With the new school year starting this week, excitement (and probably some dread) has set in at households across the city, province, and country. As families have gone to the big box stores to buy supplies for the kids, things like pens, pencils, pencil crayons, erasers, paper, glue, scissors and white out are items typically found at the top of the shopping list. One thing that is not found on the yearly back-to-school shopping list are back packs. Normally, a good quality backpack should be able to hold up for several years, but what if your child doesn’t have a good quality backpack? Yes, it may not hold up as long, but there also is a concern that it could in fact be causing your child pain.
With all the things required for school these days (school supplies, lunches, water, etc.) the weight of children’s backpacks have continued to increase. With increased backpack weight, children are more susceptible to musculoskeletal injuries. This is because when children are still growing, their growth plates are made of cartilage which makes them less strong compared to normal bone (1,2). Additionally, spinal development occurs over a longer period of time compared to other skeletal tissues; thus increased load on the spine can greatly influence postural development (2). It is important to note that growth rates peak at different times for boys and girls. Girls’ growth rates peak between 10-12 years old, while boys’ growth rates peak between 13-15 years old (1). These age ranges are especially important to note as they coincide with the transition between elementary and middle school, as well as from middle to high school, respectively. As children advance through the grade levels, more and more supplies are needed on a daily basis, which contributes to increased backpack weights.
The Issue
What is not as well known as it should be, is that the recommended weight limit of a backpack should be 10-15% of the child’s body weight (1,3). Studies have shown that the average child carries between 22-27% of their body weight, with a maximum of 46% body weight seen in one study (1). This is worrisome because as backpack weight increases, load, and stress on the low back increases non-linearly. This means that if you were to double the weight of the backpack (in terms of body weight percentage), the load on the low back wouldn’t just be doubled. For example, the following load increases were found in one study:
15% BW = 26.7% increase of load on the low back
30% BW = 64% increase of load on low back
Part of the issue with increased load on the low back, is that the child’s centre of mass changes. As backpack weight increases, the centre of mass moves posteriorly/backwards which forces the child to compensate in one of two ways; either they lean forward at the ankles or hips, or they extend their head and neck (1-3). As a result, several downstream effects take place.
First, changes to the spine can occur. The spinal curves will decrease in the low back (lumbar lordosis) and increase in the midback (thoracic kyphosis) (2). Postural muscles become rigid to support this new load (2) and can lead to muscle soreness and back pain (4). On top of changing spinal curves, a decrease in total length of the spine was also seen in one study (3).
Not only can an increased backpack weight increase load on the low back, it can also alter the Cranio-vertebral Angle (CVA) (1). The CVA is a measure of the neck position relative to the upper trunk; the smaller the angle, the further forward the head is. As the head begins to move forward relative to the trunk, the lower part of the neck moves into flexion, while the upper part of the neck moves into extension and is followed by changes in the upper back such as rounding of the shoulders (protracted scapulae) (2). It was found that backpack weights of 15% of the child’s body weight can cause significant changes to the CVA and therefore neck posture (1). Another study by Vaghela et al. also showed a decrease in CVA in both standing posture and posture after a dynamic activity like stair walking was completed, while wearing a backpack that weighed 18% of the child’s body weight (2)
As posture changes with heavier backpack loads, gait can also be affected which could lead to further injury. As mentioned previously, with heavier backpacks the child’s center of mass moves posteriorly which can decrease stride length, cadence and walking speed (1), increase stance time while walking which can cause increased foot discomfort, decrease torso angle which then further increases forces on the low back and is associated with low back pain (1).
Nerves can also be compressed under the weight of the back-pack straps. The brachial plexus, a collection of nerves which supplies the entire arm with sensation and motor coordination, can be compressed. Compression can cause weakness in the rhomboid and deltoid muscles and can cause sensory impairment in the C5 and C6 nerve distribution. If this was to occur, recovery can take anywhere from 3 weeks to 3 months on its own (1).
It is important to check in with your child to see how they feel after a day of school and carrying their backpack around. There are signs and symptoms that your child may display which can indicate that their backpack may be too heavy. These include:
· General body pain
· Redness (over the shoulders)
· Swelling
· Fatigue
If any of these are present, your child’s backpack is too heavy. But not to fear, there are some simple solutions to help ensure backpack safety and to help prevent injuries.
Tips for Safe Backpack Use
Limit items in the backpack to the essentials – the reality is that the more stuff that is in the backpack, the heavier it will be. Try to limit items to things that are needed for that day specifically. If possible, have your child leave items that they use every day at school in their cubby, desk or locker, that way they don’t have to pack it in their bag every day.
Ensure that your child’s backpack does not exceed 15% of their body weight – by limiting the weight in the backpack, the load on the spine will also be reduced, thus reducing the risk of injury. To do this, use a scale to weigh your child and take their weight and multiply it by 0.15. This will give you the maximum recommended weight limit for your child’s backpack. Here is what that calculation would look like for a 90lb child:
90lbs X 0.15 = 13.5lbs
Therefore, if your child weighs 90lbs, the weight limit of their backpack should be 13.5lbs. Next fill your child’s backpack with the items deemed to be essential and put the backpack on the scale. The backpack exceeds the weight limit that you just calculated, remove non-essential items until it falls under the weight limit.
Use both shoulder straps – by using both shoulder straps, the load created by the backpack can be more evenly distributed and thus reducing pressure points over the shoulders. Even better if there are hip and chest straps available to use!
Utilize the compartments to distribute the weight inside – today’s backpacks have many compartments that are designed to help distribute the items in your bag more evenly. By doing so, this ensures that the weight of the backpack is not concentrated in one spot in the bag.
Tips for Choosing a Backpack
If you feel like it is time for your child to get a new backpack, here are a few suggestions on what to look for before making a purchase (1):
1. The backpack should have padding to reduce pressure in the back and enhance comfort
2. The backpack should have 2 contoured and padded shoulder straps to reduce pressure on the shoulders and permit free movement of the arms
3. Hip and chest belts are preferred in order to transfer some of the backpack weight from the back and shoulders to the hips and torso
4. The backpack should have multiple compartments to better distribute the weight in the backpack, keep items secure and enhance access to the content
5. The backpack should have compression straps to stabilize items inside the bag, and compress the contents so that items are as close to the back as possible
6. The backpack should have reflective material to enhance visibility of the child to drivers at night
By knowing the signs and symptoms to look for, how to properly select and use a backpack, you can help prevent your child from developing an injury from their backpack. If you’d like further information, an assessment of a backpack or treatment for an existing injury, please book in with Dr. Jared or one of the other team members at New Era Wellness Chiropractic to learn more.
Dr. Jared Borosch
References:
1. Ross K. Back Packs [unpublished lecture notes]. AN3203: Advanced Biomechanics, Canadian Memorial Chiropractic College; lecture given in 2022
2. Vaghela, N., Parekh, S., Padsala, D., Patel, D. Effect of backpack loading on cervical and sagittal shoulder posture in standing and after dynamic activity in school going children. Journal of Family Medicine and Primary Care [Internet]. 2019 March [cited 2023 Aug 24]; 8(3):p 1076-1081. Available from: https://journals.lww.com/jfmpc/fulltext/2019/08030/effect_of_backpack_loading_on_cervical_and.56.aspx
3. Walicka-Cuprys, K., Skalska-Izdebska, R., Rachwal, M., Truszczynska, A. Influence of the weight of a school backpack on spinal curvature in the sagittal plane of seven-year-old children. BioMed Research International [Internet]. 2015, Aug 18 [cited 2023 Aug 24]. Available from: https://downloads.hindawi.com/journals/bmri/2015/817913.pdf
4. Zhao, G., Wang, H., Wang, L., Ibrahim, Y., Wan, Y., Sun, J. et al. The biomechanical effects of different bag-carrying styles on lumbar spine and paraspinal muscles: a combined musculoskeletal and finite element study. Ortho Surg [Internet]. 2022 Oct 10 [cited 2023 Aug 31]; 2023(15):315-327. Available from: https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/os.13573
Comentaris