Chris Hemsworth's huge bicep has prompted ridicule of his leg muscles - from his own brother

Watch: Chris Hemsworth's huge arm muscles have brought scrutiny on his legs

Chris Hemsworth's right bicep has become a meme after he shared a picture of himself online in which his upper arm appeared the same size as his seven-year-old child.

The 37-year-old Thor star posted a picture of himself on Instagram walking down the street, holding hands with one of his seven-year-old twin sons.

Hemsworth's upper-arm muscles are so huge they appear bigger than his son's head, while his calf muscles appear to be average size, and therefore dramatically out of proportion.

His older brother - 40-year-old actor Luke Hemsworth - teased him by commenting: "Bro?! You’ve been skipping leg days again?!"

Hemsworth captioned the picture: "Holding my little man’s hand and asking him the age old question. 'What do you want to be when you grow up?'

"'Dad I wanna be Superman'. Lucky I have two other kids."

Read more: Chris Hemsworth opens up about his most disappointing roles

Superman is a member of the DC comics' Justice League of superheroes, while the Australian actor stars as Thor — a member of rival franchise: Marvel's Avengers.

Other Instagram users joined with Luke to mock Chris's arm to leg muscle ratio, with one commenting: "Probably because Superman doesn’t skip Leg Day."

The post prompted amused responses from fellow Hollywood stars, including Avenger's co-star Josh Brolin, Ryan Reynolds, star of Marvel's Deadpool movies, and Gal Gadot, who play's Justice League's Wonder Woman.

Read more: Gal Gadot says Joss Whedon 'threatened' her career during 'Justice League' reshoots

Hemsworth and his wife, Spanish model and actress Elsa Pataky are parents to nine-year-old daughter and seven-year-old twin sons.

Watch: Chris Hemsworth's son wants to be Superman!