Infinite position lift chairs (sometimes referred to as Four Position) have dual motors which allow for the back and the ottoman to act independently.  The infinite lift chairs can achieve an almost flat state. How flat depends upon the manufacturer. The Golden Tech lift chairs for instance can achieve a "flatter" state than the Pride lift chairs. The infinite position lift chairs can also achieve the "Trendelenburg position", named for the German surgeon Friedrich Trendelenburg. The Trendelenburg position is when the head is lower than the pelvis.