A seat assembly including a seat, a backrest and a mounting assembly mounting the seat in a near horizontal orientation for movement along an upwardly concaved arcuate seat path having a center of curvature proximate the center of mass of a person seated on the seat, and mounting assembly further mounting the backrest in a near vertical orientation for movement independently of the seat along a forwardly concaved arcuate path having a center curvature proximate the center of mass of the person. An adjustment assembly is provided for adjusting the radius of curvature of the path of motion of the backrest. Also provided are a backrest tilt adjustment assembly, an armrest adjustment assembly, a seat biasing assembly and a seat motion latching assembly. A method of self-adjusting support and alignment of a backrest also is disclosed.