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?!"

CHICAGO, ILLINOIS - OCTOBER 13: Chris Hemsworth speaks on stage during ACE Comic Con Midwest at Donald E. Stephens Convention Center on October 13, 2019 in Rosemont, Illinois. (Photo by Daniel Boczarski/Getty Images)
Chris Hemsworth has been working hard to build his upper body strength. (Getty Images)

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.

Liam Hemsworth, from left, Chris Hemsworth and Luke Hemsworth arrive at the Los Angeles premiere of
Chris Hemsworth (C) with brothers Liam (L) and Luke Hemsworth (R) who are both also actors. (AP)

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."

Chris Hemsworth in action in Thor: The Dark World, which Kenneth Branagh didn't direct (Image by Marvel Studios)
Chris Hemsworth must wield an enormous hammer as superhero Thor. (Marvel Studios)

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!