GMC 2011 Sierra Denali Owner's Manual page 71

WARNING
You can be seriously injured if
your belt goes over an armrest
like this. The belt would be much
too high. In a crash, you can slide
under the belt. The belt force
would then be applied on the
abdomen, not on the pelvic
bones, and that could cause
serious or fatal injuries. Be sure
the belt goes under the armrests.
Q: What is wrong with this?
A: The shoulder belt is worn under
the arm. It should be worn over
the shoulder at all times.
Seats and Restraints
WARNING
You can be seriously injured if
you wear the shoulder belt under
your arm. In a crash, your body
would move too far forward,
which would increase the chance
of head and neck injury. Also, the
belt would apply too much force
to the ribs, which are not as
strong as shoulder bones.
You could also severely injure
internal organs like your liver or
spleen. The shoulder belt should
go over the shoulder and across
the chest.
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