Biomechanical Aspects of Military Footwear Usage and their Relationship with Lower Extremity Overuse Injuries

Professional military service involves high-intensity physical training, including field training exercises and marching, which increase the risk of musculoskeletal injuries (MSKIs). In the military, MSKIs represent a significant medical concern, leading to an increased financial strain on military healthcare and a decrease in military preparedness. Acute and overuse lower extremity MSKIs are more common in the knee, lower leg, and foot. The role of military footwear in the development of overuse injuries is currently unresolved, and more research is suggested on the relationship between military footwear and overuse injuries. The purpose of this work was to determine the incidence of overuse MSKI in the lower and investigate its possible relationship with military footwear usage among the Latvian Land Forces. The research was carried out on infantry soldiers during their annual medical examinations at the Military Medical Support Centre of the Latvian National Army Logistic Command from 2018 to 2020. In a cross-sectional study on the epidemiology of MSKI, a total of n = 227 active duty infantry soldiers participated. Among study participants, 42.7 % had a history of lower extremity injuries, with a higher prevalence of overuse injuries in the lower leg. Study participants who wore inappropriate size of military boots reported lower comfort ratings for all parameters, irrespective of their history of injuries. Gait analysis was performed barefoot and wearing military boots during the case-control study (n = 66) where subjects were divided into groups according to their history of overuse injuries. Both groups showed an elevation in the foot contact angle, while simultaneously showing a reduction in the eversion of the rearfoot and the angular velocities of the ankle when wearing military footwear. The conditional logistic regression model revealed that stride time variability (OR = 2.71, 95 % CI 1.31 – 5.60) during barefoot gait demonstrated statistical significance in predicting the risk of lower leg overuse injury. The optimal threshold for stride time variability was determined to be 1.95 %, which could effectively predict the occurrence of lower leg overuse injuries, showing a sensitivity of 56 % and a specificity of 88 %. Based on research findings, walking in military footwear improves stability and encourages gait symmetry, and the risk of overuse injuries to the lower extremities does not appear to be influenced by gait with footwear. The research results support the importance of further investigating gait variability as a possible risk factor for MSKI and lay the groundwork for the establishment of guidelines for medical gait and foot screening in the military.