Respiratory Rate Threshold Accurately Estimates the Second Lactate Threshold

Abstract

Purpose: The modified Dmax method can accurately determine the second lactate threshold (LT2), which is valuable for predicting aerobic performance and prescribing exercise. The purpose of this study is to determine if the modified Dmax method can accurately find thresholds in V_E (VT2), VCO₂ (VCO₂T), RER (RERT), and RR (RRT) to estimate LT2.

Methods: Forty-one participants (females n=23, males n=18) completed an incremental exercise test to determine LT2, VT2, VCO₂T, RERT, RRT, and blood lactate=4 mmol/L (La4).

Results: VT2 and RRT were strongly correlated with VO₂ and HR at LT2, with very small bias and limits of agreement, indicating that VT2 and RRT provide accurate estimates of LT2 (VO₂ at VT2-LT2 mean difference=0.37±1.91 ml/kg/min, p=0.95; HR at VT2-LT2 mean difference=0.25±2.58 bpm, p=0.99; VO₂ at RRT-LT2 mean difference 0.26±2.11 ml/kg/min, p=0.99; HR at RRT-LT mean difference 0.44±3.31 bpm, p=0.99). VCO₂T, RERT, and La4 were either accurate for VO₂ or HR estimates of LT2, but not both.

Conclusions: VT2 and RRT provide accurate estimates of LT2 using the modified Dmax method. There is the potential to use RRT in developing field tests to estimate LT2 in practical settings.