Just a word of warning to anyone starting P90X.
I went from years of inactivity, straight into P90X. I wasn't overweight or exceptionally unfit, but my body wasn't conditioned to any sort of exercise. I first started P90X in February of 2010, and stopped in July.
Several weeks after starting P90X I had sore shins after some exercises, some people told me I might have shin splints, and they would go away, others said it was just the body getting used to exercising.
Fast forward to now, and the problem is still very evident. After visiting 2 doctors, a physiotherapist, and finally a sports medicine specialist, I've been diagnosed with having Tibial Stress Fractures. It's not serious, but will take a couple of months to heal.
The cause? Plyometrics. Speaking with athletics trainers, my specialist, personal trainers, they all agreed that Plyometrics was the cause, and should not be attempted by anyone who isn't ready for it. The athletics trainer said his jumpers would do two plyo sessions a week, but only after 16 weeks of conditioning.
Don't get me wrong, P90X is a fantastic training program, and I would recommend it to anyone, but I would stay away from Plyometrics until you are strong enough to handle the stress involved.