OK I tried the high intensity workout below and it was rough. You just have to keep thinking that it's ONLY three minutes of each level and you can get through it. 15 minutes total. NOT that bad!
I do have another workout though that might make your bones ache:
5 minutes, Run, 3.0 incline, 7.0 speed
5 minutes, Stairs (run REAL stairs (not the machine), preferably TALL ones that make you keep going up and up and up! I use the ones at the local high school's pool in the winter, and at the football stadium in the summer)
5 minutes, Run, 0.0 incline, 7.5-8.0 speed
2 minutes, Jump Rope - QUICK!
1 minute, Squat Jump - It's going to hurt, but keep going! Only 1 minute!
1 minute, Jump Jacks
1 minute, Jump Rope
5 minutes, Run, 5.0 incline, 6.5 speed
5 minutes, Elliptical - FAST!
5 minutes, Bike - MEDIUM
and the best part ... REPEAT!!!