Studies done by orthopedic surgeons show that more than half of shoulder and back pain reports in children is caused by heavy backpacks. Some of this is related to the way the backpack is worn — either low over the buttocks or slung over one shoulder.
The distribution of load has a direct effect on the pressure over shoulders and back. Uneven or excessive loads can create enough pressure to actually cut off blood flow to the skin under the straps.
Postural changes occur even when backpacks are worn evenly on both shoulders. For example, children commonly raise the right shoulder up when wearing a backpack. This movement is even more exaggerated when the pack is only worn over the right shoulder. It’s possible that with chronic use of a backpack over one shoulder (usually the right), the shoulder responds with the same movement pattern even when the pack is worn over both shoulders.
Back pain has been reported more often among children who wear a backpack with one strap instead of both straps. If the pack is worn low enough, then the weight is supported by the low back and/or buttocks. It is suspected that this pattern may be part of the problem leading to back pain in younger children.