Gradualism during steering a curvilinear trajectory
During the learning process on how to ride a bicycle or drive a car, there is an initial tendency to sharply turn the handlebars or the steering wheel towards the desired direction. With practice, the turning action is moderated until the necessary gradualism is reached.
It is seen that the performing roughness in the beginner’s turning actions while skiing is due because of his immediacy behavior, inducing anxiety for completing the actions as soon as possible to reach the new skis’ position. He perceives that the longer he remains sliding downhill, the more difficult it will be to control speed and to stop, so he strives to place his skis across the fall line as quick as possible.
The gradualism of skis’ turning action in a curvilinear trajectory has to do with motion speed and the distance between us and our next turning point. The direction change point and the destination point are the best references for our turning actions, so it is advisable to determine them before starting to turn.
While pointing our skis to the desired direction, emerging variables must be taken into account since they influence the turning result. These variables are motion speed, direction change frequency and duration, slope conditions (tilt, snow surface, traffic, visibility), and turn radius.
To graduate the turning action, we must develop an internal model (mental representation) of the needed effort to turn our skis. To perceive and regulate this activity, we should take as references the sensation of the muscular effort of our feet and legs to produce the rotation force (torque) and the angle between our skis and the destination point. This rotational force (steering action) is indispensable to turn our skis around their axis in skidded turns and this magnitude depends on the applied force, skis’ length, and snow friction. The beginner skier tends to use more rotational force than required because does not distinguish yet the precise application point of that force to his skis.
The influence of head and trunk orientation in determining direction changes
Our head has important participation at the time of changing direction while skiing. It is oriented in advance towards our next destination, confirming its initial inertial role during direction change guidance. If head orientation occurs suddenly, probably our trunk will also rotate in the same direction, causing instability that will affect gradualism in changing direction.
In addition, our neck has proprioceptive receptors involved in balance maintenance and these may be altered by sudden head movements. On the contrary, if our head is orientated gradually, it will help to stabilize our gaze allowing stable skiing. Aligning our head and eyes towards the destination or the direction change points is the prior step to an efficient turning action.
While changing direction when walking or running, our eyes, head, shoulders, and trunk are directed toward the desired direction and then the rest of our body lines up gradually. Orienting our body directly to the target is normal when starting to ski: the beginner rotates his upper body to steer his skis towards the desired direction. It is an inefficient strategy but training will modify this habit, controlling direction changes with feet and legs’ actions, maintaining a quiet and well-balanced trunk.
Attraction and exclusion points
At setting possible paths to move by sliding on a slope, we detect possibilities for actions (attraction points) while others are discarded (exclusion points).
Attraction points are slope areas that can guarantee certain stability, promoting adequate skiing conditions such as groomed snow, a gentle slope or a low traffic area; or on the contrary, places inducing dynamic skiing conditions as jumps, bumps, trees or untracked snow. In these cases, the majority of possible trajectories tend to orient to attraction points, which are considered as “targets”.
Exclusion points are areas that we tend to avoid as slope limits, intersections, drop-offs, irregular ground or snow, traffic, etc. They are points considered as “obstacles” restricting affordances and limiting possible trajectories.
It must be considered, in both circumstances, the target attractive force as well as the obstacle repellent force. Using the strategy of moving towards attraction points is a method to avoid exclusion points, influencing our trajectory decisions.
Visual perspectives of memorizing trajectories for spatial orientation
To memorize the paths of descent used in a ski resort, we make use of two types of visual perspectives. One is ground level perspective and the other is aerial perspective. The ground level or egocentric perspective refers to spatial vision in three dimensions such as we perceive it while moving through the environment. The aerial or allocentric perspective is the spatial aerial view in two dimensions as by looking at a trail map. Both perspectives are used to process our orientation in a ski resort.
Ground perspective requires dynamic orientation since environmental characteristics are seen from the ground. Aerial perspective uses fixed orientation applied to different distances from one run to another. Visual perspectives allow path integration by constant updating our internal representations based on our location and orientation skills.
References for trajectory control
References of skis’ orientation control regarding trajectory could be classified in feedback references, which we control permanently as differences between the real and the intended path, concerning lateral and angular deviations; and feedforward references obtained by visual anticipation of the immediate or future space through we will ski by.
Ideal trajectory
Turning is to align our skis to the visual trajectory that we previously determine. At skiing towards a target, the ideal trajectory is the one leading to our goal without making adjustments. If we do not set a reference point in advance, our trajectory could not be ideal since we would need steering and/or edging adjustments to rectify our direction of motion.
