P90x is a very intense workout regimen, it's not for the casual weight-loss candidate. You need to have the time and dedication available to stick to something like that. The main difference I see between P90x and Crossfit is the self-motivating factor needed to do P90x. Crossfit is in a gym setting, where you have peers pushing you and motivating you. P90x is done in your home typically by yourself, to do this you need to be able to keep yourself motivated.
That being said, I did P90x for about 4-6 weeks on and off and saw incredible results when it came to building muscle. It definitely works, it's just a very intense workout and takes a lot of time and dedication.
Now I just do things like pullups, pushups, dips, etc. I still use some of the moves I've learned from P90x though (deep prayer squats, dive bomber pushups, chair dips, etc) Tony Horton definitely knows what he's doing, and there's a lot of good practical exercises in there.
If you're stilling looking for input on this topic, here is mine:
Pros: Very thorough; Tony Horton is easy to listen to 6 times a week; a decent setup (weights, cardio, plyo, yoga); one-time purchase, with most supporting gear not being too expensive; can do it whenever; legs & back, chest & back, core synergistics and plyo very good and fun workouts
Cons: The workouts are extremely time-consuming - 6 days a week (with optional 7th stretch day) - yoga workout is 90 minutes, many workouts doubled-up with an ab workout which is about 300 crunches; some of the workouts are tricky for those with less coordination (like me!), particularly the Kenpo workout; lots of isolation moves, particularly in shoulder & arms and back & biceps workouts (I got tennis elbow from the endless curls in shoulder & arms).
My Experience: I worked through the program, with some modifications due to the tennis elbow (I had not done an isolation exercise in 9 months - stupid curls!). I did not follow the diet portion very strictly. I lost 7 pounds, doubled my pullups and increased my pushups by 30%. But it was really tedious to work in those long workouts, even though I have a very flexible and generous schedule.
Pros: Whole-body compound moves; short and sweet workouts; community; gym environment where you can make noise without treadmill zombies complaining that you are making it hard for them to talk on their cell phones; getting to play with fun things like tires, etc
Cons: Moves can be difficult for novices (make sure you get a good and watchful trainer to help - particularly with things like barbell cleans and snatches); keeping up with community could lead to injury
I have done Crossfit-like workouts, but not the WOD, website stuff per se. I enjoy whole body things, kettle bells, and so forth. And when I was in a gym, I did make a bit of noise. So I have an affinity to this sort of thing.
If you must choose between the two, I would go with Crossfit, and ease into it a bit.
Best of luck!
BTW, if you want to look like a Spartan (as in the 300), there is a very nice workout book by Dave Randolph called the Spartan Warrior Workout (he is an RKC guy who helped design the 300 workout). My wife and I worked through a few rounds/versions last summer, with very good results. It's fairly cheap and accessible.
Based on your goal of trying to lose weight, if that is your primary or only goal then:
1. Don't do any working out unless you want to and you feel like it. Then do whatever is fun. Just don't over-do it, or you'll tend to eat more to compensate.
2. Quit it with the 20% cheats. DO NOT take the "80/20 rule" literal. Mark's point (google his post about this) is that you should be striving for 100%, but we know that's not achievable for most folks, so the occasional beer or two at a party, etc. is fine. But saying, "Okay, I'm eating 5 times per day, so one of those times I'll have bread" is just wasting your time and will result in mitigating any possible weight loss. That said, CrossFit will burn those carbs off (assuming that's what your 20% cheats consist of, as most people can't cheat on steak or chicken...). But you won't lose weight by simply working out. It's another CW myth.
I dropped a total of ~70lbs and have maintained it for over a year now, down from 258lbs (male). Dropped the first 40lbs in 4 months without working out at all - just cutting carbs to less than 30g per day. After the 4 months/40lbs I had so much energy I figured I'd try working out. Once I started doing some exercising at a globo-gym I still lost weight but the rate slowed drastically. It took another 6 months to lose the remaining 30lbs.
I maintained that weight loss through the remainder of last year and, for 2012, decided I wanted to set a goal of achieving "workout warrior" status. I started CrossFit a couple of months ago, with 2x per week the first 6 weeks and now 3x per week. I'm 41yo and having never seriously exercised before, CrossFit is HARD. Honestly, I hate the workouts DURING the workouts. I think it's too much. And, based purely on Mark Sisson's PB philosophy/writings, CrossFit is a fail unless you're doing it once per week only (which no CrossFit box has a 1x per week membership, though I guess you could do a drop-in rate). Even the strength/lifting-focused days are basically HIIT/chronic cardio. Unless my box is more 'hardcore' than others (I seriously doubt it), then the warm-up is well above "move slowly" heart rate levels, let alone the actual WODs. Let's be honest - CrossFit is both strength training AND chronic cardio. Except most globo-gym chronic cardio folks don't get their heart rate up as high as CrossFitters do during a WOD! And while most WODs are shorter, when you include the warmup you're still looking at a minimum 30 minutes and sometimes 50 minutes of high intensity. Doing that multiple times per week goes against Mark's recommendation.
That said, I do enjoy the challenge and am seeing definite measurement results (waist shrinking, leaning out, and muscle/toning). But I guarantee I wouldn't have lost the 70lbs that I lost last year if I had relied on CrossFit or any exercise as a method to do it. It's all diet, and I found once I started exercising, weight loss slowed for me. About 10% of the folks at my CrossFit gym are overweight/obese and many have been CrossFitting for years. They can lift twice the weight that I can and run circles around me in metcons. But I can't help but think, when I see them, that I'd love to have the balls to pull them aside and tell them to quit the CrossFit for a few months, eat very low carb Paleo and drop the fat, and then come back if they still feel so inclined.
As for P90X...the videos looks corny as hell. I guess if you have the self-motivation/discipline then it'd certainly be cheaper than CrossFit. But I would think 99% of people would not be able to stick with P90X, whereas most people do seem to stick with CrossFit.
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