Abstract: A seat assembly for a vehicle which includes a seat, a seat back, and mounting means mounting the seat for movement in fore and aft directions in the vehicle along an upwardly concaved arcuate path. The arcuate path has a radius of curvature which is sufficiently large to timely move in front of and to contain the person's buttocks, to significantly slow the rate of deceleration of the person seated on said seat, and being sufficiently small to convert a portion of the linear momentum of the person's buttocks to angular momentum thus maintaining frictional contact of the person's buttocks with the seat during stopping at a high rate of deceleration. A seat assembly which includes a lower lumbar support member that is coupled from movement in response to pelvic tilting movement of the seat also is shown.