I have these workouts, which are great, they have three or fours muscle groups each workout. I have previously done P90x, which i find to be considerably different. My question is why do most workouts do say 3 Chest exercises then 3 Tricep exercises then 3 shoulder exercises? I don't get it because P90x does one chest, then one tricep, then one shoulder, then one chest, then one tricep etc.. Which method is more effective?