[WashingtonSource]

Thanks. I may try for twice a week and see how that works.

[RoosterRedux]

I used to be a runner. Still run (very slowly) every other week for a couple of miles. Forefoot/midfoot strike now. Not heel.

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.