A small, light, handy personal fitness device offers both support and/or instability during abdominal and other exercises. The lumbar support (1) allows hyperextension during rocking motion. When the user is positioned with buttock in pelvic basin (3a), lumbar support (1) in combination with end contour (4b) gives support such that the body's own weight assists in the upward crunching motion. The inverted domed surface (2) offers instability in all directions.