Joshua Jackson may have picked up a thing or two from “Karate Kid: Legends” … we got video of him going H.A.M. in a boxing gym with a trainer.

Watch the video … the 47-year-old actor ditched his shirt for the workout, really working up a sweat as he bobbed and weaved in the ring while throwing in some pretty impressive jabs!

He later goes to work solo on a speed bag like an old pro.