Not for most. The jaw muscles get bigger while on gear usually because they flex the jaw muscles when working out. Like clenching your teeth. I have a square jaw due to mainly genetics but try this: Get a huge was of double-bubble and chew it until your mouth literally wont chew it anymore. Then keep going and going. The next day your jaws will be so soar you'll wanna die. Try it! I was a baseball player for 9 years and thats part of it too.