How to Find Your Lactate Threshold

The most practical way to find your lactate threshold is a 30-minute solo time trial. Warm up, then ride or run as hard as you can sustain for 30 minutes. Your average heart rate over the final 20 minutes is your lactate-threshold heart rate (LTHR), and that one number sets every training zone. Below: what the threshold is, why it is the best anchor, and how to find it in pace or power instead.

What is lactate threshold?

Your muscles always produce lactate. At easy intensities your body clears it as fast as you make it. As you go harder, production outpaces clearance and lactate accumulates in the blood. The intensity where that happens is your lactate threshold.

There are two landmarks. LT1, the aerobic threshold, is where blood lactate first rises above resting baseline, typically around 2 mmol/L. It marks the top of easy, conversational pace. LT2, the anaerobic threshold (also called maximal lactate steady state), is where lactate climbs steeply and can no longer be held stable, typically around 4 mmol/L. LT2 is the ceiling most threshold tests are chasing.

The two landmarks split training into three intensities: easy below LT1, the gray zone between, and hard at or above LT2.

Why is threshold the best anchor for training zones?

Max heart rate is a poor anchor. It is hard to measure safely, barely responds to training, and the same percentage means different things for two athletes with the same max.

Threshold is a physiological event you can feel, and it shifts as you get fitter. Two runners with identical max HR can have very different thresholds. Anchoring zones to threshold puts the boundaries where your physiology changes and lets them move up with fitness. That is why Friel's HR zones and Coggan's power zones are built on threshold. Compare the systems on the heart-rate zone models page.

How do you do the 30-minute LTHR field test?

Coach Joe Friel's field test estimates LT2 heart rate.

1. Warm up 10 to 15 minutes easy with a few short pickups.
2. Go alone. Racing or drafting skews effort and heart rate.
3. Time-trial 30 minutes at the hardest pace you can hold evenly. Do not sprint the start.
4. Start the lap at the 10-minute mark and record your average heart rate for the final 20 minutes.

That average is your LTHR. The first 10 minutes are ignored because heart rate lags effort early on.

How the bands are derived is on the LTHR zones page.

How do you find your threshold pace from a race?

A recent all-out race already contains the answer. The Daniels-Gilbert VDOT system converts race time and distance into a fitness score, then derives threshold (tempo), easy and interval paces from it. A recent 5K, 10K or half marathon works. Enter it in the VDOT calculator.

How do you find threshold power on the bike?

Cyclists anchor to power because it responds instantly and ignores heat, fatigue and caffeine. The common test is a 20-minute time trial: average power × 0.95 estimates Functional Threshold Power (FTP), roughly the power you could hold for an hour.

Critical Power is more robust. It uses two or three all-out efforts of different durations (for example 3 and 12 minutes) to model the highest power you can sustain aerobically, and it tracks LT2 more reliably than a single 20-minute test. Model it on the Critical Power page.

Heart rate, pace, or power: which threshold should you use?

Use the metric that matches your sport and equipment. The three will not line up perfectly.

• Power reacts immediately and ignores conditions. Best when you have a meter.
• Pace is direct on flat ground but lies on hills, in wind and on trails.
• Heart rate is available to everyone and reflects internal strain, but it drifts upward over long efforts, lags sudden changes, and responds to heat, sleep and caffeine.

Many athletes set workout targets by power or pace and watch heart rate as a sanity check.

What are the caveats?

The "4 mmol/L" definition of LT2 is a population average. Individual thresholds range roughly from 2.5 to 6 mmol/L. Field tests can be off if you pace badly, test on a bad day, or are new to hard efforts.

Heat, altitude, dehydration, illness and poor sleep all move your numbers, so test in the conditions you train in. Retest every 6 to 8 weeks during a training block, because the threshold is supposed to move.

What about a lab test?

The gold standard is a graded lab test: increasing intensities with a small blood sample at each stage, lactate plotted against intensity. It is the only method that measures lactate directly, and it pins down LT1 and LT2 individually instead of assuming fixed values. Worth doing once if you have access. For most athletes the field tests above are close enough.

Sources

• Joe Friel, the 30-minute time-trial method for LTHR and the zones derived from it
• Jack Daniels and Jimmy Gilbert, the VDOT system for threshold and training paces