Threshold Heart Rate Calculator
Estimate your lactate threshold heart rate (LTHR) and build Friel’s training zones around it — the anchor point for tempo and threshold work.
How it works
Estimated LTHR ≈ 0.88 × max HR · Friel zones set as % of LTHR (Z4 threshold = 95–99%)
Lactate threshold heart rate is the pulse you can hold for roughly an hour of hard, sustainable effort, and it is a better training anchor than max HR because it tracks your actual fitness. A 30-minute solo time trial — averaging the heart rate of the final 20 minutes — gives the most reliable LTHR; absent that, about 88% of max is a serviceable estimate. Joe Friel’s zones then hang off that number.
Worked example
With a 190 bpm max and no field test, estimated LTHR = 0.88 × 190 ≈ 167 bpm. Threshold (Zone 4) runs at 95–99% of that, about 159–166 bpm, while easy Zone 2 sits below roughly 149 bpm.
Frequently asked questions
How do I test my LTHR properly?
Warm up, then run or ride an all-out 30-minute time trial alone. Record the average heart rate of only the last 20 minutes — that value is your LTHR. Testing solo matters, because racing others inflates the number.
Why base zones on LTHR instead of max HR?
Max HR is fixed and hard to measure safely, and it does not move as you get fitter. LTHR shifts with training, so zones built on it stay meaningful and are easier to test yourself.
Is 88% of max always right?
No — it is only an estimate and varies from about 85% to 92% between individuals. Use it to get started, then replace it with a measured LTHR as soon as you can.
Related calculators
Heart-rate and body-weight estimates are educational, based on population formulas — confirm with a coach or clinician before hard training, especially if you have any cardiac risk.