I’m a 37-year-old cycling beginner, not very athletic. For the past three months I’ve been riding 1–3 times a week, both outdoors and on Zwift. I use Favero Assioma Uno power-meter pedals inside and outside.
My FTP had been about 190 watts.
For months I’ve been sleeping only 4–5 hours a night, so I’m often overtired. But yesterday and the day before I slept 9–10 hours, and this morning I felt unusually refreshed—better than I ever do.
I then did a one-hour VO₂-max workout in Zwift, using my set FTP of 190 W. My heart rate never went above 135 bpm (my estimated max is ~180 bpm), and even the 220 W intervals felt surprisingly easy. (See the Xert screenshot.)
After the hour I thought, “Okay, that’s strange.” So I added a Zwift ramp test: starting at 100 W, increasing by 20 W every minute. I topped out at 540 W, and Zwift calculated an FTP of 320 W. (Screenshot in Xert.)
Xert itself then calculated an FTP of 377 W, which is obviously impossible.
Assuming the Favero Assioma pedals aren’t faulty, that they really do measure only the left leg and then double it (as the Uno model does—I calibrated beforehand), and that I don’t have an extreme left/right imbalance—how can this be? Both the 377 W FTP from Xert and the 320 W FTP from Zwift are clearly nonsense. Even with the progress I might have made in these few months, my real FTP would be at most around 220 W, if that.
How do you explain these screenshots and the sudden, apparently huge jump in power that obviously can’t be real?
I’d appreciate any ideas so I can figure out what’s going wrong and fix it.
Something seems amiss with power reporting.
What model trainer do you have?
Here’s a test you could try.
Flag the ramp test workout that generated the BT so signature returns to previous values.
Select this workout from the Library to ride indoors. It is set to 85% LTP.
Start the workout, warm-up for 10 minutes, then start adjusting % until you hit what you feel is your ceiling for LTP (conversational pace). Note the watts.
Select the Sensors menu while continuing to ride.
Tap on Power and switch from Favero pedals to your trainer. (This assumes you normally use Powermatch with your pedals paired to Power.)
Is there a noticeable difference in resistance when you change between pedals and trainer?
You could also raise % to a higher watt value and run same test.
It is normal for power at the pedals to be different than trainer (hub), but ideally there won’t be a large difference.
Once power issue is resolved you can ride a fitness test like this one to establish your fitness signature in Xert. Ride entirely in Slope mode using gears/cadence to hit or exceed targets and make sure to ride final interval to a failure point. On the two short sprints jump up and go as hard as you can for at least 5-7 secs.
A ramp test isn’t the best way to establish a fitness signature in Xert but it will be close for many users. See: Breaking Through the Xert Way! – Xert
Thanks everyone for your replies. In the end, it was a simple mistake: Apparently, Zwift interprets the power measurement from the Favero Assioma as twice as high if you’re using a Uno version that used to be a Duo (the right pedal had to be deactivated due to a malfunction, and then the pedals were converted to a Uno via software). In the Favero app, you simply select “halve,” and then you get exactly the same values as a Garmin via ANT+—so the actual, correct power values. Back to 180 FTP (see screenshot)
But one question remains: I did a sprint in Zwift and hit 2000 watts. That’s actually realistic (as in, double the real value), since my real power max is around 1000–1050 watts. I know, that’s quite a lot for a total beginner, but it seems plausible due to my high body weight.
So here’s my question: Why did Xert calculate “only” 1339 watts and not the double of the real value?
Xert does some data filtering on the server to prevent power spikes from skewing a user’s signature. It won’t detect things like the doubled power data since those power values are still reasonable for an athlete to have. It can’t know if the power data is doubled or not.
If you’re unsure of your max power, the best way (in my opinion) is to do a couple 5-10s all-out sprints up a slight uphill and check the max power of each effort!
Besides the filtering aspect mentioned Xert’s calculatiion of your power curve does not rely solely on MMP sampling.
Take a look at any of your past HIT activities and select the Power Duration tab.
Notice there are three lines. MMP for the activity, current signature, and calculated signature from the activity data.
On the flipside there are also situations where a bump in PP can occur if a max effort under fatigue is expressed that doesn’t jive with your current signature. For example, you hit 852 watts (for 5-7 secs minimum) when 838 was your predicted MPA at that moment. An adjustment to PP is warranted.
See: Is PP a theoretical number? - General - Xert Community Forum
(see screenshot)