Lactate threshold analyser

How to use this tool

① Enter your data

For each step, enter power (W) and lactate (mmol/L) — both are required. Heart rate (HR) and RPE (0–10) are optional but unlock additional charts. Press Tab to move down within the same column.

💡 No test data? Click "Load example (incl. HR & RPE)" for a realistic sample dataset, or "📋 Load validation example" for the published reference dataset.

② Analyse

Click "Analyse" — whether you entered your own data or loaded an example. The tool automatically computes LT1 (baseline +0.3 mmol/L) and LT2 (D-max method), plus LT1 and LT2 from the log-log curve. All charts and training zones are displayed immediately.

③ Calibrate zones

In the "Rouvy zone calibration" section, enter how long you could hold your LT2 power (TTE in minutes) to compute a corrected FTP. Then choose a zone model (Rouvy/Coggan, Seiler, Coggan 5-zone, or Norwegian).

④ Use your results

Download the training recommendations as PDF, export the references as .ris for your reference manager, or explore the charts — lactate curve, log-log, heart rate, RPE and more. Every chart can be exported individually as PNG.

Threshold estimates

Charts

Why LT1 anchors the Z2 ceiling — and not 75% of FTP (Meixner et al., 2025). A controlled laboratory study of 50 cyclists compared nine common Zone 2 markers (HRmax percentages, fixed blood lactate concentrations, VT1, FatMax, etc.) for interindividual variability. Coefficients of variation for power output ranged from 6% to 29% — fixed %HRmax targets (HR72%, HR82%) and fixed lactate concentrations (e.g. 2 mmol/L) showed the greatest individual scatter. VT1 (≈ LT1) and BLamin+0.5 (baseline + 0.5 mmol/L) showed the closest mutual agreement (Bland-Altman bias −0.7 W, LoA ±37 W) and are considered the most physiologically valid markers for the Z2 upper boundary.
This tool anchors Z2 directly to your measured LT1 — rather than the population-average 75% of FTP. This is not just a methodological choice; it is supported by current evidence.

FTP, Critical Power and MLSS — clarifying the concepts. FTP (Functional Threshold Power) and Critical Power (CP) target the same physiological boundary — the maximal lactate steady state (MLSS) — but are not identical. CP, derived from exhaustive time trials using the power-duration hyperbolic model, typically sits slightly above FTP (~5–10 W in trained cyclists; Karsten et al., 2021). FTP is operationally estimated as 95% of a 20-min maximal effort. The approximate hierarchy is: CP ≥ FTP ≥ MLSS ≈ LT2 — with differences small in well-trained athletes but potentially meaningful in recreational cyclists.

Important caveat on LT2 precision (Valenzuela et al., 2021, Front. Physiol.). The D-max polynomial method shows good group-level agreement with Critical Power (mean bias ~0.5 W, Hedges' g = 0.01), but with wide individual limits of agreement (±52 W). This means that in any given athlete, measured LT2 may differ from true CP by 50 W or more — without either measurement being incorrect. Zone prescriptions should therefore be treated as a physiologically grounded starting point, to be refined using perceived exertion, heart rate response, and training performance data.

Zone model