News: According to a clinical study from Oklahoma State University, replacing old mattresses with new, medium-firm mattresses not only reduces back pain, shoulder pain, spine stiffness and positively affects sleep quality, but it also significantly decreases stress (Bed Times, April 2009: 8). Which type of mattress provided test subjects with new levels of comfort and healthy sleep? INNERSPRING, of course! More specifically, a mattress with foam-encased Bonnell spring units and Leggett and Platt's Semi-Flex foundation.