I have done it a few times, It is a challenging work out. I would recommend to develop a good cardio program before trying it though.
The first time I did it I nearly puked. I think it was the one where you did as many sets of 20 pull-ups, 20 body squats, and double under jump ropes (50 or 100 count I forget) in 20 minutes.
Out of all the people I have worked out with each develop their own routine. Even the people that did crossfit adapted it to make it work for them.
This is hands down one of the best workout systems you can implement.
As FJ Marine said, it has been embraced by the US Marines, MMA trainers and many Law Enforcement agencies throughout North America. I tried it just over a year ago and I have been hooked ever since. It is simple and concise and is guaranteed to whoop your butt everytime. I particularily like it b/c with traditional work out systems you had to do "cardio days" whereas with Crossfit, you are combining your resistance with cardio in the form of integrated running or supersets. Try it, you won't be disappointed!
__________________ '08 Off Road Pkg. MT
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