There's really not much more to know; it's a weight maintenance technique, since cellulose is indigestible. Force = mass*gravity and all that. The lighter they weigh, the more height they can achieve. Gymnasts have to worry about their weight for the same reason; that's why child gymnasts actually have an advantage over adult gymnasts, hence the Chinese gymnast boondoggle. But they can be stockier as they're always moving under their own power. Ballerinas are under even greater pressure to be light because their partners have to lift them.