Comment by jeremytliles

I guess if you're completely unfamiliar with running, lifting, and movements like pullups and pushups, then you should probably start by going to an affiliate where a trainer can start you out on proper progressions, as opposed to learning the movements yourself. But I don't think going from couch-potato to Crossfit is any worse/harder than going from couch-potato to the sorts of low-effectiveness workouts I see out-of-shape people doing at the gym all the time. The key is knowing or getting to know your own body.