Lactate Test: Find Your Anaerobic Threshold

Training plans stand or fall with intensity control — and intensity control stands or falls with the anaerobic threshold. Estimate it 10 watts or 15 heartbeats too high and every threshold run becomes an interval session, every easy run becomes half-marathon race pace. The lactate test is the most accurate tool for measuring this threshold: in the lab as a step test with blood sampling, or outdoors as a field test. This article explains both approaches, how to read the lactate curve, and the mistakes even experienced athletes make.

What is the anaerobic threshold?

Every effort produces lactate in the muscles — an intermediate product of energy release from carbohydrates. Lactate is not waste but a valuable fuel, recycled by the heart, slow-twitch fibres and even the brain. As long as production and clearance are balanced, metabolism stays stable. That tipping point is the anaerobic threshold, or more precisely the maximal lactate steady state (MLSS) — the highest workload at which blood lactate concentration remains constant over time.

Above the threshold, lactate accumulates, muscle pH drops and fatigue becomes inevitable. In trained endurance athletes the threshold typically sits at 80–90% of maximum heart rate, and it is the best single predictor of endurance performance — more telling than VO2max, because it describes the pace you can actually sustain. Two athletes with identical VO2max values can finish an hour apart if one tips into the red at 90% of maximum capacity and the other at 75%. If you want to dig into the terminology, the Peakora glossary defines lactate, thresholds and training zones.

Two thresholds matter:

• Aerobic threshold (LT1, ~2 mmol/l): The point where lactate rises above baseline. It marks the upper limit of easy aerobic pace — the foundation of 80/20 training.
• Anaerobic threshold (LT2, individually 3–6 mmol/l): The MLSS tipping point. It defines the pace for threshold runs and largely determines race pace from 10K to the marathon.

The lab lactate test: how the step test works

Classic performance diagnostics take place on a treadmill or cycle ergometer following a standardised protocol:

• Stage duration: 3 to 5 minutes per stage — shorter stages underestimate the threshold because lactate lags behind pace.
• Increments: For running, typically 1 km/h per stage (starting at 8–10 km/h); on the bike, 20–40 watts. The starting load should sit well below the aerobic threshold.
• Measurement: A brief stop after each stage, a drop of blood from the earlobe or fingertip, analysed in a lactate meter. Heart rate and usually perceived exertion (Borg scale) are recorded in parallel.
• Termination: The test runs to submaximal or maximal exhaustion — typically 6 to 9 stages.

Many labs combine the test with spiroergometry (gas analysis), which adds ventilatory thresholds and actual maximal oxygen uptake — useful, but not strictly necessary for zone setting. Expect to pay 80 to 200 euros depending on scope. Bring your usual running shoes if the lab uses a regular treadmill, and avoid hard sessions and caffeine for 24 hours beforehand.

The field test: finding your threshold without a lab

No lab nearby or no budget? Field tests deliver surprisingly solid values if you execute them with discipline. Three protocols have proven themselves:

• 30-minute time trial (after Joe Friel): After a thorough warm-up, run or ride 30 minutes as hard as you can sustain evenly — do not overpace the first 5 minutes. Your average heart rate over the last 20 minutes is your threshold heart rate; the average speed is your threshold pace. Accuracy compared to a lab test: usually within ±3 beats.
• 20-minute test with correction factor: 20 minutes all-out, then multiply average power or pace by 0.95 — the result approximates your one-hour threshold performance. On the bike this is the standard FTP protocol; details in the article on power training and the FTP test.
• Step field test with a lactate meter: If you own a consumer lactate meter (from about 200 euros, test strips roughly 2 euros per reading), you can replicate the lab protocol on a 400-m track: 3–5 stages of 4 minutes with 30–60 second stops for sampling. A second person to handle sampling and logging is almost mandatory.

The Conconi test (reading a heart-rate deflection point from a step test without lactate measurement) should be avoided: the method is considered scientifically disproven because the deflection simply does not exist in a large share of athletes.

Analysis: from lactate curve to training zones

The raw data of the step test — lactate value and heart rate per stage — form the lactate performance curve. You read three things from it:

• Baseline and rise: The point where the curve breaks away from the flat baseline is the aerobic threshold (LT1), often defined as the first clear rise of at least 0.4 mmol/l.
• The anaerobic threshold (LT2): The fixed 4 mmol mark is only an approximation. More precise is the Dmax method: draw a straight line between the first and last data points of the curve and find the point with the greatest perpendicular distance from that line. That is your individual threshold — for ambitious runners often between 3 and 5 mmol/l, not exactly 4.
• The curve shape: A flat curve shifted to the right shows good fat metabolism and a broad aerobic base. A curve that climbs steeply early reveals a base deficit — the answer is more easy volume, not more speed work.

From LT1 and LT2 you derive the zones for your heart rate zone training: easy aerobic work ends at LT1, the threshold band sits tightly around LT2 (about ±3 beats), intervals lie above. An example: with LT2 at 168 bpm and 4:20 min/km, you run threshold blocks at 165–171 bpm or 4:15–4:25 min/km — no faster, otherwise threshold work becomes interval work at double the recovery cost. Race paces follow from this: the marathon sits at roughly 95–98%, the half marathon at 98–102% of threshold heart rate — background in the article on marathon pacing strategy.

The most common lactate test mistakes

• Stages too short. Under 3 minutes per stage, lactate lags behind the workload — the measured threshold comes out systematically too high and every derived zone is too fast.
• Hard training the day before. Residual fatigue and elevated baseline lactate distort the curve. Only easy running or rest for 24–48 hours before the test.
• Caffeine and fuelling errors. Caffeine on test day can shift heart rate and perceived exertion; a heavy meal within the last 2–3 hours does the same. Standardise the conditions identically for every test — otherwise you are comparing apples with oranges.
• Overpacing the field test. The 30-minute test is not a 5K race. If you start the first 10 minutes 20 seconds above threshold pace, you collapse late and measure your pain tolerance instead of your threshold.
• Test once, ride forever. The threshold is not a fixed value — it rises noticeably during a build-up, by 5–10 watts or several beats per season phase. Training with twelve-month-old zones means training past reality.

How Peakora uses your threshold

Peakora works with your real performance data instead of age-based estimation formulas. Enter your measured threshold heart rate or threshold pace, and the training plan places threshold runs, intervals and easy sessions in exactly the right ranges. Continuous form analysis via the Training Stress Score also shows whether your load matches your recovery — so you can spot progress between two tests without going back to the lab every time: if your heart rate drops at a familiar pace, your threshold has improved and a new field test is worthwhile. Adaptive planning then recalibrates the intensities accordingly.

Frequently asked questions about lactate testing