Trigger mechanism for an active headrest system and seat back

A trigger mechanism (10) for an active headrest system comprises a support member (11) configured to support upholstery of a seat back (2) of a vehicle seat (1) and a coupling arrangement (13) affixed to the support member (11). The support member (11) has a first side (12) and a second side. The coupling arrangement (13) is configured to pivotably couple the support member (11) to a seat back frame (9) of the vehicle seat (1). A pivot axis (14) defined by the coupling arrangement (13) is spaced from the ends of the first and second sides (12) of the support member (11).