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Blanche McCrary Boyd on the edge of the inhabitable world: Iceland

Skiing is a popular winter activity spanning various subdisciplines. Key hardware are ski boots, bindings, and skis, which are designed to withstand loads generated during skiing. Obtaining service forces and moments has always been challenging to researchers in the past. The goal of the present study is to develop and test a lightweight and compact measurement system to obtain the Ground Reaction Forces and the kinematics for ski touring and alpine ski. To do so, we adapted two six-axis load cells to fit into ski touring and alpine skis adding 20 mm height and 500 g weight to the original ski. To measure kinematics, we created custom angular sensors from rotary potentiometers. The system was tested indoors using a force platform and motion capture system before a first set of field tests in which the sensors were used to measure ski touring and alpine skis kinetics and kinematics. Validation trials showed maximum errors of 10% for kinetics and 5% for kinematics. Field tests showed data in agreement with previous findings on the topic. The results of this study show the possibility of using our system to study biomechanics and equipment performances for ski touring, alpine skiing, and possibly other disciplines.

To obtain valid 3D joint angles with inertial sensors careful sensor-to-segment calibration (i.e. functional or anatomical calibration) is required and measured angular velocity at each sensor needs to be integrated to obtain segment and joint orientation (i.e. joint angles). Existing functional and anatomical calibration procedures were optimized for gait analysis and calibration movements were impractical to perform in outdoor settings. Thus, the aims of this study were 1) to propose and validate a set of calibration movements that were optimized for alpine skiing and could be performed outdoors and 2) to validate the 3D joint angles of the knee, hip, and trunk during alpine skiing. The proposed functional calibration movements consisted of squats, trunk rotations, hip ad/abductions, and upright standing. The joint drift correction previously proposed for alpine ski racing was improved by adding a second step to reduce separately azimuth drift. The system was validated indoors on a skiing carpet at the maximum belt speed of 21 km/h and for measurement durations of 120 seconds. Calibration repeatability was on average <2.7° (i.e. 3D joint angles changed on average <2.7° for two repeated sets of calibration movements) and all movements could be executed wearing ski-boots. Joint angle precision was <4.9° for all angles and accuracy ranged from -10.7° to 4.2° where the presence of an athlete-specific bias was observed especially for the flexion angle. The improved joint drift correction reduced azimuth drift from over 25° to less than 5°. In conclusion, the system was valid for measuring 3D joint angles during alpine skiing and could be used outdoors. Errors were similar to the values reported in other studies for gait. The system may be well suited for within-athlete analysis but care should be taken for between-athlete analysis because of a possible athlete-specific joint angle bias.

Develop a method to examine the effects of component geometry and force-deflection on the release process of Tech/Pin alpine touring (AT) ski boots and bindings. For seven AT boots, we measured the critical geometric dimensions of the metal inserts at the toe region of the boots. Binding geometry (including the pins and rocker arms) and the force-angular deflection curves of typical AT bindings were measured. A kinematic model was derived to predict the contact force between the metal inserts of the AT boots and the pins of the AT bindings, dependent on angular displacement of the binding rocker arms. By combining the kinematic model, the force-angular deflection curves, and moment equilibrium, we determined the force and binding rotation angle needed to release the AT boot in a direction normal to the ski. The metal AT boot insert geometry and AT binding pin geometry and dimensions can affect significantly the contact states and kinematics of release. Two load-deflection curves of similar peak loads can result in significantly different maximal forces and angles to release the binding, even when the geometry and dimensions of the binding pins and boot inserts remain unchanged. The geometry and dimensions of the binding (pins and rocker arm) and the boot inserts define the kinematics of the binding release. The model can be used to test the effects of varying parameters on the release and retention characteristics of Tech/Pin boot-binding systems to optimize the release and retention characteristics.

Background: In recreational alpine skiing, the anterior cruciate ligament (ACL) is affected in approximately 50% of serious knee injuries. There are established sex-based and skill-based differences in ACL injury risk, but the potential impact of equipment used (eg, skis, bindings, and boots) has not been evaluated. Purpose: To evaluate individual and equipment-related risk factors for an ACL injury depending on sex and skill level. Study Design: Case-control study; Level of evidence, 3. Methods: This was a retrospective questionnaire-based, case-control study of female and male skiers with and without ACL injuries during 6 winter seasons (from 2014-2015 to 2019-2020). Demographic data, skill level, equipment specifications, risk-taking behavior, and ownership of ski equipment were recorded. Ski geometry (ski length; sidecut radius; and widths of the tip, waist, and tail) was taken from each participant’s ski. The standing heights of the front and back part of the ski binding were measured using a digital sliding caliper, and the standing height ratio was calculated. Abrasion of the ski boot sole was also measured at the toe and heel. Participants were divided by sex into less and more skilled skiers. Results: A total of 1817 recreational skiers participated in this study, of whom 392 (21.6%) sustained an ACL injury. A greater standing height ratio and more abrasion at the toe of the boot sole were associated with increased ACL injury risk in both sexes, independent of the skill level. Riskier behavior increased the injury risk only in male skiers, independent of the skill level, and longer skis increased the injury risk only in less skilled female skiers. Older age, the use of rented/borrowed skis, and more abrasion at the heel of the boot sole were independent risk factors for ACL injury in the more skilled skiers of both sexes. Conclusion: Individual and equipment-related risk factors for an ACL injury partly differed according to skill level and sex. Consideration of the demonstrated equipment-related factors should be implemented in order to reduce ACL injuries in recreational skiers.

Ski boots are designed to transfer forces from skier to ski. This transfer is among others affected by the flexion stiffness (FS) and so effects safety and skiing performance. Previous studies have used devices with prosthetic legs to evaluate FS, however, influencing factors like the foot and lower leg shape or individual buckle closure are not considered. The purpose of the study was to (i) develop a device to measure the individual flexion stiffness (IFS) of ski boots worn by skiers, to (ii) determine the repeatability of the measurement, and to (iii) compare the IFS with the nominal flex index of the manufacturers. 21 subjects were tested twice to assess repeatability. The IFS of 135 subjects were measured on ski slopes and compared with the nominal flex indices. Repeated measurements revealed a correlation rp of 0.98 (p<0.001) and a relative standard error of SEMrel=3.0%. The correlation between IFS and nominal flex index was moderate with rs=0.64 (p<0.001). Post hoc analysis showed no statistical differences between flex index 80 and 90 (p=0.29) and flex index 100 and 110 (p=0.60). The determination of IFS was sufficiently repeatable. Considerable differences were found between IFS and the nominal flex indices of the manufacturers. The introduction of a measurement standard may improve the comparability among the manufacturers. Our method is not suitable as standardization method due to the measurements with subjects. However, the data collected may provide a valuable baseline for a future standardization.

This review article reports the recent advances in the study, design and production of ski-boots for alpine skiing. An overview of the different designs and the materials used in ski-boot construction is provided giving particular emphasis to the effect of these parameters on the final performances and on the prevention of injuries. The use of specific materials for ski-boots dedicated to different disciplines (race skiing, mogul skiing, ski-mountaineering etc.) has been correlated with the chemical and physical properties of the polymeric materials employed. A review of the scientific literature and the most interesting patents is also presented, correlating the results reported with the performances and industrial production of ski-boots. Suggestions for new studies and the use of advanced materials are also provided. A final section dedicated to the standards involved in ski-boot design completes this review article.

Real winter dressing for après-ski, for country or city weekends: big sweaters and slim pants, shearlings in icy pales, mixes of matte and shine. Here, photograp in Iceland by Hans Feurer