A backrest assembly of a wheelchair seat has a tubular seating frame. The backrest assembly further includes a backrest, two hollow backrest tubes connecting the backrest to the seat, and at least two joints allowing movement of the backrest tubes between at least first and second end positions. Two locking means are provided for locking and/or unlocking the joints. A hollow handle tube has a single handle for effecting the locking means to lock and/or unlock the joints. The handle is arranged between the backrest tubes and is mechanically connected to the locking means via cables that effect at least the unlocking of the locking means. The handle further effects movement of the backrest tubes, via the joints, with use of one hand in constant grip of the handle. The handle is actuated by at least partly sliding, rotating, squeezing, pushing and/or pulling. The locking means automatically re-locks after unlocking and reaching the first or second end positions.
