I did this for the first time tonight. I was really worried it would be too hard for me but suprisingly enough I got thru it pretty darn good. I even extended the last sprint at the high end for the entire 4 minutes without music . I burned them to cds today and for some reason the last few minutes cut off. but I thought it would be harder than Itrain 21 because it only has 3 sprints and this one had 6. Maybe it was because she gave walking breaks or maybe because I have done 21 2x now and I am seeing a difference in my endurance already! I hope so. for the first time ever I was able to run faster than I ever have been able to on the treadmill. I for only one minute was under a 7minute pace and the last interval that I maintained for 4 minutes was a 7:30 pace. YOWZA!!!! that is good for me. thanks to all who recommended these workouts, I never thought I would enjoy intervals on the treadmill!