Terrain Park Jump Design: Would Limiting Equivalent Fall Height Reduce Spine Injuries?
Authors: Scher Irving , Shealy Jasper , Stepan Lenka , Thomas Reed , Hoover Ryan 
Published: March 2015

It has been suggested that contouring the landing area of a terrain park jump, by increasing the landing slope with increasing horizontal distance from the takeoff ramp of a jump, would reduce the likelihood of injury. In theory, this limits the component of center-of-mass velocity that is normal to the snow surface at contact. In published works that recommend this jump design, velocity normal to the snow surface at contact is converted into an equivalent height above the ground, referred to as equivalent fall height (EFH). The purpose of the current research is to evaluate the injury mitigation potential of a landing surface that limits EFH. An instrumented 50th-percentile male Hybrid III anthropomorphic test device (ATD) fitted with snowboarding equipment was used to determine the head accelerations, cervical spine loads, and lumbar spine loads associated with landing on a snow surface in backward rotated configurations. For these tests, the ATD was suspended above a hard-packed, snow-filled box, rotated backwards, and allowed to fall onto the snow. The ATD fall distance and backward rotation were varied in order to adjust the EFH (range: 0.23 to 1.52 m) and torso to snow angle at impact (range: 0 to 92°). The peak resultant linear and angular head accelerations, peak cervical spine load, and peak lumbar spine load were determined for each trial and compared to the loads associated with severe injuries from the biomechanical engineering literature. Full sets of data were recorded for thirteen test trials. The peak resultant linear and angular head accelerations were well below the levels associated with severe brain injury. For eight of the tests, the cervical spine compression exceeded the average compression known to create severe injuries [Nightingale, R. W., McElhaney, J. H., Richardson, W. J. and Myers, B. S., “Dynamic Responses of the Head and Cervical Spine to Axial Impact Loading,” J. Biomech., Vol. 29, 1996, pp. 307–318; Maiman, D. J., Sances, A. Jr., Myklebust, J. B., Larson, S. J., Houterman, C., Chilbert, M., and El-Ghatit, A. Z., “Compression Injuries of the Cervical Spine: A Biomechanical Analysis,” Neurosurgery, Vol. 13, 1983, pp. 254–260]. All of the tests produced cervical spine flexion moments above those associated with cervical spine failure found in the literature. There was no correlation between cervical spine compression and EFH (R2 = 0.03), but there was a significant correlation with torso to snow surface angle at landing (R2 = 0.90). Results of the present study indicate that the likelihood of severe brain injury was low for all impacts within the EFHs examined. Despite this, even low EFHs can produce cervical spine loads well above the levels associated with severe cervical spine injury; these results support the findings of Dressler et al. [Dressler, D., Richards, D., Bates, E., Van Toen, C. and Cripton, P., “Head and Neck Injury Potential With and Without Helmets During Head-First Impacts on Snow,” Skiing Trauma Safety, 19th Volume, STP 1553, R. Johnson, J. Shealy, R. Greenwald and I. Scher, Eds., ASTM International, West Conshohocken, PA, 2012, pp. 235–249], who used a partial ATD without rotational kinematics. Furthermore, the lack of relationship between EFH and the metrics related to severe neck injury in the testing suggest that landing configuration is more important than EFH in determining injury likelihood of cervical spine from a backward rotated, unsuccessful jump landing.