Postural sway and foot-ground relationship are significantly modified by backpack carriage during upright stance: A study on primary school children

School is a person's first workplace and, from the age of six, children experience activities such as lifting, pulling and carrying a load (typically in the form of a backpack) which often represents an important percentage of their body weight. Among the possible consequences originated by back overload we have balance impairment and altered plantar pressure distribution, which however have been scarcely explored in children. On the basis of these considerations, this study intends to assess modifications in sway parameters, foot-ground contact area and pressure distribution introduced by backpack carriage in Italian primary school children. Two 30-second trials (with and without backpack) were performed directly at a school on a regular school day to collect data on sway area, centre of pressure path length, maximum displacement range in Antero-Posterior and Medio-Lateral directions, foot-ground contact area and pressure distribution. The results show a significant load-induced increase in all sway parameters and the existence of a linear relationship between sway area and backpack weight. Contact area also varies linearly with load and peak pressure values are significantly altered by the presence of a backpack in midfoot and forefoot, with increases up to 30%. These findings, together with the fact that about half the children carry a load exceeding 15% of their body weight, suggest that concern about severe postural alterations associated with carriage of overweight backpacks, remains justified.