GMC Yukon XL Denali 2005 Owner's Manual page 49

3. To make the lap part tight, pull down on the buckle
end of the belt as you pull up on the shoulder part.
The lap part of the belt should be worn low and snug on
the hips, just touching the thighs. In a crash, this
applies force to the strong pelvic bones. And you would
be less likely to slide under the lap belt. If you slid
under it, the belt would apply force at your abdomen.
This could cause serious or even fatal injuries. The
shoulder belt should go over the shoulder and across
the chest. These parts of the body are best able to take
belt restraining forces.
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