What the two lactate breakpoints represent
Lactate threshold is not a single point but a pair of physiological inflections. The first (often called LT1 or the aerobic threshold) is where blood lactate first rises measurably above resting baseline, typically near 2 mmol/L in many testing conventions. The second (LT2, the anaerobic or maximal lactate steady state) is the highest intensity at which lactate production and clearance stay balanced, often discussed around 4 mmol/L, though the true value varies widely between individuals.
Below LT1 the body clears lactate easily and effort feels sustainable for hours. Between LT1 and LT2 sits the threshold zone, sustainable for tens of minutes. Above LT2 lactate accumulates faster than it can be cleared and time to exhaustion shortens sharply.
Why thresholds matter more than VO2max for endurance pacing
Two athletes with identical VO2max can perform very differently because the one who can hold a higher fraction of that ceiling without accumulating lactate sustains race pace longer. This is why threshold velocity or power often predicts endurance results better than VO2max alone.
The fixed 2 and 4 mmol/L cutoffs are conventions, not laws; lab testing or field tests individualize them. This is general educational information about exercise physiology, not training or medical advice; consult a qualified coach or clinician before structuring training around test numbers.