Pressure Control

Whereas rotational- and edge-control skills affect specific actions of the skis (i.e., turn the skis and tip the skis, respectively), pressure control influences the ski in a slightly different manner. Rather than using movements to manipulate the ski directly, pressure control requires movements to manipulate forces. It is those forces that affect the action of the skis on the snow. Pressure control has three distinct functions: to control the distribution of pressure from the tip of the ski to the tail, control the distribution of pressure from one ski to the other, and control the overall magnitude of pressure acting on the base and/or edge of the skis.

Controlling Pressure Along the Ski’s Length

Skiers primarily have three means of distributing pressure along the length of the ski, all of which require a forward or backward (i.e. fore or aft) adjustment between the skier’s center of mass (CM) and his or her base of support (BOS). The CM is the central balance point of a person’s body mass. The BOS is where the person’s weight is distributed on the snow. A skier may move his or her CM forward or backward relative to the BOS. Alternately, he or she may move the BOS forward or backward underneath the CM. Both of these actions produce the same result by adjusting pressure forward or backward on the skis. A third and very effective approach combines these two actions, moving the CM and the BOS in opposite directions, allowing for a quicker adjustment in pressure along the skis.

Moving the center of Mass

Fore/aft movement of the CM is most effective when it originates and is controlled by flexing and extending the ankles. Flexing, or closing, the ankle joints can move more the CM forward relative to the feet, moving pressure toward the tips of the skis. Extending, or opening, the ankle joints can move the CM back relative to the feet, moving pressure toward the waist or tail of the skis. As much as possible, the fore/aft movement of CM and fore/aft adjustment of pressure should be contorolled with the range of motion in the ankles first, and then complemented by movements in the rest of the body (knees, hips, and upper body). Flexing at the knee joint alone moves the CM backward. Extending at the knee joint moves the CM forward. This movement is much like sitting down and standing up from a chair. Flexing at the hip joint alone moves the CM forward Extending at the hip joint moves the CM backward. This movement is much like bowing.

Moving the Base of Support

Effectively adjusting the base of support involves shifting the position of the feet forward or backward underneath the CM. This action can be done simultaneously with both feet or with one foot. Similar to the movements described previously, flexing and extending the ankles is the primary movement used to move the BOS. Ankle flexion can be used to pull the feet backward, underneath the body, which moves pressure forward on the skis. Conversely, ankle extension can be used to push the feet forward, moving pressure toward the back of the skis.

Combination of Moving the Center of Mass and Base of Support

In a combination movement, the skier shifts the CM and the BOS in opposite directions at the same time. The body moves in the manners described previously, but since the movements work against each other (e.g., the CM moves forward while the feet are pulled back), the redistribution of pressure along the ski can happen more quickly.

Controlling Pressure from Ski to Ski

Any direction change in skiing produces a force as the snow pushes on the skis, causing them to turn. Skiers perceive this force as pressure, and since pressure on the outside ski controls the arc of a turn, a skier must change the way the force pushes on the skis in order to turn in a new direction. To move from turn to turn, or link turns, the skier must reduce the pressure on the outside ski through the finish of one turn, and transfer pressure to the new outside ski. This exchange allows the snow to push the ski in the new direction. This transfer of pressure (and balance) from one ski to the other is one of the most fundamental aspects of alpine skiing. To accomplish this, the skier must move the CM toward the inside of each turn and direct his or her balance toward the outside ski. Through this transition, the distribution of pressure from ski to ski may range from a complete transfer - in which 100 percent of the force is directed toward the outside ski - or partial transfer with only slightly more pressure directed toward the outside ski. This redistribution of pressure from ski to ski requires releasing pressure from the old outside ski and establishing pressure on the new outside ski, which can be done in any of the following ways.

Flexion of Outside Leg with Extension of New Outside Leg

In one approach, the old outside leg (that is, the leg that was outside at the start of the turn) relaxes or flexes (reducing pressure) at the finish of the turn as the new outside leg extends and lengthens (increasing pressure) to complete the transfer of pressure. The extension of the new outside leg helps control the direction of movement of the CM as it actively moves the CM across the BOS.

Extension of Both Legs

Alternatively, a skier can extend both legs through the transition from one turn to the next. The new outside leg extends at a faster rate than the old outside leg, transferring the weight to the new outside ski. In this method, the CM travels upward as the extension of the new outside leg, along with edge change, directs the body down the hill and across the BOS. Common in medium- and long-radius turns, the weight transfer can happen gradually or quickly since the skier has control over the amount, direction, and rate of extension.

Flexion of Both Legs

In another approach, both legs flex through the transition from one turn to the next. The old outside leg flexes at a faster rate than the new outside leg. Along with edge change this transfers weight to the new outside ski. The rate of flexion of the old outside ski. The rate of flexion of the old outside leg controls the rate at which transfer takes place. In this method, the CM lowers or remains level with the ground as weight is transferred and the CM and the BOS realign. This occurs in bumps and other variable terrain, and in dynamic short turns when the skier needs to release a great amount of pressure through the finish of a turn. Each of these examples of how a skier transfers pressure from ski to ski, or shifts weight, involves similar mechanics. A slightly different intensity, rate, and/or timing of weight shift occur. Generally, a combination of these examples is used on a given run depending on tactics, conditions and/or intent.

Controlling the Magnitude of Pressure

The most direct means of managing the overall magnitude of forces in a turn is to increase or decrease the rotation or edge angle of the skis. These actions change the relationship of the skis to the snow, increase or decreasing resistance and resulting in a corresponding increase or decrease in pressure. Resisting or absorbing forces with extension and flexion movements of the legs and spine can also manage the forces acting on a skier. Rotational- and edge-control skills have been covered previously, and the following describes flexion and extension movements that manage the overall pressure acting on the skis and skier.

Up Unweighting

In this movement, a quick extension of the legs produces a momentary reduction in pressure when the skier’s CM slows or reaches the top of its movement. Up unweighting is used, for example, to hop the skis off the snow.

Down Unweighting

Here, a quick flexion of the legs produces a momentary reduction of pressure as the skier’s center of mass drops. Pressure returns as the CM reaches the bottom of its movement. The rate of flexion is very fast and short in duration. Down unweighting is used to lighten pressure on the skis immediately, such as when suddenly encountering the steep upside of a bump.

Retraction

In this movement, actively pulling up (lifting) the legs can lighten the connection between the skis and the snow, momentarily reducing pressure. At slower speeds and in deep snow, the intensity or physical exertion of this movement can be significant. At all speeds, timing is crucial to reduce pressure on the skis at the critical moment. Retraction can be used to clear an obstacle in the snow, pull skis out of heavy snow, or to facilitate transition in dynamic short-radius turns on steep terrain.

Absorption

Allowing muscles to relax and give in to the forces pushing on the skis create momentary reduction in force. The rate of flexion occurs more slowly than with down unweighting and retraction, and for a longer duration. Absorption is used to regulate pressure over varied terrain such as round bumps or rolls.