EE WAS ASSISTING 3 OTHER EE'S CARRY A 4'X8' VIBRATOR SCREEN UP THE STEPS FROM THE GROUND LEVEL TO THE FIRST FLOOR OF THE CRUSHER TOWER. THE SCREEN WAS BEING CARRIED UP THE STEPS TO THE 1ST FLO OR TO ACCESS THE CHAIN HOIST. AS THEY NEARED THE TOP OF THE STEPS & WERE NEGOTITING THE SCRE3N OVER THE HANDRAIL EE FELT A SHARP PAIN IN THE ABODMEN AREA. HE HAD A PREVIOUS NON WORK RELATED