Volume 5, Issue 6 (June 2008)
Head Kinematics During Experimental Snowboard Falls: Implications for Snow Helmet Standards
A study by Nakaguchi and Tsutsumi [“Mechanisms of Snowboarding-Related Severe Head Injury: Shear Strain Induced by the Opposite-Edge Phenomenon,” J. Neurosurg, Vol. 97, 2002, pp. 542–548] showed that 68 % of all snowboarders’ head injuries were associated with backward falls, with beginner and intermediate snowboarders constituting the majority of the injured. We previously fabricated a test apparatus that replicated the fall kinematics of a snowboarder during a back-edge trip. A Hybrid-III anthropomorphic test device (ATD) outfitted with a snowboard and snowboarding gear was accelerated to a typical intermediate snowboarder’s speed (30.5 ± 1.5 kph) and tripped resulting in a backward fall that terminated in a head-to-slope impact. This test protocol produced repeatable fall kinematics under realistic on-slope conditions. In this study, we characterized the fall kinematics and quantified head velocity in order to evaluate the helmet energy management requirements associated with a back-edge trip. Digital high-speed video recorded at 500 frames per second was used to quantify the snowboarder’s head kinematics: (i) prior to the trip; (ii) during trip phase; (iii) during free fall; and (iv) at ground impact. Translational energy of the ATD was rapidly converted to a combination of linear and angular energy during the trip phase. Although the speed of the ATD’s center of gravity decreased during the trip phase, the test data showed the absolute speed of the head increased rapidly during the fall as a result of the body’s induced angular rotation. The mean head velocity normal to the slope increased from approximately zero at fall initiation to as much as 37.1 kph during the fall (122 % of the initial velocity), and was 29.1 kph at snow contact (95 % of the initial velocity). Resultant head velocity peaked at 54.3 kph (178 % of the initial velocity), and was 38.2 kph at snow contact (125 % of the initial velocity). The data presented here may be useful for assessing drop height requirements for snow helmet evaluations.