Abstract: The chair has a back rest provided with stiffening means which impart to the back rest a substantially stiff form up to about the level of the sixth lumbar vertebra of the chair occupant, thus ensuring a continuous transition from the chair seat to the back rest, but allow the back rest an increasingly greater flexibility from said level upwards with the result that the upper part of the back rest bends backwards when the occupant leans back, further characterized in that the upper end of the back rest is joined to the shoulder rest via a bracing corrugation in order to ensure that the chair profile in the region of the occupant's shoulder is a smooth curve matching that of the occupant's spine.

Abstract: A work chair with an upholstered, adjustable seat and back which gives ergonomically correct support to the occupant's spine. The chair back comprises a back support and a shoulder support. The lower end of the back support is pivotally mounted in a rounded buttocks support at the rear of the chair seat. The shoulder support is pivotally mounted at the upper end of the back support. Both parts are contoured to correspond to the natural position of the spine. The inclinations of the back support and shoulder support are independently governed by a gas spring device and a torsion member respectively.