School bells are ringing across Iowa and homework will soon be an evening ritual. Most children bring books, computers and supplies to and from school in a backpack. Gibb Willet, a physical therapist in Omaha/Council Bluffs, says heavy backpacks can damage a kid’s back and spine.

“One-third of children report experiencing back pain that caused them to visit a doctor or miss school or stop doing gym class and they felt backpacks are a component of that,” Willet says. “Fifteen-percent of the child’s body weight should be the maximum a backpack should weigh, so if you are a 100-pound child, your backpack should not weigh more than 15 pounds.”

Wearing the backpack properly is a must. Willet says kids need to use both straps to evenly distribute the weight. “One of the problems with carrying it with one strap, even though the kids think that looks really cool, if it’s heavy, it puts more of a strain on the nerves that go from the neck into the arm so you can get numbness and tingling and can have injury to those nerves due to that pull,” he says.

“It also puts an asymmetrical stress on your spine.”

Willet says there are signs the backpack is too heavy for the child, like red marks on their shoulders from the weight. He says, “If they get any numbing or tingling, like their hands or fingers falling asleep, that is a red flag for that backpack, it’s too heavy, or if they’re having pain in their back or upper shoulder region.”

Willet says if children complain of these symptoms, a backpack could be the culprit. “Low back pain is probably the most common, especially in someone whose spine is still growing, so children, adolescents,” he says, “nerve injuries down the shoulder, numbness into the hands.”

Parents should also make sure the backpack never hangs more than four-inches below the waistline. He adds, bigger is not better when it comes to backpacks as that means there is more room to fill up and the heavier it will be.