EMPLOYEE WAS BOLTING WHEN HE STATED A SMALL PIECE OF ROCK HIT HIM IN THE BACK. EMPLOYEE HAD BEEN COMPLAINING OF BACK PROBLEMS TO HIS FELLOW EMPLOYEES WEEKS BEFORE THIS INCIDENT. HE STATED TH AT HE HAS HAD BACK PROBLEMS BEFORE. EE DID NOT SEEK MEDICAL ATTENTION UNTIL 3-30-00. FIRST DAY OF WORK MISSED 4-24-00.