Tony Hawk -- Backflip Dude Adam Miller Nearly 'Broke Himself' Practicing Amazing Stunt

Tony Hawk says the only thing more impressive than Adam Miller's amazing skateboard-to-skateboard backflip -- is the fact Miller survived 3 bone-crushing days of practicing the ridunkulous maneuver.

Miller was at Tony's Southern Cali skate park when he pulled off the stunt -- which Tony describes as "part gymnastics, parkour, and skateboarding." Video of the move racked up nearly 2 million views on Tony's Ride Channel in less than a week.

But when TMZ caught up with the godfather of skateboarding he told us Miller busted his ass over, and over, and over (below) on pavement -- and without a helmet or pads -- before nailing the backflip.

"He tried it for a couple days and he kinda broke himself off ... He goes hard, and he takes it ... one after the other just slamming into the cement."

Tony added ... Miller deserves all the attention he's getting because "it's hard to come up with something really brand new and different" in skateboarding.

As for attempting the backflip himself ... Tony says, "I would love to try stuff like that, honestly, but I don't have that body sense, and that gymnastics background at all."

Uhh, it's cool Mr. 900 ... you don't have to prove anything to us.