Lactate threshold
/ ˈlæk.teɪt ˈθrɛʃ.hoʊld / · noun
Also: LT, anaerobic threshold, maximal lactate steady state, MLSS
The exercise intensity at which blood lactate concentration begins to rise exponentially above resting baseline. Below the threshold, lactate is cleared as fast as it is produced; above it, lactate accumulates faster than the body can buffer or oxidize it, and effort becomes time-limited. For trained endurance athletes, the lactate threshold typically sits at 80-90% of VO2max.
Two thresholds, often conflated
- LT1 (aerobic threshold): the first detectable rise above baseline lactate (typically 2 mmol/L). Below this, fat is the dominant fuel; effort feels easy and is sustainable for hours.
- LT2 (anaerobic threshold / MLSS): the highest intensity at which blood lactate stabilizes (typically 4 mmol/L). Above this, lactate accumulates exponentially; sustainable for 30-60 minutes.
The "anaerobic threshold" terminology is technically misleading: energy production at LT2 is still primarily aerobic. The term persists because LT2 marks the practical ceiling for steady-state racing.
Why it matters
For events lasting 30-90 minutes (HYROX, 10K running, half-marathon), LT2 is more predictive of performance than VO2max. Two athletes with identical VO2max but different LT2 will finish minutes apart at race distance. The athlete who races at 90% of VO2max sustainably outperforms the one who can only sustain 80%.
How to measure it
- Lab graded test: incremental running or cycling test with finger-prick blood draws at each stage. Most accurate.
- Field test (Conconi / 30-minute TT): the average heart rate of a 30-minute time trial approximates LT2 within 2-5 bpm.
- Talk test: LT1 = the highest intensity at which you can speak in full sentences; LT2 = the intensity at which you can speak only in 3-4 word phrases.
- Wearable lactate meters: finger-prick devices ($150-$300) allow self-testing. Useful for tracking but require careful warm-up protocols.
Training to raise the threshold
- Threshold intervals (LT2): 2-3 × 8-15 minutes at goal threshold pace, 2-min rest. The most direct stimulus.
- Sub-threshold (sweet-spot): 2-3 × 20-30 minutes at 88-93% of threshold heart rate. Lower stress, higher volume; popular for hybrid athletes who also lift.
- Z2 base (LT1): 80% of weekly aerobic time below LT1. The most dose-dependent variable; raises both LT1 and LT2 over months.
Limits
Threshold percentage of VO2max is more trainable than VO2max itself. An untrained athlete might race at 65% VO2max; an elite endurance athlete races at 85-90%. The difference is decades of aerobic volume: not interval intensity. Hybrid athletes who balance lifting with running typically max out around 80-85% in their primary endurance modality.