In a Direction Change by Extension, the Center of Mass (located at the pelvis) actively moves up from the Center of Pressure (located at the feet). It is also known as a “cross-over”, “extended transition” or “eccentric turning” because the pelvis crosses over the Base of Support (BoS) after an extended body position.
Upon reaching a certain point in the extension, the CoM is projected laterally (lateral oscillation) toward the inside of the turn, determining an elliptical trajectory (from bottom to top, from back to front, and from side to side).
The peculiarity of this direction change is the tendency to shift weight from one foot to the other and then to change edges, i.e., the extension precedes the edge change as weight shifting begins on the “old” edge (little-toe edge of the uphill ski).
In this mode, the strategy to change direction is engage-to-release, this is, engaging the uphill ski to then release the downhill ski. This strategy is mostly applied in wide turns when there is enough time and space availability.
We can say that it is effective but not efficient because we actively use the hamstring core of the uphill leg to support ourselves on the little-toe edge, thus wasting muscle effort and failing to take advantage of the external forces generated by motion.
In addition, the other drawbacks of the Direction Change by Extension is that, as the CoM moves away from the CoP, there is a tendency for stability to decrease, as well as it presents a loss of snow contact sensation at the first part of the turn (the skis feel “floating”).
Likewise, due to the vertical extension, the CoM is first projected upwards and then laterally towards the center of the new turn, when it would be more efficient to project it diagonally forward.
The biomechanical phases in a Direction Change by Extension are as follows:
1. Generation Phase
The generating movement is the verging, which could be slight or moderate depending on skier’s and turn characteristics, of the CoM to the CoP prior to extension by flexing both legs.
2. Monopodal Phase
This occurs just before the direction change by tensing the leading uphill foot (the now ‘standing foot’). The entire body weight is transferred to the 5th metatarsal (little toe) of this foot and its corresponding edge, forming the CoP on which the active and precise extension of the uphill knee is performed using the gluteal and hamstring muscles. The extension of the uphill knee can, in certain cases, be full. At this point, the pelvis tends to sagittally align over the standing foot.
The extension of the uphill knee is active, while that of the downhill knee tends to be passive. In many cases, the extension of the uphill knee reaches its maximum and is not limited to the leg, but extends through the trunk, producing an extension of the hips.
The trunk, which in some cases becomes completely upright, then tends to lean toward downhill. Because of this, through the lengthening of the iliopsoas muscle of the external hip, the pelvis moves momentarily away from the center of the new turn.
The CoM tends to align itself over the little toe edge of the uphill foot and then move explosively, through the shortening of the iliopsoas muscle of the inner hip which contributes to its flexion, into a lateral trajectory towards the inside of the new direction during the Oscillation Phase.
This extension movement prior to the direction change is generated from the CoP situated on the uphill foot, causing an active and punctual pressure on the snow through the extension of the uphill knee. Both knee and hips extensions can be performed simultaneously or alternately: first the knee and then the hips, or vice versa. Due to the marked knee extension on the uphill foot, the downhill foot may lose contact with the snow.
3. Oscillation Phase
This phase is named after the oscillation of the CoM toward the new turning direction. As the extension of the uphill knee comes to an end, the ankle of the standing uphill foot begins to evert along with the lateral oscillation of the pelvis toward the inside of the turn, while the ankle of the now leading inside foot, with a certain delay, begins to invert (supination of the foot towards the little-toe edge). We say that it oscillates laterally because it is the only direction in which it can move, since the uphill supporting leg has exhausted all its joint range of motion.
This phase begins when the big-toe edge of the uphill ski makes contact with the snow through the pronation of the uphill foot supported on the 1st metatarsal (ball of the foot).
The inside hip moves slightly or markedly forward together with the inside knee which flex passively. The now leading inside foot rests on the little-toe edge.
Due to an explosive translation of the CoM first upward and then laterally toward the inside of the turn, the now inside ski tends to remain momentarily unloaded. The edge change of both skis tends to be alternating: first the uphill ski changes its edges then, immediately after, the downhill ski.
The drawback of this type of quick lateral translation of the CoM is that the initiation of the direction change is ‘floated’, i.e., no pressure is generated on the big-toe edge of the uphill ski (no “early edging”), so the Centripetal Force is delayed. This is mainly due, in most cases, to a pause at the end of the extension (“up and waiting”), as the skier ‘waits’ to move the CoM.
4. Bipodal Phase
This is the longest stage of the turn in which the support between both feet tends to level out until the cycle is completed and repeated in a new direction change. There is a marked flexion of the inside ankle and knee. The hips continue their movement towards the inside of the turn, maintaining the necessary centripetal posture, mainly carried out by the gluteus and, especially, the piriformis muscle of the outside hip.
The pelvis as a whole tends to remain slightly behind the frontal plane of the ankles or the heels, depending on whether there is a sway-back posture due to an imbalance or if the skier intends to generate more pressure on the tails of the skis to accelerate. The shoulders tend to remain on the same frontal plane as the knees. The arms are forward in relation to the trunk, separated from each other, and are used to compensate imbalanced situations.
Technical Framework Matrix for Direction Change by Extension
| Geometric Force Trajectory | Musculoskeletal Kinetic Chain | Tool Edge & Platform State | Tactical Space / Speed Strategy | Attentional Load & Sensation Response |
| Elliptical CoM Trajectory | Displace pelvic mass vertically upward away from foot-based Center of Pressure | Complete full uphill knee extension using synchronized hip joint adjustments | Eccentric Turning: Upward-directed path architecture slowing initial entry | Track multi-planar movement mapping from back-to-front and side-to-side |
| Lateral Oscillation Vector | Project pelvic mass purely sideways toward the center of the upcoming arc | Exhaust complete joint range of motion on the supporting uphill limb | Cross-over: High-altitude mass transfer passing over the base support | Inhibit forward-diagonal projection tendencies during the peak rise phase |
| Uphill Platform Loading | Transfer entire body weight onto the 5th metatarsal of the upper foot (little toe) | Tense leading uphill foot to construct a singular, solid tracking anchor | Engage-to-Release: Weight shift begins on old upper little-toe edge | Commit full skeletal load to the single outside foot before edge swap |
| Sagittal Alignment Phase | Align pelvic center of mass directly over the active uphill foot sole | Lengthen the external hip iliopsoas muscle to step out of old arc | Extended Transition: Upright skeletal frame structure preceding entry | Suppress early inward dropping until vertical stacking completes |
| Hamstring Force Waste | Isolate uphill leg hamstrings and gluteals to support un-swapped edges | Alternating or simultaneous firing patterns of knee and hip extensors | Uphill Little-Toe Anchor: High-energy stance wasting motion forces | Process elevated muscular fatigue inside the posterior leg chain |
| Downhill Foot Unweighting | Elevate lower foot trajectory off the snow surface pack | Passive extension of the lower knee matching the rising upper side | Single-Limb Standoff: Pronounced leg extension causing lower unweighting | Manage balance disruptions if lower ski tail catches on surface chunks |
| Explosive Inner Hip Flexion | Shorten the inner hip iliopsoas muscle to pull mass inside the arc | Drive rapid inward pelvic translation immediately following peak extension | Delayed Core Entry: Explosive lateral velocity shift post-vertical rise | Time the pelvic drop to match the arriving turn fall line |
| Alternating Edge Swapping | Tendency to step edges sequentially: first the uphill ski, then the downhill ski | Pronate uphill foot onto the 1st metatarsal ball joint zone | Alternating Edge Change: Split-second non-simultaneous platform roll | Overcome the lack of early edging bite at the turn entry throat |
| Initiation Float Phase | Move through a temporary zero-pressure window at turn entry | Execute ankle eversion on the upper foot with slight delayed inversion | Floated Initiation: Air-cushioned entry track delaying centripetal grip | Suppress panic when tactile snow contact pressure signatures vanish |
| Up-and-Waiting Delay | Create a distinct movement pause at peak structural vertical height | Retain high center of mass extensions while waiting to drop weight | Up-and-Waiting Pause: Tactical speed scrub delaying turn hook | Resist freezing at the apex of the extension phase loop |
| Dual Platform Equalization | Level out loading values between both feet across the main turn duration | Deepen inside knee and ankle joint flexion angles symmetrically | Bipodal Phase: Long-duration stability track balancing turn loads | Maintain constant tracking monitoring through the deepest arc depth |
| Centripetal Hip Drive | Deepen internal pelvic tilt angles to counter high cornering force | Fire outside hip gluteus and piriformis muscles to lock position | Centripetal Posture: Angular hip structure holding high edge angles | Resist structural collapsing under heavy lateral cornering forces |
| Sway-Back Acceleration | Position pelvis slightly behind the ankle-heel frontal plane line | Use wide arm separation layout forward of trunk to control sway | Tail Pressure Loading: Intentional rear-seat shift to shoot out of arc | Balance the system via active hand placements during tail acceleration |
