Can going to the gym make you taller? Of course not. Everybody knows that, nobody is so dumb to believe it could. So I'm pretty sure its an elaborate joke on those fellow human beings who tell everybody who (in their eye!) is a fatty to "hit the gym cause there's no excuse" to be not skinny.
You can unfold a few centimeters of spine when you're in your forties but that's about it.
Edit: I claimed that from anecdotal evidence in my surroundings, but I may have underestimated when I said "that's about it"; see below.
Actually I was obese as a child and peaked at 5'10". At 20 years old I joined the Army, lost 65 lbs. in 13 weeks and grew 3 inches. Im not saying the girl isn't stupid, but I honestly believe my weight was holding me back and the doctor agreed.
Edit: I claimed that from anecdotal evidence in my surroundings, but I may have underestimated when I said "that's about it"; see below.