Measuring centre of gravity and postural shifts in first year primary school students encumbered with a schoolbag

Abstract

Background: To this date there have been a number of studies which determined an anterior shift of centre of gravity (COG) in the sagittal plane as the result of carrying a schoolbag. However, few of them measured the exact change of COG and how that change affects postural angles. Purpose: The purpose of this study is to determine the influence of mass of a typical Croatian schoolbag (4.51kg) on standing posture in first year elementary school children, and measure the change of centre of gravity (COG) as well as change in postural angles of head, neck and pelvis using free, open source software and inexpensive anthropometric methods. Methods: 76 first year elementary school students (35 male, 41 female) from two Zagreb elementary schools participated in this study. Anthropometric methods were used to acquire data regarding height, mass and anterior pelvic tilt angle, while digital photography (kinematic methods) was used to ascertain position of COG, craniovertebral and craniocervical angles in lateral view. The data was digitalised and analysed using SkillSpector™ and Kinovea™, open source, video based, motion analysis software. This study has analysed data regarding change of COG in sagittal plane as well as change in anterior pelvic tilt angle, craniovertebral and craniocervical angle in subjects during normal, unencumbered standing position and while carrying a schoolbag. IBM SPSS 17.0 statistical software was used to perform statistical analysis. The Shapiro-Wilk test was used as a test of normality (p>0.05 for all reported variables). Results: Mean (SD) height, weight and Body Mass Index were 129.34 (6.3) cm, 27.95 (5.6) kg and 16.63 (2.57) respectively. Student's test has shown an anterior shift of COG in the sagittal plane (x=2.407 cm, σ(x)=1.73, p< 0.001, N=71) as well as a change in two out of three measured postural angles - craniovertebral (x=-5.169°, σ(x)=4.019°, p< 0.001, N=60) and craniocervical (x=2.466°, σ(x)=6.843°, p< 0.01, N=59). Anterior shift of COG was in moderate, negative correlation with students' body mass (Pearson r=-0.436, p< 0.001, N=71). Conclusion(s): Analysis of COG and postural angles have shown that when 1st year primary students are encumbered with a schoolbag (which on average weighs 16.13% of their body mass) their head and neck posture shifts to a more protracted posture. Implications: Future studies should emphasize the possibility that such a shift in posture could lead to various neck related musculoskeletal disorders and how those could be lessened or prevented by physiotherapeutic, ergonomic and educational interventions. Funding acknowledgements: This research received no grant from any funding agency in the public, commercial or not-for-profit sectors. Ethics approval: Signed consent from parents was obtained.