WHILE SHOVELING SAND TO MAKE SMALL TRENCH HE TWISTED AROUND TO DUMP SHOVEL WHEN BACK MADE POPPING SOUND LIKE BREAKING A STICK. LOWER LEFT SIDE OF BACK WAS VERY PAINFUL BUT COMPLETED WORK DAY & WENT HOME.DECIDED LATER THAT NITE TO GO TO E.R. WHERE DR. EXAMINED & PRESCRIBED MEDS WITH LIGHT DUTY. WAS TOLD IF PAIN PERSISTS TO SEEK FURTHER MEDICAL ATTENTION.