Justin Bieber's Body -- Check Out My Muscles

Justin Bieber luxuriated on a yacht in Monaco Saturday.

Bieber looked more ripped than ever as he took a break from the Monaco Grand Prix, kicking back and drinking a brewski.

As we reported ... sources very close to the singer tell us he's off Sizzurp ... in no small part because it screws up his workout routine. One source very close to Biebs says in the past 3 weeks he's been like a different person.

Cutting out Sizzurp ... it does a body good.