BENT OVER TO PICK UP 50 LB BAGS OF MATERIAL WHEN HE FELT SHARP PAIN IN LOWER BACK. EMPLOYEE EXPLAINED THAT HE DID ROLL THE BAG TO HIM, BENT HIS KNESS TO PICK UP UP BAG AND KEPT BAG CLOSE TO HI S BODY AS HE WAS STRAIGHTENING HIS KNEES HE FELTA SHARP PAIN IN HIS LOWER BACK.