Abstract: A lumbosacral backrest for use with chairs, beds and various other furniture, vehicle seats, and wheelchairs. The device, which may be portable or built-in, has an upstanding foundation frame of generally rectangular form, a yieldable back support on that frame, and a regulator spindle interposed between the frame and the yieldable back support. The regulator spindle is journalled for rotation longitudinally of the yieldable back support and may be stopped at any selected position within its range of rotational adjustment. This provides a transverse plane of rigidity across the back support at such selected position and thereby effects an adjustment in the contour of the back support. Adjustment of the regulator spindle may be accomplished manually or by power means.