A gray area surrounds our use of the term “anaerobic threshold”, and especially in endurance sports where FTP is commonly used to describe it. Conflicting opinions exist on what actually constitutes the anaerobic threshold. Terms like lactate threshold and OBLA (onset of blood lactate accumulation) are used interchangeably with anaerobic threshold—and for good reason. Outside of a research setting, those using these terms are all attempting to describe the same thing. The point where exercise intensity can no longer be maintained. It’s like the tipping point of exercise. Similar to hitting your 25^th birthday—the ball starts rolling out of control and it’s all downhill from there. In this incredible moment of exercise a spectacular number of changes to your physiology occur. 

 Seemingly all at once…

”there is nonlinear steep increase in ventilation, known as ventilatory anaerobic threshold, a non linear increase in blood lactate concentration, known as lactate threshold , a non linear increase in CO₂ production, an increase in end tidal oxygen, an increase in CO₂ production, an arterial lactate level of 4 mM/L, known as onset of blood lactate accumulation (OBLA), and an abrupt increase of FEO₂ (expired O₂ fraction).” ¹

 What does this all mean?— It means your body isn’t keeping up with the demands of the activity you’re doing.

 What is Anaerobic Threshold?

 If you’re an endurance athlete, you’re all too familiar with your anaerobic threshold. Your legs start to burn, catching your breath becomes more difficult—you can’t maintain this speed. Once beyond your AT it’s only a matter of time before you become exhausted or you must slow down.

 Staying just below anaerobic threshold is the max level an athlete can work at for a long time without experiencing a significant increase in blood lactate levels.

 Increased blood lactate levels are a marker showing that your mitochondrial respiration is falling behind in production of ATP. Without the necessary amounts of ATP (energy) we can’t maintain that level of exercise.

 The “father” of the term anaerobic threshold made this statement in his original paper on the subject:

“The onset of anaerobic metabolism during exercise can thus be detected in three ways: (1) as an increase in the lactate concentration in blood, (2) as a decrease in arterial blood bicarbonate and pH and (3) as an increase in the respiratory gas exchange ratio (R).”

-Karlman Wasserman

 This was written in 1964. Since then the understanding of anaerobic threshold and how it impacts performance has been developed and refined—but this statement still holds true.

How Anaerobic Threshold Limits Performance

 Most endurance athletes are familiar with the importance of their Vo2 – it’s a representation of your aerobic ability. But perhaps anaerobic threshold is an even more important factor in your performance.

Vo2 max is a measurement of how much oxygen your working muscles can consume at their highest capacity. Having a high Vo2 shows you have a high cardiovascular potential—your body can deliver large amounts of oxygen to your muscles. This is an important aspect of performing at a high level—but what it doesn’t tell us is what percentage of your Vo2 you can maintain for an extended period. That’s what anaerobic threshold tells us.

This means it’s possible for an athlete with a Vo2 max of 50ml/kg/min to outperform an athlete with a Vo2 max of 57ml/kg/min. It all depends on when they reach threshold. Threshold levels range drastically across training statuses, with untrained individuals having the lowest relative levels and elite athletes having the highest.

Average people hit their anaerobic threshold around 50-60% of the Vo2 max, while trained athletes don’t experience threshold until 70-80% of their max. And elite athletes? Some don’t reach anaerobic threshold until 90-95% of their Vo2 max. 

Common Tests to Estimate Anaerobic Threshold / FTP

Outside of a laboratory setting its difficult to precisely pinpoint the level at which you reach anaerobic threshold, but there are several ways of getting an accurate estimate.

Old Faithful – The 20 Minute Test

• Warm up for 10-15 minutes.
• Ride ALL OUT for 20 minutes.
• Record what your average power was for the 20 minutes.
• Multiply that number by .95.
• Voila!  You have your FTP.

This is the most common test used currently, and probably the one you’ll see during your workout plans.  Remember though, if you have a strong anaerobic capacity, or are a new rider, you can have an inflated result.  I suggest going hard and over-pacing the test for the first 3 minutes to exhaust your creatine phosphate system, and to decrease the anaerobic system energy contribution, to hopefully see your power drop and eventually plateau to your true FTP.  Ideally you’ll see a gradually increasing heart rate and subsequent power drop for the first 3-5 minutes, then a plateau for the final 15 minutes at your actual FTP.

2x 8 Minutes Test

• Warm up for 10-15 minutes.
• Ride ALL OUT for 8 minutes.
• Rest for 10 minutes.
• Ride ALL OUT for 8 minutes.
• Record what your average power was for both 8 minute tests.
  • Add both of the averages together, and divide by 2.
• Multiply that number by .90.
• Voila!  You have your FTP.

This testing protocol is the least accurate, in my experience, however
In 2007, Klika et al. demonstrated that a cycling based field test was found to be accurate and repeatable in estimating threshold levels. This test is relatively simple to complete.  Test participants are asked to cycle for 8 minutes, between 80-100RPM at the gear of their choice. This was shown to produce about the same power output associated with lactate threshold in a laboratory setting. At the end of the 8 minutes, record your heart rate. That heart rate should be close to your threshold level.

The Ramp Test (Max Aerobic Power, MAP).

• Warm up for 10-15 minutes.
• Having a smart trainer makes life much easier here.
  • I start my athletes off at 60% of their FTP, and increase by 8% every minute or 2 (based on athlete fitness), until failure is reached.
  • Once you settle into a cadence of your choice you must maintain that cadence, or pedal faster, throughout the rest of the test. For instance, if you ride at 90 RPM for the test you can’t then have your cadence fall off to 85, 80 and even 75 RPM in the final stages. Once you can’t maintain your cadence the test is over, but you must push to the point of failure and not give up!

You are looking for a heart rate inflection point for this test.  The inflection point signals the lactate threshold (FTP) and can be very hard to see in my experience.  Another way is to take the last COMPLETED step of the test, and multiply this by .75.  This test is also called a Conconi Test.

Outside of a laboratory setting, it’s difficult to precisely pinpoint the level at which you reach anaerobic threshold, but hopefully the test examples above help your estimate become a bit more accurate.

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References:

1. A.K.Ghosh. Anaerobic threshold: its concept and role in endurance sport.Malays J. Med. Sci., 11 (2004), pp. 24-36
2. Wasserman, K., and M. B. McIlroy. Detectingthe threshold of anaerobic metabolism. Am. J. Cardiol. 14: 844-852, 1964.
3. KlikaRJ, Alderdice MS, Kvale JJ, Kearney JT. Efficacy of cycling training based on apower field test. J Strength Cond Res. Feb 2007;21(1):265 – 269.