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4 Ways to Test Your Functional Threshold Power, Including 1 That is More Useful

The functional threshold power test is supposed to approximate your power or heart rate so you can accurately set up your training zones.

Three Things to Know about Testing for Your Anaerobic Threshold

  1. All testing options are just tools and estimates.
  2. Ramp tests from Zwift and Trainer Road seem to be fairly accurate options.
  3. INSCYD tests provide the most useful metrics.

Many people are not fans, for one reason or another of functional threshold power tests as a way to set up training zones. 

The tests tend to be painfully long 20-minute efforts, require a big dose of mental focus, and we’re rarely ever happy with the results. 

Plus because the tests and subsequent zones are established with percentages, there is a mathematical error that can hurt your long-term performance.

Yet some kind of testing is usually necessary in order to understand training zones.

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You have several ways to measure your functional threshold power

Your functional threshold is supposed to be the point at which your anaerobic system takes over from the aerobic system. 

Another way of looking at your “threshold” is your maximum lactate steady state, the point at which you are consuming as much lactate as you produce. 

Your goal is training is to both increase your FTP and to increase the amount of time you can spend at FTP. 

So knowing that power or heart rate is an important tool in helping you set up training zones

If you do interval work too hard, you’ll likely cook yourself with too much training stress.

If you do interval work too easy, you won’t get the training adaptations you’re looking for.

The issues with measuring FTP

The functional threshold power test is supposed to approximate your power or heart rate at your threshold so you can use that number to set up your training zones. 

However, the FTP test has some accuracy issues as well as the challenge of completing it. 

How you feel on a given day and factors such as nutrition, fatigue, prior training all contribute to your results on that day. 

Moreover, there’s even a lot of debate whether it’s an effective way to set up training zones, mostly because the percentages used to create the zones are averages and may not be appropriate for you. 

Critical power tests, talk tests, and using current data on Training Peaks/WKO are other options to figure out your functional threshold power and training zones. 

For runners, doing a percentage of a 5k is typically a threshold pace. 

Why some of the FTP testing is tedious

One of my Simple Adventure Team members is coming back after a long break.

We’ve been trying to estimate his power output, but finally, I scheduled a 20-minute FTP test for him. 

He emailed me the next day and told me how much he hated the 20-minute tests. 

I agreed with him. I dislike them so I avoid doing them. 

They’re long, I can’t keep focus for that long, and the results always make me feel inadequate in some way. 

My best is never “enough” and I’m always feeling like there could have been more.

Here are four options to measure functional threshold power

Essentially, there are several “easy” options to measure functional threshold power. 

If you or your coach has WKO, you can also use a critical power curve based on prior training data. 

1. The 20-minute test. 

Go as hard as you can for 20 minutes. That’s it. 

The 20-minute test has some correlation to your MLSS. 

But again, that’s based on averages and may not work for you. 

Here’s a few things that may help with the 20-minute test. 

  • The 20-minute session is just one interval. That’s it. It’s a marker of where you are on one day. Like a screenshot. Again, it’s just an interval. 
  • Here’s one way to do an FTP from Bicycling magazine. The suggestions are a ways down the page with the headline “How to Measure Your FTP.” 
  • In the article in Bicycling, the coach also argues his position of doing the test as training as well as training for the test. 

2. Two eight-minute tests

This is originally a Carmichael test. 

Doing the two eight-minute sessions with a 10-minute break can give us a picture into your aerobic capacity. 

You can look at the differences between the two. 

An eight-minute test is, at the very least, a decent estimate of your VO2 max. 

So it’s usable as a test of fitness. 

Several science and coaching sites questioned its accuracy in measuring your anaerobic threshold.

However, doing an eight-minute test once or twice a month can simply be a good gauge of your fitness. 

If you get faster, have a lower heart rate, or use less power over the eight minutes, you’re making progress.

3. Ramp test

Ironically, this is what we used to do back in the day as the only real option to measure threshold.

The coach would use the CompuTrainer and graph paper to measure HR as the coach increased the power by 10 watts per minute, hence the name ramp test. 

What we were looking for were the places in the graph where there were changes or flattening. Those were the first and second threshold points. 

The research seems to indicate that a percentage of the last full one-minute power is a pretty good estimation of threshold. 

Zwift has a ramp (MAP) test as does Trainer Road. 

These use 75 percent of your maximum one-minute effort as your FTP. 

That number may be a little high or low (72 to 77 percent is the range), but we’ll have a good number to start with.

4. INSCYD testing

We recently started working with INSCYD to help our athletes find what I’m calling functional training zones.

INSCYD figured out an algorithm that uses the four critical power tests to find more accurate training zones. 

It still requires four different workouts: a 30-second, two to three-minute test, a six-minute test, and a 12-minute test. 

The results from these critical power tests are plugged into the algorithm and produce individualized aerobic threshold and FTP (MLSS or anaerobic threshold) power, plus your VO2max.

These results give you a more accurate picture into the energy systems you want to target to create more accurate training zones. 

So what options do you have to measure your functional threshold power? 

The INSCYD test is the most accurate and useful of all the functional threshold power tests. 

It breaks down functional training zones based on energy systems and provides additional data about fueling and recovery times.

The only challenge with INSCYD, which I use with my athletes, is the cost. 

Otherwise, if you have Zwift, Trainer Road, or another program that has a ramp test, do that. (If you have Sufferfest, do the Half-Monty.)

I tried the Zwift Ramp test and INSCYD

I tried the Zwift Ramp Test and INSCYD. 

The results were similar although the INSYCD provided what seems to be more accurate power numbers based on my past training.

The INSCYD tests also gave me a lot of insight into my VO2max and how to do intervals to increase it. 

Plus INSCYD gives me power levels to use to increase my VO2max, ride at my aerobic threshold, and ride at a tempo pace. 

The Zwift test is still a good tool.

The bottom line is that these tests are tools. 

You still have to pay attention to your body and its reactions after training in your new zones. 

For example, the client I mentioned earlier did both the Zwift and INSCYD tests. 

We’ve been doing a lot of functional threshold power work, and his zones seem to be a bit lower for his heart rate and effort.

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