A University of Iowa professor sees too many students mis-using theirbackpacks — and abusing their own backs in the process. Nancy Hamiltonsays rather than slinging the backpack over one shoulder, you shouldposition it over both shoulders.Hamilton says the weight should be as close to the body as possible.Hamilton says research has found that students who carry their bookbag overone shoulder end up with one shoulder higher than the other, which means thespine is out of whack. The advent of kiddie backpacks worries people likeHamilton, who is a professor in U-N-I’s school of health.Hamilton says there’s a new style of bookbag that is better for posture andthe spine as the strap goes across the whole body.The “messenger bag” — which is like a papercarrier’s bag — is patternedafter the bags used by bicycle messengers, which Hamilton hopes makes it acool alternative to the backpack.