toward the waist or tail of the skis. As much as possible, the fore/aft movement of the CM and fore/aft adjustment of pressure should be controlled 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. Tis 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. Tis 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. Tis 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.
PHOTO 1.16: Fore/aft pressure along the length of the ski can be controlled by moving the CM, moving the BOS, or a combination of both (shown).
CM FORWARD CM BACK BOS FORWARD CENTERED
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. Te 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. (As described further in the next chapter, the ski that is farthest from the center of the turn’s circle is referred to as the “outside” ski, and the ski closest to the center of the turn’s circle is the “inside” ski. Tis “outside” and “inside” terminology also applies to the skiers legs in the turn sequence.) To move from turn to
28 PSIA ALPINE TECHNICAL MANUAL
TheSnowPros.org
BOS BACK
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