or any other intense cathe cardio. how many of you never do the whole thing and just do half? like just doing intervals 1-5 or 6-10. i'm finding that i get the most intensity in those first 5 intervals (30 min) and if i try to do the next 5 i'm starting to crap out and my intensity diminishes and my form starts changing. actually i'm noticing this with a lot of cardio workouts that are intense. anyone else feel like this? for me i think intense 30 min of cardio works best