There's a new cartoon on Disney XD called Camp Lakebottom. In the most recent episode a girl tries to intimidate her little brother. She does so by randomly getting massively muscled arms. It's a quick scene and only lasts a second or two.
You can see the ep here.
http://www.justanimedubbed.tv/camp-l...n-1-episode-5/ The growth happens at 3:14. A note about the website. It's slightly odd, first click the continue video button, then a short commercial places. Once that's over click load video and just hit the play button.