Hi Kristi!!
On the treadmill, let's see....yesterday I did 22 mins. of HIT work. It consisted of 2 mins "off" and 1 min. "on". My "off" phase was an 8:20 mile pace and my "on" phase was a 6:11 mile pace.
Some of my experiments running on a treadmill:
1. change the amount of time in "off" and "on" phases. Some days go longer in the "on" phase and shorter in the "off" phase, or vice versa.
2. change the pace in each phase.
3. mess with various inclines.
4. slow the paces in both the "on" and "off" phases and put a big incline on.
5. if you are using an HR monitor, let your HR dictate when you start and stop each phase. Some days give yourself less HR recovery time, other days more time.
On a stairmaster, try doing one pace, but alternate taking two steps for a time and then going back to taking one step at a time. Or do the "on" and "off" phase just like you do on a treadmill. Another good stairmaster workout is to "run" to the top of the steps on the machine, stand on the top, let the machine "carry" you to the bottom, and then "run" back up it again. This stuff is killer!! In fact, a stairmaster is one monster piece of equipment in my view.
Of course, you can do all of this above mentioned stuff outside too.
Want something else that'll shock your legs? Try running backwards! Just backpedal like a cornerback in football. Your legs will be so sore! I guarantee it! I ran 2 miles backwards one time and my legs were so sore for about a week! And I thought I was hitting everything in the gym! How wrong! LOL!!
Anyway, hope this helps some. Good luck!
Trevor