GMC 2008 Acadia - Manual (Page 14)

Head Restraints
Adjust the head restraint so that the top of the restraint
is at the same height as the top of the occupant’s
head. This position reduces the chance of a neck injury
in a crash.
Pull the head restraint
up to raise it. To lower the
head restraint, press the
release button, located on
the head restraint post on
the top of the seatback,
while you push the head
restraint down.
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