I’ve tried making my own Tabata Workout on Zwift. Unfortunately, when I set it at Zone 5, the resistance isn’t high enough for that interval for me to get my hear rate up as high as I had hoped. When I took a spin class, I was able to crank up my resistance and really get my heart rate up during Tabatas.
Is there a way to use workouts where you can increase resistance above Zone 5?
Thanks
Jason
What trainer are you using?
And what FTP, have you done FTP test recently, you need that to be fairly accurate for the workouts to have the right benefit (ie, be not too hard, but not too easy).
On a Tacx Neo or Kickr Bike it should be possible to give huge resistance, I used both previously with Zwift. Other smart trainers should be similar.
Please send some of that power my way too. 
As mentioned above probably your FTP isn’t set correctly.
I’d also add Tabata intervals are usually too short to do a workout in ERG mode and get the proper benefit. I’d switch to slope mode and play around with the slope setting and gearing so you can drop a few cogs, crank out the interval and then shift back up the cassette for your recovery.
Not sure which facility you used to build your own workout, there are several out there. If you built it using the Zwift Custom Workout editor then “Dragging the top of the block up or down will change the power level”.
More info in links below with alternative options for building and editing workouts.
https://www.zwift.com/news/12975-zwift-how-to-creating-a-custom-workout?__znl=en-gb
Edit Update - the point made above about whether to leave erg mode on or turn it off is very valid. If you go down the route of just increasing your power target on the 20 second interval and can’t put out the power you will hit the Spiral of Death and come to a halt. Something you don’t really want to do at the middle/end of a set of intervals.
A couple of video links below:
one giving option to change your 20 second sprint (170% Tabata effort) to Free Ride (video might be a bit dated)
The other showing turning ERG Off.
I know they both talk about maximum sprints but I think they are relevant for your 400+ watts Tabata intervals.
