Snow Skiing Research Articles

A review of the friction of snow skis

Snow friction results from a mixture of processes. With little meltwater present, the surfaces are partially separated and, when too much water is present, the contact area increases and there may be capillary attachments. Slider thermal conductivity and even colour are very important. Heat is generated by friction and solar radiation absorbtion and is conducted away by both slider and ice particles. The remaining heat is available to generate meltwater which acts as a lubricant. While sliders must be designed for use over a narrow range of snow and weather conditions, polyethylene bases can be structured and waxed to broaden that range. The important processes operate not at the air temperature, but at the ski base temperature, which is highly dependent on such things as snow-surface temperature, load and speed. The roughness elements and contact areas must be characterized before the basic processes can be understood further.

Mechanics of a turning snow ski

Modelling the turning motion of snow skis is simulated via a single-ski representation followed by numerically solving the associated differential equations of motion. The forces applied to the ski are assumed to be gravity, the longitudinal friction occurring between the ski and snow, and a skidding force (snow resistance force) corresponding to a system centripetal force and making curvilinear motion possible. The skidding force is calculated via a water jet analogy. Our model quantitatively shows that a ski's side-cut, i.e. its midlength taper, remarkably effects the radius of curvature of a ski trail made when skiing down a ski slope.

The incidence of meniscal tears associated with acute anterior cruciate ligament disruption secondary to snow skiing accidents

In the acutely traumatized knee, meniscal tears are commonly encountered with an anterior cruciate ligament (ACL) injury. Because of the high incidence of ACL injuries related to snow skiing, a retrospective study was conducted to determine the incidence and location of concomitant meniscal injuries in a series of 328 acute ACL tears resulting from snow-skiing accidents. Seventy-five (23%) of the ACL injuries had coexistent meniscal injuries--43 (13%) lateral and 32 (10%) medial menisci. Thirty-two (43%) of the 75 meniscal tears were peripheral detachments from the capsule (red-red tears), which often heal without surgical intervention. Findings from this study indicate that the incidence of meniscal damage in acute knee injuries secondary to snow skiing accidents is substantially lower than in knee injuries sustained during other sports activities, which range from 53% to 65% in previous studies.

Snow skiing combined anterior cruciate ligament/medical collateral ligament disruptions

Recent reports indicate that combined anterior cruciate ligament/medial collateral ligament (ACL/MCL) knee injuries are usually associated with a lateral meniscus tear. In our center, snow skiing is the athletic activity most frequently associated with this double-ligament injury complex. A sports-specific analysis was undertaken to evaluate the hypothesis that the snow skiing ligament injury is different from similar injuries caused by other athletic activities. Of a total of 64 acute arthroscopically confirmed tears of both the MCL and ACL, 23 were caused by snow skiing and 41 by nonskiing activities. There were fewer lateral meniscus tears in skiers (43%) when compared with the nonskiers (88%). Skiers also had fewer medial meniscus tears (13%) than did nonskiers (37%). No medial meniscus tears occurred in the absence of a lateral meniscus tear. Although 78% of the skiers were women, only 12% of the nonskiers were women. Skiers were older (average age 35 years) than the nonskiers (average age 28 years). The right knee was injured almost twice as frequently as the left. These data suggest that the double (ACL/MCL) ligament injury in skiers might be distinctly different from that in nonskiers.

A New Method of Measuring 3-D Ground Reaction Forces under the Ski during Skiing on Snow.

A new method was developed for measuring the distribution of real time ground reaction forces under the snow ski. A platform composed of 20 separate beams was buried in snow under the ski track. Vertical, cross horizontal, and longitudinal horizontal force components were measured with strain gauge bridges separately on each beam, and the results were recorded with a data logger at 90 Hz. The test results for two types of skating skis are described. Anomalous behavior was observed in horizontal force components, where negative force values were recorded on some sections of the ski at the end of the initial kick phase. This suggests that some parts of the ski edge pushed in the opposite direction from the kicking force. This is interpreted to be due to a sharp bending along the bottom edge of the ski. It is concluded that the method could be used to measure 3-D dynamic forces under snow.

Treatment of Unstable Tibial Shaft Fractures by Closed Intramedullary Nailing With Flexible (Ender-Type) Pins

Eighty patients with unstable tibial diaphyseal fractures were treated by closed intramedullary nailing with Ender-type flexible pins. The majority of injuries occurred from falling while snow skiing. Sixty-six fractures were closed and 14 were open. Fifty-eight fractures involved the distal, 21 fractures the middle, and one fracture the proximal one third of the tibial shaft. The average time to roentgenographic union was 15.5 weeks (range, ten to 34 weeks) for closed and open Grade I and II fractures. The time to union in Grade III fractures was 50 weeks (range, 36-64 weeks). There were two nonunions and two delayed unions. Both nonunions occurred in Grade IIIA open shaft fractures. Intramedullary stabilization with flexible, Ender-type pins provides good control of unstable tibial shaft fractures. The use of pins with a smaller diameter (3.5 or 4 mm) allows the surgeon to place more pins across the fracture site. The use of multiple pins and packing the intramedullary canal may provide better rotational stability. The use of Ender-type pins for fixation of Type IIIA open tibial shaft fractures is contraindicated.

Snow Skiing for the Physically Disabled

The sport of snow skiing by the physically disabled, which originated in Europe in 1935 and first received attention in the United States in the 1940s, is reviewed in terms of opportunities available, instructions, adaptive equipment necessary, and benefits provided. Persons with a wide variety of disabilities (such as cerebral palsy, multiple sclerosis, spinal cord injury, hemiplegia, amputation, blindness, spina bifida, and muscular dystrophy) can participate. Accordingly, a wide range of adaptive equipment is available--including outrigger skis, flip-skis, canting wedges, ski bras, "toe spreaders," sit-skis, and mono-skis--to allow safe enjoyment of the sport. Programs for instruction of the disabled skier are increasing in number and popularity, and numerous opportunities are available to enter competitive events sponsored by National Handicapped Sports. Both the participants and the instructors relate the numerous physical and psychologic benefits that can be derived from skiing; the sport provides an almost universal enjoyment of the sense of freedom and independence. Snow skiing is an enjoyable, beneficial, outdoor cold-weather activity that the disabled population can safely learn with proper instruction.

Influence of Body Mass on Energy Cost of Roller Skiing

A theoretical analysis was used to evaluate the effect of body mass on the mechanical power cost of cross-country skiing and roller skiing on flat terrain. The relationships between body mass and the power cost of overcoming friction were found to be different between cross-country skiing on snow and roller skiing. Nevertheless, it was predicted that the heavier skier should have a lower oxygen cost per unit of body mass for roller skiing, as is the case for snow skiing. To determine whether the theoretical analysis was supported by experimental data, oxygen consumption measurements were performed during roller skiing by six male cross-country ski racers who spanned a 17.3-kg range in body mass. The theoretical analysis was supported by the experimental findings of decreases in oxygen consumption for each kg increase in body mass of approximately 1.0% for the double pole technique, 1.8% for the kick double pole technique, and 0.6% for the VI skate technique.

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.

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.

A model for the turning snow ski

A model is developed to investigate the steady-state solutions of a turning snow ski. In computing equilibrium of the skier/ski system, two types of forces are assumed along the ski bottom: skidding forces, which arise when shearing a virgin snow surface, and carving forces, which maintain the curvature of the ski when it slides in its own track. Turn radius and speed are insufficient to specify a unique turn solution. To quantify the effects of different ski designs on the model, a range of possible solutions is calculated for each turn radius and speed and compared using two indices, one measuring the mechanical efficiency of the turn resulting from the energy dissipation of shearing the snow surface, and the second measuring the equilibrium solution sensitivity to human control and regulation. When possible solutions are mapped onto the plane of these two indices, a characteristic solution behavior emerges corroborating experimental results found using a model ski turning on astroturf. This behavior provides a quantitative basis for comparing different ski designs and proposing new design strategies.

Randomly oriented reinforcing fibers in a snow ski : Meatto, F.D. and Pilpel, E.D. (TriStar Sports Inc., Middletown, CN, USA) US Pat 4 679 814 (14 July 1987)

Randomly oriented reinforcing fibers in a snow ski : Meatto, F.D. and Pilpel, E.D. (TriStar Sports Inc., Middletown, CN, USA) US Pat 4 679 814 (14 July 1987)

The Marathon Skate in Nordic Skiing Performed on Roller Skates, Roller Skis, and Snow Skis

In the past few years there has been a change from emphasizing the classical cross-country ski technique to introducing the skating technique. Use of the skating stride has led to the adoption of roller skates instead of the ratchet-type roller skis for dryland training. Therefore the question arises as to whether the roller skates simulate the movement pattern observed on snow. This study attempted to answer this question and to evaluate the movement similarity between a newly designed skating-specific roller ski and snow skis in performing the skating stride. The marathon skate was chosen for analysis as it was the most established and consistent skating stride. Biomechanical cinematography was used to acquire a sagittal and anterior view of the skiers. Temporal and angular kinematic data were collected. Both dryland devices approximated the snow skiing pattern, yet it was found that due to the discrepancies in the propulsion phase between the roller skates and the snow skis, the “Nordic Skate” roller skis proved to more closely simulate the on-snow technique.

Segmenting Texas snow Skiers

This article describes the expenditures and characteristics of Texans who travel to places outside of Texas to participate in snow skiing. The Texas skier market is segmented into two groups, heavy and light spenders. These segments are dijJerentiated from one another and from other Texans in terms of socio-demographic characteristics.

Artificial ski slope injuries: a 1-year prospective study

Skiing is one of the fastest growing sports in the United Kingdom. A prospective study of 119 patients who sustained injuries while skiing on the Edinburgh artificial ski slope was performed. The ratio of injury of the arm to that of the leg was 4.2:1, which is the reverse of that found with snow skiing. In particular, thumb injuries accounted for 32 per cent of all injuries. Attention is drawn to the high incidence of damage to the ulnar collateral ligament of the metacarpophalangeal joint of the thumb, which is related to the construction of the ‘snow slope’ matting. The pattern of injury is described and the mechanisms of injury discussed.

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.

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.

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.

Traumatic dislocations of the peroneal tendons.

Traumatic dislocation of the peroneal tendons is an often unrecognized injury which has been reported to occur most commonly during snow skiing. The strength of the peroneal retinaculum is exceeded during resistance to violent passive dorsiflexion or to inversion stress. Pain, swelling, and ecchymosis may hinder early diagnosis; however, intense retromalleolar pain on active eversion is a specific, highly suggestive finding. Fracture of a thin shell of the lateral malleolar cortex is diagnostic. In chronic cases, marked dislocation of the tendons is frequently demonstrable, with more than the usual degree of snapping. Surgical repair is advocated, using one of several procedures available. Most acute cases can be treated by simple repair of the torn or fractured structures. In chronic cases, or in acute cases with deficient structures predisposing to dislocation, it is necessary to reconstruct the peroneal retinaculum and/or deepen the peroneal groove. Longitudinal splitting of the peroneus brevis tendon was a new finding in this series.

Design of an actively controlled snow ski release binding.

A new electronic ski binding has been designed which may better protect skiers from lower extremity injuries. A four-step procedure for developing binding release criteria aimed at preventing specific injuries is outlined. Using simplified biomechanical models, the release criteria for tibia fracture in both torsion and flexion are derived. A binding design which embodies the derived release criteria is described. The binding consists of three subsystems: 1) a dynamometer, 2) an analog computer controller, and 3) an electromechanical release mechanism. The strain gage dynamometer directly measures torsion and bending moments between the boot and ski. An analog computer controlled processes dynamometer signals. Dual release mode capability is achieved by parallel solution of differential equations which model the leg in both medial-lateral rotation and flexion. When the model solution reaches a critical value, the controller actuates the release mechanism. The release mechanism incorporates a unique closed circuit hydraulic system which rigidly locks the boot to the ski until release. Laboratory tests on a prototype confirm that the computer-controlled binding prevents inadvertent release under noninjurious high-magnitude, short-duration loads but releases before quasi-static loads reach injurious levels.