% ftp at 40/20?

Having a bit of trouble finding good information about at what % ftp you should do 40/20.
Barnard is at 130-145 % and that’s on the higher side. The corresponding Zwift 40/20 workout is with 120% on the lower side.
Anyone have an opinion or some study for me to read?

Looking at it from interval time first is a bit backwards.

The primary goal is to choose a training level or zone, then set the time to lead to the desired adaptation.

120% is the top of VO2 Max.
130-145% is Anaerobic.

Each has very good reasons to be used that aren’t dictated by the interval timing, which is effectively secondary.

1 Like

120% “works” for me. How many repeats are you doing?

I do 12 with 40@120% and 20@35%, which checking in workout creator gives me an intensity factor of 1 for the whole interval. So 3 blocks of those is equivalent to 3x12 minutes at threshold.


Thanks @mcneese.chad and @martinheadon for your answers.
Did Barnard tisdag which is 6*(540/20) so total of 3040/20 at 130-145% and especially the ones at 145% were killing my legs.

Oof, that workout is 0.98IF for an hour. Which might as well be a race. No wonder it was killing your legs.

Anyway, I don’t think Barnard is really what you’d call a standard 40/20. The one I’ve heard described by (I think) a Cannondale coach was like I mentioned; 3 blocks of 12 with the “on” at 120%. So I just built that in Workout Creator and use that sometimes.

1 Like

It’s very difficult to say exactly what percentage of FTP these type of intervals should be done at because of differences between individuals, but the whole point is to spend as much time as possible at greater than 90% of VO2max.

It’s worth remembering that VO2max is NOT a power - it is a physiological state where the body us using all of the oxygen it can take in through the respiratory and circulatory systems.

This happens over a range of power levels: doing intervals up towards the maximum power that elicits VO2max will severely limit the amount of time that you can train in that zone. Too low and you never get to VO2max.

As others have said, this lower value is typically around 120% of FTP and can be held for between 4 and 6 minutes.

The number of micro intervals will depend on the individual, so you’ll need to play about with the intensity and number to keep the effort maintainable for 8 to 10 minutes or so. Rest shouldn’t be much lower than 50% of the work period intensity (120%/60% for example).

I’ve been playing around with my own 30/15 intervals and found that I could hold 116%/58% for 12 reps x 3 blocks with 3 minutes rest between. It was a tough workout as it’s a LOT of time at >90% VO2max.


This presentation by Prof. Bent Rønnestad is worth a watch.



@themagicspanner thanks a lot for the info and the link to the video. Very good information in it!

No worries - I’ve been doing quite a bit of reading to try to understand what’s going on at VO2max.


1 Like

Interesting warm up!

I was playing around with a power meter/trainer comparison workout that had large and small jumps in power and I found that I quite liked it so modified it to make all the intervals at 40%.

There was something about doing the slightly easier work period second that made me feel more warmed up, so I stuck with it.