A seat (1"") for a vehicle, comprising: a seatback structure (5"") comprising a seatback frame and a plurality of vertically oriented seatback support members (9""), said seatback support members (9""') being connected to a seatback frame (7""); a seat frame (11""), said seatback structure (5"") being connected to said seat frame (11""), said seat frame (11"") comprising a first side member (13"") and a second side member (15""), wherein said plurality of seatback support members (9"") are integrally connected to said seatback frame (7"") to form a single, one-piece seatback structure (5""), wherein each of said plurality of seatback support members (9"") is elastically deformable, at least a portion of said plurality of seatback support members (9"") defining a concave surface with a first concavity in a normal state, said at least said portion of said plurality of seatback support members (9"") defining said concave surface with a second concavity in a crash state, said second concavity being greater than said first concavity, wherein an elastic deformation of said plurality of seatback support members (9"") is greater in said crash state than an elastic deformation of said plurality of seatback support members (9"") in said normal state; a lumbar support structure comprising a first lumbar support structure element and a second lumbar support structure element, the first lumbar support structure element being connected to the second lumbar support structure element via at least one lumbar support structure connecting element, said first lumbar support structure element engaging said first side member (13"") of the seat frame (11"") and said second lumbar support structure element engaging said second side member (15"") of the seat frame (11""), wherein said plurality of seatback support members (9"") define a user support seat surface, each of said plurality of seatback support members (9"") comprising a shoulder support surface and a lumbar support surface, said shoulder support surface of each of said seatback support members (9"") defining a shoulder support region of said user support seat surface, said lumbar support surface of each of said seatback support members (9"") defining a lumbar support region of said user seat surface, said lumbar support region of said user seat surface being concave, said shoulder support region having a concavity that is less than a concavity of said lumbar support region. a seatback structure (5"") comprising a seatback frame and a plurality of vertically oriented seatback support members (9""), said seatback support members (9""') being connected to a seatback frame (7""); a seat frame (11""), said seatback structure (5"") being connected to said seat frame (11""), said seat frame (11"") comprising a first side member (13"") and a second side member (15""), wherein said plurality of seatback support members (9"") are integrally connected to said seatback frame (7"") to form a single, one-piece seatback structure (5""), wherein each of said plurality of seatback support members (9"") is elastically deformable, at least a portion of said plurality of seatback support members (9"") defining a concave surface with a first concavity in a normal state, said at least said portion of said plurality of seatback support members (9"") defining said concave surface with a second concavity in a crash state, said second concavity being greater than said first concavity, wherein an elastic deformation of said plurality of seatback support members (9"") is greater in said crash state than an elastic deformation of said plurality of seatback support members (9"") in said normal state; a lumbar support structure comprising a first lumbar support structure element and a second lumbar support structure element, the first lumbar support structure element being connected to the second lumbar support structure element via at least one lumbar support structure connecting element, said first lumbar support structure element engaging said first side member (13"") of the seat frame (11"") and said second lumbar support structure element engaging said second side member (15"") of the seat frame (11""), wherein said plurality of seatback support members (9"") define a user support seat surface, each of said plurality of seatback support members (9"") comprising a shoulder support surface and a lumbar support surface, said shoulder support surface of each of said seatback support members (9"") defining a shoulder support region of said user support seat surface, said lumbar support surface of each of said seatback support members (9"") defining a lumbar support region of said user seat surface, said lumbar support region of said user seat surface being concave, said shoulder support region having a concavity that is less than a concavity of said lumbar support region.