CSE_HVY, and CSE_SEV measured end-exercise $\dot{V}$ O₂ was compared to predicted $\dot{V}$ O₂ based on the: (i) "SRS-corrected" $\dot{V}$ O₂-to-speed relationship (where MOD_step and HVY_step were used to adjust the $\dot{V}$ O₂ relative to speed); and (ii) linear "uncorrected" data.

Results: Average treadmill speeds for CSE_MOD and CSE_HVY were 7.8 ± 0.8 and 11.0 ± 1.4 km·h^-1, respectively, eliciting end-exercise $\dot{V}$ O₂ of 1979 ± 390 and 2574 ± 540 mL·min^-1. End-exercise $\dot{V}$ O₂ values were not different compared to SRS-predicted $\dot{V}$ O₂ at CSE_MOD (mean difference: 5 ± 166 mL·min^-1; p = 0.912) and CSE_HVY (20 ± 128 mL·min^-1; p = 0.568). The linear "uncorrected" estimates were not different for CSE_MOD (- 91 ± 172 mL·min^-1; p = 0.068) but lower for CSE_HVY (- 195 ± 146 mL·min^-1; p < 0.001). For CSE_SEV (running speed: 13.8 ± 1.7 km·h^-1), the end-exercise $\dot{V}$ O₂ was not different from peak $\dot{V}$ O₂ achieved during the ramp (3027 ± 682 vs. 2979 ± 655 mL·min^-1; p = 0.231).

Conclusion: In healthy individuals, the SRS protocol more accurately predicts speeds for a target $\dot{V}$ O₂ compared to traditional approaches.