Key result
Breakpoint models show poor agreement with conventional lactate threshold methods, while alternative indices correlate strongly.
Why the study?
The study aimed to compare lactate indices from single- and double-breakpoint models with conventional lactate threshold methods during ramp exercise.
Do breakpoint models provide comparable lactate thresholds to conventional methods during ramp exercise?
Do breakpoint models provide comparable lactate thresholds to conventional methods during ramp exercise?
Breakpoint models (Mod P and Mod M) show poor agreement with conventional methods for detecting lactate thresholds, questioning their utility compared to LT4, LSI, Dmax, and RER=1.
Breakpoint models show poor agreement with conventional lactate thresholds; hypothesis-generating and should not yet change exercise testing practice.
The aim of this study was to compare the lactate indices provided by single- and double-breakpoint models with lactate thresholds obtained with conventional methods. Arterial samples for the determination of lactate concentrations were drawn from eight participants at rest and every minute during a ramp test (15 W · min−1) on a cycle ergometer. Lactate thresholds were determined from a blood lactate concentration equal to 4 mM (LT4), from an increase of 1 mM above the resting level (Δ1 mM), and from indirect methods using ventilatory parameters. Other indices were computed from the modelling of the lactate curve using an exponential function (LSI), a polynomial function (Dmax), a semi-log model (SLog), a parabola plus delay model (Mod P), and a two-breakpoint model (Mod M). Mod P and Mod M showed poor agreement with the other methods. LT4, Dmax, LSI, and respiratory exchange ratio equal to 1 were correlated with each other (0.81 ≤ R ≤ 0.92) and their mean differences ranged from 2.8 to 15 W, with limits of agreement within the range ± 24.6 to ± 42.4 W. These results question the interest in breakpoints models to detect lactate thresholds, knowing that LT4, LSI, Dmax, and respiratory exchange ratio equal to 1 provide indices that occur at similar power outputs.
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Thomas et al. (2008) studied this question. Breakpoint models (Mod P, Mod M) vs. Conventional methods (LT4, Dmax, LSI, respiratory exchange ratio) was evaluated on Agreement and correlation between lactate threshold detection methods. Breakpoint models (Mod P and Mod M) showed poor agreement with conventional methods, whereas LT4, Dmax, LSI, and respiratory exchange ratio equal to 1 were correlated (0.81 ≤ R ≤ 0.92).
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