Adrian Peterson BEASTING OUT In Gym ... I'm NOT On a Decline (VIDEO)

Adrian Peterson is showing NFL teams he's still a FREAK IN THE GYM ... posting footage from a recent workout to prove he's still got the power and explosiveness to dominate in the league.

In the footage, AP knocks out 23 reps on the bench press -- it looks like he's pushing 225 lbs.

Then he grabs the squat bar -- loads it up with another 50 pounds -- and starts doing box jumps!

Peterson added a message -- "Not on a decline, rather an incline! 32 in a few weeks and still schooling!"