Motion is the act of moving from one place to another: we move through sliding on snow. Skiing is a singular sport performed by keeping specific postures while sliding over a slippery element on inclined surfaces.
Skiing motion is a constant equilibrium between controlling and letting go, it is at the same time sliding and stopping, accelerating and slowing down. We move while in motion. We perform movements over our base of support (BoS). i.e., our skis, as they glide down the hill. We must control our own movements as well as our skis’ movements by guiding them towards anticipated points.
Skiing generates forces that are applied to our body producing sensory information needed for our perceptual process. This information includes speed estimation, acceleration, deceleration, braking, and the anticipation of other people’s actions.
While sliding on snow, external forces change so it is necessary to adapt by keeping balance and speed controlling in relation to terrain configuration. The environment displays many variables. Ground configuration changes in shape and snow texture in friction and consistency. The slope varies in extension and expansion, contains fixed and mobile obstacles (other people moving). The weather perturbs our motion if it snows, rains, it is foggy, windy or there is flat light. To advanced skiers, sliding over a snowy environment may seem relatively easy and exciting, but for the beginner, it may be initially a complex and discouraging task since he must contemplate these variables while incorporating the concept of tilt and sliding, which could be completely new for him or her.
Motion is composed of two aspects which are orientation and mobility. Orientation refers to determine where we want to get to and mobility is the way to reach the intended place, including direction and speed control. Path orientation suffers modifications since guiding the skis and waiting for them to get to a previewed point it is not automatic as it may be altered by modifications like other people’s paths.
Orientation is the knowledge of distance and direction in relation to a destination point, plus the maintenance of these two references during skiing motion. Distance perception could be based not only on the spatial extension but also on the intentions of the actions we want to perform and the effort associated with those actions. If our intention is to slide to a specific place of the slope, then we may perceive distance as the effort needed to get to that point. Knowing how to orient is essential to perceive the space where we are located in relation to the environment and its contents, and this is essential in developing a behavioral adaptation to it. To orient ourselves, we need to assess the environment and plan our trajectories in advance.
Motion is just one and refers always to an imaginary straight line from a starting point to a destination point. Trajectories, instead, could vary and are used to get to the destination point as, e.g., a succession of curvilinear trajectories. The line of motion merges with the skiing trajectory when this one is straight.
Perception of Sliding
When walking or running, we unconsciously seek a steady feet-ground contact. While skiing, the sensation of adherence disappears because it is replaced by sliding. Perceiving sliding is essential for action control, adapting it to the ground surface, and the sensation resulting from our skis’ base gliding over the snow.
Snow friction is the resistance force produced by the moving skis in contact with the snow. It usually occurs we are surprised by friction changes because we did not visually anticipate snow texture, which allows adapting beforehand our actions according to the estimated friction magnitude.
The snow surface features we use as references are texture, coarseness, areas of light reflection, shade zones, and shape uniformity or irregularity. Texture is the result of snow surface properties perceived according to contrast and motion direction.
Effects of Vibration in Sliding
Our skis tend to vibrate while descending on irregular terrain, hard snow or ice, at high speed, or by our own faulty performance. Vibrations are due to terrain or snow irregularities or because of an inaccurate guiding control of the skis. While skidding, vibrations spread to up to our body, and we absorb or resist them according to our proficiency level and sensory skill.
When vibrating, our skis loose snow contact affecting their control and our balance. Skis too short and hard snow amplify vibrations that not only are uncomfortable; they also interfere with movement performance precision, triggering potential falls.
Vibrations tend to make our body to oscillate, but these oscillations can be absorbed by muscle actions depending on posture. If our posture is rigid, vibrations disturb our sensory information pickup, balance, and, at high frequencies, even vision could be affected. If we adopt a flexible posture, the greater part of vibrations of any frequency will be absorbed by the knees, low-frequency vibrations by the ankles, and high-frequency vibrations by the hips.
Framework Matrix of Skiing Motion
| Afferent Force & Vibration Filtering | Anatomical Joint & Posture Mechanics | Environ-mental Property Calibration | Spatio-temporal Planning & Line Selection | Kinetic Stability & Base Regulation | Learning Progression Stage |
| Mechanical Impulse Conversion Converting raw forces generated by slope descent into functional speed, acceleration, and braking estimation signals. | Low-Frequency Ankle Absorption Engaging active ankle flexors and extensors to absorb low-frequency vibrations caused by hard snow. | Snow Friction Calibration Visually scanning snow texture, coarseness, and gloss to anticipate friction magnitude and adapt movements beforehand. | Egocentric Orientation Mapping Maintaining distance and direction references in relation to a single destination point across the run. | Base of Support Centering Controlling body mass displacements over the skis to guide them toward anticipated points. | Novice Variable Overload Experiencing discourage-ment and complexity when attempting to fuse slope tilt with unfamiliar sliding sensations. |
| High-Frequency Hip Damping Utilizing deep hip joint articulation to damp high-frequency vibrations before they reach the sensory systems. | Mid-Frequency Knee Damping Deploying flexible knee joint articulation to isolate and absorb the greater part of all terrain vibrations. | Contrast-Based Texture Tracking Tracking snow surface properties based on visible lighting contrasts, shade zones, and motion direction. | Effort-Based Distance Projection Perceiving physical slope distances as the precise amount of muscular effort required to reach a target area. | Adherence-to-Sliding Transition Suppressing the subconscious gait instinct for steady ground-adherence; replacing it with pure sliding control. | Novice Ground Adherence Fixation Unconsciously seeking static feet-ground contact, which disrupts sliding progression and fluid motion. |
| Sensory Signal Preservation Avoiding rigid body postures to prevent vibrations from disturbing sensory information pickup and balance. | Flexible Posture Stabilization Adopting a highly flexible posture to minimize body oscillations on hard snow or irregular icy patches. | Weather Disturbance Buffering Modifying technical approaches to buffer against rain, snow, heavy winds, dense fog, and flat light. | Proactive Trajectory Pre-Planning Assessing the immediate macro-environment to plan curvilinear trajectories and avoid mobile obstacles. | Contact Maintenance Tracking Preventing high-frequency ski chatter from breaking ski-to-snow contact to maintain absolute steering command. | Novice Interruption Vulnerability Suffering trajectory disruptions because path adjustments to avoid other skiers are not yet automatic. |
| Ocular Fixation Defense Isolating the skull from high-frequency terrain vibration to prevent severe visual tracking and vision degradation. | Rigidity Pattern De-construction Deconstructing rigid postures that transmit skidding vibrations directly up through the skeletal framework. | Shape Uniformity Assessment Evaluating shape uniformity versus trail irregularity to predict sudden underfoot deceleration forces. | Linear-to-Curvilinear Blending Merging straight motion lines into successive curvilinear trajectories to control descent velocities. | Dynamic Skidding Guidance Guiding skidding actions smoothly across irregular terrain to prevent inaccurate ski tracking and edge catches. | Advanced Environ-mental Adaptation Navigating changing terrain shapes and shifting friction zones with high excitement and technical ease. |
| Friction Shock Preemption Preventing sudden friction shock by matching visual snow texture anticipation with proactive joint bracing. | Postural Balance Equilibrium Maintaining a constant postural equilibrium between active kinetic control and purposeful letting go. | Mobile Obstacle Interception Tracking the paths of other moving people to calculate necessary line deviations through the slope. | Non-Symmetrical Path Modification Modifying path orientation dynamically to bypass intersecting skier lines and fixed obstacles. | Short-Ski Vibration Mitigation Adjusting edge pressure and stance width when using short skis to offset amplified vibration patterns. | Elite Tactical Command Commanding complex mountain environments by executing planned trajectories along an imaginary straight line. |
