An energy management device (10) for seat belt webbing (18) for restraining a vehicle occupant includes a base (40) for attachment to the vehicle. The device (10) also includes a plastically deformable torsion bar (60) having a first portion (66) fixed relative to the base (40) and a second portion (72) rotatable relative to the first portion and the base. The torsion bar (60) twists upon rotation of the second portion (72) relative to the first portion (66). A spool (80) is supported on the base (40) and is fixed for rotation with the second portion (72) of the torsion bar (60) relative to the first portion (66) of the torsion bar. The spool (80) has an outer peripheral surface (90). A flexible member (100) is wound on the outer peripheral surface (90) of the spool (80). The flexible member (100) has a first end portion (104) connected with the spool (80) and a second end portion (110) extending from the spool (80) for connection with the seat belt webbing (14) of the vehicle. The torsion bar (60) twists and the spool (80) rotates in an unwinding direction upon the application of tensile force from the seat belt webbing (18) to the flexible member (100) in an amount exceeding a predetermined amount. The torsion bar (60) when twisting resists unwinding of the flexible member (100) from the spool (80). The distance between the axis of rotation (54) of the spool (80) and the outer peripheral surface (90) of the spool (80) varies to vary the resistance to unwinding of the flexible member (100) felt by the occupant. The resistance to unwinding varies as a function of the amount of the flexible member that is unwound from the spool.