As kids head back to school the shops are filled with back to school supplies. That adorable flip sequin backpack that your tween wants may be cute, but is it a wise choice for their back? Parents often don’t consider the impact that a school bag can have on their child’s spine or shoulders. Here are three questions chiropractors consider when choosing school bags.One strap or two?Whether a school bag has one or two straps is important. Two straps are recommended to allow even weight distribution across the body. Two straps allow more weight to be safely carried as well as reducing asymmetrical pressures on the body on the shoulders, spine and hips. This asymmetrical pressure can cause increased stress in the trapezius muscles as the body tries to compensate for the uneven load. Postural scoliosis has also been noted with one shoulder bags as well as reducing core stability. All of these changes can lead to back pain. In addition to spinal health carrying a heavy load in a bag with just one shoulder strap can reduce lung function. It’s important to not only choose a bag with two straps but to make sure your child is using both of them and not slinging just the one strap across a shoulder.Long or short straps?Straps which are short and close together are ideal. Longer straps increase strain on the trapezius muscles and the position of the neck which may lead to increased pain and long-term alterations in the biomechanics of the spine. In an ideal bag, the shorter straps will hold weight securely to the body. This reduces a rotational force known as torque, which increases as weight is further from the body. Think of how much easier it is to push open a door when you’re pushing it at the far edge rather than right next to the hinge. This is due to torque. The further the weight in a school bag is from your child’s spine, the easier it is to pull and distort it. How much weight is being carried?The most well-designed school bag in the world is still going to cause problems if the contents are too heavy. While there is no clear consensus on what the exact weight limit is, a 2004 review in the well regarded scientific journal Spine found that a maximum of 10-15% of an individual’s body weight should be carried in their backpack. Carrying a heavier bag puts increased strain on the bones, muscles and soft tissues in the spine. Amongst other things, this leads to a reduction of the protective lordosis curve in the lower back which causes an imbalance within the spine. Choose a bag which is no bigger than is necessary and encourage your child to go through their bag regularly to make sure extra items aren’t being carried.A general chiropractor will be able to answer questions about this, but taking your child to see a children’s chiropractor is the optimum way to ensure you’re choosing a school bag well suited to their individual situation.