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A backrest for use with a chair includes a support structure. The support structure has a rigid outer rim and flexible inner back support section. The support section consist of a number of generally parallel slats (vertically extending members) which seperately support parallel longitudinal section

A backrest for use with a chair includes a support structure. The support structure has a rigid outer rim and flexible inner back support section. The support section consist of a number of generally parallel slats (vertically extending members) which seperately support parallel longitudinal sections of the person's back. Each slat produces a force against the person's back responsive to the weight placed on the slat by the person's back. As the person shifts positions, each slat moves to dynamically provide an increased or decreased force against the person's back, depending on whether the person is applying an increased or decreased force against the slat.

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1. A backrest for attachment to a chair having a seat, the backrest having a front and a back and comprising:(a) a frame having a top and a bottom and comprising an outer peripheral portion which surrounds a central open portion;(b) a support shell mounted on the frame; and,(c) a plurality of flexib

1. A backrest for attachment to a chair having a seat, the backrest having a front and a back and comprising:(a) a frame having a top and a bottom and comprising an outer peripheral portion which surrounds a central open portion;(b) a support shell mounted on the frame; and,(c) a plurality of flexible, independently moveable, vertically extending members mounted to said support shell and positioned to engage at least a portion of a back of a person when the person is seated in the chair, whereby the support shell and the vertically extending members are formed integrally, the vertically extending members are positioned in the central open portion when the backrest is assembled and the vertically extending members engage the frame only at the top and the bottom whereby the vertically extending members support the back of the person without engaging any structural member positioned behind the vertically extending members. 2. The backrest of claim 1 wherein the vertically extending members are positioned to engage at least the lumbar and mid-back of the person when the person is seated in the chair. 3. The backrest of claim 1 wherein the vertically extending members are positioned to engage substantially the entirety of the portion of the back of the person which is supported by the back rest. 4. The backrest of claim 1 wherein the flexion of the vertically extending members conforms to the shape of the back of the person as the position of the back of the person with respect to the backrest is adjusted. 5. The backrest of claim 1 wherein the support shell and the frame each have an outer peripheral portion and a central opening and the vertically extending members are positioned in the central openings. 6. The backrest of claim 1 wherein the vertically extending members have a bottom portion that is vertically adjustable. 7. A backrest for attachment to a chair having a seat, the backrest comprising:(a) a support structure having a top and a bottom and a central open portion; and, a plurality of flexible, independently moveable, vertically extending members positioned in the central open portion to engage at least a portion of a back of a person when the person is seated in the chair, the vertically extending members have a front face, a rear face, a forward extent of movement and a rearward extent of movement wherein at the forward extent of movement the front face of the vertically extending members is spaced from any other structural member of the backrest and at the rearward extent of movement the rear face of the vertically extending members is spaced from any other structural member of the backrest, wherein the vertically extending members have a bottom portion that is vertically adjustable. 8. The backrest of claim 7 wherein the bottom portion is engagable at a plurality of vertically spaced apart engagement members provided on a bottom portion of the back rest. 9. The backrest of claim 7 wherein the vertically extending members are positioned to engage at least the lumbar and mid-back of the person when the person is seated in the chair. 10. The backrest of claim 7 wherein the vertically extending members are positioned to engage substantially the entirety of the portion of the back of the person which is supported by the back rest. 11. The backrest of claim 7 wherein the flexion of the vertically extending members conforms to the shape of the back of the person as the position of the person with respect to the backrest is adjusted. 12. A backrest for attachment to a chair having a seat, the backrest comprising:(a) a support structure having a top and a bottom and a central open portion;(b) a plurality of vertically extending members having a top portion and a bottom portion, said vertically extending members being positioned in the central opening and laterally spaced apart for at least a portion of their height to permit independent movement of adjacent vertically extending members, wherein each of the vertically exte nding members supports a longitudinal section of at least the lumbar region of a person seated on the chair without engaging a supplemental support member, the vertically extending members are adjustable by raising or lowering one of the top portion or the bottom portion. 13. The backrest of claim 12 wherein the vertically extending members are adjustable for controlling the amount of support provided to the lumbar region of the person. 14. The backrest of claim 12 wherein one of the top portion or the bottom portion is attached directly to the support structure and the other of the top portion or the bottom portion is engagable at a plurality of vertically spaced apart engagement members provided on the support structure. 15. The backrest of claim 13 wherein the vertically extending member has a bottom portion that is vertically adjustable to vary the amount of support provided to the lumbar region of the person. 16. The backrest of claim 15 wherein the bottom portion is engagable at a plurality of vertically spaced apart engagement members provided on a bottom portion of the support structure. 17. The backrest of claim 15 wherein the support structure comprises a frame and a support shell mounted thereon and wherein the vertically extending members are provided on the support shell at one vertical end thereof and wherein the engagement members are provided on the frame. 18. The backrest of claim 12 wherein the support structure and the vertically extending members are formed integrally.