INTRODUCTION: The main purpose of the current work was to determine net joint moments and forces during landing in freestyle aerial skiing and to investigate if insufficient generation of muscle moments was the cause of the rather regularly observed backward falling upon landing. METHOD: Side-views of landings performed by several Swiss National freestyle aerial skiers were filmed using a high-speed CMOS camera operated at 231 frames per second. Ankle, hip, knee, shoulder, elbow, wrist joints as well the head center were tracked using the Dartfish analysis Software. From the tracking data, net joint moments and forces were derived for a 6-segment body model using 2-dimensional inverse dynamics as formulated by Bogert [1] and adjusted 2-dimensional body segment parameters furnished by Dempster [2]. Moments were computed body-upward, starting with the tibia as the first body segment. Prior to this the external ground reaction forces Fext, the external moment Mext and the net ankle moment Mankie were derived from the acceleration of the body's center of mass and the total angular moment using Newton's second law (Fext=m*acom, Mext=rankle x Fext d/dtLcom=Mext, com+Mankle) RESULTS + DISCUSSION: Figure 1 shows net ankle, knee and hip joint moments as well as the external force moment for two different landings of the same athlete, one without and one with backward falling. Whereas the knee and hip joint moments do not differ significantly between the landings there is an important difference in the external moment, and to a lesser extent in the ankle joint moment. The reason for the difference is the more backward leaning body position upon impact during the landing with backward falling. CONCLUSION: In aerial skiing insufficient application of muscle moments can be (example not shown here), but generally is not the cause for backward falling upon landing (current example). The fall is often caused by backward leaning, leading to an insufficiently high external moment to counteract, together with the moment generated at the ankle, the backward somersault angular impulse from the run-in. In order to prevent falling, the Jumpers must therefore pay special attention to adopt an appropriate body position on impact. In particular, any degree of backward leaning must be avoided.
© Copyright 2007 4th International Congress on Science and Skiing. Veröffentlicht von University of Salzburg. Alle Rechte vorbehalten.