NBA Star Myles Turner is Getting Jacked ... To Stop LeBron??

Here's what it looks like when you've had enough of losing to LeBron James.

Indiana Pacers star Myles Turner -- just weeks after losing another playoff series to LBJ and the Cavs -- decided to go from skinny fat to shredded ... and we gotta say, the results so far are impressive.

The almost 7-footer's been hitting the weights the last five weeks ... but he's also been moving his big-ass frame around in boxing sparring sessions.

FYI ... prior to Turner beefing up this summer -- he weighed in at 255 pounds. LeBron -- the guy who's killed Turner and the Pacers' playoff dreams the past two years -- clocked in at 250 ... at three inches shorter!