Stability and posture orientation
We have seen that to maintain a proper posture while skiing we have to control our body in space in relation to two aspects: stability (ability to control our weight in relation to the base of support) and orientation (ability to control the relationship of our body parts between them and the environment). For example, in the orientation of body parts, the beginner is likely to move the upper body towards the turn while the expert skier tends to orient his pelvis to the inside of the curve.
Stability refers to when we assume a disturbance-resistant posture or when we quickly return to our reference stance after a balance disruption. An appropriate postural control allows us keeping a stable posture after disequilibrium. For instance, in turn initiation, it is experienced a transitory instability which leads to stability once the turn is initiated.
Postural references
Controlling our body motion in space presupposes the existence of reference systems. Body stabilization requires the appreciation of separation between the current position and a certain reference position (Paillard, 1971).
References influencing our skiing posture may come from:
- Information about our head, arms and hands positioning (bones direction).
- From support surface information about snow, skis, and feet.
- From vertical and horizontal information.
- From information about our body’s longitudinal axis.
- From our motion (speed, vibrations).
- From our spatial positioning (self-centered, geocentric, or exocentric).
- From environmental elements (topographical references).
The significance of references in the postural organization
We rely on references for skiing postural organization. We seek to compare information about something that we identify to establish our own posture when sliding.
The reference set is called reference frame which includes the following:
- The vertical reference refers to axis vertical detection, and it is one of the most used since we have a sense of verticality incorporated in our visual perception of the environment.
- The horizontal reference as the perception of our gaze horizontality and the automatic stabilization related to that.
- The spatial reference involves our perception and location into the surrounding space, i.e., the space of central vision for objects positioning in relation to us, and the space of peripheral vision as warning and location function.
- The body axis reference is our perception of the longitudinal axis that allows organizing body lateralization using a balanced performance of both sides of our body.
- Podal reference in terms of perceiving feet positioning related to our support surface (plantar proprioception).
- The manual reference is applied when using our hands location for postural reorganization after balance disturbances.
The oblique effect
The oblique effect, proposed by Appelle (1972), refers to that our perceptive performance is better for vertical and horizontal stimuli than for oblique stimuli. We perceive vertical or horizontal axis with better accuracy but have less precision to determine the degree of inclination of an object or, in our case, a slope. Appelle & Gravetter (1985) conclude that the haptic oblique effect is influenced more by our visual experience than by haptic experience (touch in motion). We can conclude that in posture orientation, we generally use vertical and horizontal more than oblique references.
Referential posture
The referential posture is the fundamental dynamic body stance that we should achieve and maintain since it allows a better perceiving and controlling the execution of specific technical gestures. All posture changes, as well as all our movements and actions, relate to this posture.
Skiing postural oscillations due to instability are interpreted by us as the posture of reference deviation errors. This stance, adapted to the situation we are in, comes from our mental representation of an internal model based on sensory information that is constantly updated. Indeed, body oscillations are one way we use to explore the space around our body, allowing establishing reference limits that define our skiing posture.
When becoming aware we are able to modify it, we can discover stance centrality even not having total control over our actions. Perceiving our body centrality is our body consciousness informing that our defense or rejection mechanism was disabled, becoming a reference which we try to preserve.
This skiing referential posture is achieved by constant fluctuation between muscle tension and relaxation, minimizing balance alterations, and keeping us within our base of support. While improving our proprioception, we also improve the centrality of our referential posture and the use of anticipation mechanisms. With training, this becomes a habit that our body and motor consciousness regenerate constantly.
Centripetal posture
To initiate a turn, we must generate a centripetal force towards the center of the future curve through the inclination of all or part of our body, and thus can tilt the skis on its edges toward the direction of the new trajectory. To obtain it, we must assume a centripetal posture by body positioning on the side we pretend to turn to, organizing postural movements calculating the curvilinear trajectory and balance perturbations created by the centrifugal effect, tending to disarm the centripetal posture we are seeking.
Turning with parallel skis involves body orientation by moving forward our inside foot, knee, hip, and shoulder. This distribution begins at our feet, producing body medio-lateral displacement (slight, moderate or pronounced) towards the inside of the curve. It is seen that expert skiers constantly adopt this body orientation through segmental displacement towards turn direction, generating the necessary centripetal posture. This is more difficult to observe in beginner levels due to postural immaturity since, to release the support of the standing foot and start turning, they tend to first move the center of gravity to the uphill foot, placing their pelvis on it, inducing an upright posture and hips rotation towards the outside of the turn, which is inefficient.
