With increased military personal protection equipment, body armor, comes the addition of carried load. Such person protection in recent history has been instrumental in combating the imminent threats (e.g., improvised explosive devices) of hostile environments, preventing otherwise lethal injuries. However, body armor has been suggested to degrade warfighters’ performance and compound the risk of musculoskeletal injuries. Both performance and risk of injury are intensely related to joint biomechanics. Therefore the objective of this project was set to determine the immediate and prolonged effects of wearing body armor on biomechanics of the lower back and knee. A randomized cross-over study design, wherein 12 sex-balanced, physically fit, young participants completed a series of tests before and after 45 min of treadmill walking with and without body armor. Tests included two simple tests (i.e., toe-touch and two-legged squat), two military inspired tests (i.e., box drop and prone to standing) and four knee torque tests (i.e., maximum isometric contraction of knee flexors and extensors, and concentric and eccentric isokinetic contraction of knee flexors and extensors. During these tests, kinematic, kinetic and torque measurements were used to investigate the immediate and prolonged effects of exposure to body armor on several measures of knee and lower back mechanics related to performance and risk of injuries. For the simple tests, the immediate effects of body armor were an increase of > 40 ms (p ≤ 0.02) in flexion duration of the dominant joint and an ~1 s (p ≤ 0.02) increase in overall test duration as well as an ~18% (p = 0.03) increase in the lumbopelvic rhythm ratio near mid-range trunk flexion. For the military inspired tests, the immediate effects of body armor were an increase of ≥ 0.02 s (p ≤ 0.001) in temporal test durations and an increase of ~158 N (p = 0.01) box drop peak ground reaction force. Finally during the dynamometer testing, the BA condition was found to cause a greater reduction, ~10 N•m, in the maximum isometric strength of knee flexors (p = 0.04) and an increase (p ≤ 0.03) of strength ratios compared to the no armor condition.

While military body armor is used among warfighters for protection on and off the battlefield, it has been suggested to impede performance and act as a risk factor for the development of musculoskeletal disorders, especially low back pain. Apart from personal suffering, low back pain in soldiers is a great economic burden on the US economy. The objective of this study was to quantify the changes in trunk mechanical and neuromuscular behavior following prolonged exposure to body armor compared to exposure without. A crossover study design was used where 12 sex-balanced participants completed a series of tests before and after 45 minutes of treadmill walking with and without body armor. The tests included range of motion, isometric trunk tests, sudden perturbations, and stress relaxation. As a whole, exposure duration considered in this study resulted in no significant differences in performance between armor and no armor conditions. However, comparing the effects of body armor among the sex-differentiated groups showed a body armor -induced increase in range of trunk motion in the sagittal plane among females (p = 0.0018) and a decrease in pelvic range of motion in the transverse plane among both males (p=0.025) and females (p=0.004).