What to make of 2x20 min efforts

After a little advice from the collective please:-)

Last night I did two short races on Zwift, each around 25 mins long. I was using it as 2x20 min sweetspot session. I rode on RPE rather than to power. However the figures were pretty decent and I was wondering if there was any way of interpreting them to estimate current FTP?

The first ride was a 20 min power PB, but HR was within sweetspot range, VI of 1.05. The second ride my 20 min power was 98% of the first, HR again where I would expect for sweetspot, and VI of 1.00. There was 20 mins recovery between the efforts.

Is there any way of using those rides to estimate FTP without testing?


In terms of estimating it would likely give you a feel of what you are capable of but given that doing a test is so simple and relatively quick (and also a decent training session in it’s own right) then it would probably be more beneficial to just do a test. This will give you more confidence and rubber stamp where you are at.

What those efforts will serve as is a benchmark to the test itself. The more you train with power the better feel you have for what is capable.

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I am of the opinion that you can fairly accurately guess your ftp based on your workouts, as long as you have the full context of the workout. I also think it is important to be able to do this in season if you are racing a lot, as you may not have the time to compromise a workout for a test or you may not be in position to test if you are racing 2-3 times a week.

I recently did a 1 hour sweetspot effort on the road. I started at what i thought was sweetspot and as the effort went on I made sure to check my hr, not for the value but to make sure it wasn’t decoupling so that I knew I wasn’t above threshold. Held it in that range for an hour, felt hard but very doable and my HR ended up being very stable and within 5% of my threshold HR. From that, I think I could confidently peg my ftp about 10 watts higher than the average from that interval.

From what you describe you could reasonably put your threshold pretty close to your first 20 minute interval I would say. You could confirm it by doing a 1 hour sweetspot interval and seeing how it feels.


Do have have HR data?

Also, do you know your current TTE?

Yes. First effort was avg of 149, second effort avg 150. For me Z3 is 132 - 148, Z4 is 148 to 164.

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How do I find out TTE?

Check this article out, these are good sessions in there own right and very accurate tests, and you can apply the principles across your normal workouts as well to work out ftp.


You would know it through WKO4. No biggie. Now that I think about it, if you had that info you would already have an answer.

Was just trying to see if you were at upper or lower/mid end of SS (in terms of HR), how steady the efforts were (they were obviously repeatable), and whether or not you think you could hold those efforts out another 20mins (each) if you had to.

I was looking for justification to make it even higher than that first effort :stuck_out_tongue:.

Edit: and whether or not I’m explaining it right that article @janerney posted is behind a lot of what I’m thinking. So basically I agree with him.


Thanks! The article was really interesting. TTE wasn’t what I though it was, but it looks like it’s a bit more helpful to understand. Looks like the initial effort had a bigger anaerobic contribution, and the second effort was fairly steady.

It certainly was a type 2 fun kind of night on the bike!!!

And congrats on the new FTP.

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Xert has a fitness signature calculator. Haven’t tried it myself but looks like if you stick in that effort, and a couple others, it might be able to generate your whole new power curve for you. Maybe take something around the 50/60minute mark from it as your FTP?


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@AndyGajda that sounds to me like your FTP has FOR SURE gone up! 20 min power PB that read & felt like sweet spot?? When you re-test, you’re gonna blow your FTP away!

Cheers. I popped a few numbers in from my strava power curve over the last 6 weeks, but I didn’t have any efforts to failure. I suspect that this skewed the results.

It’s all certainly going in the right direction. Did a race on Zwift tonight that took 1hr 7min. My avg power was 298W and NP 317W. Avg HR was 149, which is still sweetspot territory. No point in pushing it harder as the course didn’t lend itself to kamikaze attacks!! Estimate my FTP now closer to 334W, which is bang on what Xert says my TP should be. That’s 14W up on my best when I had peaked for my A race last year, and I’m in the middle of a big block before peak/taper for the end of June.

Happy days!!


How did you determine your HR zones?

A combination of Strava and experience!!

So you haven’t done a 30 min LTHR test to determine?

No. I don’t see the point in getting too hung up on testing all things.

Then I’d be careful in how you designate your SS HR