INJ WAS TAKING A 12 TON MTR TO THE #3 HEADGATE WHEN HE NOTICED A ROCK ON THE TRACK HE STOPPED THE MTR & ATTEMPTING TO MOVE THE ROCK WHILE MOVING THE ROCK HE FELT A SHARP PAIN IN HIS BACK HE NOTIFIED THE FOREMAN & FINISHED HIS SHIFT PAIN INCREASED AS HE ARRIVED HOME SO HE WENT TO HOSP WHERE HE WAS DIAGNOSED WITH SPRAINED MUSCHEL IN HIS BACK