Endure IQ Functional Threshold Power Calculator

Jun 03, 2024

I talk a lot about physiological profiling, and how getting tested in an exercise physiology laboratory can be really helpful for refining your training. However, I also know that many athletes do not have access to exercise physiology labs for this testing.

Accordingly, I’ve put together a couple of calculators on the Endure IQ website that you can use to get decent estimates of things like intensity thresholds using easy-to-access field test data.

In this section we are going to talk about the metabolic calculator. I’ll walk you through how to perform the field tests to get the necessary data. But we also include calculators for fat metabolism/lactate thresholds, critical swim speed and critical running speed.

Field test estimate of cycling functional threshold power (FTP)

If you’re a cycling, you have likely heard of FTP – which is an indicator of the power you can hold for an hour. We can use FTP to generate training zones, and we can estimate FTP using a 20-minute test. Our estimate of FTP is 90% of your 20-minute power, as this is a decent marker of your hour of power (and better than the 95% that is most commonly used).

Like for the 5-min test, if you have never done a 20-min maximum effort before, it’s probably a good idea to have familiarise yourself to the test first (i.e. complete a practice effort). Again, that’s just so you are less likely to come out of the traps too hard or leave power out there.

Here’s your protocol:

  1. Perform a warm-up. This should have you ready for action, but not fatigue you. I recommend no more than ~15-20 minutes. Over the first 10 minutes, build up from a very low power to something of a more moderate intensity. I then like to perform a series of ~10-20 second openers with quick cadence, with ~40-50 seconds of easy spinning between.
  2. Complete the 20-minute time trial. This is hard! Leave nothing out there. Focus on your cadence and consider blinding yourself to real-time power output.
  3. Make sure to complete a cool down afterwards.
  4. Extract your average power over the 20 minutes. Use average power, not normalised power.

Once you have your average power over the 20 minutes head over to the Endure IQ calculator and entire your values to get your threshold and training zones. Note we take 90% of the power attained for the 20 minutes, and not 95%. As 90% has been shown to be more representative of 60 minute power.


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