My point is that you should be careful about your form when doing HIIT.
Unless you are running hills, you might hurt your feet or knees by running all out.
I have a rowing machine (Concept 2) but it doesn't work with HIIT because form is important in rowing and cannot be maintained in HIIT.
I have done a Crossfit routine for the last year or so. It really doesn't work with HIIT.
Seems you have to find an exercise that doesn't require perfect form.
I have an indoor bike trainer (Kurt Kinetic).
Swimming might work.
But swimming aside, I use the bike trainer.
My bike trainer works because I can max out without worrying about form.
I have to be careful not to fall off.
But so far...so good.
Thanks for all the suggestions.
I have an indoor track where I can run my HIIT. I used to be 50-yard dash runner in my high school years and won a few ribbons at track meets. So I developed a reasonably good form and it seems to have come back to me. Plus, I like doing a sprint for my HIIT.
I also have access to exercycles of various types.