Tom Brady Shows Off Bulging Biceps After Gym Session

Forget plyometrics, Tom Brady's clearly hitting the weights in retirement ... check out his arms following his latest gym session Wednesday -- dude's biceps are bulging!!!

TB12 got in the sweat sesh down in Miami on his off day from his Fox broadcasting duties ... and it's clear it was an upper-body hump day for the GOAT.

Take a look at what was underneath the sleeves of his tan shirt as he walked out of the fitness facility ... his pythons were hissin'!

Of course, we've known for a while now Brady's been improving his body drastically following the end of his football days ... as he's been seen topless and chiseled a whole lot over the last year or two.

Still, the images from his post-workout…