A new objective method for determining exercise gas exchange thresholds by respiratory frequency in middle-aged men

To evaluate the agreement between the two Gas Exchange Thresholds (GETs = GET1 and GET2), identified by the conventional V-Slope method, and two Respiratory Frequency Thresholds (f_RTs = f_RT1 and f_RT2) obtained from a novel, low-cost, and simple method of breakpoint determination.

Fifty middle-aged males (age: 50–58 years; \(\dot{V}\) $\dot{V}$ o_2peak: 37.5 ± 8.6 mL·Kg⁻¹·min⁻¹), either healthy or with chronic illnesses, underwent an incremental cycle exercise test to determine maximal oxygen uptake ( \(\dot{V}\) $\dot{V}$ o_2max/ \(\dot{V}\) $\dot{V}$ o_2peak), GETs and f_RTs.

There were no statistical differences [P > 0.05; ES: 0.17 to 0.32, small] between absolute and relative (56–60% \(\dot{V}\) $\dot{V}$ o_2peak) oxygen uptake ( \(\dot{V}\) $\dot{V}$ o₂) values at GET1 with those obtained at f_RT1, nor between \(\dot{V}\) $\dot{V}$ o₂ values at GET2 with those at f_RT2 (76–78% \(\dot{V}\) $\dot{V}$ o_2peak). Heart rate (HR) at f_RT1, and \(\dot{V}\) $\dot{V}$ o₂ and HR at f_RT2 showed very large correlations (r = 0.75–0.82; P < 0.001) and acceptable precision (SEE < 7–9%) in determination of their corresponding values at GET1 and GET2. The precision in the estimation of \(\dot{V}\) $\dot{V}$ o₂ at GET1 from f_RT1 was moderate (SEE = 15%), while those of power output at GET1 (SEE = 23%) and GET2 (SEE = 12%) from their corresponding f_RTs values were very poor to moderate.

HR at f_RT1 and \(\dot{V}\) $\dot{V}$ o₂ and HR at f_RT2, determined using a new objective and portable approach, may potentially serve as viable predictors of their respective GETs. This method may offer a simplified, cost-effective, and field-based approach for determining exercise threshold intensities during graded exercise.