EE WAS USING A PORTA-POWER RAM WEIGHING APPROX. 35 LB TO PRESS A BEARING ON A HARD BAR FOR A TRACTOR. HE WAS HOLDING UP THE RAM WHILE ANOTHER EE WAS RUNNING THE AIR PAD. HE STATES HE WAS IN A TWISTED POSITION CREATING A STRAIN AND FELT A TINGLING IN HIS BACK. HE WORKS A 4 ON 4 OFF SCHEDULE AND DIDN'T REPORT TO MANAGEMENT UNTIL 7/15/02