Military boot attenuates axial loading to the lower leg

Biomechanical tests to understand injury mechanisms and derive injury tolerance information using Post-Mortem Human Subjects (PMHS) have not used foot protection and they have primarily focused on civilian environments such as automotive and athletic- and sports-related events. As military personnel use boots, tests with the boot are required to understand their effect on attenuating lower leg loads. The purpose of this study was therefore, to determine the modulation of human lower leg kinematics with boot compressions and share of the force absorbed by the boot from underbody blast loading. Axial impacts were delivered to the Hybrid III dummy lower leg in the neutral position. The dummy leg was instrumented with its internal upper and lower tibia load cells, and in addition, a knee load cell was attached to the proximal end. Tests were conducted at 4.4 to 8.9 m/s, with and without boots, and repeat tests were done. Morphologies of the force-time responses were similar at the three load cell locations and for all input combinations and booted and unbooted conditions. However, booted tests resulted in considerably lower maximum forces (approximately two-third reduction) than unbooted tests. These results clearly show that boots can absorb a considerable share of the impact energy and decrease impact loads transmitted to the lower leg under vertical loading, thus necessitating the generation of tolerance data using PMHS for this environment.