Lactate Threshold Heart Rate Calculator

About this calculator

Lactate threshold heart rate (LTHR) is the heart rate at which lactate begins accumulating in the blood faster than the body can clear it — the point marking the boundary between sustainable aerobic effort and effort that fatigues quickly. Rather than requiring a lab blood-lactate test, the Joe Friel field-test protocol estimates it from a 30-minute solo time trial: average heart rate over the final 20 minutes closely approximates true LTHR.

Cyclists and runners use LTHR as the anchor for percentage-based heart-rate training zones — recovery, aerobic, tempo, threshold and anaerobic zones are each defined as a percentage range of LTHR rather than of maximum heart rate, which better reflects each athlete’s actual metabolic thresholds since two athletes with the same max HR can have very different LTHRs depending on fitness. Coaches retest LTHR periodically through a training cycle since it shifts as fitness improves.

This calculator takes your average heart rate from the final 20 minutes of a 30-minute time trial and returns your estimated LTHR along with the floor heart rate for each training zone.