Evaluation of Head and Body Kinematics Experienced During Parachute Opening Shock

Abstract

Introduction The U.S. Army conducts airborne operations in order to insert soldiers into combat. Military airborne operations are physically demanding activities with a unique loading environment compared with normal duties. A significant amount of research surrounding airborne operations has focused on assessing the incidence and type of associated injuries as well as the potential risk factors for injuries. During parachute opening shock and other high-acceleration events (e.g., fixed wing flight or vehicle crashes), the neck may be vulnerable to injury if inertial loads overcome the voluntary muscular control of the cervical spine and soft tissue structures. A recent epidemiological survey of sport skydivers showed that the neck, shoulders, and back were the most frequently reported sites of musculoskeletal pain. In addition, the survey indicated that wing loading (a measure of the jumper’s weight divided by the size of the parachute canopy) was a potential contributing factor for developing musculoskeletal pain. Recently, there have been efforts to measure the severity of parachute opening shock as an additional potential risk factor for injury; however, no studies have measured both head and body accelerations and no studies have measured head or body angular rate during parachute opening shock. The purpose of this study was to measure and characterize the accelerations and angular rates of both the head and body during parachute opening shock as well as investigate potential factors contributing to higher severity opening shock, which may link to the development of musculoskeletal pain or injury. Materials and Methods Data were collected from the U.S. Army Parachute Team, The Golden Knights, under an approved Medical Research and Material Command Institutional Review Board protocol. Subjects were instrumented with a helmet- and body-mounted sensor package, which included three angular rate sensors and three single-axis accelerometers each. Data were collected at 2,500 samples per second. Kruskal-Wallis tests were used to determine if helmet-mounted equipment (e.g., cameras), neck length, neck circumference, or wing loading (the ratio of jump weight to the size of the main parachute canopy) affected the accelerations or angular rates of the head or body. Results A total of 54 jumps conducted by 19 experienced free-fall jumpers were analyzed. For the head, the mean (± SD) resultant accelerations and angular rates were 5.8 (± 1.6) g and 255.9 (± 74.2) degrees per second (deg/s), respectively. For the body, the resultant accelerations and angular rates were 4.3 (± 1.5) g and 181.3 (± 61.2) deg/s, respectively. A wing loading above 1.4 pounds per square foot (lb/ft2) was found to have a significant effect on head (P = .001) and body (P = .001) resultant acceleration as well as body angular rate about the Y-axis (P = .001). Conclusions There is evidence to suggest that wing loading has an influence on individual head and body resultant accelerations. However, no significant effects were found for the other variables (e.g., neck length and circumference, helmet-mounted equipment, etc.). Future research should focus on identifying additional factors that result in changes in accelerations and angular rates of the head and body during parachute opening shock events.

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“… 16 , 22 , 29 This research has also been extended to focus on blunt head impacts experienced during military training. 35 Together, these studies have contributed to the body of literature that has moved concussion science forward. As the use of devices to measure head kinematics proliferates, 30 the field is ready for guidelines pertaining to methodological rigor to improve the consistency of research and reduce the risk of scientific bias.…”

Recreational Skydiving—Really That Dangerous? A Systematic Review

“…Rocks et al investigated the forces acting on the parachutist at the time of the parachute opening shock. They were able to show that at the time of the parachute opening shock, the mean (±SD) resulting accelerations and angular velocities were 5.8 (±1.6) g and 255.9 (±74.2) degrees per second (deg/s), respectively, for the head and 4.3 (±1.5) g and 181.3 (±61.2) deg/s, respectively, for the body [29]. We found two articles about injuries happening in this special moment of the jump-a case report about a hangman's fracture [20] and an analysis of musculoskeletal pain [30].…”

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“…For military paratroopers and civilian parachute enthusiasts, parachute opening shock has been associated with the incidence of neck and back injuries [ 85 ]. Wing loading, referring to the ratio of weight carried by the individual to the area of the parachute canopy, is believed to affect head acceleration responsible for these injuries [ 85 ]. NASA has worked to reduce water landing neck injuries by developing an Orion helmet support assembly (HSA) to mitigate dynamic loading on the neck [ 86 , 87 ].…”