I've learned from T25 to take the jump out of moves. That's how they modify the moves in that program. You can also step back into the suicide jumps instead of jumping back into them, you'll still get a workout, but it's not as hard the joints and knees.

I had the same concern when I started Insanity; I have a bum knee and 42 years old I was worried I couldn't handle it. I'm on week 4 now and I have to tell you... my knees are SO much stronger then they were! The routines build up the muscles in your legs and where before I use to snap+crackle+pop when bending down and not being able to get up, now I feel like a 12 year old again having stronger leg muscles to dissipate most of the impact. Some of the moves I obviously can't do but I do the best I can and modify it to fit my physical ability. Each week I found myself getting closer to how Shaun T was doing it but I have to remind myself I'm 42 not 18. I'm still stronger than I was and loving the workout.