A backrest assembly of a seat of a chair, in particular a wheelchair, having a seating frame comprising tubes (4', 4"), with the backrest assembly comprising: a backrest for supporting the back of a person; two hollow backrest tubes (6, 7; 60, 70) connecting the backrest to the seat on each side of the seat: at least two joints (14; 90, 91) for allowing a movement of the backrest tubes (6, 7; 60, 70) between at least a first end position and a second end position; two locking means for locking and/or unlocking the joints (14; 90, 91); and an hollow handle tube (8; 80) having only one handle (10; 100), which is arranged in the middle between the backrest tubes (6, 7; 60, 70) and is mechanically connected to the locking means via cables running substantially inside the hollow tubes (6, 7, 8; 60, 70, 80) to effect at least the unlocking of the locking means and the movement of the backrest tubes (6, 7; 60, 70) via the joints (14; 90, 91) when gripped by one hand of an user, without releasing the respective grip of the handle (10; 100), characterized in that the handle (10; 100) is engineered for effecting the locking means to unlock the joints (14; 90) by rotating, wherein the locking means automatically re-locks after effecting the unlocking of the joints (14; 90, 91) and reaching the first or second end positions, and the handle (10; 100) comprises an indicator device for conveying information to the user, wherein the indicator device comprises a tactile device for generating a tactile perception. a backrest for supporting the back of a person; two hollow backrest tubes (6, 7; 60, 70) connecting the backrest to the seat on each side of the seat: at least two joints (14; 90, 91) for allowing a movement of the backrest tubes (6, 7; 60, 70) between at least a first end position and a second end position; two locking means for locking and/or unlocking the joints (14; 90, 91); and an hollow handle tube (8; 80) having only one handle (10; 100), which is arranged in the middle between the backrest tubes (6, 7; 60, 70) and is mechanically connected to the locking means via cables running substantially inside the hollow tubes (6, 7, 8; 60, 70, 80) to effect at least the unlocking of the locking means and the movement of the backrest tubes (6, 7; 60, 70) via the joints (14; 90, 91) when gripped by one hand of an user, without releasing the respective grip of the handle (10; 100), characterized in that the handle (10; 100) is engineered for effecting the locking means to unlock the joints (14; 90) by rotating, wherein the locking means automatically re-locks after effecting the unlocking of the joints (14; 90, 91) and reaching the first or second end positions, and the handle (10; 100) comprises an indicator device for conveying information to the user, wherein the indicator device comprises a tactile device for generating a tactile perception. at least two joints (14; 90, 91) for allowing a movement of the backrest tubes (6, 7; 60, 70) between at least a first end position and a second end position; two locking means for locking and/or unlocking the joints (14; 90, 91); and an hollow handle tube (8; 80) having only one handle (10; 100), which is arranged in the middle between the backrest tubes (6, 7; 60, 70) and is mechanically connected to the locking means via cables running substantially inside the hollow tubes (6, 7, 8; 60, 70, 80) to effect at least the unlocking of the locking means and the movement of the backrest tubes (6, 7; 60, 70) via the joints (14; 90, 91) when gripped by one hand of an user, without releasing the respective grip of the handle (10; 100), characterized in that the handle (10; 100) is engineered for effecting the locking means to unlock the joints (14; 90) by rotating, wherein the locking means automatically re-locks after effecting the unlocking of the joints (14; 90, 91) and reaching the first or second end positions, and the handle (10; 100) comprises an indicator device for conveying information to the user, wherein the indicator device comprises a tactile device for generating a tactile perception.