For the first time, the maximum weight a child should carry using a school backpack trolley, a maximum of 20 percent of their body weight, was determined by researchers from the University of Granada (UGR) and the UK-based Liverpool John Moores University.
The scientists published their article in the prestigious Applied Ergonomics journal to describe how they have established - in a worldwide first - recommendations on the appropriate load that primary school-age children should carry when using a backpack trolley.
Till present, there have been established weight recommendations for ordinary school backpacks, as they are the most widely used type in the school context worldwide. In Spain, however, 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.
The team conducted this research through a collaborative project involving researchers from the UGR (the Department of Physical Education and Sports and the Laboratory for the Analysis of Movement and Human Behavior, Ceuta campus, or HubemaLab) and Liverpool John Moores University.
The main focus of this study was primary school pupils, and it assessed 49 primary school pupils. A kinematic analysis of the children (posture of the trunk and lower limbs) was conducted while (i) they walked freely, carrying no weight, (ii) carrying a traditional backpack, and finally (iii) pulling a backpack trolley with different loads (10 percent, 15 percent, and 20 percent of their respective body weights).
They used a three-dimensional optical motion capture system for the analysis, similar to those used in animation films and video games. The UGR researchers, in collaboration with the researchers from Liverpool John Moore University, used statistical techniques to analyze the full kinematics curves, based on tracing point trajectories.
The significant outcomes of the research indicate that the greatest alterations when using trolleys or backpacks are produced in the proximal extremities (hip and trunk), while there are little differences in the kinematics of the distal extremities (knee and ankle). Pulling the backpack trolley, however, 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 quite a little.
Ultimately, the research corroborates that schoolchildren who use backpacks should avoid carrying loads greater than 10 percent of their body weight. Furthermore, according to new findings, when pulling a school backpack trolley, the child should avoid carrying any load greater than 20 percent of their body weight.
