A Comparison of Methods to Identify the Mean Response Time of Ramp-Incremental Exercise for Exercise Prescription.

Introduction: The oxygen uptake ($\dot{V}$O₂) vs power output relationship from ramp incremental exercise is used to prescribe aerobic exercise. As power output increases, there is a delay in $\dot{V}$O₂ that contributes to a misalignment of $\dot{V}$O₂ from power output; the mean response time (MRT). If the MRT is not considered in exercise prescription, ramp incremental-identified power outputs will elicit $\dot{V}$O₂ values that are higher than intended. We compared three methods of determining MRT (exponential modeling (MRT_EXP), linear modeling (MRT_LIN), and the steady-state method (MRT_SS)) and evaluated their accuracy at predicting the $\dot{V}$O₂ associated with power outputs approximating 75% and 85% of gas exchange threshold and 15% of the difference between gas exchange threshold and maximal $\dot{V}$O₂ (Δ15). Methods: Ten males performed a 30-W∙min^-1 ramp incremental and three 30-min constant power output cycle ergometer trials with intensities at 75% gas exchange threshold, 85% gas exchange threshold, and ∆15. At each intensity, the measured steady-state $\dot{V}$O₂ during each 30-min test was compared to the $\dot{V}$O₂ predicted after adjustment by each of the three MRTs. Results: For all three MRT methods, predicted $\dot{V}$O₂ was not different (p = 1.000) from the measured $\dot{V}$O₂ at 75%GET (MRT_EXP, 31 mL, MRT_LIN, -35 mL, MRT_SS 11 mL), 85%gas exchange threshold (MRT_EXP -14 mL, MRT_LIN -80 mL, MRT_SS -32 mL). At Δ15, predicted $\dot{V}$O₂ based on MRT_EXP was not different (p = .767) from the measured $\dot{V}$O₂, but was different for MRT_LIN (p < .001) and MRT_SS (p = .03). Conclusion: Given that the intensity is below gas exchange threshold, all model predictions implemented from the current study matched the exercise prescription.