In this article, you will learn what the anaerobic threshold (AnT) is, how to evaluate it, which tests to perform, and how to train to improve it. You will discover different training methods to enhance your anaerobic threshold. The anaerobic threshold is one of the key factors that determine performance in long-distance runners, alongside maximal oxygen uptake, the aerobic threshold, and running economy.

Although training to improve maximal oxygen uptake (VO2max) through intervals is more popular, the potential for improvement is largely genetically limited. On the other hand, the anaerobic threshold is much more trainable, making it crucial to know how to calculate and train it to improve your running.

What Is the Anaerobic Threshold?

The anaerobic threshold (AT) is the maximum intensity that we can sustain over a long period, typically around one hour, without lactate accumulating in the blood.

It represents a transition zone between an intermediate intensity (where it is challenging to maintain pace but can be prolonged for several hours) and intensities where even a slight increase in pace causes fatigue to rise exponentially. Below the anaerobic threshold, as we increase the pace, fatigue gradually builds up. However, when we exceed this threshold, a small increase in running pace results in a much greater surge in perceived fatigue. This transition zone is what we know as the anaerobic threshold, and it separates the moderate-intensity zone from the high-intensity zone.

The anaerobic threshold, or AnT, is also known by other terms such as Functional Threshold Power (FTP), Critical Speed (CS), Lactate Threshold 2 (LT2), or Ventilatory Threshold 2 (VT2).

All these terms refer to what we understand as the anaerobic threshold or the maximum speed or power we can sustain for about an hour.

Anaerobic Threshold and the Absence of Oxygen

Before we continue discussing the anaerobic threshold, I’d like to dispel a common myth. Anaerobic does not mean the absence of oxygen.

The anaerobic threshold represents a pace that you can sustain for up to an hour—do you think you could go an hour without using oxygen or without breathing? Of course not.

Even in a 50-meter sprint, metabolic pathways that utilize oxygen will still be active.

How to Calculate the Anaerobic Threshold in Running?

There are different tests to evaluate or calculate the anaerobic threshold in running. Some methods are more accurate, while others have a larger margin of error, but each has its pros and cons.

Laboratory Test with Gas Analyzer and Anaerobic Threshold

The most accurate way to calculate the anaerobic threshold is by performing a laboratory test with a gas analyzer. Today, portable gas analyzers can be used for running on a track.

However, a portable gas analyzer is typically only available in research universities or elite clubs, making it difficult to access.

For most people, the most common approach is to perform a maximal test in a sports laboratory, running on a treadmill.

With a gas analyzer (a mask placed over the face), we can measure the amount of oxygen inhaled with each breath and the amount of carbon dioxide exhaled.

During the test, you’ll undergo an incremental protocol where the running speed is increased at regular intervals. As speed increases, your breathing will become more intense because you need to take in more oxygen to generate more energy and run faster.

Therefore, oxygen and carbon dioxide levels will rise as your running speed increases. At the beginning, during low intensities, the rise in oxygen and carbon dioxide will occur in parallel, but at a certain point, the line representing oxygen levels and the line representing carbon dioxide levels will intersect.

This crossing point indicates the intensity at the anaerobic threshold.

If the test protocol is correct, evaluating with a gas analyzer is the most reliable method.

The main challenge is that it’s difficult for most people to undergo multiple stress tests in a year. Therefore, we can opt for other methods that, while less precise, are more practical.

Lactate Test and Anaerobic Threshold

The next most accurate and cost-effective method after a stress test is a lactate test.

Similar to the previous method, you will perform an incremental test where you sustain each speed for 2-4 minutes. My advice is to hold each speed for 3 minutes to allow lactate levels in the blood and heart rate to stabilize properly.

At the end of each 3-minute interval, a small prick is made on the ear or fingertip (similar to a glucose test). With a drop of blood, a lactate analyzer can measure the concentration of lactate in the blood at that intensity or pace.

Here are the two most commonly used lactate analyzers that I recommend if you’re considering purchasing one: the Lactate Pro 2 Analyzer and the Lactate Plus Analyzer.

Lactate is an indicator of the level of fatigue (not the cause, just an indicator) that an athlete is experiencing at a given pace.

The faster we run, the greater the fatigue, and the higher the lactate concentration in the blood.

Our body reuses lactate to produce more energy through the Krebs cycle. For this reason, at very low intensities, the reuse of lactate for energy is equal to or greater than the lactate being produced. Therefore, during the initial stages of the incremental lactate test, lactate concentration will not rise.

Gradually, as we increase speed, lactate production will exceed reuse, causing its concentration in the blood to rise.

When blood lactate concentration reaches a value of 4 mmol, this determines the anaerobic threshold.

This method for determining the anaerobic threshold is more practical than a stress test and can be performed more easily on a running track, but not everyone has access to a lactate analyzer.

Field Test: 10-15km and Anaerobic Threshold

Finally, of the three tests, this one is the least precise but the most practical. In elite runners, precision is crucial for training, but for recreational runners, such precision isn’t always necessary.

For most runners, a margin of error of 5 seconds per kilometer up or down is acceptable. As long as the same test is consistently used, there won’t be any issues.

The anaerobic threshold test I recommend for its simplicity (and the one we use with most of our athletes) is a 10 or 15km test run at the maximum intensity you can maintain over that distance.

As mentioned earlier, the anaerobic threshold corresponds to a running intensity that you can sustain for about one hour. Therefore, depending on your level, you will use either a 10 or 15km test to determine your anaerobic threshold.

My advice: If you can run 10km faster than 4:00 min/km, use the 15km distance. If you cannot run 10km faster than 4:00 min/km, use the 10km distance to measure your AT.

The average speed, power, or heart rate maintained during this all-out effort will determine your anaerobic threshold intensity.

It doesn’t matter if you complete the distance in 52 minutes, 57 minutes, or 1 hour and 3 minutes; the average speed is your anaerobic threshold. Always use the same distance and course for the test if possible.

There’s no issue with using competitions of this distance to evaluate your anaerobic threshold. This will help you push yourself harder and produce more reliable data.

Although not as exact, the great advantage of this method for determining the anaerobic threshold is that it requires no special equipment—just running and your watch. Anyone can do it.

How to Train the Anaerobic Threshold in Running?

Once we know our anaerobic threshold speed and have established our training zones based on the previous tests or a combination of the anaerobic threshold test and a MAS test, we can start training to improve our AnT.

There are different training methods to enhance the anaerobic threshold:

• 90% MAS Intervals and Anaerobic Threshold: The first method I recommend to improve the anaerobic threshold is to perform intervals at maximal oxygen uptake speed or maximal aerobic speed (MAS).

  Performing intervals at VO2max speeds will primarily improve VO2max, but it will also enhance the anaerobic threshold, especially in less experienced or lower-level runners.

  Long intervals at 90% of VO2max or 90% of MAS will produce improvements in both VO2max and the anaerobic threshold. However, if you increase the intensity and approach 100%, 110%, or 120% of VO2max, you’ll improve the anaerobic threshold much less and VO2max much more. So, if your primary goal is to improve the anaerobic threshold, train by performing long intervals at 90% VAM.

  Training Example: 4×5 minutes at 90% MAS (with 4 minutes of easy recovery).

• Fartlek Training and Anaerobic Threshold: The most well-known training method for improving the anaerobic threshold is the Fartlek method.

  Fartlek training is widely known for its popularity in the training of African long-distance runners.

  During the workout, you’ll alternate periods of time running at anaerobic threshold intensity (the intensity at which you ran the 10 or 15km test) with periods of easy running.

  The recoveries between each work period will be active.

  Training Example: 40 minutes alternating 2 minutes at anaerobic threshold speed with 1 minute easy. You can then progress week by week with 3-1, 4-1, 5-1, etc.

• Long Anaerobic Threshold Intervals: Another training method is long intervals at anaerobic threshold intensity. This is a segmented method with intervals lasting more than 5 minutes, up to 30 minutes continuously, always running at anaerobic threshold intensity.

  Personally, I like this method a lot for progressing after a few weeks of Fartlek training. It’s a tougher workout than Fartlek since it works the anaerobic threshold more extensively.

  Training Example: 5×5 minutes at AT (with 2’30» easy or walking recovery) or 3×10 minutes at AT (with 5′ easy recovery).

• Tempo Runs and Anaerobic Threshold: Finally, another method I like a lot, especially for long-distance runners both on the road and in trail running, is tempo runs.

  The anaerobic threshold is worked from a lower intensity with extensive intervals at tempo speed. The goal is to progress and sustain longer periods in the tempo zone, helping to push the anaerobic threshold upward.

  Training Example: 2×20 minutes at Tempo (with 6 minutes of easy recovery), 2×30 minutes (with 10 minutes of easy recovery), etc.

VO2max and Anaerobic Threshold Relationship

Most recreational runners have their anaerobic threshold around 80-85% of maximal aerobic speed (MAS). However, elite athletes can raise it to 95% of MAS.

Elite runners can sustain speeds very close to VO2max for extended periods.

As you can see, this percentage varies depending on your fitness level and how you’ve trained in recent years. Therefore, you shouldn’t determine your anaerobic threshold based on a MAS test but rather on an anaerobic threshold test like those discussed earlier.

What can greatly improve your training is knowing your exact percentage relationship between the anaerobic threshold and VO2max.

If you know your pace from one of the anaerobic threshold tests and your pace from a MAS test, you can easily calculate this percentage using a simple formula.

Example:

• VO2max Test = 18 km/h
• Anaerobic Threshold Test = 15 km/h
• If 100% MAS is 18 km/h
• X% Anaerobic Threshold is 15 km/h

(15*100)/18 = 83%

This calculation lets you determine the exact percentage of your anaerobic threshold relative to VO2max.

• If the percentage is above 85%, you need to improve your VO2max.
• If the percentage is below 85%, you need to raise your anaerobic threshold («you need more endurance»).

Is the Garmin Estimation of the Anaerobic Threshold Reliable?

Currently, the reality is that Garmin’s estimates are not very accurate overall. Therefore, it’s important to perform tests to calculate your anaerobic threshold rather than relying on your watch’s estimates for training.

Perform tests, calculate your individual training zones, and train based on these real zones to improve your running.

Anaerobic Threshold Heart Rate

If you want to train based on heart rate, you need to calculate your training zones based on heart rate.

As with determining anaerobic threshold pace, don’t use formulas to calculate your heart rate. The same tests we discussed for calculating pace can also be used to calculate heart rate at the anaerobic threshold.

The average heart rate during the 10 or 15km test will be your heart rate at the anaerobic threshold.

If you perform a lactate test, the average heart rate during the 3-minute stage of the lactate test that ends with 4 mmol will be your heart rate at the anaerobic threshold.

Finally, if you perform a stress test, the heart rate at the point where the oxygen and carbon dioxide lines cross will be your heart rate at the anaerobic threshold.

It’s important to use a chest strap heart rate monitor rather than a wrist-based one for these tests to ensure reliable heart rate values.

I hope you enjoyed this article.

If you’d like personal help to improve your running times and avoid injuries, you can tell me about your situation, and I’ll get in touch with you.

Best regards, and happy running!