Many things can lead to back pain — like playing sports or exercising a lot, poor posture while sitting, and long periods of inactivity. But some kids have backaches because they're lugging around their entire locker's worth of books, school supplies, and personal items all day long. 

Doctors and physical therapists recommend that kids carry no more than 10% to 15% of their body weight in their packs. But many carry a lot more than that. When a heavy backpack is incorrectly placed on the shoulders, the weight's force can pull a child backward. To compensate, the child might bend forward at the hips or arch the back. This can make the spine compress unnaturally, leading to shoulder, neck, and back pain.

Kids who wear their backpacks over just one shoulder — as many do, because they think it looks better or just feels easier — may end up leaning to one side to offset the extra weight. They might develop lower and upper back pain and strain their shoulders and neck.

Improper backpack use can also lead to bad posture. Girls and younger kids may be especially at risk for backpack-related injuries because they're smaller and may carry loads that are heavier in proportion to their body weight.

Also, backpacks with tight, narrow straps that dig into the shoulders can interfere with circulation and nerves. These types of straps can lead to tingling, numbness, and weakness in the arms and hands.

And bulky or heavy backpacks don't just cause back injuries. Other safety issues to consider:

Kids who carry large packs often aren't aware of how much space the packs take up and can hit others with their packs when turning around or moving through tight spaces, such as the aisles of a school bus.

Students can be injured if they trip over large packs or a pack falls on them.

Carrying a heavy pack changes the way kids walk and puts them at risk of falling, particularly on stairs or other places where a backpack puts a student off balance.