Zwift calculated FTP test (long) mimic Garmin FTP detection

Zwift calculated FTP test (long) mimic Garmin FTP detection.

In race FTP was 218w.

I wonder if it’s a rounding up/down issue.

Do you know what your 20 minute power in Strava was?

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My experience of Garmin FTP estimates is that they can be far removed from more traditional results. They appear to be based on your heart rate response rather than your actual Watts over time.

For example, i recently performed a Zwift ramp test, which completed with an estimate of 257W. That very same test gave me a new Garmin FTP of 221W, a small increase from the previous 219W.

Since then i have had a ride with a one hour average of 234W including 20 minute power of 250W. That must at least credit me with an FTP of 234W, if not more. Not a peep out of Garmin.

So with all that in mind i am sticking with 257W across platforms. Garmin has since proposed revising my FTP back down to 228W (declined) and then 227W (also declined).

Maybe my heart is weird, but you can’t say that someone averaging 234W for an hour has an FTP of just 221 or even 227.


I am not sure if this is data you are asking for:


But here is the full data:

I would not have imagined that the heart rate would be included in the calculation of the FTP. I did Zwift Ramp Test without much luck, the results were very high. In the real world i simply can’t sustain that power for 1 hour.

The good point about Garmin, compared with Zwift, is that propose you to low your FTP. Now i understand that a racer can’t be at 100% during the whole racing season (the whole year in Zwift!).

It’s not the heart rate as an absolute. It is a change in HRV that occurs when you transition through your threshold. They don’t care about your Watts performance, only what your Wattage is when that transition occurs.

That point is best established with a ramp test, gradually raising the power until that point is reached. This is the basis of Garmin’s own FTP test - a gradual ramp. Unlike most ramp tests you do not continue the test till failure. You only continue the test until that inflection point is detected in your HR/HRV. Then Garmin will announce your result.

I think that for success you need to have your heart rate zones set correctly. Otherwise you may actually fail to complete the test because you reach exhaustion before you reach the trigger point.

Note : I’m not in the least an expert in all this, but it is my understanding.

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My guess is that Garmin is using something like this technique…

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Which has been called into question in this article…

Of course, perhaps Garmin is doing something else, but I generally find their estimates to fall below others.

EDIT : Here you go… A reference to the FTP Test mechanism used by Garmin/Firstbeat…

They really have no interest in how long you can hold or a hit a power target. They look at the HR/HRV. They may use a ramp for the test, but it’s your HRV which determines when the test is complete, not your legs.

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