A seat assembly 21 including a seat 22, a backrest 23 and a mounting assembly 24 mounting the seat 22 in a near horizontal orientation for movement along an upwardly concaved arcuate seat path having a center of curvature 37 proximate the center of mass 39 of a person seated on the seat, and mounting assembly 24 further mounting the backrest 23 in a near vertical orientation for movement independently of the seat along a forwardly concaved arcuate path having a center curvature 37 proximate the center of mass 39 of the person. An adjustment assembly 61 is provided for adjusting the radius of curvature of the path of motion of the backrest 23. Also provided are a backrest tilt adjustment assembly 71, an armrest adjustment assembly 90, a seat biasing assembly 110 and a seat motion latching assembly 111. A method of self-adjusting support and alignment of a backrest also is disclosed.