Effects of Extremity Armor on Metabolic Cost and Gait Biomechanics

Adams, Albert A.

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Effects of Extremity Armor on Metabolic Cost and Gait Biomechanics

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Modern ballistic armor can protect soldiers against gunfire and shrapnel. The added weight and movement restriction of armor on the extremities may negatively impact soldier performance. Loading the limbs with weight has been found to increase metabolic cost in locomotion and alter gait kinematics. It was hypothesized that increases in metabolic cost and alterations in gait kinematics would result from the use of extremity armor. Fifteen healthy U.S. Army men walked (1.34 m/s) and ran (2.46 m/s) on a level treadmill with three different levels of extremity armor configuration: a no armor condition (4.3 lbs) that consisted of minimal clothing, combat boots, and a helmet; a partial extremity armor configuration (27.2 lbs) that consisted of an armor vest and extremity armor on the upper arms and thighs plus the minimal clothing; and a full extremity armor configuration (29.2 lbs) that consisted of forearm and shank armor in addition to the partial extremity armor configuration. In walking and running on the treadmill, metabolic cost normalized to body mass increased significantly when extremity armor was worn, as compared to the no armor condition. No difference was found in metabolic cost scaled to total mass (body mass + mass of armor), indicating no effect of mass placement. When walking on the treadmill, double support time was the only temporal variable found to increase with use of extremity armor; no differences between partial and full armor configurations were found. Range of motion (ROM) of the ankle decreased in walking with extremity armor, while hip and knee ROMs increased with the use of extremity armor. In running, only hip ROM and trunk lean increased significantly with the use of extremity armor, while no difference was found between the two extremity armor configurations. In conclusion, use of extremity armor on soldiers walking and running on a level treadmill resulted in a metabolic cost increase as the mass of the armor increased and did affect gait kinematics. The distal placement of the armor on the extremities at the low mass tested did not significantly affect metabolic cost or gait kinematics.

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