| Over the years, the soldier's load has increased; weapon system improvements and the need for increased protection and firepower require individuals to carry more equipment. Although the current army field manual provides recommended guidelines for a soldier's load per operation, soldiers typically carry loads exceeding the recommended guidelines. The overall effect of these heavy loads on the soldier's body and the impact on the soldier's performance is still uncertain.;In this study, we analyzed the existing and proposed Korean army backpack designs and determined how each of the designs impacts stress on the soldier's upper body.;Twenty healthy male subjects participated in this study. Subjects were selected from among University of Utah students who have not experienced or have fully recovered from discomfort, injuries, or disorders that could affect normal gait.;Each trial had 3 repetitions. The independent variables being controlled were surface types and orientations, backpack types and loads, and marching speed.;While each subject walked on the tracks with or without a backpack, three-dimensional motion data and analog data (EMG, load cell) were collected with 16 Optitrack V100:R2 cameras, AMASS software, and LabVIEW. The captured data were then processed with Visual3D, Vicon Nexus, and MATLAB software.;Using inverse dynamics and recorded erector spinae electromyography (EMG) data, force on the L5/S1 disc was estimated using the proposed biomechanical model. Shoulder force data was measured from customized load cells integrated into the shoulder straps of the backpacks.;Upper body segments exhibited greater deviations from neutral positions (i.e., greater thorax flexion, greater thorax lateral flexion, and more pelvic anterior tilt) when carrying a backpack than under normal walking conditions. These deviations resulted in increased shoulder tension, which, in turn, increased compressive and shear forces on the L5/S1 disc. |
