INFLUENCE OF DIFFERENT BACKPACK WEIGHTS ON TRUNK POSTURE OF PRIMARY SCHOOL AGED CHILDREN DURING WALKING: A PILOT STUDY

J. Mueller¹, J. Simmer¹, C. Zinnen¹, S. Schmid^2,3, S. Mueller¹

¹Trier University of Applied Sciences, Department of Computer Science - Therapeutic Sciences, Trier, Germany, ²Bern University of Applied Sciences, Department of Health Professions, Division of Physiotherapy, Spinal Movement Biomechanics Group, Bern, Switzerland, ³University of Basel, Faculty of Medicine, Basel, Switzerland

Background: For children of primary school age, the backpack is an indispensable utensil in everyday life. Although the WHO recommends a maximum carrying weight of 12.5% of a child's body weight to prevent overloading of the back, studies have shown that these recommendations are often exceeded. In addition, recent studies indicated a correlation between a heavy backpack and an altered (trunk) posture during standing. Nevertheless, how backpack weight affects the children´s posture during gait has not yet been sufficiently investigated.

Purpose: To analyze the influence of different backpack weights on the trunk kinematics during standing and walking in school children.

Methods: Sixteen school children (age: 9.3±1.6years, mass: 32.4±8.4kg, height: 137.1±10.2cm) walked on a 5m-walkway with a backpack-simulating carrying system, allowing the simulation of an unloaded backpack as well as a backpack with loads corresponding to 10%, 20% and 30% of individual body mass (applied in random order). A 3D-motion-analysis-system (120Hz) was used to capture whole body kinematics (Rizzoli marker model) during normal gait and standing. Primary outcome measure during walking was maximum range of motion (RoM [°]) of the thoracic and lumbar trunk segments in the sagittal, frontal and transverse planes. During standing, the average angle [°] during a period of 5 seconds was measured in all three planes. Secondary outcome measures were stride length (m), stride time (sec) and gait velocity (m/s) during walking. In addition, the weights of the own school backpacks brought along were measured and expressed as percentage of body weight for each child. Descriptive (mean±SD) and inferential statistics (repeated-measures ANOVA, α=0.05; post hoc test (Tukey-Kramer)) were performed.

Results: On average, the weight of the children’s own backpack was 15.4±7.4% body weight. For the weight conditions, the weights added to the carrying system was 3.3±0.8kg (10%), 6.5±1.7kg (20%) and 9.8±2.5kg (30%), respectively. During standing, the average trunk flexion angles (sagittal plane) of the lumbar trunk segment significantly increased with higher backpack weight (p=0.002). During gait, no changes in average RoM in the sagittal plane but significant decreases in transversal and frontal plane for lumbar and thoracic RoM (p<0.001), stride length (p=0.047) and gait velocity (p=0.041) were observed with increasing weight. No significant differences were observed for stride time between the tested conditions.

Conclusions: In most cases, the weight of the children’s own backpack exceeded the WHO recommendation of 12.5% of body mass. Furthermore, a higher carrying weight resulted in a more flexed posture of the trunk during standing as well as a reduction in transversal and frontal plane trunk movement amplitude, stride length and gait velocity during walking. These mechanisms might have taken place to compensate for the increasing dorsally displaced center of mass as well as to minimize energy expenditure by reducing the angular momentum of the trunk-backpack-unit during walking.

Implications: The study results indicated that increased backpack carrying weight leading to a reduced RoM during standing and walking might be interpreted as increased trunk stiffness, which could predispose the children for low back pain.

Funding acknowledgements: not applicable.

Keywords:
Trunk kinematics
Gait
School bag

Topics:
Musculoskeletal: spine
Paediatrics

Did this work require ethics approval? Yes

Institution: Trier University of Applied Sciences

Committee: Ethics Committee of the Department of Computer Sciences

Ethics number: 43800