INJURED WAS WORKING ON KNEES, REQUIRED IN LOW COAL, AND WAS MOVING ROCK DUST, 50LB BAG, IN ORDERTO SPREAD ON SECTION. HE LOST GRIP AND DROPPED THE BAG AND IN TRYING TO REGRIP IT AND KEEP IT FROM DROPPING HE STRAINED HIS BACK. NO EQUIPMENTSAFETY OR MINING WAS INVOLVED AND WAS A NATURAL REACTION ON PART OF THE MINER. FIRST VISIT TO DOCTOR ON 8/4/00 AND FIRST DAY MISSED 8/5/00.