Lactate threshold analyser

Evidence-based tool for analysing lactate step tests and calibrating training zones for cycling (e.g. Rouvy).

🚧 Beta version: This tool is under active development. Methods, thresholds and content are continuously reviewed and updated.

✉ Send feedback

🔒 Privacy: This tool does not store any data. All data you enter or upload is processed exclusively in your browser. Nothing is sent to or stored on any server. When you close or reload the page, all data is permanently gone. If you would like to keep your data, download the Excel template, enter your measurements there, and save the file on your computer – you can upload it at any time to view your results again.

How to use this tool

① Direct data entry

Scroll down to "Step data" and enter power (W) and lactate (mmol/L) for each stage – both are required fields. Heart rate and RPE are optional but unlock extra charts. Then click "Analyse".

→ For a single test, quick and easy

② Excel upload (1 test)

Download the Excel template (button below). Fill in your data in the "Test_1" tab – athlete name, date and measurements. Upload the file under "Upload single test". The tool loads and analyses the test automatically – just like direct entry.

→ For structured data entry outside the browser

③ Excel upload (multiple tests)

Fill the template with multiple tabs (Test_1, Test_2, Test_3…), one tab per test and athlete. Upload under "Upload multiple tests". All tests are then available for comparison and longitudinal analysis.

→ For cross-sectional and longitudinal athlete analysis

④ Sample data

Three pre-built athlete profiles are available – a sprinter, an endurance cyclist, and a Zone-2 training effect example. Click "Test 1" or "Test 2" for single analysis, or "Load all" for comparison and longitudinal view.

→ To explore the tool without your own data

What this tool offers

📈 Threshold analysis
Automatically computes LT1 (baseline +0.3 mmol/L) and LT2 (D-max method), plus LT1 and LT2 from the log-log curve. All methods with scientific references.

🏋️ Zone models
Four zone systems to choose from: Rouvy/Coggan 7-zone, Seiler 3-zone, Coggan 5-zone, and the Norwegian 5-zone model – each anchored to your individual LT1 and LT2.

⚡ FTP calibration
Enter how long you could sustain your LT2 power (TTE in minutes) to compute a corrected FTP using the power-duration relationship (Coggan & Allen, 2010).

📄 Training recommendations
Evidence-based training advice tailored to your thresholds and chosen zone model – downloadable as a PDF for use with your athletes or for your own training.

📊 Charts & export
Lactate curve, log-log curve, heart rate, RPE and more – all charts exportable as PNG. References downloadable as .ris for Zotero, Mendeley, or EndNote.

🔬 Scientific background
Detailed explanations of training models (polarised, Norwegian, threshold), the physiology of fat oxidation, FatMax, the Talk Test, and over 50 peer-reviewed references.

📥 Download Excel template

The template includes an instructions tab, a filled example (Test_1) and an empty second tab (Test_2). Columns: Step · Power (W) · Lactate (mmol/L) · HR (bpm) · RPE (Borg). Duplicate tabs for additional tests.

② Upload single test & analyse

📊

Drop Excel here (1 test)

Analysed immediately like direct entry

③ Upload multiple tests (comparison)

📂

Drop Excel here (multiple tests)

Loads all tabs for comparison & trends

④ Sample data

Note: These curves are constructed from published group means as representative example profiles – not raw data from individual athletes. References are shown on each card.

Test comparison & longitudinal trends

Compare two tests

● Test A

vs.

● Test B

Longitudinal trend

Select an athlete to display LT1/LT2 development across all loaded tests over time.

Step data

Step	Power (W) *	Lactate (mmol/L) *	HR (bpm)	RPE (0–10)

Shift from row:

Training models — polarized & Norwegian

Scientific background — lactate, FatMax, Talk Test & evidence

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

Developed with Claude (Anthropic) as an AI coding assistant. Scientific content, methodology, and reference selection reflect the author's expertise. All 54 references were individually verified for DOI accuracy and bibliographic correctness.