Calvin Harris works out like a real-life pro athlete ... so says Minnesota Vikings safety Antone Exum , who says the DJ blew him away during a Thursday gym sesh.
Exum and Harris were puttin' in work at Heart & Hustle in L.A. -- a pretty elite gym where tons of pro athletes and big stars go to get swole.
Harris was such an animal during the workout, Exum didn't realize he wasn't a pro jock -- and when he figured out who he was, he raced after Calvin to introduce himself.