EE was getting material samples in 16 ounce cups and was returning to the slab when he slipped. EE did not fall. He regained balanced but felt a ""twinge"" in his back.EE did not want medical attention. On Sept 8 EE said back was still bothering him and made appointment with a PA for Sept 9.PA recommended EE not work until Sept 13 and then on restricted duty for at least one week.