What you’re doing is not HIIT…. as in High Intensity Interval Training.
Sure, that <insert all 45-90 second circuit based classes> got your heart rate to a decent level, made you sweat and possibly even caused some muscular fatigue to some level.
It’s still not HIIT.
The first part of this acronym can be misconstrued pretty easily. That workout felt hard and at a high intensity. Plus, there were some short rests involved. But often the 3rd letter is missing from the program design… interval.
The purpose of HIIT training is to create a linear increase in your heart rate up to around 90% of max. It does this by raising it in aggressive short bursts of effort and enough rest to allow for heart rate to drop between 40-50% (as the high HR increases the recovery/low HR will increase concurrently).
I think circuits circuit training gyms are a fantastic introduction to fitness and health for people new to training. Any safe training method is a great tool for improving the health of our population.
I also know that if you want real quality of life improvement long term, changes will need to be made eventually to progress your mastery of self.