During Month 1, I did add the Upper Body Weight Training on the recovery and rest days. With Month 2, I didn't have the time, nor did I feel the need. I gave it my all, and I didn't have anything left to give!
Here's what Steve Edwards has to say about it:
Here's a more detailed discussion about this:
So I'm considering starting Insanity soon as the max interval training concept is really appealing to me but I have one thing giving me doubt as whether I really should. P90X works all areas of the body w/equipment required. Insanity however requires no equipment which is a great advantage but I don't see how you can work your back in the program whereas P90X uses a pullup bar. Insanity has pushups in the program to develop your chest but if you only work your front eventually they will be more developed than your back muscles and create a hunch. I can't think of any back exercises you can do w/your bodyweight besides pull ups which are non-existent in the program. I have not seen the Insanity videos yet but are there workouts in there that incorporate your back to balance everything?
None of the strength work in Insanity will build the type of muscular imbalance you are describing. It uses floor movements in a way where all of the upper body muscles are stressed but it's not a muscle building program per se. It's a muscle strengthening program, especially static strength that comes from floor work, but there is no targeted hypertrophy like you get in Tony's programs. It's cardio based, meaning that it targets various energy systems (VO2/max, lactate threshold, anaerobic and aerobiv efficiency). It never targets muscle hypertrophy over the eight weeks, though there is an "extra" weight training workout that you can use as an option. But the test group did not do this, so it's not part of the Insanity schedule. Depending on your goals, you may want to keep doing some X upper body work. For most of us, and eight week cycle that leaves hypertrophy out of the equation will be fine as we'll improve our base fitness, increase our workload capacity for further rounds of hypertrophy.