Plantar force distribution and pressure center oscillation in relation to the weight and positioning of school supplies and books in student's backpack

Objective: The influence of the weight and positioning of school supplies and books in backpacks, on plantar force distribution (PFD) and pressure center location, was investigated among students. Methods: Thirty volunteers of both genders participated in the study. Their mean age was 10.76 ( plus or minus 1.35) years and none of them had postural abnormalities. Baropodometric data were collected using a computerized baropodometric system (Matscan Research, Tekscan registered , 5.72): without load (control) and with loads of 5, 10 and 15% of body weight in a backpack, positioned on the back, on the chest and on the right and left shoulders. Results: The PFD without load was greater on the left heel than on the right heel (p< 0.05). With a load of 10% on the left shoulder, the PFD was greater on the right and smaller on the left foot, in comparison with the control (p< 0.05). With a load of 5% on the back, the PFD was smaller on the right midfoot (RMF) and left forefoot (lff); with 10%, it was smaller on the RMF and left midfoot (LMF) and greater on the right toes (RT); with 15%, it was smaller on the RMF and greater on the RT (p< 0.05). The plantar force was greater on the RT with loads of 10% and 15% than it was with loads of 5% (p< 0.05). With loads of 15% on the back and on the chest, the pressure center displacement was greater than with a load of 5% (p< 0.05). The PFD was not influenced by the different loads and backpack positions. Conclusions: Taking into consideration the increased pressure center displacement with a load of 15%, it is recommended that school backpack loads should not exceed 10% of body mass. Investigations on posture adaptations to different loads and backpack positions are suggested, in order to detect possible abnormalities and propose preventive actions.