Lactate Threshold Formula
Lactate threshold (LT1 and LT2) formulas for endurance training.
Covers field test estimation, percent of VO2max, heart rate zones, and pace zone calculations.
Lactate Accumulation Concept
Below LT1 (about 2 mmol/L), the body clears lactate easily. Between LT1 and LT2 is the moderate training zone. Above LT2, accumulation outpaces clearance and fatigue sets in quickly.
FTP as LT2 Estimate (Cycling)
Functional Threshold Power is the cyclist equivalent of LT2 — it represents the highest power sustainable for approximately one hour.
LT2 Heart Rate Estimate
For trained athletes, lactate threshold heart rate typically falls in this range. Less trained individuals may find their LT2 at a lower percentage.
Variables
| Term | Meaning | Typical Value |
|---|---|---|
| LT1 | First lactate threshold (aerobic threshold) | ~2 mmol/L |
| LT2 | Second lactate threshold (anaerobic threshold) | ~4 mmol/L |
| OBLA | Onset of blood lactate accumulation | 4 mmol/L |
| FTP | Functional Threshold Power (cycling) | 95% of 20-min power |
Example 1 — Cycling FTP Test
A cyclist averages 310 W over a 20-minute all-out effort.
FTP ≈ 0.95 × 310
FTP ≈ 294 W — this is their estimated LT2 power
Example 2 — LT2 Heart Rate
A trained runner has a max HR of 190 bpm.
LT2 HR ≈ 0.85 × 190 to 0.92 × 190
LT2 HR ≈ 162–175 bpm — the threshold training zone
When to Use It
- Setting tempo and threshold workout paces
- Planning race pacing strategies for distances of 5K to marathon
- Measuring training adaptations over a season
- Identifying when to push harder versus stay easy
Key Notes
- Two thresholds: LT1 (aerobic threshold) is where lactate begins to rise above baseline (~2 mmol/L) — the upper limit of "all-day" aerobic effort. LT2 (anaerobic threshold / MLSS) is where lactate accumulation exceeds clearance (~4 mmol/L), sustainable for roughly 30–60 minutes.
- Field test estimate: LT2 power (cycling) ≈ 95% of 20-minute maximal power output. LT2 pace (running) ≈ recent 1-hour race pace, or approximately 30-second-per-mile slower than 10K race pace. These are validated approximations, not exact measurements.
- Heart rate at threshold: LT2 heart rate is typically 85–90% of HRmax, but varies significantly between individuals. HR-based estimates are less accurate than power-based ones because cardiac drift, temperature, and fatigue affect HR independently of lactate.
- Training at LT2 improves threshold: Regular "threshold training" at or slightly above LT2 intensity raises the power/pace at which lactate starts to accumulate — the primary adaptation responsible for improved endurance performance in trained athletes.
- Applications: Lactate threshold is used to set training zones, predict race performance, select pacing strategy, monitor fitness adaptation over a training block, and compare training responses across athletes in sports science research.