What's in your backpack? Textbooks? Cell phone? Water bottle? Sneakers? Science project? Gym clothes? Musical instrument? If you're anything like the kids we interviewed, we bet it's all of the above. And if that's the case, you're one of millions of students who walk the halls hunched forward in an attempt to keep from tipping over and don't know much about backpack ergonomics. Lugging around the weight of the world has resulted in a new phenomenon —backpack pain. It's probably not news to you that kids are carrying weightier piles of books home as part of a drive to boost academic performance through increased homework. School children often report shoulder and back pain due to ferrying too heavy a load back and forth to school. With some kids, it's not the weight that's causing the pain, but the way they carry their backpack over one shoulder, causing them to walk with an incorrect posture. Some schools are so concerned about this problem that they're coming up with their own solutions. A school district in Seattle forbids the use of backpacks beyond the locker area. A few towns on Long Island are trying to supply two sets of science and social studies textbooks, one for school, and the other for home. If you're experiencing discomfort, learn about backpack ergonomics in order to save your back. The American Academy of Pediatrics recommends that children carry no more than ten to twenty percent of their own body weight in their backpack. Typically that means the bags should weigh less than fifteen pounds. Backpacks should be strapped around the waist to prohibit the bag from bouncing against the spine. This will help to prevent slouching, which can cause spinal misalignments and a lifetime of spinal problems. Both straps should be used so that the weight being carried is distributed evenly. Lots of kids just pick up their bags and fling them over one shoulder. It might be the quickest and easiest way at the moment but the imbalance can lead to a strain in the spine and chronic lower back pain. If you have only a single strap, cross it over your shoulder so that the weight is equally balanced. If the bag is resting on your right hip, have the strap on your left shoulder. The best backpacks have straps that are at least two inches wide and well padded. The bottom of the backpack should not go below the waistline. The heaviest objects should be packed closest to the back. But if the backpack has compartments, the weight should be distributed as evenly as possible. Make sure the backpack is neither too big, causing it to ride up on your hip, or too small, causing you to carry the weight in the upper part of your back. Rolling backpacks or "rollies," have retractable handles and rubber wheels. That's the good news. Unfortunately they have to be hauled up staircases, don't roll well in the snow, and are too bulky to fit in some school lockers. Learn about backpack ergonomics and get helpful tips and advice at BeingGirl.com.