There’s accumulating evidence that in absence of better information, zFTP is as simple as your best 60-min power over the past 90 days. A couple of other folks have shown this. Here’s mine:
It would never be that simple. Anyone could go out and do an hour at 50 watts, and we wouldn’t all end up with zFTPs of 50
Yeah not for me. I do a fair number of > 60 minute races, and I recently did one just over an hour where I felt great, it was super hard from start to finish, I performed well (5th out of 366) and 60 minute power remains below zFTP by around 5% which seems significant. My zFTP is my 40 minute power.
My zFTP is sitting at 282W, my 90-day 60min is 273W, I wonder if what happens is if the 60min power is greater than the other points they use on the shorter side of the curve (12-15min max) would suggest it should be then they use the 60min number? .
The maths doesn’t allow that. 60 minute average can’t be higher than 30 minute average or anything shorter than that.
No, but if you have a very flat curve the 30min power might be very close to the 60min power. In a normal 2-point curve selection the FTP estimate might be under what they did for 60mins because it could estimate a larger drop by the 60min point for that case.
Only if you have an unusually flat power curve.
If you have a flat power curve and zFTP is the same as your 60 minute power, it implies that you could be pushing harder at shorter durations, e.g. for 20 minutes.
If you ride at the same pace all the time, e.g. you just do endurance rides, then you’ll probably have a flat curve. Which is fine. Just don’t expect your zFTP to be accurate.
Zwift tell you themselves, if you search for zFTP
https://support.zwift.com/en_us/fitness-metrics-faq-Sk0Cebzti
basically it looks like a 3 or 4 point system
Zwifting for the following durations within the last 90 days:
30 seconds.
5 minutes.
8 minutes.
12-15 minutes
this does mean it wobbles a bit if you have a kick and/or can do strong 5min it will negatively affect your zFTP, whereas a strong 8min will improve it, I’ve had both scenarios !
I use Golden Cheetah and have my CP graph set to 5 point (extrnded CP), this uses 4 points under 20 mins and a 5th (in my case) at 3h30, ie it ties down the wagging tail and represnts the decay of the line over time riding.
Then there is zMAP, which is your VO2max.
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All I’m saying is three people in this thread reported that their zFTP was exactly the same as their best 60 minute power over the prior 90 days. I showed that this is the case for me.
I know for sure that I can push more than 249 watts for 60 minutes but that I haven’t had occasion to do so in the past 90 days, so to that extent whatever algorithm they use that might alternatively extrapolate my zFTP from shorter efforts I’ve done at closer to max effort did not work for me. [Will be interesting to see how my zFTP changes after I race the Accelerate to Elevate stage of TdZ next weekend.]
Why is this important? To the extent that zFTP is a component of category enforcement, users like me who have zFTP set to a best 60-min effort that is not close to an actual max effort over that duration may be in too low of a category. Now, since Zwift also uses zMAP, this problem is probably addressed by the fact most regular race participants will have to do close-to-max 4-6 min efforts more frequently than ~60 min efforts. But then why even use zFTP if it is so inconsistent or biased down for many riders?
Finally the main point I wanted to make is that the exact match between zFTP and best (but not max) 60-min effort that many people report seems to not be a coincidence. In my particular case, I have done close to max efforts over 3, 5, 10, 15, and 20 (but not 60) minutes in the past 90 days, and if the zFTP curve works as it is advertised, the zFTP should be a better estimate of my 40-60 min power than whatever number I happened to put up for 60 min.
Ok I raced Achterbahn this morning and did 277 for 20 min, which bumped my zFTP up to 252 (from 249). That’s 91% of 20 min power.
It seems like Zwift’s curve dies off faster than the 95% of 20 min power rule of thumb…this probably leads to situations, like mine and others in this thread, where the curve predicts a lower zFTP than what the user has actually achieved over 60 min, so the rule is like max(zFTP_from_curve, actual_60_min_power).
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yeah, but as smart as you no doubt are, idiots like myself already sussed out the broad strokes on day 1, and had practical evidence by week 2. zhq, to their immense credit, have managed to keep it very vague for the vast majority. and, i wont criticise them for it too hard for it but i do think it all the same, have kept it too vague, for the vast majority.
which is why these threads keep showing up
and this faq that mr kazmi has linked is a good faq. it’s a shame that people don’t read it, because it’s both concise and correct
I’m not smart enough to find the link
don’t worry, i’m a professional idiot - when you need to know a fact, just make sh*t up and wait for someone to come along with the correct answer
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You’re definitely a professional ■■■■■■■
haha. that’s for sure
Found the post after searching a second time…
If Zwift have implemented a supposed push and pull between zMAP and zFTP, it’s not in accordance with physiology I’m familiar with.
In running, for example, it’s pretty well agreed upon that the 800 (<2min) that straddles the border between mostly anaerobic and mostly aerobic. The 1500 and up are primarily aerobic efforts. If you improve your 1500 PR it implies you could also run a faster 5k or 10k, not the opposite!
It makes sense that some riders will have strength in 4-6 min zMAP range while others do relatively better in 20+ min zFTP range, but the question is more like which side do they tilt. It doesn’t make any sense that improving on one end would imply a decrease on the other.
in an attempt to be actually helpful instead of annoying, your zftp is simply a derivative of what zwift interprets your, man i’m prolly gonna get this terminology wrong but words don’t mean much to me anyway, “critical power” and “w’ balance” to be. as far as zmap, it’s their attempt at a calculation of your 6 min. they say 4-6, it’s really just 6.
it’s “like” critical power, but it’s not, basically. there’s some other little clauses and dumb stuff, but nothing major. no one knows the exact formula but zhq, certainly not me. but it’s not that deep really. i dunno if you’re trying to hustle your category or just want to understand the principle, but i hope this actually does help a bit. when CE was first introduced, zftp wasn’t called zftp, it was called critical power - on zwiftpower. so i ain’t guessing
and just to be clear, there is a serious grounding in sports science there. i only do layman’s terms, so i’m only gonna be capable of giving a layman’s explanation: if you spend your time training to be good at the short efforts, you’re gonna suffer in the longer ones. if you train for longer efforts, your anaerobic capacity suffers for it.
if you wanna know the deeper science behind it, that’s some reading up you gotta do on your own, because i keep it simple and plain
Yes, it’s a Critical Power Curve, just realised I’d said CP and curve without saying it’s full name.
So anyone who wants to know more lookup W Prime (W’ ) and Critical Power, they are related to each other, it’s why Wahoo have/ had the 4DP test, as these are the 4 points they use to build their graph, also I think, draining each system in turn.
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