We will have to tryI have been doing CrossFit for about 3 years and love it. I modify the daily workout significantly to fit my personal needs but the underlying principles of short, intense, functional movements are still there. It's been very effective airway clearance for me as well as improving my overall fitness and stamina. Not all crossfit gyms are the same and the critiques of crossfit are not unwarranted because many coaches just don't have enough training and experience to properly teach correct form, how to scale workouts for your personal needs, etc. However, if you find a gym with coaches that have extensive training and backgrounds in fitness, weightlifting, etc. and you take the time to be trained properly by them you will not hurt yourself as many do when they try to go balls to the wall on their first workout. That really goes for all forms of exercise. Probably shouldn't start out, as Ethan said, going for your max effort on the first day and totally kill yourself.