The way i do elliptical is at the same resistance, balls to wall for 1 minute and rest period (slower pace) 2 mins, i do 3 sessions of HIIT of 20 mins each combined of elliptical, stairs, bike, treadmill, etc. On either equipment you use the basic still applies, i think 15 second burst is enough to bring your HR high enough to the peak....

If you wanna run without too much impact in your joints, you can try to find a parking lot with several floors...jogging within the floor and run when you are going to the next floor. It's a very good exercise and the impact (due to the incline surface) is less. :)

I did HIIT cardio for cycle the last 12 weeks. I pass of 22% Body Fat to 12.8 %. It really works. Before I was doing cardio 2 times a week, 30 minutes. Now 12 minutes after my training. I do 30 seconds of tempo cardio on my bike, and 30 of sprint. For 12 times. For sure, nutrition help, but HIIT helped a lot too. Thx to Jim Stoppani