There are many questions and concerns about children carrying heavy loads in backpacks. Does it matter if they sling it over just one shoulder? Should they carry it evenly across the upper back? Can they wear it down over the low back and sacrum?
Studies so far have shown that the load when evenly distributed over shoulders and upper back creates pressure. The pressure is high enough to cut off the blood flow to the skin under the straps.
In this study, the focus is on how loads are distributed under the shoulder straps. If researchers can measure the pressures from typical loads, we may be able to come up with some helpful guidelines for wearing backpacks.
The authors looked at four separate carrying patterns: 1) high on the upper back with straps over both shoulders, 2) down low on the back over both shoulders, 3) over the right shoulder only in the high back position, and 4) over the right shoulder in the low back position.
Ten children (boys and girls) were included in the study. All were healthy and between the ages of 12 and 14. Everyone wore backpack on a regular basis. The backpack was loaded at zero, 10, 20, and 30 per cent of the child’s body weight in each of the positions.
Skin sensors were used to measure contact pressures under the shoulder straps. Measurements were taken as the child was putting the backpack on. Pressure was also recorded in the standing position and while walking.
Contact pressure increased in all positions for all loads. And the level of pressure was enough to block blood flow to the skin under the straps. Pressures were highest in the right shoulder even when the pack was placed over both shoulders. This may be related to posture and the fact that children raise the right shoulder. Altering their posture in this way places more pressure in the area.
As might be expected, pressures were higher when the pack was down low over the back. This was compared with pressures with the load supported in the upper back area. Pain was also reported more often and at higher levels of intensity when backpacks were worn in the low-back over one shoulder.
The method by which the child put the pack on did not seem to influence load pattern. But the load increased when wearing the pack over one shoulder and while standing and walking. Loads were not greater for walking than when just standing quietly. And the pressure was highest along the front of the shoulder just above the collarbone when the backpack was worn low over the spine and sacrum.
The authors point out some limitations of their study. The number of children involved was low. The length of time the backpacks were worn before measuring skin pressure contact was short (25 seconds). Most children wear backpacks for much longer than 25 seconds. So over time, the pressures may be even greater than reported here.
Based on these results, children are advised to avoid wearing heavy backpacks. It’s best to keep the weight in the backpack no more than 10 per cent of the child’s total body weight. The pack should be worn close to the body as high up on the back as possible. Both shoulder straps should be adjusted evenly and used together.