Did a mellow 5 x 8 minute spin/RipRow workout a couple days ago. Really felt it in the butt/back and later coming down the stairs, definitely not how I’d feel with 45 minutes of easy trainer work!
I have a CycleOps Hammer smart trainer, used it in erg mode at around 170 watts and adjusted as I warmed up and aimed for about 100 RPM. On the RipRow the fours pattern on about 3 or 4.
Interesting to look at the workout from Training Peaks so you can see heart rate during the RipRow intervals (when power goes to 0). Heart rate is either the same or increases during the RipRow efforts.