For the first time ever, researchers have found out the maximum weight that children should be carrying in their pull-along school backpacks -- and it's no more than 20 percent of their body weight.
Carried out by researchers from the University of Granada (UGR), Spain, and Liverpool John Moores University, UK, the new small-scale study is the first to determine the maximum weight for backpacks on wheeled trolleys, used by more than 40 percent of children in Spain.
To carry out the research, the team used a kinematic analysis of 49 primary school children, which assesses the posture of the trunk and lower limbs. The analysis was carried out while the children walked freely in three different situations -- when carrying no weight, when carrying a traditional backpack, and when pulling a backpack trolley.
Each assessment also looked at the effect of carrying different loads in the backpacks -- 10 percent, 15 percent, and 20 percent of the children's respective body weights.
The findings, published in the journal Applied Ergonomics, showed that when pulling a school backpack trolley, children should not be carrying loads greater than 20 percent of their body weight.
The team also found that children who use traditional backpacks should avoid carrying loads greater than 10 percent of their body weight, a finding which supports existing recommendations for this type of backpack.
The study also showed that using trolley backpacks and regular backpacks causes the greatest changes in motion in the proximal extremities (the hips and trunk), and small changes in the distal extremities (the knees and ankles). However, pulling the backpack on a trolley produces fewer changes in motion overall, and compared to carrying a regular backpack, even with a small load, resembles more closely a child's movement when walking free of any load.