Abstract: A seat belt system conventionally includes a shoulder belt deflected across the occupant torso by a guide loop and wound upon a reel having a spring winding the belt taut about the occupant torso so that forward movement of the occupant in the seat is enabled by unwinding of the belt from the reel against the bias of the winding spring. An auxiliary spring is interposed in the shoulder belt system between the retractor and the occupant and is effective to permit limited contraction and extension of the seat belt independent of the winding and unwinding of the belt by the retractor. The auxiliary spring has a normal position adapted to retain the belt contracted when the occupant is seated stationary in the seat, and enables limited extension of the belt to accommodate breathing and limited forward movement of the occupant during normal wearing of the belt without unwinding the belt from the reel.