Recommendations For a Healthy Back
Choose a backpack with well padded
straps.
Always use both straps of your backpack.
Use the "hip straps" of your
backpack if it has them.
Put your backpack on by placing it
on a level surface at about waist level; then slide the backpack onto both
shoulders at once. Try to avoid swinging your backpack onto your back.
Carry some of your heavier books in
your arms, to balance the weight you are carrying.
Clean out extra books and supplies
from your backpack regularly. Don't carry more than you need.
This website contains some very informative articles about backpack weight and how it relates to the health of your back.
http://www.rollerbags.com/resource/articles.html