INTRODUCTION: There is currently no established Standard for the mounting of the boot to the binding, with each manufacturer producing a System that fits only a specific type of boots. Unlike ski bindings, snowboard bindings do not automatically release. Despite the availability of hard boots, soft boots are still broadly used. Soft boots provide little protection to the ankle but allow a wide range of movement, as necessary to perform aerial maneuvers. The present study focuses on rotation of the ankle joint complex (AJC) during snowboarding maneuvers. It also examines the effect of boot stiffness on ankle loading. METHOD: Nine male volunteer snowboarders with no previous lower limb injuries, aged 20 to 34, participated in the study. Each snowboarder was equipped with a Fastrak electromagnetic motion tracking System (Polhemus, Colchester, VT), including four six-degree-of-freedom sensors. The System was made portable using two 12-volt batteries and was connected to a notebook Computer. The sensors were glued to the skin of the snowboarder on the back of each heel and on the front of each tibia. Each snowboarder was asked to perform a total of six trials, which consisted of three trials with a snowboard equipped with soft boots and strap bindings (A) and three trials with stiffer step-in boots and bindings (B). Each trial consisted in snowboarding down a course of 10 turns on a beginner-level slope of groomed snow. The Signals were decomposed into cycles of one heel turn and one toe turn. During the trials, the motion tracking system recorded the Position and orientation of each sensor relative to the snowboard at a rate of 30 Hz, with a precision of 0.8 mm and 0.15°. RESULTS & DISCUSSION: The results were expressed in anatomically relevant rotations of the ankle joint complex, namely dorsi-/plantar flexion, e-/inversion and ad-/abduction. The measured ankle rotations show differences in the movement patterns of the front and back legs. The observed high adduction levels are attributed to improper binding adjustment. Step-in boots were shown to allow less dorsiflexion, inversion and adduction than softer boots. These differences could mean that the step-in boots resist more than the soft boots to external rotation of the foot. Infernal rotation, inversion and plantar flexion are AJC rotations that Stretch the anterior talo-fibular ligament (ATFL), which is the most often sprained ligament of the ankle; this ligament runs horizontally from the lateral malleolus to the head of the talus. Very little movement of these types was observed in the present study. On the contrary, most of the time, both feet were externally rotated, everted and dorsiflexed. Therefore, it is very difficult to assess whether one type of snowboard equipment would better protect the ATFL against overstretching than the other. CONCLUSION: The present study indicates that, during regular snowboarding maneuvers, the right and left AJC, while asymmetrically loaded, are mostly dorsiflexed, everted and externally rotated. The anterior talo-fibular ligament is typically stretched by the opposite of these rotations, i.e plantar flexion, inversion and internal rotation. Therefore, although significantly lower rotation levels were observed with step-in boots and bindings than with soft boots and strap bindings, we cannot yet conclude that stiffer step-in boots would better protect the ankle against sprains of the anterior talo-fibular ligament.
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