From the FIRM website message board.  This is something I want to work toward doing at the advanced level (right now, walking out to the truck makes me tired.  Stupid Graves disease!!!!!!!)

CHALLENGE CARDIO WORKOUT

This is advanced but can be modified for intermediate level by ending the workout at the
first 5 minute jog (about 27 minutes total) OR by reducing the intensity throughout.

This can be done inside on a elliptical or treadmill or outside on roads or a track.

5-10 minute walk/jog warm up (low level on machine)

4 minutes jog/run moderately high intensity (or .25 mile). This should feel difficult but not impossible.

2 minute recovery walk/jog

3 minutes moderately high to high intensity (.25 mile). This should be slightly more intense than the last interval but still not at your peak.

2 minute recovery walk/jog

1 minute high intensity sprint. ALL OUT.

5 minute jog

4 minutes jog/run moderately high intensity (or .25 mile). This should feel difficult but not impossible.

2 minute recovery walk/jog

3 minutes moderately high to high intensity (.25 mile). This should be slightly more intense than the last interval but still not at your peak.

2 minute recovery walk/jog

1 minute high intensity sprint. ALL OUT.

5 minute cool down