Assessing your Aerobic and Anaerobic Thresholds is important for every mountain athlete because that is how you will correctly define your training intensities for different workouts. This article summarizes the current best-practice recommendations for aerobic self-assessment. Embedded throughout you will find links to older articles—for those who want more information about a specific method.

In our books Training for the New Alpinism and Training for the Uphill Athlete, as well on this site, we have devoted copious amounts of ink to helping athletes assess their fitness. In our efforts to cover all the angles, we’ve created a sprawling menu of options. Note that a similar article for assessing strength can be found here.


Why is assessing aerobic fitness so important that we’ve devoted all this effort to the subject? Simply put, because for any athletic event lasting longer than 2 minutes, the energy used for propulsion will come primarily from the aerobic metabolic pathway. The longer the event, the greater the dependence on the aerobic system for that energy. The more energy the aerobic metabolism can produce, and the faster it can do it, the longer an athlete can sustain a higher output. If this sounds like the definition of endurance, then you see why we place so much emphasis on aerobic assessment. (For a full discussion of the physiology of endurance, please read Chapter Two in Training for the Uphill Athlete.) We assess aerobic fitness for several purposes:
  • To determine appropriate aerobic training intensities. We do this by establishing intensity zones.
  • To determine whether or not an athlete has what is known as Aerobic Deficiency.
  • To allow for future checks on progress in aerobic capacity development.

Aerobic Self-Assessment: The Two Tests

Ideally you will perform two tests to get a picture of your personal aerobic response to different intensities. The first of these tests will pinpoint your Aerobic Threshold (AeT), which you reach at a rather low intensity. It can be determined by a number of different tests, each one discussed in the next section. The AeT sets the top of your Zone 2 (Z2) in a four-zone intensity scale, explained below. The second test, explained later, determines your Anaerobic Threshold (AnT, also called Lactate Threshold). The AnT/LT sets the top of your Z3


By anchoring this system to two important metabolic markers (AeT and AnT/LT), our zones do a good job of personalizing intensities to your unique metabolic response.

Zone 1

Heart Rate: AeT-20% to AeT-10%
Perceived Effort: Very easy to easy
Training Effect/Purpose: Aerobic conditioning
Metabolism: Aerobic-fat
Muscle Fiber Recruitment: ST
Training Method: Continuous 30 min to several hours

Zone 2

Heart Rate: AeT-10% to AeT
Perceived Effort: Moderate for those with high AeT, easy for those with low AeT
Training Effect/Purpose: Aerobic capacity, economy
Metabolism: Aerobic-fat dominates, maximum fat utilization
Muscle Fiber Recruitment: Most ST
Training Method: Continuous 30–90 min

Zone 3

Heart Rate: AeT to Lactate Threshold
Perceived Effort: Medium, fun-hard not exhausting
Training Effect/Purpose: Aerobic capacity, anaerobic capacity, lactate shuttle, economy
Metabolism: Glycolytic/anaerobic begins to dominate
Muscle Fiber Recruitment: All ST + some FT
Training Method: Interval 10–20 min, continuous to 60 min

Zone 4

Heart Rate: Lactate Threshold to LT to maxHR
Perceived Effort: Hard, max sustainable
Training Effect/Purpose: Maximal aerobic power, strength/speed endurance, economy, technique
Metabolism: Both aerobic and anaerobic capacities maxed out
Muscle Fiber Recruitment: All ST + most FT
Training Method: Interval 30 sec–8 min


Assessment of the aerobic system’s capacity for providing the needed energy can run from expensive laboratory tests to formulaic educated guess. In this section we’ll go through the various options for determining your AeT—from least to most expensive and least often to most often accurate—and discuss the pluses and minuses of each one.

MAF (Maximum Aerobic Function) Formula

Longtime endurance coach Phil Maffetone, most famous for coaching Mark Allen to six Kona Ironman Triathlon wins, came up with a simple formula to help people determine the heart rate that corresponds to the top of their aerobic base training zone. He did this through observations of many athletes. The MAF formula is simple to use but is based on a statistical average of a large population. Like any such result, it will give a statistically accurate answer when applied to the group but may or may not be accurate for any one individual. This means that if you apply this formula to 100 people it will have an 85–90 percent chance of predicting the AeT heart rate. The problem is that no individual can know if their personal prediction is correct.

The MAF formula is useful as a quick-and-dirty first stab. When compared to other tests, it tends to give a lower or more conservative AeT heart rate. This is a plus for most people who tend to do most of their aerobic base training at too high of an intensity.

The formula is simple: 180 minus your age. In order to semi-personalize it, you can use the following modifiers:

  • If you are recovering from a major illness or on significant medications, subtract 10 bpm from the result.
  • If you have been sick or injured and not training regularly, subtract 5 bpm from the result.
  • If you have been training consistently for two years with neither a) nor b), use the formula 180 – Age.
  • If you have been training consistently for more than two years and seeing improvements with neither a) nor b), add 5 bpm to the result.
MAF Formula Takeaways

Pluses: Simplicity.

Minuses: Besides the statistical shortcoming mentioned above, its narrow window for improvement—only +5 bpm—does not allow for the significant improvement that will come with training correctly. We have seen hundreds of athletes with ADS improve their aerobic threshold by 25–30 bpm over several months to a year.

Rating: 1–2 stars

Nose Breathing/Conversational Test

During the training of high-level endurance athletes, we noticed that the upper intensity limit of their ability to breathe through the nose or carry on a conversation in full sentences corresponded very well with tests for the AeT, such as a blood lactate test. This led us to propose in our earliest writings that we could substitute this simple noninvasive test for the more complex and expensive ones. 

All you need to do is close your mouth during a run and see if you can sustain breathing through your nose for several minutes at a time. Alternatively, see if you can carry on a conversation in medium-length full sentences.

We were not inventing anything new here. Exercise science uses the ventilatory markers rate and depth of breathing for this same purpose when doing a Gas Exchange Test (GET, discussed later), albeit with more accuracy. However, once we began to work with untrained and less well-trained climbers, we discovered that this nice, simple test no longer worked.

Nose Breathing Takeaways

Pluses: Simplicity and real-time feedback. If you have a long history of aerobic training, this test is likely to work for you. It can be used frequently for checks on improvement.

Minuses: If you’re not well trained aerobically, forget it and move on to the next test.

Rating: 0–3 stars

Heart Rate Drift Test

This test has become our go-to test for all our coached athletes. We like it so much that we include it as the first workout in every aerobically based training plan we offer. This article provides a full description of the test, so we won’t repeat the instructions here. We have found it to be well correlated (95+ percent) with Metabolic Efficiency Tests (the gold standard, explained later). 

Simple in concept, this test uses the principle that when you hold an aerobic pace (<AeT), your heart rate will remain nearly constant for as long as an hour. If your heart rate rises more than 5 percent at that steady pace, your starting heart rate was higher than AeT. If the heart rate drift is less than 5 percent, your starting heart rate was below AeT.  

Here is a video tutorial on how to properly conduct a Heart Rate Drift Test.

If you are conducting your Heart Rate Drift test on a running track, be sure to read this very short post to get the most accurate data.

Heart Rate Drift Takeaways

Pluses: The test is free and can be performed frequently to assess improvement.

Minuses: To get an accurate result, you need to follow the directions carefully. It is best performed on a treadmill. While not required, it is helpful to have a TrainingPeaks premium account.

Rating: 3 stars

Blood Lactate Concentration Test

With the advent of relatively cheap portable lactate monitors in the 1990s, it became possible for amateurs to conduct a test previously reserved for exercise science labs. We consider blood lactate testing to be useful for determining AeT if the stages are at least 3 minutes long. Many labs offer this type of test either alone or in conjunction with a Gas Exchange or Metabolic Efficiency Test. We’re not fans of using the blood lactate test to determine the anaerobic threshold (AnT). Read below to see why.

Links to longer articles on this test:
Blood Lactate Test Protocol: Tips and Tricks
Blood Lactate Testing: The Silver Standard

Blood Lactate Test Takeaways

Pluses: Accuracy in determining AeT. You can use this test to confirm the result of your heart rate drift test, and it gives a good idea of your dependence on carbs for fuel.

Minuses: Somewhat complex and fiddly to get good test samples. Expense is considerable, either in a lab or if you buy your own meter. Best if blood samples taken by a partner. Has a learning curve if you are self-testing rather than going to a lab.  Blood lactate is a proxy for intensity.  To determine AnT, why use a proxy when you can do a field performance test as explained below.

Rating: 2 stars

Gas Exchange Test and Metabolic Efficiency Test

A Gas Exchange Test (GET) is conducted in a laboratory and explained in more depth here. You use a treadmill, the angle of which is decided by the event you are training for—flatter for runners and steeper for climbers. You breathe through a mask connected to a sensitive device that measures many parameters, with rate and depth of breathing and the concentrations of oxygen and carbon dioxide in your expired breath being the principal ones of interest to us. 

While this type of test is considered the gold standard for determining AeT, we advise caution in selecting a lab. Not all labs conduct these tests in a manner that will give you the results you need. If the lab calls this test a maxVO2 (or VO2max) test, you will want to ask how long the warm-up is and how long each intensity stage is.

If you can find a lab that will conduct a Metabolic Efficiency Test (MET) then you might want to do this test.  An MET is a special type of GET using the same lab equipment but with a very different test protocol. With an MET, you will get a detailed analysis of your body’s preference for fuel type—carbs or fat—at each of the intensities you are tested at. This is useful and actionable data for all endurance athletes but especially for those taking part in events lasting several hours or more, and for high-altitude mountaineers.

Find out how to locate a testing lab here.

GET and MET Takeaways

Pluses: Accuracy, accuracy, accuracy. You get additional actionable information to guide training decisions. You can use this test result to confirm the result of your heart rate drift test.

Minuses: Expensive (typically $250–$400). Can be hard to find a good lab. The expense and logistical hassle make it less practical for follow-up tests.

Rating: 4 stars

1:1 Coaching

Personalized and direct accountability for your training


Your AnT or LT represents the highest power output, speed, or heart rate that you can sustain for an extended period (30–60 minutes). It is the definition of endurance, personalized to your physiology and activity. While lab tests (both GET and Lactate Tests) will often claim to pinpoint this, we advise skepticism. Such tests, of necessity, keep you at an intensity stage for only a few minutes before raising the intensity to the next level. The transitory nature of that protocol undermines the determination of what is supposed to be a long-duration threshold. Instead, we prefer the following field test.

Field Testing of Anaerobic or Lactate Threshold

For a full explanation, please read this article about how to conduct a DIY AnT test. Unlike the AeT test, which is conducted at low to moderate intensity, this test requires you to go as hard as you can for between 30 and 60 minutes (appropriate length explained in the linked article). You will want to use the most event-specific test you can arrange. In other words, runners should do a running test, and mountaineers and alpinists should do a very steep uphill hike. Your average heart rate during this test will be, by definition, the maximum that you can sustain for that duration.

AnT/LT Field Test Takeaways

Pluses: Accurate. No cost other than your effort. Easy to repeat to check for future improvements. 

Minuses: None.

Rating: 4 stars



With proper training, your AeT and AnT/LT will improve in terms of both heart rate and the speed you can move at that heart rate. The tests reviewed here are all meant to allow you to assess your current position along your journey of aerobic development, some more accurately than others. It is important to know where you started if you want to be able to chart your progress and know where you end up.

You might also be interested in:

Overtraining Syndrome: The Elephant in the Ultrarunning Room
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