Hi, i prefer the spin bike for
HIIT since it's easier for you to start and stop the hard intervals. On the elliptical, I find that when my hard interval is ending, it takes a bit for me to slow down. If your new to hit, I suggest you do the following:
5 minute warm up
1 minute at an exertion level 4 ( meaning it should feel like a 4 out of 10. You should be able to easily hold a conversation. The speed will vary by the person - just go by how you feel)
30 Seconds at a level 7 (if you had to talk, you could but you would rather not). During this time you can either speed up or increase the resistance. Do whatever you want to push yourself to a level 7.
Repeat this for 5 - 6 times
5 minute cool down
The intervals could either be with speed or resistance. As you progress you can either shorten the rest period, increase the level of exertion during the interval or increase the duration of the intervals.
Good luck!