While reducing our speed, we should adopt a conservative behavior minimizing potential collisions, making adjustments to maintain an ideal deceleration near the limit of the safety zone (the space considered as safe enough when maneuvering between nearby fixed or moving obstacles). We could also adopt a more aggressive behavior by a sudden deceleration in the safety zone limit.
The speed of the radial flow expansion determines the collision time with objects or persons, helping speed reduction and an eventual stop. When approaching an obstacle, we perceive its expansion, and this mechanism is used as a reference for controlling our braking.
During braking, our stopping limits divide situations in which it is possible to stop and the ones which are not. Being aware of these limits, we must be sensitive to our actions’ capacity since this is crucial for effective braking. Vision, specifically the focus of expansion, provides us with fundamental information at deciding when and where to stop.
Deceleration and braking adjustment
During braking, the ideal condition would be the progressive level of our deceleration leading us to stop in the desired place without adjustment needs. The difference between ideal and actual braking conditions is a common miscalculation between skiers that should be corrected for actions’ efficacy.
Normally, we do not stop immediately while detecting an obstacle or another person, but adjust our braking based on the situation, using visual information (visual anticipation, central and peripheral vision) to measure the approaching speed. If this information is insufficient, our braking adjustment will not be effective. The more anticipated is this measurement, the more effective the deceleration or, in other words, the greater the deceleration, the shorter will be the braking distance (Lee, 1976).
Adjusting our braking level not only is applicable to a full stop; it is also towards reducing the approaching speed to a slower skier or snowboarder. This situation reveals that the beginner tends to slow down using more effort because still does not regulate speed and, in many cases, slows down or stops unnecessarily because of misjudging the situation. The expert instead starts braking after assessing the emergency of the situation.
When approaching a static or a moving obstacle, we must evaluate variables such as spatial proximity, sliding speed, and time to the potential contact or collision. In these cases, it is noted that the beginner tends to slow down and then analyze the situation as the expert skier usually evaluates the situation and assesses whether it deserves stopping, slowing down, or changing the trajectory. When following another one, such as in group lessons, we should keep a prudential distance, and at faster speeds, the greater the distance.
Collision path
Detecting the path of collision with an object or person depends largely on our experience. The beginner has difficulty to detect it early enough due to gaze restriction and because of that, tends to slow down at each direction change.
The expert skier distinguishes when he is in a collision path and due to his experience knows whether should slow down or has sufficient maneuvering time and space to avoid colliding.
Braking control stages and critical times
Braking control consists of specified stages:
- The first one is detecting the situation in which it is necessary to stop.
- It follows then our evaluation of when starting to slow down.
- Finally, we need to define the muscular effort to be applied using information about the deceleration in course.
Without this information, we would be slowing down blindly that, in the case of beginner skiers, could be a common situation. It is noticed that the expert instinctively applies the three stages for smooth controlled braking.
Lee (1976) proposes two critical braking times:
- The registration of approach is when we detect the approaching time to the point of the future braking.
- The braking initiation time (in case of following someone), when somebody in front of us begins to stop, is the time we have before starting our own braking.
Time to contact
According to Gibson’s theory (1950), our brain uses the object’s expansion degree in the retina to determine the approach towards that object. For Lee (1976), our brain also estimates the time starting from this expansion.
To avoid an obstacle during motion, our brain would use a mechanism called time to contact. This means that it would not calculate distances but time until contact, using indicators from the optic flow. This concept would apply to skiing, for example, on a mogul field, a slalom course or jumping; all situations in which we calculate the time to contact the next bump, the gate, or the landing.
Objective and subjective factors in braking
We begin to stop when becoming aware that we are in a collision path, evaluating the degree of urgency of that possible collision. This urgency has objective factors:
- Our own deceleration.
- The other person’s speed (in case of a potential collision with someone).
- The approaching distance.
- Our own muscular effort for the braking action.
Subjective factors may include:
- Our experience.
- The degree of distance estimation.
- Confidence in our technical capacity.
There is a low probability that we consider all objective factors so the majority of the events will recourse to reaction time based on our experience, being this inversely proportional, i.e., the more our experience, the less our reaction time and vice versa.
Braking strategies
Facing a risky situation, our immediate concern should focus on whether it is or it is not necessary to stop and if so, if it is possible to succeed. Our own interpretation of the environment such as slope inclination, braking distance and time, snow type, speed, or the required deceleration will be relevant to perceive if it is likely to stop.
If choosing to brake, we can adopt a conservative behavior minimizing potential collisions, making constant adjustments to maintain gradual or ideal deceleration. Also, we could adopt a more aggressive behavior allowing the ideal deceleration to get closer to the stopping point.
In this regard, it is observed two strategies:
- The first one is when we get close to the stopping point with constant speed and then stop suddenly.
- The second strategy is applied when choosing to perform a significant deceleration at the initial instant of the approach towards the braking endpoint but we continue sliding slowly and controlled until coming to a full stop.
