I find the biggest barrier to doing anything like this is the laziness itself. Thinking clearly about the choices I'm (not) making, and the trade offs I'm choos

I find the biggest barrier to doing anything like this is the laziness itself. Thinking clearly about the choices I'm (not) making, and the trade offs I'm choosing helps me decide what I'd prefer to do. Reminding myself that activity makes me feel much better helps a lot too. I hate gyms as well (I see them as a necessary evil these days). Personally I grab my bike and go mountain biking a lot. Not HIIT per-se, but very spikey bursts of effort. You could accomplish some high quality interval work with a simple road bike (a hill helps) and a good attitude. The benefit to this being far less impact compared to sprints. Just be a little careful starting with high intensity stuff - you want to slowly ramp this up over a handful of weeks or more. True high intensity work with insufficient muscle conditioning is a quick way to get injured (think ham/glute/calf pulls, tears, etc), and you do need to be careful when ramping up the cardio side - heart issues aren't fun.