"Don't be discouraged! When I first did Imax, I could barely get through the warm-up! Now, I add 8-16 reps to each and every interval. Something I found to be really helpful with interval #8 is to do other Cathe workouts that contain 'power scissors' - Legs & Glutes, Supersets, Body Max, Step Fit, CTX Kickbox, Kickmax, and High Step Training Advance - all of these contain Power Scissors. Try to do some a few times a week - the body will get used to movement and it will become easier. Trust me!"
What The Bean said.
Another really good trick is to "sprinkle" those "power scissors" (also more recently referred to as "explosive lunges") in your other workouts, maybe just 8 here and there in substitution for another move. I like to substitute the dreaded explosive lunges for mambo-cha-chas and other fancy-footwork things. The more you're accustomed to having explosive lunges / power scissors as a regular drill in all of your workouts (and obviously you can do them during hi/lo, kickbox and step workouts) the less of a shock to the system they will be when they are their own interval.
Just keep at it. Commit yourself to doing Interval Max at least once a week, and further commit yourself to doing just one more rep than you did the last time. I promise you, you will make it, and like The Bean and The Bald One, you will be extending that interval out beyond what Cathe & The Gang do before you know it.
HTH -
A-JOck