Whilst many laughed at Chris' caption, other fans couldn't resist commenting on the difference between the star's arms and legs.
"Probably because Superman doesn’t skip Leg Day," one quipped along with a crying with laughter emoji.
"Don't forget leg day!" another advised.
One even wrote: "Damn Thor, how do you toss that hammer and not fall with those neglected legs my man? Double up those leg days and cut back on the arm and chest and get more symmetry."
The arms and legs may not match but judging by Chris' gruelling diet and exercise regime, we doubt he's skipping any workouts!
“Dude, listen, everyone is like ‘wow look at the size of him’ and I’m like, yeah, that’s brilliant, I’m that guy's double so I text him I’m like, ‘thanks very much dude you’ve just made this even harder,’” he told Nova's Fitzy and Wippa in February.
“I train with him a lot, we train all the time, we’re on the same diet regime and training. He’s the biggest he’s ever been so I have to be the biggest I’ve ever been which is a challenge but I’m up for it.”
Chris even helped his wife Elsa Pataky, with whom he shares daughter India and twins Sasha and Tristan, to get into shape for her physically demanding role in Interceptor.
Along with his personal trainer, the couple focused on weights and fitness and it sounded gruelling to say the least.
“We worked with big weights and, at the same time, exercises that improve functional movement – we were swimming, we were climbing ropes, we were doing burpees, we were doing a lot of moving and acceleration," Elsa told Women's Health back in March.
“It’s a mix of everything that really helps, and my body started to change a lot in just four weeks.”