Beats me, then again I don't know anyone named Ralph.
My guess is hormones. When the mutigen reacted with them as infants they gained some human genes, and when boys hit puberty it can turn any baby faced boy into a muscle bound guy.
Just biology working.
Who's Ralph? It's Raph lol.
Lol. Ralphael.
I guess he was born cute and innocent and wanted to change his stance on how people looked at him.. Kinda like Miley cyrus LOL O___O
Or maybe one time, he was weak at first when a gang attacked him. Then, Splinter teached him to fight and turn cute Ralph to tough Ralph.
Well the turtles have been trained to be ninja probably at a very young age like maybe 8. Since they're working out for like 7 and stuff they started to become very muscluar. Have you guys that all the turtles are all muscluar. Even Mickey and Donnie who seem like the least atheltic. So I'm guessing Raph was as strong as a regular baby until he started training that made him really strong.