I've been doing CrossFit for a year now. I couldn't articulate enough how it has improved my posture and general fitness. There isn't one particular thing about CrossFit, rather the whole. I'd recommend to anyone.
For those who want to get started, but don't know how checkout Nerd Fitness: http://www.nerdfitness.com/blog/ I have no ties, only that it's a great place to start learning about how to take care of yourself.