Abstract: There is provided a chair with an improved back support system and method for adjusting and arranging the same. The back support device having a rigid member with a continuously curved projection part along three dimensional curve direction to enable correction of a user's posture or spinal orientation via a plurality of fixed or positionable undulating curved supports, or a monolithic rigid support body. The proposed system and method improves user fatigue, relieves pressures to internal organs, and minimizes unintended body movement causing undesirable muscle tensions.