In my opinion, the physical training during the academy wasn't too difficult. I'm sure some academies are tougher than others, but I wouldn't worry about it. Almost everyone that is in average condition that puts forth their best effort can pass. Start out slow, and try to get in better and better condition. Push-ups, sit-ups, and running are are great activities to get in shape and prepare you for the academy. I would also do some pull-ups and interval training when you're fit enough. Stay away from the sugar and saturated fat.