When a skier's two skis are perpendicular to the fall line, the skier applies and releases pressure on the outer ski (the downhill ski), similar to drawing and releasing a bow. Applying pressure = drawing the bow, releasing pressure = releasing the arrow. However, the bowstring is the ski, which is integrated with the arrow (the skier). When the arrow is released, the bowstring (ski) and the arrow (skier) are both shot together. Clearly, the more concentrated the force, the greater the pressure, and consequently, the more noticeable the effect of the pressure release. Therefore, it is very important to focus the main force, maintain the pressure, and apply pressure to the downhill ski, forming a non-bending plane of pressure. The image below shows the result of not applying pressure on a single plane—just like drawing a bow and releasing a bent arrow, which obviously won’t fly far or well.
On the other hand, when standing on a slope and releasing an arrow, an arrow that is at a 90-degree angle to the slope (fall line) will fly higher and farther. As shown in the third figure below.
To achieve this effect, the line connecting the skier’s two shoulders needs to be parallel to the fall line.
Under normal circumstances, because a person’s two legs are of equal length, when standing sideways on a slope while climbing, the instinctive reaction to prevent falling off a cliff is to straighten the downhill leg and bend the uphill knee. The steeper the slope, the greater the ratio of straightness to bend in the downhill/uphill knees, thereby always keeping the line connecting the person’s two shoulders parallel to the horizon.
As shown in the fourth figure below:
When skiing, the two skis increase a person’s base of support, so there’s no need to worry about falling off. This allows the skier to break the instinctive reaction and adopt the posture shown in Figure 3.
As can be seen in Figure 5, the skier’s knees have the same degree of bend, and the line connecting the two knees is parallel to the fall line, as is the line connecting the shoulders.