P90X
I have both p90 and p90x. I can get about half way through p90. My 17 year old son and his friends do the p90x. It took them a couple of weeks to be able to fini**** This was his work out prior to p90x. 6-8 mile daily run. 1-2 hours of heavy lifting daily. It was more cardio then any of them were used to and it kicked their butts. He loves it but is still a bit sore when he is done.