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Free lactate threshold tool for athletes: translate a field heart-rate test into an LTHR estimate and a common %LTHR zone chart, or enter a 20-minute average power for an FTP-style anchor with power zones. Pair with VO₂ estimates and pace math for planning—this page is educational, not a medical or lab replacement.
Last updated: April 11, 2026
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Method
20-minute test average × 0.95 (common cycling / mixed field rule)
Estimated LTHR: 162 bpm
| Zone | Name | % LTHR | BPM |
|---|---|---|---|
| Z1 | Recovery | < 85% | < 138 bpm |
| Z2 | Aerobic | 85–89% | 138–144 bpm |
| Z3 | Tempo | 90–94% | 146–152 bpm |
| Z4 | Sub-threshold | 95–99% | 154–160 bpm |
| Z5a | Super-threshold | 100–102% | 162–165 bpm |
| Z5b | Aerobic capacity | 103–106% | 167–172 bpm |
| Z5c | Anaerobic | ≥ 107% | ≥ 173 bpm |
Not medical advice. Heat, fatigue, caffeine, and device error change HR; power needs a calibrated meter. Compare with our target heart rate and FTP calculator for alternate methods.
Field proxy
BPM anchor
20-minute correction, 30-minute “last 20,” or direct known LTHR.
Ballpark
Adjust % slider
Useful for exploration; a solo time trial usually tracks fitness better.
× 0.95
Watts estimate
Same family of idea as our dedicated FTP calculator with more duration options.
Seven rows
Z1–Z5c
Common coaching-style splits for endurance and threshold work.
Seven zones
Z1–Z7
Endurance through neuromuscular targets from estimated FTP.
Disclaimer
Trends > one number
Medications, arrhythmia, and heat illness change HR response—get professional guidance when unsure.
170 bpm average from a 20-minute test, protocol × 0.95 → LTHR ≈ 162 bpm with a full %LTHR zone chart in the calculator card.
In the lab, lactate threshold is identified with blood or ventilatory markers. In training, athletes use repeatable field tests so they can set zones without constant lab visits. This calculator applies widely taught scaling rules (for example, 95% of a 20-minute power average) and percentage-of-LTHR bands for heart rate. Numbers are rounded for readability. For more fitness and lifestyle tools, combine threshold planning with pacing and recovery calculators on the same hub.
Want more power-duration options? Open the cycling FTP power calculator.
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Suggested hashtags: #LactateThreshold #Cycling #Running #Endurance #Calculator