Since there is no prize...(there is no prize right? ^^) I think it should just be male / female catagory, then when the comp ends those who are still taking part upload the after pics, and all the other users vote on who has "transformed" the most. Just who looks the most different. Bigger, smaller, more shredded etc.
Keeps it simple that way.
Autobots!? Transform and ROLL OUT!