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Abstract.[Purpose] The purpose of the present study was to analyze the effect of backpack heaviness on trunk-lower limb kinematics at the start of gait.[Subjects] Ten university male students (age=20.3 ± 0.98 years, height=1.69 ± 0.04 m, weight=59.5 ± 5.3 kg) participated in the present study.[Methods] Each subject was asked to stand erect then walk forward in a straight line in four modes: unloaded, and with loads of 10%, 15%, and 20% body weight (BW). A VICON 250 motion analysis system was utilized to study changes in the trunk and lower limb kinematics at the start of gait.[Results] The results show significant trunk backward lean changes between the unloaded mode and loaded modes even with no changes in the center of mass (COM), velocity or displacement.[Conclusion] A 20%BW backpack caused the highest trunk kinematic changes, so backpack weight should be limited to 15%BW. It is also important to be aware of other factors correlated to backpack usage to provide better usage recommendations.

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