Lactate Threshold Calculator

The lactate threshold (LT) is the exercise intensity at which lactate begins to accumulate in the blood faster than it can be cleared. Below LT, you can sustain effort indefinitely. Above LT, lactate builds up rapidly, causing fatigue. LT corresponds to roughly 85-90% of maximal heart rate in trained athletes.

Field tests estimate LT from a 30-60 minute maximal time trial: average heart rate over the last 20 minutes approximates LT heart rate. Alternatively, the calculator uses 85-90% of maximum heart rate as a proxy for LT in untrained to moderately trained individuals.

LT is the strongest single predictor of endurance performance, more so than VO2 max in trained athletes. Training at or just below LT pace improves the threshold, allowing you to race faster before fatigue. Threshold workouts (tempo runs, cruise intervals) specifically target this adaptation.

LT1 (aerobic threshold) is where lactate first begins to rise above resting baseline, roughly 65-75% of max HR. LT2 (anaerobic threshold or onset of blood lactate accumulation) is where lactate rises steeply - this is what most athletes refer to as lactate threshold. LT2 corresponds to 'comfortably hard' pace.

Heart rate at LT varies between individuals. The 85% of max HR estimate is a population average for moderately trained individuals. Actual LT heart rate can range from 80-95% of max HR. For precise measurement, a lactate step test at a sports physiology laboratory is the gold standard.