The invention relates to a support element (11) for the human body, in particular to a backrest, of a chair or armchair.The support element (11) has a support face (21) that forms a front side of the support element. The support element is equipped with a self-adapting longitudinal structure (13), which includes at least one front, first longitudinal element (15), and at least one rear, second longitudinal element (17), extending parallel to the first longitudinal element (15), as well as a plurality of spacers (19), which are each pivotably connected to the first longitudinal element (15) and to the second longitudinal element (17). The second longitudinal element (17) is connected at a rigid angle to the first longitudinal element (15) at at least one connection point (27) and is borne at a support point (29) spaced apart from the connection point (27). The spacers (19) keep the second longitudinal element (17) spaced apart from the first longitudinal element (15) between the connection point (27) and the support point (29). Bearer means (15, 37) are present, for instance two elongated peripheral parts (15), which extend in the same direction as the longitudinal elements (15, 17), and/or a plurality of riblike members (37).