3 Very Reliable Ways to Determine FTP (Including Test-Instructions)

The FTP is one of the fundamental metrics to assess an athlete’s capability on the bike.

A proper FTP test delivers you with the desired data to extrapolate the different training zones and more. FTP stands for “functional threshold power” and is the power in watts a cyclist can sustain for a 60-minute paced all-out effort.

There are, however, different methods to obtain FTP data with some being inaccurate and some establishing themselves as very useful. Today I will show you the top 3 test protocols with instructions to get the best out of your performance.

1. The Pro Default: Advanced lab testing

Visiting a lab to gather data on your current physiology isn’t always easy. At first, you need to find a modern lab that delivers you with everything you need. But it can be worth the effort and money as you will get a comprehensive insight into your capabilities.

An advanced cycling lab won’t just give you an FTP value and bounce you out into the wild world of cycling. No, they will supply you with a whole metabolic profile by extrapolating your maximum lactate steady state (MLSS). MLSS is what FTP often stands for. A steady state, where lactate production and clearance are at equilibrium.

This is done by undergoing several tests. It usually starts with a 15-second all-out seated sprint, where lactate is measured at rest, before and for several minutes after the effort till lactate peaks. This way you will get your maximum lactate production rate (VLamax) measured in mmol lactate per liter blood per second (mmol/l/s). This describes your anaerobic capacity. As an endurance athlete, you usually want this to be in the lower range.

The next test is often a ramp test with a spiroergometry mask that measures the gas exchange of oxygen and carbon dioxide. Thereby, VO2 can be measured and a whole metabolic profile including MLSS, your fatmax zone (aerobic threshold, where fat oxidation is highest) as well as carbohydrate and fat consumption, can be rendered.

The last round is usually a VO2max test: An all-out ramp test, where steps grow faster and in a shorter time. Thereby you will push your limits. And with the mask on obtain your maximum oxygen uptake or aerobic capacity.

A modern lab test that supplies you with all the described data is a great way to understand your physiology and metabolism. You will get your FTP and so much more. Therefore, training can be planned toward what should be improved. Like threshold or VO2max for instance.

2. Critical Power Testing in The Field

The Critical Power model is a well-researched and applied method in international sports science. The basis of the critical power concept is that there is a hyperbolic relationship between power output and the time the power output can be sustained. This relationship can be described based on a series of all-out efforts ranging from 2 to 12 minutes. Power output at CP can be maintained in reality for around 30 minutes. At CP, VO2max remains relatively stable. Therefore, CP counts as a fatigue threshold, where going above CP fatigue sets in quickly.

The second parameter (above CP) is called W’ (pronounced W prime) measured in kJ and is associated with anaerobic capacity. This anaerobic capacity concept states that work above CP is limited like a battery: Once you empty your W’ battery, you need to reduce power below CP to recharge it. W’ is important as the higher your W’, the lower your CP. As a result, the CP concept might be particularly interesting for anaerobically strong riders.

Studies have shown that Critical Power is higher than FTP, which seems logical as FTP is a power that can be maintained for around 60 minutes. However, from my experience and the evidence we have, I think that a proper CP test and a fresh 20 minute test will result in a pretty similar CP to FTP.

If you want to accurately determine your CP and W’ you will need two to three all-out test efforts. I suggest the following protocol:

On a Friday complete a 3 and 12 minute all-out test
Complete a 5 Minute all-out effort 2 days after the first test, i.e. on Sunday
Google Critical Power Calculator or use the following equation from a two-test trial

Firstly, multiply your average 12 minute power by 12. Secondly, multiply your average 3 minute power by 3. Thirdly, subtract the 3 minute result from the 12 minute result and divide it by 9. Here’s my test example: 12x 398 watts – 3×510 watts divided by 9 = 360 watts Critical power.

Now, to calculate your W’ subtract your 12 minute power from your 3 minute power and multiply the result by 0.24. In my example that means 510-398 watts x 0.24 = 26.88 kJ W’.

on white background it shows in a blue graph the workout description for a two-test trial in one single session to determine critical power.

3. The Famous 20-minute FTP Test

The 20-minute FTP test is the most widespread protocol to obtain FTP data. In this way, you can derive individual training zones and capabilities. Having been criticized in recent years due to inaccuracy compared to advanced lab testing and all, I think the 20-minute test is still valid. As I compared lab data to the 20-minute test, it worked for me. There’s more to it than just an all-out effort. Additionally, current research comes up with new perspectives on how we can get the 20 minute test results closer to our maximal lactate steady state. I wrote a whole article about it.

And it highly depends on executing the FTP test correctly.

So, let’s elaborate on what you should pay attention to if you want to create a test set that is reproducible and reliable: Firstly, get used to doing FTP tests on the indoor trainer on zwift or on a road, where you can ride uninterrupted. Secondly, pace it smoothly. Thirdly, do a 2-3 minute effort to get ready for the test and plan adequate rest in between the effort and the test.

Analyzing the test result

If done correctly, upload the data into trainingpeaks and analyze it. For the interval you want your Variability Index (VI) to be as close to 1.00 as possible. Up to 1.04 should be okay. This ensures that you don’t overestimate your FTP. Because the greater the VI the more variable and inconsistent the effort is.

Now, take the average power for the 20 min test and multiply it by 0.95. Voila, you have your FTP. Let’s say you averaged 400 watts. Then 400×0.95 results in a 380-watt FTP. By collecting data about yourself you will likely find that you may need to subtract more percentages like 0.93 or even 0.9. It’s a bit individual.

And it’s not only data you get with the test. Because when you put yourself in the hurtbox for so long you will learn a lot about yourself. And you’ll get used to riding at such high powers. In addition, the test is highly variable. You can do it at the end of a ride with tempo work to mimic race demands and see how you perform at threshold, when fatigued.

And as you can see it’s not about the highest average power at all cost. Because in the end, it’s about meeting the goal of an FTP test: Gaining the right training zones for yourself. Only then can you train in the right zones and set the intended training stimulus.

Takeaways

What kind of test you use depends on your possibilities as well as your preferences. However, if you decide on a method you’re happy with, stick to it. Always do the same protocol on the same setup (road or zwift). Same procedure. For an FTP Test, a silde uphill might help to squeeze out a few more watts. Just choose the option you’re more comfortable with.

Good luck with the test.

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Footnotes

The concept of maximal lactate steady state: a bridge between biochemistry, physiology, and sport science: https://pubmed.ncbi.nlm.nih.gov/12744715/#:~:text=Abstract,a%20continual%20blood%20lactate%20accumulation.

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