Joseph Baena's looking like he wants to compete in Mr. Universe ... 'cause his sculpted bod's the muscular spitting image of Arnold Schwarzenegger, and he's even striking similar poses.
Joseph pumped some iron Thursday and showed fans what it takes to get those gains. He was in the middle of doing chest flies with 50 lb. dumbbells ... and, after finishing a set, dude took down his Gold's Gym tank to put on a pec-tacular show.
The way he's flexing, it's impossible not to compare his workout sesh to the ones his pop mastered as the world's most-famous bodybuilder.