Lactate Threshold (LT1 and LT2)
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The exercise intensities at which blood lactate first rises above baseline (LT1) and then climbs sharply faster than it can be cleared (LT2) — key markers that divide training zones.
Detail
As exercise intensity rises, blood lactate concentration increases. Two inflection points matter for training:
- First lactate threshold (LT1): the intensity at which lactate begins to rise measurably above the resting baseline (often near ≈2 mmol/L). LT1 marks the boundary between light and moderate intensity and the upper limit of zone 2; below it, the body clears lactate about as fast as it is produced (see Zone 2 Training).
- Second lactate threshold (LT2): the intensity at which lactate production decisively outpaces clearance and accumulation accelerates (often near ≈4 mmol/L, sometimes called the maximal lactate steady state or "anaerobic threshold"). LT2 marks the ceiling of sustainable steady work and is the target of tempo/threshold training (see Tempo / Threshold Training).
These thresholds correspond closely to the first and second ventilatory thresholds (VT1, VT2; see Ventilatory Thresholds (VT1 and VT2)) and to the field-measured functional threshold power/pace (≈ LT2; see Critical Power & Functional Threshold Power (FTP)). They are the physiologically real borders that the percentage-based heart-rate zones only approximate (see Heart-Rate Zones (5-Zone Model)), and because they shift with fitness, threshold-based prescription is highly individualized.
Lactate is not merely a "fatigue waste product": it is a usable fuel and a normal product of glycolysis. The threshold concept is about the rate of accumulation relative to clearance, not a toxic byproduct (see Lactic Acid (Glycolytic) System). Training raises both thresholds, letting an athlete sustain a higher absolute pace before accumulation forces a slowdown.
Key facts
- LT1: lactate first rises above baseline (~2 mmol/L); boundary of light/moderate; top of zone 2.
- LT2: lactate production outpaces clearance (~4 mmol/L; maximal lactate steady state / "anaerobic threshold").
- LT1 ≈ VT1; LT2 ≈ VT2 ≈ functional threshold (FTP).
- These are the true zone borders that %HR zones approximate; they shift with fitness.
- Training raises both thresholds → higher sustainable pace/power.
Connections
- Ventilatory Thresholds (VT1 and VT2) — the breathing-based counterparts (VT1, VT2).
- Zone 2 Training — defined as work just below LT1.
- Tempo / Threshold Training — work at/just below LT2.
- Critical Power & Functional Threshold Power (FTP) — the field anchor near LT2.
- Lactic Acid (Glycolytic) System — the underlying glycolytic metabolism.
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Educational content only — not medical advice. Always consult a qualified professional for individualized guidance, especially around injury, pregnancy, or medical conditions.