An adjustable lumbar support mechanism includes a flexible support member, a device for longitudinally subtending the support member, an apex shift linkage, and a loading device engaging the apex shift linkage. The flexible support member has oppositely disposed first and second longitudinal ends. The device for longitudinally subtending the support member is disposed between the first longitudinal end and the second longitudinal end and causes the support member to arch outwardly to define an apex engaging a users back. The apex shift linkage includes a first shift link and a second shift link. The first shift link has a first end pivotably connected to the flexible support member proximate to the first longitudinal end. The second shift link is pivotably connected on a first end thereof to the flexible support at a point between the second longitudinal end and the first end of the apex shift link. The second shift link is also pivotably connected to the first shift link at a hinge point wherein the first shift link and the second shift link define an obtuse angle therebetween. The loading device engages one of the first shift link and the second shift link at a load point wherein applying a load at the load point in a direction toward the flexible support mechanism tends to shift the apex toward the second longitudinal end.