Lactate Threshold & LTHR Calculator
Estimate your lactate threshold heart rate (LTHR) and threshold pace from a 30-minute time trial or a recent 5K/10K race result. Get five training zones anchored on your personal threshold.
Lactate threshold (LT) is the exercise intensity at which lactate accumulates in the blood faster than the body can clear it — the highest effort you can sustain for 30–60 minutes. The lactate threshold heart rate (LTHR) is the corresponding heart rate.
30-minute time trial (most accurate field test): Run solo at maximum sustainable effort for 30 minutes. Record average heart rate for the final 20 minutes only — the first 10 minutes are excluded because cardiac output hasn’t reached steady state. That average is your estimated LTHR. Average pace over the full 30 minutes is your threshold pace.
Race result (quick estimate): Your 10K race pace is a widely used threshold-pace proxy (Friel, Daniels), accurate to within ~3% for well-rested race efforts. A 5K pace is roughly 5% faster than threshold, so we adjust accordingly. LTHR cannot be derived from race data alone.
Training zones are set as percentages of LTHR (heart rate) or threshold pace speed (pace), following the Friel/Coggan 5-zone model used by most endurance coaches.
Your lactate threshold is not static. A block of threshold work can shift your LT pace by 10–20 sec/km in 6–8 weeks — faster than most athletes re-test. If you keep training to a stale threshold, easy days drift too hard and tempo days may be undercooked.
Field tests also have real measurement error: a 30-minute TT pace can vary by 3–5% on different days depending on fatigue, weather, and motivation. Most athletes overestimate performance on a good day and underestimate on a bad one. LTHR measured from a race is even less precise if the race wasn’t run at a true threshold effort from the start.
Vertical re-estimates your threshold continuously from every run — detecting shifts in your HR-to-pace response and updating your zones before they drift. Your threshold isn’t a number you test once; it’s a signal your training data reveals session by session.
Start free →Looking for VDOT-based training paces from a race result? Training Pace Calculator →