Lower Extremity Musculoskeletal Injury History, Strength, and Biomechanics in Female US Army Soldiers

Abstract

Female Soldiers have a significantly higher rate of injury, specifically low back and lower extremity (LB/LE) injuries, compared to male Soldiers. Despite return to full activity following an injury, LE biomechanical asymmetries may persist, likely leading to an increased risk for recurrent injuries. PURPOSE: To assess musculoskeletal and biomechanical asymmetries that may relate to the development of injury in female Soldiers. METHODS: Female 101st Airborne Division (Air Assault) Soldiers’ (n=77; age=27.1±5.9) LE strength (% body weight) and LE biomechanics were collected with 3D motion analysis during a drop landing task. Paired samples t-tests compared bilateral strength and landing biomechanics in female Soldiers. SPSS v.23 was utilized for analysis (p<0.05). RESULTS: Among all female Soldiers, 15.6% (12/77) reported at least one LB/LE injury within the last year, with half of those with injuries reporting a knee injury. The majority of all injuries and specifically knee injuries occurred on the right side. Significant asymmetries were found in knee extension strength (R:186.8±39.0 %BW vs L:171.9 ± 39.5 %BW, p<0.001), knee flexion strength (R:90.9.8±22.3 %BW vs L:86.5±21.1 %BW, p=0.001), knee flexion at initial contact (IC) (R:19.9±6.9° vs L:21.2±6.7°, p=0.33), knee flexion excursion (R:69.5±11.8° vs L:67.5±12.0°, p=0.004) and peak vertical ground reaction force (PvGRF) (R:350.3±88.6 %BW vs L:327.2±84.8 %BW, p<0.001). CONCLUSION: Female Soldiers demonstrated asymmetrical landing strategies, including decreased right knee flexion at IC and increased right PvGRF, potentially placing an increased load on the right limb, which was also the most injured limb. This stiffened landing position and greater PvGRF were found despite greater knee strength and increased knee flexion excursion on the right. These results suggest that in female Soldiers, shock absorption strategies at the knee may be influenced by mechanisms other than maximal knee strength. Further research is needed to determine the interaction between sagittal and frontal plane mechanics during landing in female Soldiers. With the expanded role of women in the military, understanding the mechanisms associated with these asymmetrical movement patterns and increased risk of injury should be a priority in military medicine.