Drake -- Rock Hard ... For Serena?

Drake is taking this SWOLL patrol thing very seriously, especially in the arms department ... and it might have something to do with impressing his lady friend Serena Williams.

Champagne Papi hit the gym -- it was a curls-for-the-girls day ... and you gotta think all that upper body strength will come in handy on date night. Fact is, Serena's physique is world class -- so you'd expect Drizzy to step up his game too.

When Serena's the gain, you don't mind the pain.