Abstract: A dynamic, sitting apparatus for strengthening muscles of the lumbosacral spine and abdomen, which also provides a comfortable sitting environment. The device consists of two oppositely facing, sitting platforms that are separated by a pivoting member secured to the undersurfaces of both platforms. The points of attachments of the pivoting member are at the off-center and at the on-center positions, with respect to each platform's own geometrical centers. This allows for comfortable variability of sitting tilting angles for individuals with differing lumbosacral anatomies and pathologies. The outer surfaces of each platform depict indicia showing the locations of each of the platform's center points of pivoting and rotation.