A microcomputer controlled snow ski binding system--I. Instrumentation and field evaluation

This paper presents the design and field evaluation of the first microcomputer controlled ski binding system. This system incorporates an Intel 8086 microcomputer controller and an integral binding/dynamometer. This instrumentation system not only undertakes real time control, but also it records dynamometer data via a miniature digital cassette tape recorder. The integral binding/dynamometer offers the same operational and mounting convenience of commercially available mechanical bindings. The binding may be released either manually or electrically via the controller. Comprised of four octagonal half strain rings, the strain gage dynamometer measures the three moment load components at the boot. To enable the user to conveniently operate the computer, extensive operating software was developed. The operating software is discussed in relation to both the acquisition and storage of data from the dynamometer and the control of the electro-mechanical snow ski binding. The binding system has been used successfully to both record boot moment components and control ski binding release during actual skiing maneuvers. Moment histories typical of three common recreational skiing maneuvers are presented.     

Pulse code modulation telemetry in ski injury research. II. Preliminary results.

The excitation between the boot and the ski was measured in maneuvers skied over a variety of snow conditions. A precision pulse-code modulation (PCM) - frequency modulation (FM) telemetry system was custom built to transmit data from strain-gage force transducers mounted inside the test ski to a receiving station about 3 km distant. Field tests gathered cruising data from three basic maneuvers - snowplow, stem christiana, and parallel christiana. Some classic falls resulting from inadvertent release of the ski bindings were also recorded. For comparative purposes, the maneuvers were skied over a standard five-turn slalom course. Examination of the loading histories reveals that: (1) the data are nonstationary random; (2) boot compression for the test binding system exceeds 500 N and is caused by ski flexure; (3) an 80 Hz resonance of the particular toe binding mechanism is excited; (4) combined impulsive loading is significant; (5) the loading is related to the maneuver type; (6) bending components during forward falls exceed the tibia flexural strength even though heel binding release occurs at the laboratory setting, and (7) torsion and bending components exceed tibia fracture levels during elementary ski maneuvers.     

A microcomputer controlled snow ski binding system--II. Release decision theories

A hierarchy of release decision theories for both tibia fracture and knee ligamentous injury are defined and simulated on a computer. Moment loading data, recorded during actual skiing by the microcomputer-based ski binding system described in Part I, are processed by the various release decision theories. At the bottom of the hierarchy is the simplest theory which treats boot loading as quasi-static and compares moment components to threshold levels. Another stage of the hierarchy defines an analytic expression for a combined loading failure locus. Note that this is the first formulation of a combined loading release decision theory. Yet another stage of the hierarchy computes bone moments via dynamic system leg models. The various release decision theories are evaluated by comparing processed results to both pain and bone failure limits. For the data generated by the field tests conducted to date, the simplest release decision theory satisfied the retention requirement for pain limits in the presence of muscle activity for both torsion and forward bending. For pain limits in the absence of muscle activity the retention requirement was not satisfied however. Another result is that leg dynamics are significant. A final result is that combined loading considerations lead to a more conservative theory.     

Measurement of strength and loading variables on the knee during Alpine skiing

The study focusses on the prevention of knee injuries during snow skiing. In order to develop a technology of knee injury prevention, both the strength and loading on the knee during skiing activity must be known. This paper reports measurements of variables influencing both knee strength and loading of the joint. The strength variables measured included the degree of activity in six muscles crossing the knee, the knee flexion angle, and the axial load (i.e. weight bearing) transmitted to the knee. Transducers included surface electrodes to monitor electromyogram signals indicating the degree of muscle activity and a goniometer to measure both hip and knee flexion angles. The complete loading on the knee was derived from a dynamometer which measured the six load components at the boot-dynamometer interface. The transducer data were acquired and stored by a compact, battery powered digital data acquisition-controller system. Three male subjects of similar physical size (nominal was 1.8 m and 75 kg) and skiing ability (advanced intermediate to expert) were tested under similar conditions. Each subject skied a total of four slalom runs--one snowplow and three parallel. The total time of each test was 21 s. Example data plots from different types of runs are presented and discussed. Based on observations from the data, necessary performance features for ski bindings offering improved protection from knee ligamentous injuries are defined.     

Differential specific mechanical energy as a quality parameter in racing alpine skiing

An important question in alpine skiing is how to determine characteristics of well-performed ski turns, an issue that has become more crucial with the arrival of new carving skis. This article introduces a new method for estimating the quality of skiing at each point of observation based on mechanical energy behavior that can be measured using established motion analysis techniques. It can be used for single or multiple-skier analyses for evaluation of skiing technique as well as racing tactics. An illustration of its use is shown by analyzing 16 top-level racers using a 3-D kinematical system and video recorded during an alpine ski world cup race. Based on energy behavior of several racers, it is demonstrated that the most direct line with shortest radius of turn is not necessarily the most effective strategy in contrast to what some coaches believe.     

Effect of ski boot settings on tibio-femoral abduction and rotation during standing and simulated skiing

Ski boots are designed to transfer high forces from the skier to the ski. For this purpose they are made of stiff materials and constrain the leg of the skier to an unnatural position. To overcome the problem of unnatural knee posture, the ski boots can be adjusted in the frontal plane as well as in the horizontal plane by the canting mechanism and the "v-position", respectively. Canting enables lateral and medial orientation of the shaft with respect to the base of the boot. The "v-position" is a pronounced outward rotation of the boot's base with respect to the ski's long axis. The purpose of this study is to investigate the effect of different foot rotations and ski boot canting settings on knee kinematics during standing and simulated skiing. Knee kinematics was measured by means of motion analysis and with the help of skin-mounted markers on 20 subjects. The ski boots in their standard settings significantly constrained the skier to an unnatural valgus position. Ski boot base rotation had a significant effect on internal external knee rotation, whereas canting had an effect on varus-valgus angles during standing. However, for the simulated skiing position no effects were observed. The study suggests that the constraints of the ski boots result in a clinically relevant valgus misalignment. Canting settings reduced the misalignment but only by about 10%. Increased ski boot canting settings would therefore be desirable. Knee kinematics showed that rotational misalignment could not be linked to any significant increase in injury risk.     

Identification of knee joint models for varus-valgus and internal-external rotations: snow skiing experiments

Sprains at the knee are the most frequent of the severe injuries occurring during alpine snow skiing. This paper discusses the development of analytical models describing rotations across the knee joint caused by varus-valgus and internal-external moments applied at the foot during skiing. Identification of an ARMAX model requires simultaneous measurements of the rotations across the knee and the moments at the foot during skiing. As the models only relate the measured input (moment) and output (rotation) data, they also identify components of apparent rotation resulting from imperfect fixation of the rotation measuring instrument on the test subject and resulting from other inputs. The models identified for all subjects are of order four or five for both varus-valgus and internal-external rotation, and they describe modes with oscillatory and exponentially decaying components. Application of the models to prediction of rotation across the knee from the measured moment at the foot is illustrated by example. A new, and virtually mechanically uncoupled, six degrees-of-freedom, strain gauge dynamometer is developed to record the moments at the foot during skiing. The concept of the dynamometer design has general application.     

Management,winter climate and plant–soil feedbacks on ski slopes: a synthesis

Owing to the increasing popularity of skiing and the upslope movement of the snow reliability line in mountain regions, more and more alpine environments are being turned into skiing areas, with strong impacts on ecosystem functions and biodiversity. Creation and management of ski slopes cause physical disturbance to soil and vegetation, while (artificial) snow supplements affect soil structure, chemistry, moisture and temperature regimes as well as shifts in snow season and growing season length. Vegetation–soil feedbacks may influence the outcome of these interactive effects on soil and vegetation, with possible consequences for soil erosion. Moreover, climate warming will lead to changing snow cover and duration, which will interact with ski slope management effects on soil and vegetation and its feedbacks. Based on a conceptual framework we review the main elements of these interactive effects on soil and vegetation on new and established ski slopes. We also set a research agenda with specific studies that could further advance our understanding of interacting ski slope management, winter climate, vegetation–soil feedbacks and ecosystem functioning. In such new investigations, alpine climate change ecology can probably learn much from the “experimental” disturbance and snow manipulations on ski slopes and vice versa.     

Prediction of the loading along the leg during snow skiing.

The complete force and moment of each cross section of the leg between the ski boot top and the knee during normal skiing were predicted from measurements of the force and moment under the toe and heel of the boot and the flexion of the ankle. The force and moment components predicted at the base of the boot were significantly different from those predicted at sites of potential injury at the boot top and the knee. The maximum torsional and maximum varus-valgus moments predicted at the knee over all subjects tested were 70 Nm and 149 Nm, which are within the estimated range of the ultimate strength of the knee without support from contracted muscles crossing the knee. Regression analyses were used to find the force components at the base of the boot that best predict the bending and torsional moments at the boot top and knee. The torsional moments at the boot top and knee are best predicted by the medial-lateral force at the toe. The varus-valgus moment at the boot top and knee are best predicted by the resultant medial-lateral force component at the base of the boot. The set of best predictors of the anterior-posterior bending moments at the boot top and knee includes the vertical force at the toe, the vertical force at the heel and the component of the total vertical force directed perpendicular to the leg.     

Surface EMG and torsion measurements during snow skiing: laboratory and field tests

The relationship between mean rectified EMG (MREMG) measured with surface electrodes and the longitudinal torsion of the lower extremity was investigated in laboratory and snow skiing experiments. Linear regression of the MREMG from the gluteus medius and the peroneus longus with the torsion measured at the foot in the laboratory tests showed that torsion can be predicted with correlation coefficients greater than 0.95 and with a standard deviation less than 5 Nm over all knee flexions and weight bearing. A similar correspondence between MREMG and torsion during skiing does not exist. MREMG is dominantly correlated to posture and body position control functions in skiing. During falling, during ski binding release, and during possible injury sustaining situations, the MREMG was always relatively large, but it was not distinguishable from that associated with smaller torsion of the lower extremity.     

A parameter optimization method to determine ski stiffness properties from ski deformation data

The deformation of skis and the contact pressure between skis and snow are crucial factors for carved turns in alpine skiing. The purpose of the current study was to develop and to evaluate an optimization method to determine the bending and torsional stiffness that lead to a given bending and torsional deflection of the ski. Euler-Bernoulli beam theory and classical torsion theory were applied to model the deformation of the ski. Bending and torsional stiffness were approximated as linear combinations of B-splines. To compute the unknown coefficients, a parameter optimization problem was formulated and successfully solved by multiple shooting and least squares data fitting. The proposed optimization method was evaluated based on ski stiffness data and ski deformation data taken from a recently published simulation study. The ski deformation data were used as input data to the optimization method. The optimization method was capable of successfully reproducing the shape of the original bending and torsional stiffness data of the ski with a root mean square error below 1 N m2. In conclusion, the proposed computational method offers the possibility to calculate ski stiffness properties with respect to a given ski deformation.     

Influential Factors on the Relative Age Effect in Alpine Ski Racing

The relative age effect (RAE), which refers to an over-representation of selected athletes born early in the selection year, was proven to be present in alpine ski racing in all age categories at both national and international levels. However, the influential factors on, or the causal mechanisms of, the RAE are still unknown. Therefore, the aim of the present study was to examine three possible influential factors on the relative age effect in alpine skiing: physical performance, anthropometric characteristics and biological maturational status. The study included the investigation of 282 elite Austrian youth ski racers and 413 non-athletes (comparison group) of the same age (10–13 years) and region. Six physical performance tests were performed, body mass and height were assessed, and the age at peak height velocity (APHV) was calculated. A significant RAE was present in the ski racers. No differences were shown in the physical performance characteristics or in the calculated APHV between the relative age quarters. These results suggest that ski racers born in the last quarter can counteract the relative age disadvantages if they already present the same level of physical performance and maturational status as those born at the beginning of the year. The height and weight of ski racers born at the beginning of the year were significantly higher compared to the non-athletes, and ski racers born in relative age quarter 1 were taller and heavier compared to the ski racers of the other quarters. This indicates that the anthropometric characteristics influence the selection process in alpine ski racing, and that relatively older athletes are more likely to be selected if they exhibit advanced anthropometric characteristics.     

Direct and indirect effects of ski run management on alpine Orthoptera

Alpine landscapes are heavily influenced by ski run management, which can have severe impacts on alpine biodiversity. To assess these impacts on alpine Orthoptera, we compared species richness and species abundance in 41 plot pairs on ski runs and adjacent off-slope control plots in three ski resorts in Austria and Germany. A mixed modelling approach was used to assess the impacts of ski run preparation, artificial snow-making and environmental variables such as altitude, cover of dwarf shrubs and the application of fertilizer. Ski run plots showed a significantly lower species richness and number of individuals than control plots. Moreover, artificial snow led to a further decrease in species number. Hierarchical variance partitioning revealed that Orthoptera community composition is best predicted by environmental variables indirectly related to ski run management (fertilization, cover of dwarf shrubs) and to altitude. Only one out of five species significantly decreased in abundance after artificial snow-making. Other species were more sensitive to fertilizing and altitude. Dwarf shrubs were negatively associated with ski run management but positively associated with abundance of three species and species richness. Our data provide evidence for both direct and indirect consequences of ski runs and artificial snow-making on alpine Orthoptera. Overall, Orthoptera communities are suitable indicators for human-induced changes in alpine environments. In particular, a shift towards generalist species such as Chorthippus parallelus along with a decrease in typical alpine species gives cause for concern as this implies a homogenisation of biodiversity owing to ski run management.     

Alpine skiing is associated with higher femoral neck bone mineral density

Objective:

To evaluate the influence of elite-level alpine skiing on athletes’ skeleton.

Methods:

Thirteen professional alpine skiers (9 males and 4 females with mean age of 22.6 years) and their age- and height matched control subjects were measured with dual energy X-ray absorptiometry (total body, lumbar spine, proximal femur, forearm) and quantitative ultrasound (hand).

Results:

After adjusting for sex, age, weight and height, between-group differences were 15% (p=0.012) for the lumbar spine, 14% (p=0.022) for the femoral neck, 10% (p=0.051) for the total hip, and 11% (p=0.001) for the total body favoring the alpine skiers. However, after controlling for total body lean mass (~muscle mass), the group-differences lost their statistical significance, the borderline 10% difference (p=0.051) in femoral neck BMD excluded.

Conclusion:

Factors contributing to the alpine skiers’ higher BMD may not only include the greater muscle mass (~stronger muscles) of these athletes but also a large number of impacts and possibly other high-frequency features in external loading generated by the high-speed skiing performance.     

Assessment of plasma opioid peptides, beta-endorphin and met-enkephalin, at the end of an international nordic ski race

Plasma met-enkephalin, beta-endorphin, cortisol and lactic acid concentrations were measured in seventeen volunteer male subjects at rest and after a long-distance nordic ski race. Immediately after the race, mean plasma met-enkephalin did not show any significant change, but significant rises in beta-endorphin, cortisol and lactic acid were noted in all skiers. The change in beta-endorphin with exercise was significantly related to the change in cortisol (r = 0.68; p less than 0.001) and to the change in plasma lactic acid (r = 0.60; p less than 0.001). Furthermore, the experienced skiers training over 150 km X week-1 of nordic ski had significantly faster skiing times in this event and showed greater beta-endorphin, cortisol and lactic acid levels than the recreational skiers who trained for 20 km X week-1. Our results imply that the changes in plasma beta-endorphin depend on the intensity of exercise. However the significance of higher levels of skiing training or previous nordic ski experience in the release of beta-endorphin is expected and cannot be excluded.     

Measurment of pedal loading in bicycling: I. Instrumentation

This paper presents a new instrumentation system to precisely measure pedal loads and pedal position. A pedal/dynamometer unit implementing four octagonal strain rings measures all six load components between the foot and pedal. To study the relationship between foot position and loading, the pedal/dynamometer offers three degree-of-freedom adjustability. Pedal position along the pedal arc is precisely described by measuring crank arm angle and relative angle between pedal and crank arm. Linear, continuous rotation potentiometers measure the two angles. Transducer signals are sampled by a digital computer which calculates resultant loads and pedal position as functions of crank arm angle. Transducers are designed to mount on most bicycles without modification. Test subjects ride their own bicycles unconstrained on rollers so that loading data is representative of actual cycling.     

Factors Associated with the Perception of Speed among Recreational Skiers

Background

Skiers have to differ between slow to moderate and fast skiing speed to determine their skiing style according to the ISO 11088 standard for setting binding release values. Despite existing evidence that males ski significantly faster than females, no sex-specific factor was inserted into the ISO 11088 standard.

Objective

To evaluate factors potentially associated with the perception of individual skiing speed among recreational skiers.

Methods

Skiing speeds of 416 adult skiers (62% males,) were measured with a radar speed gun. Skiers were interviewed about their age, sex, skill level, risk taking behaviour and helmet use. Finally, skiers had to rate their perceived speed on one out of three speed categories (fast, moderate, slow).

Results

The measured mean speed of this cohort was 48.2±14.3 km/h (30.0±8.9 mph). A total of 32%, 52%, and 16% of skiers perceived their actual speed as fast, moderate and slow, respectively. Mean speed differed significantly between the 3 speed categories with a mean of about 53.5±13.7 km/h (33.2±8.5 mph) for fast, 47.6±14.0 km/h (29.6±8.7 mph) for moderate, and 39.4±12.2 km/h (24.5±7.6 mph) for slow skiing, respectively. Sex (η² = .074), skill level (η² = .035) and risk taking behavior (η² = .033) showed significant differences of skiing speeds with regard to the 3 categories of speed perception (all p < .001) while age groups and ski helmet use did not. Males, more skilled skiers and risky skiers perceived their actual speed as fast, moderate and slow, when skiing up to 10 km/h (6 mph) faster compared to females, less skilled and cautious skiers.

Conclusion

The perception of skiing speed as fast, moderate or slow depends on sex, skill level, and risk taking behaviour. These findings should be considered when discussing the introduction of a sex factor into the ISO 11088 standard for setting binding release values.     

Application of a full body inertial measurement system in alpine skiing: a comparison with an optical video based system

This study aims at determining the accuracy of a full body inertial measurement system in a real skiing environment in comparison with an optical video based system. Recent studies have shown the use of inertial measurement systems for the determination of kinematical parameters in alpine skiing. However, a quantitative validation of a full body inertial measurement system for the application in alpine skiing is so far not available. For the purpose of this study, a skier performed a test-run equipped with a full body inertial measurement system in combination with a DGPS. In addition, one turn of the test-run was analyzed by an optical video based system. With respect to the analyzed angles, a maximum mean difference of 4.9° was measured. No differences in the measured angles between the inertial measurement system and the combined usage with a DGPS were found. Concerning the determination of the skier's trajectory, an additional system (e.g., DGPS) must be used. As opposed to optical methods, the main advantages of the inertial measurement system are the determination of kinematical parameters without the limitation of restricted capture volume, and small time costs for the measurement preparation and data analysis.     

Skiing Injuries

This report, based on a study of 471 consecutive skiing accidents, is concerned with the contributory causes, mechanisms, treatment and prevention of the more common skiing injuries.Over 80% of injuries occur in skiers under the age of 30 years. Most injuries involve the lower extremities, and are ligamentous. One-third of all injuries are fractures. This distribution is the common experience in most ski centres which have organized facilities for treatment of such injuries.This study shows that rapid handling and early treatment of casualties ensures minimal suffering, accurate diagnosis, prevention of complications and earlier rehabilitation of injured skiers. Many of the causes of skiing accidents can be prevented by control of skiing conditions, and proper instruction of younger skiers.     

理论雪期和滑雪气候适宜度评价——以长白山滑雪场为例

为科学分析雪资源气候属性,定量评价滑雪运动气候适宜度概况,本研究基于天气学原理,从气候角度设定了理论雪期概念;设定与滑雪运动密切相关的气温、风速、雪期降雪量3个指标的不同适宜度等级阈值,对各指标进行归一化处理并设计其转换函数;运用灰色关联度理论,结合欧氏距离法,构建滑雪气候适宜度指数评价模型,并以长白山滑雪场为例进行评价。结果表明: 长白山地区雪资源丰富,1981—2018年,理论雪期内的平均降雪量为64.6 mm;气候变暖背景下,平均雪期日数及降雪量随年代呈略有减少趋势,雪期开始时间随年代变化呈现延后趋势,结束时间呈提前趋势,且前冬(当年雪期开始至12月底)雪期日数明显少于后冬(次年1月初至雪期结束)雪期日数;长白山滑雪场雪期内滑雪气候适宜性高,气温、风速和降雪条件的最适宜和较适宜日数累计分别占91.9%、91.8%和94.6%;滑雪综合气候适宜度日数累计占比达99.7%,绝大多数时间适宜滑雪运动的开展。理论雪期概念的提出弥补了因初、终雪气象观测资料缺乏对雪资源研究等造成的困扰;滑雪运动气候适宜度评价模型可为滑雪场地开发和经营提供管理决策,为滑雪爱好者提供出行的科学支撑。