A seat backrest includes right and left side frame segments, a pressure receiving member disposed between the side frame segments movably in a front-back direction, and a cushion pad covering the front of the side frame segments and pressure receiving member. The pressure receiving member includes a main body part, and extending parts extending laterally from both sides of the main body part. The cushion pad includes a back receiving part covering the front of the main body part, and bank parts disposed on both sides of the back receiving part, protruding forward from both sides, and covering the front of the extending parts and side frame segments. A recess is formed at an area, facing a corresponding extending part of the extending parts, of a rear surface of each bank part.

A seat device for a tilting vehicle includes: at least one seat body which has a seat surface on which a user of the tilting vehicle can be disposed and to which a force acting in a direction of action can be applied, the direction of action running transversely to the seat surface; at least one support unit which has at least one resiliently flexible and/or deformable first support portion on which the seat body is disposed, at least one rigid, non-flexible second support portion, and at least one cavity extending parallel or obliquely to the seat surface and disposed between the first support portion and the second support portion, by which cavity the first support portion and the second support portion are spaced apart from each other without touching and by which an elastic deformation of the first support portion toward the cavity is enabled. At least one adjustment unit has at least one adjustment body which is disposed movably in the cavity and by which the first support portion is supported against the second support portion and can be transferred from a first support position to a second support position.

A thoracic support assembly for a seat back of a seat assembly. The thoracic support assembly may include a cover and a thoracic support pad. The thoracic support pad may be movable with respect to the cover and may be configured to support at least a portion of a thoracic region of a user's spine.

Disclosed herein is a 4-way lumbar support capable of automatically adjusting a vertical curved position and an amount of curvature of a lumbar plate, while securely supporting the lumbar plate even when a large load, such as the rear-end collision of a vehicle, is applied to the lumbar plate. In addition, the 4-way lumbar support can adjust an amount of forward curvature of the lumbar plate using a pusher including a pair of hinge members, thereby enabling the amount of forward curvature of the lumbar plate to be adjusted across a wider range without increasing the thickness of a seat back in the forward and backward directions thereof.

A thoracic support assembly for a seat back of a seat assembly. The thoracic support assembly may include a cover and a thoracic support pad. The thoracic support pad may be movable with respect to the cover and may be configured to support at least a portion of a thoracic region of a user's spine.

A back support device, comprising: a frame portion provided at a seat on which a seated person is seated, the frame portion including a locked portion at an upper portion of the frame portion; an upper frame portion fixed to the upper portion of the frame portion and extending in a seat width direction below the locked portion; a lumbar support portion engaged with a lower portion of the frame portion and configured to support a waist of the seated person from a seat rear side; and a pressure receiving portion including, at an upper end portion thereof, a locking portion locked to the locked portion, the pressure receiving portion being supported by the upper frame portion and the lumbar support portion from the seat rear side, and being configured to be deformable by receiving a load from a back of the seated person.