It’s that time of year again. The kids are all back in school, all of their supplies have been purchased and now it’s time to check those backpacks. It’s about the time that the homework increases, the amount of book and binders needed increases, and so does the physical load on our kids.

When dropping your child off at school it is clear to see dozens of types of backpacks, worn in a multitude of ways…but what is the right way to prevent injury or pain? While a backpack is still one of the best ways to tote homework, an overloaded or improperly worn backpack gets a failing grade, according to the American Physical Therapy Association (APTA). An improper backpack use can cause pain and even injury, especially to children with young, growing muscles and joints.

A study led by APTA member Shelley Goodgold, PT, associate professor of physical therapy at Simmons College in Boston, found that 55% of the children surveyed carried backpack loads heavier than 15% of their body weight, the maximum safe weight for children recommended by most experts. “It is disturbing to find children carrying backpacks heavier than the recommended weight limit, particularly given the vulnerability of youths’ musculoskeletal systems during these growing years,” Goodgold said. It was also found that 1/3 of the children reported experiencing back pain that had caused them to visit a doctor, miss school, or abstain from physical activities. “While we do not have scientific evidence proving that heavy backpacks cause serious back or other musculoskeletal damage,” Goodgold said, “we do know that children who have back pain usually have recurrent problems, and we know that the risk of future back problems increases when a person has had one episode.”

How could my child’s backpack cause injury or pain?

Injury can occur when a child, in trying to adapt to a heavy load, uses harmful postures such as arching the back, leaning forward or, if only one strap is used, leaning to one side. Over an extended amount of time, use of poor posture can create an imbalance in muscles and uneven weight on joints. These postural adaptations can cause spinal compression and/or improper alignment, and may hamper the proper functioning of the disks between the vertebrae that provide shock absorption. Too-heavy of a load also causes muscles and soft tissues of the back to work harder, leading to strain and fatigue. This leaves the back more vulnerable to injury. A heavy load may also cause stress or compression to the shoulders and arms. When nerves are compressed, the child may experience tingling or numbness in the arms.

When worn correctly and not overloaded, a backpack is supported by some of the strongest muscles in the body: the back and abdominal muscles. These muscle groups work together to stabilize the trunk and hold the body in proper postural alignment.

Physical therapists recommend the following tips for safe backpack use:

1. Wear both straps. Using only one strap, even with backpacks that have one strap that runs across the body, causes one shoulder to bear the weight of the bag. By wearing both shoulder straps, the weight of the pack is better distributed, and a symmetrical posture is promoted. A backpack that has padded, contoured shoulder straps will also help reduce pressure on the chest and shoulders.

2. Make sure the backpack fits. It is important to pay close attention to the way a backpack is positioned on the back, and the size of the backpack should match the size of the child. The top of the backpack should not extend higher than the top of the shoulder and the bottom should not fall below the top of the hipbone. Ideally, the shoulder straps should fit comfortably on the shoulder and under the arms, so that the arms can move freely, the bottom of the pack should rest in the contour of the lower back. The pack should “sit” evenly in the middle of the back, not “sag down” toward the buttocks.

3. Your backpack should not sway from side to side as you walk. That can lead to chafing from the shoulder straps and from rubbing against your back. A stable load is better. Compression straps to keep the pack tight together (if present are on the side of the pack) should be tight to keep a less full pack from shifting weight backwards and away from the body.

4. If the backpack has a waist strap or pectoral strap, you should use it. Waist straps help to distribute the weight load to the hips, relieving shoulder pressure. A pectoral strap helps keep the shoulder straps in place and reduces swaying of the pack. A hip strap or waist belt can take as much as 50-70% of the weight off the shoulders and spine. The waist belt will equalize the strain on the bones, joints and muscles.

5. Keep shoulder straps on the shoulders. The shoulder straps should be at least 2 inches wide and should not fit too snugly around the arms, straining muscles and affecting nerves.

Physical therapists recommend the following features when selecting a backpack:

A padded back to reduce pressure on the back and prevent the pack’s contents from digging into the child’s back

A waist belt to help distribute some of the load to the pelvis

Compression straps on the sides or bottom of the backpack that, when tightened, compress the contents of the backpack and stabilize the articles a

Reflective material so that the child is visible to drivers at night

Another option in a backpack with wheels and a handle long enough so that child does not have to twist or bend and wheels that are large enough to stabilize the bag if books are heavy (Caution- wheeled backpacks may present problems, such as getting them up and down stairs or trying to fit them into cramped locker spaces, and tend to be heavier than standard canvas backpacks).

So how do you make sure that your child stays injury-free?

Here are signs that the backpack is too heavy:

Pain when wearing the backpack

Tingling or numbness in the arms

Red marks on the shoulders