US Patent 6938956 Chair backrest

Chair backrest, comprising a support structure (12), an upper backrest member (30) connected in oscillating fashion to said support structure (12), a lower backrest member (32), and a connecting element (80) which is fixed relative to one of said backrest members (32) and able to slide telescopically inside the other backrest member (30), the connecting element (80) having at least one elastically deformable zone (82) and being able to apply an elastic force to said backrest members (30, 32) as a result of a variation in the relative angular position of said backrest members (30, 32).