Backpack forces on the spine vs. sidebag carrying system

Backpacks are used as the daily carrying system by students and people of all ages around the world. New research1 has demonstrated that the force on the spine when carrying a common backpack is 7.2 times greater than the load itself. This means that 1 book in a child’s backpack, puts the weight of 7 books on their spine. A 10-pound backpack transfers 72 pounds of force to the spine. 

The load on the spine is greater if the body is leaning forward. If the body is leaning forward 20 degrees, the force on the spine is 11.6 times greater. 1 book in a child’s backpack puts the weight of 11 books on their spine. A 10 lb backpack transfers 116 pounds of force to the spine.

Young boy bent over with a heavy backpackDrawing demonstrating force vectors of BackTpack with axial loading vs standard backpack with off-axis loading

The greater the backpack load, the greater the forward body lean when using a backpack. This occurs because a backpack is not not aligned on the body’s vertical axis, but rather is some inches behind it. Every inch of distance between the backpack load and the body’s vertical axis, significantly increases spinal loads.
In two independent studies2,3, the forward body lean when carrying a backpack was compared to a side-bag carrying system (our BackTpack, of course!). There is no forward body lean with a side-bag carrying system. 

Posture comparison with BackTpack vs standard backpack with the same load

BackTpack® is a sidebag system that loads on the spinal axis in line with gravity. With a sidebag system the load to the spine is not multiplied. A ten pound load in a BackTpack transfers exactly 10 pounds of force to the spine. Students who switch their backpack loads to the BackTpack say how “light it feels.” If you think about it, all the body’s natural load, the organs and muscles are efficiently wrapped around the spine with the heavy head on the very top of the spinal axis, and we don’t even feel it! The closer we get to this perfect loading system, the lighter and healthier carrying becomes.

References
  1. Hansraj KK, Hansraj JA, Griffin-Hansraj MD, Kiernan J, Subesan N, Firtat B, Elsisi A. “Backpack Forces on the Spine.” Surg Technol Int. 2018 Nov 11;33:361-365. Click here to view the abstract.
  2. Dalia Mohammed Mosaad, Amr Almaz Abdel-aziem: “Postural balance and neck angle changes in school children while carrying a traditional backpack versus a double-sided bag.” Biomedical Human Kinetics, 10, 59–66, 2018. This study compared the body balance and neck angle differences in children when carrying a traditional backpack versus a double-sided bag. Conclusion: Carrying the double-sided bag restores the body balance and head posture to a condition that is similar to the no load condition. Download a PDF of the full article.
  3. Kimberly D. Dahl, He Wang, Jennifer K. Popp, D. Clark Dickin, “Load distribution and postural changes in young adults when wearing a traditional backpack versus the BackTpack” Gait & Posture (March 2016) Volume 45, Pages 90-96. Click here to view the abstract.
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Marilyn von Foerster PT

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