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Although the purpose of an alpine ski binding is to retain the ski during controlled maneuvers and recovery and to release the skier from the ski during situations that may lead to injury to the lower leg, most research has been conducted on the release side of the coin. A recent study related the minimum retention characteristics of alpine ski bindings in the twist release mode to skier mass, but did not address the problem of retention criteria for forward lean. Another study demonstrated that the load on the heelpiece in forward lean varies greatly among individuals and is probably related to skiing style more than to any other single factor. Several researchers have proposed that the criteria for retention in the forward lean release mode should be completely independent of the criteria for release in the twist release mode. Other studies have noted the special problems of some skiers, particularly competitors, in obtaining adequate retention characteristics even at release settings well above those thought to produce injury. In an attempt to understand this problem better, a study was made of the retention characteristics of modern bindings during actual skiing. It was discovered that specific maneuvers could be executed which would initiate release in forward lean while the skier was still in control, even at release settings well above those thought to be potentially injurious. Although these maneuvers are of no apparent practical value in either recovery or controlled maneuvers, they are possible and, in the opinion of the authors, may be the cause of inadvertent release, particularly for aggressive skiers. The authors theorize that retention problems in forward lean may not be caused only by the release setting or the design of the release mechanism, but by the way loads are sensed by existing release/retention systems. All bindings currently in use measure only a single force on the rear ledge of the ski boot. The authors propose that this force is not a good indication of the bending moment on the lower leg. Although this principle can be demonstrated by existing test methods, such tests were designed principally to detect situations in which the leg would experience a greater bending moment than that indicated by the vertical force sensed by the heelpiece. The problem described by the authors is that the leg can experience moments well below that indicated at the heelpiece in certain maneuvers. The problem described by the authors is that the leg can experience moments well below that indicated at the heelpiece in certain maneuvers. In this study, photographs of maneuvers that can produce inadvertent release at release settings well above those currently recommended were analyzed, and a model was created to explain the loads on the ski, binding, boot, and leg. Laboratory tests were performed using standard test methods to demonstrate their inadequacy in detecting the phenomenon. A new method that demonstrates the problem in the laboratory is proposed. Proposals are also made for the design of future bindings, which would integrate completely the functions of boot and binding and thereby sense directly the bending moment on the lower leg.
skiing safety, skiing trauma, bindings, binding release settings, binding retention
Brown, Christopher A.
Postdoctoral student, Ecole Polytechnique, Lausanne,
Ettlinger, Carl F.
President, Vermont Ski Safety Equipment Corp., Underhill, VT