Do you want to improve in running, cycling or triathlon without wearing yourself out in every workout? The anaerobic threshold is one of the most useful physiological numbers for giving your preparation structure. Understanding where that limit sits, knowing how to measure it without laboratory equipment and learning to push it back gradually can transform the way you train. Here is everything you need to get started.
How to find and improve your anaerobic threshold (VT2) in 3 steps
Reading time: ~6 min
Contents
- What the anaerobic threshold actually is
- Step 1: measure your anaerobic threshold without a laboratory
- Step 2: understand why you work at lactate threshold
- Step 3: structure your threshold workouts
- FAQ
- The anaerobic threshold: a lasting lever for progress
What the anaerobic threshold actually is
The definition, plainly
As you gradually increase your effort, your body produces lactate (often called lactic acid). Up to a certain intensity, the body clears that lactate as fast as it makes it. Beyond a precise point, production outruns clearance: that break point is what we call the lactate threshold.
Biochemically, that threshold has historically corresponded to a blood lactate concentration of about 4 millimoles per litre.
There is another threshold, the second ventilatory threshold (VT2), which is the moment your breathing runs away: after rising gradually with the effort, at some point the volume of gas exchanged rises faster than the intensity of the effort does.
The lactate threshold and VT2 are often very close, and people tend to treat them as two ways of measuring the same thing. That is what we are going to do in the rest of this article, for simplicity. It is also known as the anaerobic threshold.
In practice, VT2 is the maximum intensity you can hold for about an hour before muscular fatigue forces you to slow down.
In cycling, this threshold is often equated with FTP (Functional Threshold Power), meaning the maximum power you can hold for 20 to 60 minutes depending on your level.
VT1 and VT2, two distinct thresholds
Exercise physiology actually distinguishes two successive break points. The first threshold (VT1, or aerobic threshold) corresponds to a sustained but comfortable effort, where your breathing stays regular. You can still talk in full sentences. It is the upper limit of the easy endurance zone, which you can hold for several hours.
The second threshold (VT2, or anaerobic threshold) marks the border between an effort that is mainly aerobic and one where the anaerobic contribution rises sharply. Breathing becomes difficult, the muscles heat up, and you can no longer hold a normal conversation. This is the zone of sustained effort, typical of a 10 km or, for the best runners, of a half marathon run at race pace.
A simple way to tell them apart: if you can chat without forcing it, you are below VT1. If you lose your breath trying to speak, you are approaching the anaerobic threshold.
Step 1: measure your anaerobic threshold without a laboratory
Field tests anyone can do
The laboratory test (measuring blood lactate or analysing gas exchange) remains the reference method, but it is expensive and hard to get. Fortunately several field protocols give a reliable estimate.
The 20-minute test is the most widely used in running. Warm up properly, then run for 20 minutes at a sustained pace you think you could hold for an hour. If, towards the end, you feel a growing struggle to breathe and your legs start to “burn”, you are close to your anaerobic threshold. The heart rate recorded at the end of that effort corresponds to your VT2.
The step test is another option: speed up every 3 minutes and note your heart rate at each step (better still, analyse the workout with Slek afterwards). The effort has to stay constant for 3 minutes to give your heart rate time to settle. The first noticeable breathlessness gives you an approximation of VT1 (about 75% of your maximum heart rate). The moment your breathing becomes genuinely hard to control corresponds to your VT2 (between 85 and 90% of max HR).
Using maximum heart rate as a reference
If you know your maximum heart rate, you can place your thresholds directly.
From there, your anaerobic threshold sits between 85 and 90% of that value, which also corresponds to roughly 85 to 90% of your VO2max speed.
| Reference | VT1 (aerobic threshold) | VT2 (anaerobic threshold) |
|---|---|---|
| % max HR | About 75% | 85 to 90% |
| % VO2max speed | About 75 to 80% | 85 to 90% |
| Talk test | Conversation possible | Speaking is hard |
| Perceived effort (RPE) | 5 to 6 out of 10 | 7 to 8 out of 10 |
| Running example | A sustained easy run | 10 km or half marathon pace depending on level |
Step 2: understand why you work at lactate threshold
Concrete metabolic benefits
Training at anaerobic threshold intensity teaches your body to reuse the lactate it produces as an energy source. In other words, you improve your metabolic efficiency in that effort zone. Over time your threshold moves towards higher intensities: you can run or ride faster at the same heart rate.
This kind of training also improves cardiovascular factors. At VT2 intensity, heart rate is high without being maximal, and stroke volume (the amount of blood pushed out with each beat) is large. It is a particularly effective zone for developing cardiac power.
A decisive lever in endurance sports
The anaerobic threshold is often called the fatigue threshold: pushing it back lets you hold higher paces for longer. For a 10 km runner, a triathlete or a gran fondo cyclist, it is a performance factor directly tied to the final result.
In practice, if your anaerobic threshold is low, you “go into the red” as soon as you speed up a little. Develop it, and you can hold a competitive pace for the whole event without emptying yourself early.
Step 3: structure your threshold workouts
The principle of dosing (the 80/20 rule)
Before going into the workouts, one essential point: threshold training should not make up the majority of your volume. The 80/20 rule recommends devoting 80% of your training time to the low zones (aerobic endurance, below VT1), and only 20% to the high ones (around and above VT2). One or two threshold workouts a week is a reasonable frequency for most endurance athletes.
Running workout examples
The classic threshold workout is intervals of 5 to 10 minutes at the pace corresponding to your VT2 (between your 10 km pace and your half marathon pace), repeated 3 to 5 times with 2 to 3 minutes of active recovery between each repetition.
The “over/under” workout is more demanding but very effective: alternate 1 minute slightly above threshold (about 8 out of 10 perceived difficulty) and 2 minutes slightly below (about 6 out of 10), in blocks of 6 minutes repeated 2 to 3 times. This method teaches the body to handle fluctuations around the lactate break point.
Cycling workout examples
On the bike, zone 4 workouts (often between 92 and 96% of max HR) are the reference format. For example: 4 sets of 6 minutes in zone 4, with 10 minutes of recovery in zones 1 and 2 between each set.
For cyclists training with a power meter, over/unders are structured around FTP: 3 to 4 sets of 5 repetitions alternating 1 minute at 110% of FTP and 1 minute at 90% of FTP, with 3 minutes of recovery between sets. A longer variation is 3 to 4 blocks of 6 minutes at 110% of FTP followed by 6 minutes of active recovery.
The mistakes to avoid
Two traps come up regularly among athletes working on their anaerobic threshold.
The first is spending too much time in the “grey zone”, meaning a moderate intensity that tires you without genuinely developing the threshold or allowing effective recovery. That intermediate zone should be only about 10% of total training volume.
The second is stacking threshold workouts without leaving the body enough time to recover. Efforts at VT2 ask a great deal of the cardiovascular and muscular systems. Running these workouts back to back without respecting the recovery phases quickly leads to overtraining.
FAQ
What is the difference between aerobic and anaerobic threshold?
The aerobic threshold (VT1) is the first break in the ventilatory and lactate kinetics. It is the intensity at which the effort starts to call on the anaerobic pathways noticeably, while staying very manageable. The anaerobic threshold (VT2) is the second break: past that point, lactate accumulates rapidly and fatigue sets in. In practice, VT1 corresponds to a sustained but comfortable easy run, and VT2 to a racing or climbing pace you cannot hold for more than 20 to 60 minutes.
Can you improve your anaerobic threshold without going to a laboratory?
Yes, entirely. Field tests (the 20-minute test, the step test, an estimate from max HR) locate your VT2 precisely enough to structure your training. It is worth repeating those tests every 6 to 8 weeks so you can adjust the zones as you improve. Modern heart rate watches also offer automatic estimates from the data they collect during your workouts, though beware of basing your whole training on an opaque indicator.
How long before you see progress from threshold work?
The first metabolic and cardiovascular adaptations generally appear after 4 to 6 weeks of structured training, at one or two threshold workouts a week. More marked progress (a significant shift in the threshold, better racing paces) shows up over blocks of 8 to 12 weeks. Consistency, gradual progression and respecting the recovery phases are the most decisive factors.
The anaerobic threshold: a lasting lever for progress
The anaerobic threshold is a concrete physiological boundary, measurable and, above all, trainable. By understanding the difference between VT1 and VT2, testing your lactate threshold regularly with simple field protocols, and structuring your workouts around the 80/20 principle, you have a powerful lever for lasting progress in endurance sport. Preparing a triathlon, a trail race or a season of sportives, working intelligently around this intensity zone is one of the most profitable decisions you can make. To go further in structuring your training, see what Slek can do.
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