Changes in centre of gravity and head posture to schoolbag load in children: a longitudinal kinematic analysis

Purpose This study investigates how body posture and balance respond to schoolbag load during critical stages of development, with a focus on head and neck alignment and centre of gravity (CoG) shifts. Methods A longitudinal study was conducted on 60 children from two schools in Zagreb, Croatia, measured in first and fifth grades. Kinematic data were collected under load (with schoolbag) and no-load conditions. Changes in CoG, craniovertebral (CV), and craniocervical (CC) angles were analysed using linear mixed-effects models. Results Carrying a schoolbag led to a significant forward head posture, with the CV angle decreasing by 5.53° (p < 0.001) and the CC angle increasing by 2.70° (p = 0.018). The vertical CoG shift decreased significantly with age by 0.36 cm (p < 0.001), while the sagittal CoG shift remained stable (p = 0.139). Higher BMI was associated with greater postural deviation, including a 0.62° decrease in CV angle (p < 0.001) and a 0.13 cm reduction in forward CoG shift (p = 0.016). Despite the relative load reduction in older children, biomechanical compensations were still observed. Conclusions The findings highlight consistent postural adaptations to schoolbag load, particularly in the cervical region. These changes underline the importance of ergonomic education and regular monitoring to support healthy postural development during childhood.