Haul Truck Operator was bending over to get into the cab of EE's CAT 777 Haul Unit and felt a sharp pain in EE's lower back. The pain persisted and EE notified EE's supervisor and was sent home. The next day EE went to the clinic and was diagnosed with Sciatica. EE was placed on light duty for 1 week. EE returned to work on 8/26.