The Effects Of External Loading On Lower Extremity Landing Biomechanics In College Rotc Cadets

Abstract

Military personnel performs in combat and physical training with extensive external loading from combat gear that may increase risk for lower extremity musculoskeletal injury. Lower extremity musculoskeletal injury risk is high in this population and can threaten deployment, completion of duty, and quality of life. However, there is limited research determining the effects of external loading on landing biomechanics in military situations. PURPOSE: To determine if external loading affects lower extremity landing biomechanics during a jump landing task in ROTC cadets. METHODS: Twenty five ROTC cadets (age: 20.2±1.3yr; height: 174.4±11.3cm; mass: 77.0±5.1kg) were recruited and performed two conditions of three jump landings (baseline vs loaded landing with an additional 35% body weight (BW) vest) from a 30cm high box. The box was placed a distance of 50% of their height from the landing zone of two force plates. Lower extremity angular joint kinematics and ground reaction forces (GRFs) were compared between the two conditions using paired t-tests (α<.05). RESULTS: The loaded landing compared to baseline landing, resulted in decreased knee (16.8±3.7 and 19.4±4.7°) and hip (30.4±6.3° and 32.7±5.4°) flexion at initial contact (IC), and increased maximal joint flexion displacements for ankle (36.0±11.5° and 31.4±9.9°), knee (56.2±7.2° and 49.0±6.5°), and hip (23.8±5.6° and 18.5±4.9°). Furthermore, loaded landings, compared with baseline landings, exhibited significantly lower vertical GRF (2.3±0.5 N·kg-1 and 2.7±0.5 N·kg-1) and posterior GRF (0.6±0.1 N·kg-1 and 0.7±0.1 N·kg-1). CONCLUSION: Loaded landings increased key injury risk landing biomechanics. Less knee and hip flexion at IC have been associated with potential anterior cruciate ligament (ACL) injury risk and may increase ACL loading during landing. However, the less peak vertical and posterior GRFs with greater displacement of all three lower extremity joints on during loaded landing suggests cadets employed a compensation strategy that may reduce ACL loading after IC.