The Effect of Backpack Load on Muscle Activities of the Trunk and Lower Extremities and Plantar Foot Pressure in Flatfoot

[Purpose] The purpose of this study was to investigate the changes in muscle activationof the trunk and lower extremities and plantar foot pressure due to backpack loads of 0,10, 15, and 20% of body weight during level walking in individuals with flatfoot.[Methods] Fourteen young flatfoot subjects and 12 normal foot subjects participated inthis study. In each session, the subjects were assigned to carry a backpack load, andthere were four level walking modes: (1) unloaded walking (0%), (2) 10% body weight (BW)load, (3) 15% BW load, and (4) 20% BW load. Trunk and lower extremity muscle activitieswere recorded by surface EMG, and contact area and plantar foot pressure were determinedusing a RS scan system. [Results] The erector spinae, vastus medialis, tibialis anteriorand gastrocnemius muscle activities, but not the rectus femoris and rectus abdominismuscle activities of flatfoot subjects significantly and progressively increased as loadincreased in flatfoot subjects. Contact area and pressure of the lateral and medial heelzones were significantly increased too. [Conclusion] Based on this data, the weight of abackpack could influence muscle activation and plantar foot pressure in flatfoot.Key words: Flatfoot, Backpack, Plantar pressure