WHILE BEING LOADED UNDER THE SHOVEL A LARGE CHUNK DROPPED JARRING HAUL TRK. 20 MINS LATER EE REPORTED THAT HIS BACK MUSCLES WERE GETTING TIGHT. HE SAID HE HAD BEEN IN SEVERAL AUTO ACCIDENTS HIS BACK WAS BROKEN 2-3 YRS AGO & REINJURED INA HEAD ON 5/04. DR DIAGNOSED MUSCLE STRAIN & RX'D PHYSICAL THERAPY. NO VISIBLE DIFFICULTY CLIMBING DOWN LADDER OR WALKING