Postural control, or stance, can be defined as the control of our body position in space. This control depends on our ability, our actions’ requirements, and the environmental restrictions and possibilities. Proper postural control is essential for our skiing movements’ execution.
To achieve postural control, somatosensory, visual, and vestibular information take action on different areas of our brain. Also, postural control is affected by our volitional or emotional aspects.
By controlling our posture, we try to reduce the difference, if not coinciding, between our body setting and the balancing situation. Its functions are: to ensure balance, provide a stable platform for future actions, stabilize perception, and collaborate in skiing spatial representations processes.
Postural control is our body’s conscious stabilization and automatic balance maintenance by keeping the center of gravity on the base of support to prevent falls (Shaperd (2000). It is achieved through the coordination of sensory information, postural reactions, and feedback or feedforward mechanisms.
Stance control is based on two concepts that complement each other. One conceives control as an inverted pendulum in which we oscillate about a fixed point around our ankles within our ski boots attached to the skis. Oscillations cause our center of gravity to continuously move into multiple linear directions, and this is why we are never in equilibrium.
When adding rotational forces to linear oscillations, our postural control is then compared with an inverted cone, where we attempt to limit rotational oscillations. While skiing, we strive to constantly stabilize ourselves, minimizing these oscillations by keeping the center of gravity within the base of support, using our feet soles pressure centers as references. If the center of gravity moves away from the vertical axis, we move this center of pressure to locate it under the center of gravity in a bottom-up organization.
The second concept interprets that postural control is achieved through overlapping our body segments one above the other in a top-down organization. When body segments are misaligned, balance deteriorates and we increase muscle tension to keep standing, trying to find stability in our postural rigidity.
Posture control includes, according to Amblard (1985), two mechanisms: orientation and stabilization. Orientation refers to the maintenance of the relationship between our body segments and the body with the surroundings. Body orientation in space is the active alignment of our trunk and head to gravity, to the supporting surface, to the visual environment, and to our internal references. Orientation is part of our postural control and requires a representation that could be geocentric (in reference to gravity), egocentric (in reference to ourselves), or allocentric (in reference to space).
Stabilization indicates the conservation of our body position to align the center of mass on the base of support minimizing oscillations. Instability is a basic movement characteristic when skiing. As moving one body segment disturbs other segments producing instability, our stance control is achieved through the use of postural anticipatory adjustments, helping to maintain our postural stability by compensating for destabilizing forces associated with movements of one or more segments.
Berthoz (2013) proposes that to determine our posture and simplify its control, it is enough to define relations between our joint angles rather than the spatial position of each segment. Relating this to our skiing stance, the forming angles starting from flexing hips, knees, and ankles should conserve a certain relation. He suggests also that there are two sub-mechanisms of posture control: one ensuring the point of support or movement foundation, and the other, the muscle tone of the moving segments.
The beginner skier tries to control posture by focusing where the different body parts are and encourage the habit of pondering his next posture. The expert instead focuses on the space between body parts, reaching fluidity by occupying these spaces in which each part needs to be placed.
Posture control has external and internal constraints. External limits are imposed by environmental conditions as gravitational forces, accelerations, decelerations, and reactive forces of the supporting surface. Internal limits are originated from our body as internal forces (muscle contractions) and inertial characteristics of body segments. To control posture, we must take into account these limits, which require conscious learning.
Mechanisms Collaborating in Posture Maintenance
Massion (1984) proposed the following mechanisms while maintaining posture:
- Muscle tone gives a certain rigidity that helps us maintain joints in a particular position.
- Postural fixation preserves the different body segments, balancing internal and external forces.
- Coordination between different body segments are involved in movements and postures.
- Anticipatory postural adjustments adapt to movement performance.
According to Horak (2006), our postural control consists of several sub-components that can be divided into the following categories. A disorder in any of these categories could lead to postural instability.
- Biomechanical constraints such as degrees of freedom, strength, and stability limits.
- Cognitive processes as attention and learning.
- Movement strategies that could be reactive, anticipatory or voluntary.
- Sensorial strategies that include sensory integration and readjustment.
- Space orientation as perception, gravity, terrain surface, vision, and verticality.
- Dynamic control as motion and pro-action.
Skiing postural control also depends on:
- Proprioception.
- The interaction of sensory information systems.
- Motor control functions.
- Adaptive and functional strategies.
- On ankles, hips, suspension, and step strategies.
Aspects that influence our postural control when we ski are:
- Gravity
- Speed
- Environmental conditions like weather and surface of support.
- Our emotional state.
- Injuries or pains.
Postural stability control can be classified in:
- Anteroposterior control, whereby stability is controlled mostly by ankles and hips.
- Medio-lateral control, performed generally by our hips.
- Multi-directional control,being the combination of ankles and hips activity adapted to disturbances in any direction.
Postural Control Development
Our skiing postural control is organized from two mechanisms in opposite directions: the top-down mechanism is appliedfrom our head towards our feet, and the bottom-up mechanism from our feet towards our head.
In the beginning of our skiing, postural control is achieved by a top-down mechanism since our head stabilization plays an essential role in posture acquisition through visual information. Then, the control is attained in a bottom-up order based on our feet’s sensory development in which podal and proprioceptive information organize our posture. Continues then a return to the top-down organization where our head has a vestibular predominance taking mobility on our shoulders. Later, the organization becomes progressively in a double sense: head-feet and vice versa including pelvic stabilization. It could be said that our feet collaborate in our head stabilization, and in return, our head guides our feet using vision.
Framework Matrix of Skiing Postural Control
| Concept / Reference Point / Technique | Sensory Processing & Orientation Mode | Biomechanical Mechanism & Execution | Cognitive Load & Behavioral Reaction |
| Neurological Foundations | Processes somatosensory, visual, and vestibular information across different brain areas. | Translates multi-sensory inputs into motor outputs for spatial execution. | Affected and altered by skier’s volitional choices and emotional states. |
| Inverted Pendulum Model | Relies on bottom-up sensory feedback from the ski-to-snow contact point. | Body oscillates linearly in multiple directions about a fixed point around the ankles inside the ski boots. | Requires understanding that the skier is never in static equilibrium due to constant linear shifts. |
| Inverted Cone Model | References pressure centers on the soles of the feet to monitor rotational drift. | Combines rotational forces with linear oscillations, shifting the center of pressure bottom-up to realign under the center of gravity. | Conscious effort to minimize multidirectional variations and keep the center of gravity within the base of support. |
| Top-Down Segmental Overlap | Interprets balance through spatial alignment of stacked body segments. | Overlaps body segments vertically; misalignment forces an increase in muscle tension to maintain an upright posture. | Results in postural rigidity and elevated physical fatigue when segments are out of alignment. |
| Joint Angle Principle | Simplifies spatial tracking by monitoring joint relationships rather than individual segments. | Conserves a specific mathematical relation between the flexion angles of the hips, knees, and ankles. | Reduces cognitive load by focusing on relative joint angles instead of tracking every body part independently. |
| Beginner Structural Focus | Egocentric focus on identifying where individual body parts are located in space. | Executed with halting, mechanical adjustments as individual segments are checked. | High cognitive load; forced to constantly ponder and plan the next physical posture. |
| Expert Structural Focus | Allocentric focus on the dynamic space existing between body parts. | Reaches movement fluidity by continuously and automatically occupying the spatial transitions between segments. | Low cognitive load; focus is on flow, spatial awareness, and fluid positioning. |
| External Constraints Management | Processes incoming forces from gravity, accelerations, decelerations, and snow surface reactive forces. | Adapts joint stiffness and skeletal alignment to absorb external physical loads and variable terrain resistance. | Requires conscious learning to recognize, predict, and adapt to environmental limits. |
| Internal Constraints Management | Monitors internal forces via proprioception and muscle spindle feedback. | Manages internal muscular contractions and the inherent inertial characteristics of moving body segments. | Requires conscious learning to regulate internal tension against physical limits. |
| Anticipatory Adjustments | Feedforward sensory mechanism predicting environmental changes. | Adapts and realigns posture immediately prior to or during the execution of a movement performance. | Proactive cognitive strategy to neutralize forces before they cause instability. |
| Biomechanical Constraints | Proprioceptive awareness of physical boundaries. | Manages structural degrees of freedom, functional strength, and specific limits of stability. | Dictated by physical capacities and the anatomical boundaries of the skier. |
| Movement Strategies | Combines feedback (reactive) and feedforward (anticipatory) loops. | Executes reactive, anticipatory, or voluntary muscle movements to stabilize position. | Switches between reflexive safety responses and conscious tactical executions. |
| Space Orientation | Coordinates perception of gravity, terrain surface, vision, and verticality. | Aligns the skeletal frame to match the perceived vertical axis relative to the slope angle. | Establishes a mental map of spatial orientation on the mountain. |
| Ankle Strategy | Processes immediate micro-disturbances felt at the boot-sole interface. | Executes fine forward and backward balance adjustments directly at the ankle joint inside the ski boots. | Rapid, low-amplitude reflexive response to maintain equilibrium without moving larger segments. |
| Hip Strategy | Tracks mid-to-large physical disturbances along the sagittal or frontal planes. | Executes rapid angular adjustments of the pelvis and hips to correct larger balance errors or manage lateral edge pressure. | Moderately demanding motor strategy activated when ankle limits are exceeded. |
| Suspension Strategy | Monitors heavy impacts, surface ruts, and vertical compressions from the terrain. | Absorbs reactive forces through coordinated flexion and extension of the ankles, knees, and hips simultaneously. | Acts as a shock-absorption system to keep the upper body stable over uneven snow. |
| Step Strategy | Processes extreme or unrecoverable multi-directional balance disturbances. | Executes an active change in the base of support by shifting weight or stepping to re-locate the feet under the falling center of mass. | Ultimate safety mechanism triggered when internal joint adjustments fail to prevent a fall. |
| Influence of Environmental Conditions | Decodes visual data of weather (visibility) and tactile feedback of the support surface (snow texture). | Forces structural adaptation to variable terrain resistance, varying from icy rigidity to deep snow compliance. | High impact on confidence and attention allocation, shifting strategies from proactive to reactive under poor conditions. |
| Influence of Emotional State | Interacts with internal anxiety, fear, or confidence levels. | Alters baseline muscle tone, often inducing involuntary postural rigidity and restricted joint mobility when stressed. | High anxiety narrows focus, compromises feedback loops, and limits the selection of movement strategies. |
| Influence of Injuries or Pains | Tracks nociceptive (pain) signals and physical limitations within the body framework. | Causes compensatory biomechanical shifts, altering joint angles and overworking healthy segments to protect injured areas. | Spends cognitive energy tracking discomfort, slowing response times, and introducing protective rigidities. |
| Anteroposterior Stability Control | Sagittal plane sensory tracking (forward/backward balance). | Controls stability along the longitudinal axis using targeted micro-movements of the ankles and hips. | Primary balance correction mechanism used continuously during acceleration and deceleration. |
| Medio-Lateral Stability Control | Frontal plane sensory tracking (side-to-side balance). | Controls stability along the lateral axis, executed generally through lateral adjustments of the hips. | Crucial for managing edge pressure, turning forces, and lateral terrain variances. |
| Multi-Directional Stability Control | Complex, multi-planar sensory integration. | Combines synchronized ankle and hip activity, adapting dynamically to disturbances in any spatial direction. | Highly integrated, automatic response system required to navigate unpredictable alpine environments. |
| Directional Organization Mechanisms | Establishes bidirectional sensory loops processing inputs from both head-to-feet (top-down) and feet-to-head (bottom-up). | Coordinates spatial mechanics through opposing directional structures depending on the specific developmental stage. | Dictates whether motor execution is driven reflexively by ground feedback or visually guided by head positioning. |
| Initial Top-Down Stage | Leverages visual information as the dominant sensory stream for initial posture acquisition. | Prioritizes head stabilization to establish an operational baseline for lower body tracking. | High cognitive reliance on visual anchors to compensate for unrefined tactile snow feel. |
| Secondary Bottom-Up Stage | Shifts reliance toward podal and proprioceptive sensory feedback from the soles of the feet. | Organizes skeletal posture from the bottom up based on newly developed foot sensitivity and ski-snow interaction. | Shifts attention away from visual confirmation toward active tactile monitoring of pressure changes. |
| Tertiary Vestibular Top-Down Stage | Activates vestibular predominance within the inner ear to track head position. | Transitions upper-body control by allowing head tracking to guide mobility across the shoulders. | Integrates spatial equilibrium systems, freeing the upper torso from rigidity during rotational movements. |
| Integrated Bidirectional Stage | Synthesizes a reciprocal double-sense feedback mechanism (head-to-feet and feet-to-head simultaneously). | Synchronizes global balance by executing continuous pelvic stabilization to bridge upper and lower mechanics. | Low cognitive load; feet actively stabilize the head while the head simultaneously guides the feet via vision. |
