Mark Ballas -- The Shirtless, Sweaty Warrior Workout

Mark Ballas may be a dancing machine by night -- but he's also a sweaty, half-naked ass-kicking machine by day ... and TMZ has the video to prove it.

We caught the "Dancing with the Stars" pro kicking, punching, and kneeing the crap out of his trainer at True Warrior Fitness in L.A. yesterday -- and we gotta say ... it's pretty impressive.

After the session, Mark said his trainer told him, "If you can dance, you can fight."