Abstract: The invention relates to a dimensionally-stable leg part that can be allocated to a seat device, which leg part is respectively allocated to a left or right upper leg of a person from the knee to the hip and is in close contact with the upper leg form, wherein the leg part contacts flat to the outside of the hip, on the underside of the thigh at least on the distal end, and at least inside and outside on the knee. The invention is further directed to seat devices, particularly vehicle seat devices and vehicle seat extraction systems having said leg parts. In addition, the invention relates to a seat device, preferably a vehicle seat device or vehicle seat extraction system having a U-shaped support device for the back underneath the shoulder having lateral support for the chest, which solely surrounds the adjacent back and chest.