UNITED STATES  —  Buying new supplies for the start of the school year can be fun, but there is more to consider than just the design when choosing a new backpack.

A lot of supplies will go into these bags, so it’s important to get the right one–and that starts with the shoulder straps. They should be two inches wide or more, and the wider the better. This is the first step in making sure your child can handle the weight of the school year.

A chest or weight strap can help redistribute the pressure across the body, and be sure to sit up straight while wearing one, even when sitting down.

Doctor Rosalyn Nguyen from Baylor College of Medicine says this is critical to making sure your child doesn’t suffer from pain this year, or even years down the road.

“It can lead to numbness in the arms sometimes if it’s too much compression on the nerves, if it’s far too heavy. And neck pain, shoulder pain, muscle aches,” said Dr. Nguyen.

The average weight of a back pack for a sixth greater is 18.4 pounds. The American Academy of Pediatrics recommends that a child’s backpack weigh no more than 10 to 20 percent of their body weight.