I’ve been doing cycling HIIT for around 3 months – I downloaded the MM app on this website and adjusted the interval settings as per the Tabata program. There is a an ABC Catalyst program (Australia) on the net that has a lot of information on various intervals etc. Worth a look if you are just starting out.
I do the exercise 3 times a week for 9 mins per time. Quite honestly the 9 minutes is easy to fit in and is so short that there is no excuse.
I did some swimming laps yesterday after not swimming for around two months and my lung capacity was great – I was never out of breath.
I also do quite a lot of walking and my fitness has improved significantly – leg strength particularly.
I did initially consider other types of exercise for HIIT but I think it would difficult to really get the intervals right.