Re: About hitts and how much you should do them
If you're doing a session of true HIIT (where the high intensity interval is sprints or the equivelant) 15-20 minutes is plenty. There aren't really any "breaks", but you do drop the intensity for a certain amount of time. You never stop completely. There are different ways to do this. I prefer an eliptical machine because it is easier on the joints than running, but you can to the eliptical, running/sprinting, stationary bike, rowing machines, stairs... anything taht you can throw in an all out effort for a minute or two is fine. When I do HIIT sessions, I do 3 minute cycles. 1 minute low intensity, 1 minute medium and 1 minute high intensity. Repeat for 15-21 minutes. There's a lot of ways you can alter or tweak this routine, but that works very well for me.
Keep your body lean, your blood clean and your mind sharp. -Rollins