We know heavy school bags are a serious threat to the health and well-being of the children, which makes knowing how much weight shall children carry a vital aspect.
Scientists have established that schoolchildren who use backpacks should avoid loads of more than 10 percent of their body weight and those who use trolleys, 20 percent of their body weight, reported a recent study published in the Journal of Applied Ergonomics.
To date, weight recommendations have been established for ordinary school backpacks, as they are the most widely used type in the school context worldwide.
However, in Spain, more than 40 percent of children use backpacks on wheeled trolleys, and until now there have been no studies making weight recommendations for this type of backpack.
In this study, 49 primary school pupils were assessed. A kinematic analysis of the children (posture of the trunk and lower limbs) was conducted while they walked freely, carrying no weight, secondly, during children carrying a traditional backpack and finally pulling a backpack trolley with different loads (10 percent, 15 percent, and 20 percent of their respective body weights).
For the analysis, a three-dimensional optical motion capture system was used, similar to those used in animation films and video games.
In collaboration with the researchers used statistical techniques to analyze the full kinematics curves, based on tracing point trajectories.
The main findings of the study indicate that the greatest alterations when using trolleys or backpacks are produced in the proximal extremities (hip and trunk), while there is little difference in the kinematics of the distal extremities (knee and ankle).
However, pulling the backpack trolley produces fewer changes in the child's kinematics and, therefore, resembles more closely their movement when walking free of any load, compared to carrying the backpack, even when it weighs very little.
As an overall conclusion, the study corroborates that school children who use backpacks should avoid carrying loads greater than 10 percent of their body weight. Furthermore, in a new finding, when pulling a school backpack trolley, the child should avoid carrying any load greater than 20 percent of their body weight.