Apolo Ohno -- Check Out My Jacked Up Gun Show!

He may be on "Dancing with the Stars," but based on this pic ... it's all about watching Apolo Ohno's massive gun show.

After a kickboxing session on Sunday, the 30-year-old Olympian tweeted a humble pic of himself ... flexing his huge yoked arms.

Doing the Cha-Cha-Cha with Karina Smirnoff does the body good.