Ski Turns Research Articles

Body leaning adjustments during sitting ski turns in different injury situations

Body leaning adjustments during sitting ski turns in different injury situations

A screening instrument for side dominance in competitive adolescent alpine skiers.

Previous research has shown that high school ski students injure their left anterior cruciate ligament (ACL) more often than their right ACL, and that a prevention program focusing on equal load to the right and left ski turns prevents ACL injuries. Whether the injuries were in the dominant or non-dominant side of ski students was not determined but may be important knowledge to ski coaches for future design of ski-specific training programs. There is no gold standard on how to investigate the dominant side of alpine skiers. Therefore, the aim of this study was to develop a screening instrument consisting of five questions for identifying side dominance and to evaluate side dominance in competitive adolescent alpine skiers. First, 121 competitive adolescent alpine skiers answered the questions on side dominance using a test-retest design. The questions were: which hand/arm (left/right) or foot/leg (left/right) one uses as the first choice when writing, throwing, kicking a ball, jumping over a fence and stair-climbing. A question about safer/better ski turn to the left or to the right was also added. Second, 274 skiers answered the questions at one occasion. A very good agreement was shown in writing and throwing and kicking a ball, and a fair agreement was shown in jumping over a fence and stair climbing. A total of 243 skiers reported right-sided dominance, and seven skiers reported left-sided dominance. One hundred and nineteen of the 121 skiers who took part in the test-retest design answered the question safer/better ski turn, and of those 70 (59%) reported that they had a safer/better ski turn to one side than to the other side. However, the side was not consistent between the two test occasions, and the question did not correlate with side dominance. A combination of the three questions “What hand/arm do you use as first choice when writing?” “What hand/arm do you use as first choice when throwing?” and “What foot/leg do you use as first choice when kicking a ball?”, may be used to decide side dominance in adolescent alpine skiers. Most adolescent alpine skiers reported right-sided dominance.

Wide Skis As a Potential Knee Injury Risk Factor in Alpine Skiing

Alpine skis with wider waist widths have recently become more popular. With such skis, the contact point of the ground reaction force during ski turns is displaced more medially from beneath the sole of the outer ski, which may present an increased risk of injury. The aim of this study was to investigate knee joint kinetics, kinematics, and lower limb muscle activation as a function of changes of the ski waist width in a laboratory setting. A custom skiing simulator was constructed to enable simulation of different ski waist widths in a quasi-static ski turn position. An optical system was used for capturing knee joint kinematics of the outer leg, whereas a force plate was used to determine the ground reaction force vector. The combination of both systems enabled values for external torques acting on the knee joint to be calculated, whereas electromyographic measurements enabled an analysis of knee flexor muscle activation. With respect to the outer ski, the knee joint external torques were independent of ski waist width, whereas knee joint external rotation and biceps femoris activation increased significantly with the increase of the ski waist width. Skier muscle and kinematics adaptation most probably took place to diminish the external knee joint torque changes when the waist width of the ski was increased. The laboratory results suggest that using skis with large waist widths on hard, frozen surfaces may change the load of knee joint surfaces. However, future research is needed to clarify if this may result in the increased risk of knee injury.

Dynamics of carving runs in alpine skiing. I. The basic centrifugal pendulum

ABSTRACT We studied perfect carving turns of alpine skiing using the simple model of an inverted pendulum which is subject to the gravity force and the force mimicking the centrifugal force emerging in the turns. Depending on the turn speed the model describes two different regimes. In the subcritical regime, there exist three equilibrium positions of the pendulum where the total torque applied to the pendulum vanishes—the marginally stable vertical position and two unstable tilted positions on both sides of the vertical. The tilted equilibria correspond to the ski turns executed in perfect balance. The vertical equilibrium corresponds to gliding down the fall line without turns. In the supercritical regime, the tilted equilibria disappear. In addition to the equilibria, the model allows fall-rise solutions, where the pendulum (skier) rises from the ground on one side and hits the ground on the other side, and solutions describing oscillations about the vertical equilibrium. These oscillations correspond to the so-called dynamic skiing where the skier never settles to a balanced position in the turn. Analysis of the available data on World Cup races shows that elite racers ski mostly in the supercritical regime.

Alpine Skiing Robot Using a Passive Turn with Variable Mechanism

Recently, the number of alpine ski junior players in Japan has drastically decreased. The causes include a decrease in ski areas and instructors, along with difficulty of early childhood alpine ski guidance. The alpine ski competition is not simply a glide on a slope. It requires understanding of ski deflection and skier posture mechanics. Therefore, a passive ski robot without an actuator was developed for junior racers of the alpine ski competition to facilitate understanding of the turn mechanism. Using this robot can elucidate factors affecting ski turns, such as the position of the center of gravity (COG) and the ski shape. Furthermore, a mechanism for changing the COG height, the edge angle and the ski deflection is added to the passive turn type ski robot. The developed ski robot can freely control the turn by changing those parameters during sliding.

Leg Compression Tights Reduce Muscle Activation by Altering Ski Turning Technique

PURPOSE: To determine the influence of leg compression tights on the kinematic and neuromuscular performance of alpine ski turns. METHODS: Wireless inertial measurement units (IMUs) and surface electromyography (EMG) electrodes captured bilateral segmental orientations and unilateral vastus lateralis (VL), rectus femoris (RF), biceps femoris (BF) and gluteus medius (GM) muscle activations during slalom race simulations from 9 collegiate alpine ski racers. Average ankle, knee and hip positions and turn durations were calculated from the downhill leg during 18 turns (9 right; 9 left) while wearing either directional compression (DCP) or standard compression (SCP) tights. Average VL, RF, BF and GM EMG amplitudes from the right leg were measured during 9 turns. The order of DCP and SCP conditions was balanced. A 3-way mixed factor, repeated measures ANOVA compared the effects of turn direction and compression type across the 18 turns and one-way repeated measures ANOVA compared the effect of compression type on EMG amplitudes. RESULTS: Average turn duration was 4% longer for the left leg (right, .94 ± .02; left, .980 ± .021 s; p=.039). Average knee position was 3% more flexed during the DCP condition (DCP, 117.1 ± 1.4 deg; SCP, 120.8 ± 1.3 deg; p=.010) and the right leg was 4% more flexed (right, 116.5 ± 1.5 deg; left, 121.3 ± 1.1 deg; p=.020). Average hip position was 5% more flexed during the DCP condition (DCP, 145.4 ± 1.5 deg; SCP, 153.5 ± 1.2 deg; p<.001) and the right leg was 3% more flexed (right, 147.6 ± 1.3 deg; left, 151.3 ± 1.2 deg; p=.012). Average GM, RF and VL activations were 26%, 17% and 17% lower for the DCP condition, respectively (GM: DCP, 2.7 ± 1.9 mV; SCP, 3.7 ± 2.6 mV; p<.001; RF: DCP, 3.0 ± 2.0 mV; SCP, 3.6 ± 2.7 mV; p=.020; VL: DCP, 2.4 ± 1.5 mV; SCP, 2.9 ± 2.1 mV; p=.020). CONCLUSION: The DCP tights demonstrated an alpine skiing turn technique with greater hip and knee flexion and reduced VL, RF and GM muscle activations, which may indicate a mechanism of reduced fatigue for these muscles.

Potential of IMU Sensors in Performance Analysis of Professional Alpine Skiers.

In this paper, we present an analysis to identify a sensor location for an inertial measurement unit (IMU) on the body of a skier and propose the best location to capture turn motions for training. We also validate the manner in which the data from the IMU sensor on the proposed location can characterize ski turns and performance with a series of statistical analyses, including a comparison with data collected from foot pressure sensors. The goal of the study is to logically identify the ideal location on the skier’s body to attach the IMU sensor and the best use of the data collected for the skier. The statistical analyses and the hierarchical clustering method indicate that the pelvis is the best location for attachment of an IMU, and numerical validation shows that the data collected from this location can effectively estimate the performance and characteristics of the skier. Moreover, placement of the sensor at this location does not distract the skier’s motion, and the sensor can be easily attached and detached. The findings of this study can be used for the development of a wearable device for the routine training of professional skiers.

An Attempt for Developing the Measurement System of Reaction Force from Snow Surface for Private Ski Boots by Compact Force Sensors

This paper proposes a new measurement system which measures the reaction force from snow surface for skiing. It is important to analyze the reaction force from snow surface of the skier gliding on the actual snow field to clarify the mechanism of ski turns. In the previous studies, we have used the measurement system of reaction force from snow surface installing the 6-axis force sensor. The system installed the 6-axis force sensor to each foot, and the skier had to carry a data recording PC. Therefore, the entire system was heavy. Furthermore, the system could be used only for the specific ski boots. In this study, we developed a new measurement system of reaction force from snow surface for skiing installing the compact 3-axis force sensors. The 6-axis force components could be calculated by using the information of the compact 3-axis force sensors. We developed a special data logger for saving the sensor outputs, and the skier could glide without loading PC. The system is smaller and lighter than the previous system. The system can be attached between private ski boots and bindings. The system can be adjusted the size of private ski boots. The body of the system was produced by using the personal 3D printer. The verification experiment was conducted to confirm the accuracy of the system. The results of the 6-axis force components calculated by the system were compared to the values of the 6-axis force sensor. These results approximately correspond in all axes. We conducted the measurement experiment of the skier gliding on the actual snow field, and we showed the reaction force from snow surface of the skier by using the system. The system can be applied to motion analysis of the skier gliding on the actual snow field.

Comparison of Carving and Skidding Turns by Joint Torque of Skier and Gliding Velocities in Ski Running on Alpine Ski Slope

This paper deals with the motion analysis of ski turns using the joint torque of skier and the gliding velocity. In this study, we used the inertial and magnetic field sensors, 6-axis force sensors and the GPS receiver for the motion measurement of skier. The joint angles and torque of skier and the gliding velocity are estimated from the measurement information by using the Kalman filter, the Extended Kalman filter and the Newton-Euler method. We conducted the measurement experiment of carving and skidding turns by skier gliding on an alpine ski slope, and we estimated the joint torque of skier and the gliding velocity. The analytical results by the joint torque of skier showed the force information about the usage of side curve in carving turns and the usage of side skidding in skidding turns. The analytical results by the gliding velocity showed the smoothness of turns and the effect by side skidding of skis. The analytical results by combining the joint torque and the gliding velocity indicated the relationship between the control force of skier and the change of gliding velocity. We could indicate the factors of mechanism of ski turns and the major features of ski turns. These results can be used to clarify the mechanism of ski turns.

Dynamic Analysis and Motion Measurement of Ski Turns Using Inertial and Force Sensors

This paper proposes the dynamic motion analysis method of ski turns using inertial and force sensors. The motion analysis of ski turns in gliding on an actual field is important to resolve the mechanism of ski turns. However, it is difficult to measure physical exertion due to the severe experimental surrounding such as the outside snow conditions and the weather on the mountain. Therefore, few studies have analyzed ski turns quantitatively. The control force of skier gliding on the actual snow field must be clarified to resolve the mechanism of ski turns. In the previous studies, we developed the 3D posture estimation method of skier gliding at high speed. This method can estimate the Roll- Pitch-Yaw angles in local coordinate by the information of inertial sensors using the Unscented Kalman filter. The control force of skier (joint torque) can be calculated by combining this method and the measurement of reaction force from snow surface. We conducted the experiment of skier gliding on the actual snow field. The inertial sensors were attached to the body segments (upper body, lumber, femur, and lower thigh) of skier and ski boots, and the 6- axis force sensors were installed between boots and skis. The inertial sensors measure angular velocity and acceleration of body segments, and the force sensors measure the reaction force from snow surface. The joint torque (lumber spine, hip, knee and ankle) of skier is calculated by applying the measurement information to the Newton- Euler method. The analysis results using joint torque indicates the control force of skier gliding on the actual snow field. Therefore, the analysis method and results can be used to evaluate the skill of turns and to resolve the mechanism of ski turns.

Motion Analysis and Joint Angle Measurement of Skier Gliding on the Actual Snow Field Using Inertial Sensors

This paper deals with the motion analysis of skier gliding on the actual snow field using inertial sensors. It is difficult to measure the motion of skier gliding on the actual snow field since the gliding velocity is fast and the measurement area is large. Therefore, few studies have analyzed ski turns in gliding on the actual snow field. It is necessary to analyze the skier gliding on the actual snow field in resolving the mechanism of ski turns. In our previous study, we developed the motion measurement method of skier using inertial and magnetic field sensors. The 3D posture is estimated by applying the sensor fusion method, and the method can estimate the 3D posture compensating the drift error of gyro sensor and reducing the effect of dynamic acceleration of accelerometer. Furthermore, we developed the sensor fusion method estimating the 3D posture in local coordinate by the information of inertial sensors attaching the body segments. The joint angle of skier in gliding on the actual snow field can be estimated by this method and inverse kinematics. We conducted the measurement experiment by skier gliding on the actual snow field. The inertial sensors and the GPS receiver were attached to the body segments and the top of skier, respectively. Skier conducted carving and skidding turns in this experiment. We calculated the joint angles of skier by the information of inertial sensors, and the switchovers of turns are estimated by the GPS receiver output. The results of motion analysis indicated the major feature of skier's motion and the difference between carving and skidding turns. Therefore, the analysis results can be used to the skill rating, the clarification of the mechanism of ski turns and the suggestion of more ideal turning form.

321 拡張カルマンフィルタを用いたスキーヤーのばね・減衰係数推定に関する研究(スキー)

This paper proposes the estimation method of spring and attenuation constants of skier. Skier conducts ski turns three-dimentionaly, and the motion is complexity. The joints of skier are used such as spring and damper in turns. Therefore, it is necessary to claryfy the effect of spring and attenuation by the joints of skier gliding on the actual snow field. However, the spring and attenuation constants change during turns. In this study, we propose the estimation method of spring and attenuation method using the joint internal force, relative displacement and relative velocity. The Extended Kalman filter is used as the estimation algorithm. We applied the estimation method to the motion information of skier gliding on the actual snow field, and we estimated the spring and attenuation constants. These results indicated the major features of skier's motion.

Studies on the Motion Analysis of Ski Turns and the 3D Posture Measurement of Skier in Gliding on the Actual Snow Field

Studies on the Motion Analysis of Ski Turns and the 3D Posture Measurement of Skier in Gliding on the Actual Snow Field

Three-Dimensional Knee Joint Loading in Alpine Skiing: A Comparison Between a Carved and a Skidded Turn

Limited data exists on knee biomechanics in alpine ski turns despite the high rate of injuries associated with this maneuver. The purpose of the current study was to compare knee joint loading between a carved and a skidded ski turn and between the inner and outer leg. Kinetic data were collected using Kistler mobile force plates. Kinematic data were collected with five synchronized, panning, tilting, and zooming cameras. Inertial properties of the segments were calculated using an extended version of the Yeadon model. Knee joint forces and moments were calculated using inverse dynamics analysis. The obtained results indicate that knee joint loading in carving is not consistently greater than knee joint loading in skidding. In addition, knee joint loading at the outer leg is not always greater than at the inner leg. Differentiation is required between forces and moments, the direction of the forces and moments, and the phase of the turn that is considered. Even though the authors believe that the analyzed turns are representative, results have to be interpreted with caution due to the small sample size.

Development of a Passive Turn Type Skiing Robot with Variable Height Mechanism of Gravitational Center

In recent years, sports engineering has become an active area of research. It has produced important contributions of many kinds in the development of sports. Ski turns have been investigated from various viewpoints such as the motion analysis of skiers and ski robots and dynamic simulation. Nevertheless, despite considerable research, the mechanisms of ski turns remain to be completely elucidated. Mechanical models derived using approximate expressions do not, furthermore, match alpine ski turns and results are therefore not reflected concretely. To facilitate theoretical considerations, a passive skiing robot was developed. Influences on ski turns, such as the position of the center-of-gravity, can be examined easily using this robot. In a passive turn type of ski robot, a difference in the turn cycle appeared in a difference in leg height. We noticed the influence of turning in the difference in the center-of-gravity height and appended mechanism to change the height of the legs to a passive turn type of ski robot in order to verify whether turns can be controlled by changing the position of the gravitational center. As described here, we examined ski turn dynamics to help skiers improve their athletic performance.

An attempt of a new motion measurement method for alpine ski turns using inertial sensors

This paper proposes the motion measurement method of skiing turn using inertial sensor. This method calculates the joint angle of the skier gliding on the actual snow field using the information from the inertial sensor units. The sensor fusion estimates the 3D posture (Roll-Pitch-Yaw angle) of local coordinate system compensated drift error of gyro sensor output using acceleration sensor output. The unscented Kalman filter is used to apply the sensor fusion. The joint angle is calculated by applying inverse kinematics to the 3D posture. In this study, the measurement experiment was conducted by the skier gliding on the actual snow field. The inertial sensor units were attached to body segments of skier. We obtained the joint angle of skier (Lumber, hip, knee and ankle). The results of motion analysis represented the major features of skiing turn, and the effectiveness of our proposed method was indicated.

Kinetic Analysis of Ski Turns Based on Measured Ground Reaction Forces

The objective of this study was to devise a method of kinetic analysis of the ground reaction force that enables the durations and magnitudes of forces acting during the individual phases of ski turns to be described exactly. The method is based on a theoretical analysis of physical forces acting during the ski turn. Two elementary phases were defined: (1) preparing to turn (initiation) and (2) actual turning, during which the center of gravity of the skier-ski system moves along a curvilinear trajectory (steering). The starting point of the turn analysis is a dynamometric record of the resultant acting ground reaction force applied perpendicularly on the ski surface. The method was applied to six expert skiers. They completed a slalom course comprising five gates arranged on the fall line of a 26° slope at a competition speed using symmetrical carving turns (30 evaluated turns). A dynamometric measurement system was placed on the carving skis (168 cm long, radius 16 m, data were recorded at 100 Hz). MATLAB procedures were used to evaluate eight variables during each turn: five time variables and three force variables. Comparison of the turn analysis results between individuals showed that the method is useful for answering various research questions associated with ski turns.

Reaction Forces and Moments in Carved Turns

AbstractWe computed reaction forces and moments acting on a skier during a carved turn. We performed an inverse and a forward dynamic analysis. For a run of an elite skier, marker positions on skier and skis were obtained as functions of time from a video analysis and smoothed by splines. Linear velocities and accelerations were computed by differentiating the splines, angular velocities, and accelerations via rotation matrices. The forces acting at the right ski were measured with two Kistler force plates. For the inverse dynamics, we used an adapted Hanavan model for a skier consisting of upper body, left and right thighs, shanks, and skis. Applied forces considered were weight and ski-snow friction. Drag was neglected. By prescribing a lateral weight distribution from the outer to the inner ski during the turn, reaction forces and moments at the left and right ankle, knee and hip joints were computed from the Newton–Euler equations of motion for constrained rigid multibody systems. The forward dynamics was performed with a three-segment model of a mono-skier consisting of trunk, thigh, and shank. Rotational joints were assumed in knee and hip. The track and the joint angles were prescribed. The inward lean angle was determined by a balance condition that led to nonholonomic constraints. After formulating the equations of motion in descriptor form, the resulting differential-algebraic system was solved with the numerical code RADAU5. Computed and measured reaction forces and moments agreed well within the accuracy of the measurements. The calculated joint loads are consistent with results from the literature. The forward dynamics model can be used to simulate consecutive ski turns. With parameter studies, the effects of slope, tracks, segment properties, ski-snow friction, and velocity of the skier on joint loads and performance of a run can be investigated. Further, injury mechanisms can be analyzed.

Design of Ski Boots for Alpine Ski Racing Based on Leg Frame of the Skier

A ski boot is important to make progress in ski turning technique as an interface between a skier and a ski. Especially in alpine ski races, suitability of design of the boots for racers becomes more important to achieve accurate and quick lean of the leg in ski turns. This study is aimed at building a new design concept of a ski boot that can improve the results of alpine ski races. In this paper, new design of an upper shell of a ski boot that was adjusted to the features of the frame of alpine ski racers was experimentally examined. As a result, it was demonstrated that a front and a rear part of the upper shell of a ski boot should be separately adjusted to the length of a shank of each player for well-balanced quick lean of the leg in the ski turn. Finally, the effect of new design of an upper shell was examined in giant slalom and slalom tests by Japanese alpine ski racers of the first rank. Consequently, the results showed that lean angle during turns was increased and finish time was shortened when the skiers wore the newly designed boots.

Computer Simulation of Consecutive Ski Turns

Abstract A computer model was developed to simulate consecutive ski turns. The model consists of a segment model for two skis and a single body for the skier. It was implemented in the multibody simulation software LMS Virtual.Lab. The interaction of ski and snow leads to a normal and a shearing force. For the normal force a hypoplastic relation between force and penetration depth was used. Hypoplasticity considers the effect that compacted snow is inelastic and deformations remain. For the shearing force orthogonal metal cutting theory was applied. During turns the skier has to keep balance. He leans inward to compensate centrifugal force. Neglecting angulation the complement of the inward lean angle is the mean value of the edge angles of the left and the right ski. With a suitable choice of the edge angles the skier kept the balance. Using this model the trajectory of the skier was simulated over four and a half turns. The first turn was rather carved, but in the last turn strong skidding was present. Due to increasing speed the centrifugal force considerably exceeded the shearing strength of snow. The hypoplastic force-penetration relation led to a reasonable penetration depth, which is a crucial factor for the shearing force. Based on this reference simulation the influence of edge angle and forward/backward lean was assessed by performing parameter studies. An increased edge angle caused smaller turn radii. Surprisingly, forward lean caused larger and backward lean smaller turn radii. This phenomenon could be explained by the turn moment of the skier. Both effects were more dominant when the skis skidded.