Tuesday, December 27, 2011

Audrey / Huw

The day started out by testing the skiing of Audrey and Huw on a steep piste. This was partly a response to some technical question Audrey was trying to ask but couldn't quite communicate clearly. Lack of angulation and excessive rotation, plus a tendency to stay in the vertical and not use the ski poles - were all evident and captured on video. Audrey and Huw needed to be properly prepared for heading out into deep, unpredictable wind pack and crud. We set about working on developing the appropriate skills. Technical work commenced with a brief look at walking and at how the spine, hip and leg functions are coordinated. We rapidly established that neither Audrey or Huw knew how to walk.

Crescent moon over the Rocher du Charvet at the end of the day.

Walking (Opposite with a twist!)
Using ski poles I showed how, with the aid of gravity, we can walk efficiently and how the lower spine twists (up to the rib cage) to allow the hip to follow the foot left behind the body as you fall forwards. Walking is all about how you get one foot behind the other! In skiing however the support  foot is not able to move behind so there is already a problem for using the body in the way that it is designed to be used. In addition the support foot is not in a fixed place on the ground. It is almost certain that anyone pushing a ski forwards (to tighten a turn) while extending the leg will also allow the hip to follow forwards and for the spine to twist in that direction. During the extension of the leg the hip should really be moving backwards and the spine twisting in the opposite direction. This movement has to be learned in skiing - it prevents the hip from following the foot and thus rotating the upper body into the turn - it aligns the hip appropriately beneath the centre of mass (in relation to overall resultant forces) and from a muscular perspective also. 

Perching the entire upper body on top on one hip joint so that it is free to move is not an easy business. It requires the pelvis and upper body to tilt down slightly at the front and then to swivel around. This is aided by pulling inwards with the adductor muscles on the support leg - keeping the hip joint tucked in beneath the centre of mass.

Audrey showed that if I physically pulled her downhill and she resisted the pull - she would go into a correct hip alignment - though she had a tendency to buckle at the waist instead of resisting the force. My intention was for her to feel the correct sensations so that she would know what they were meant to be.

The hip being pulled backwards actively provides an effective upper/lower body separation and an opportunity for angulation to be developed if the upper body is tilted forwards from the hip at the same time. This angle permits the body to sink more deeply into the turn as the lifting force of the ski peaks during the final loading up of the forces in the turn. In crud this is necessary to prevent the ski from spitting you out of the turn if it suddenly breaks through and digs into the snow - at least this is the case if you are closing/finishing the turns to control speed. The angulated body then "anticipates" the following turn and this provides and agile and rapid way to get the Centre of mass back out of the turn and over into the next one. An upper body rotated (following the skis or facing inwards during the turn) cannot be so agile for making adjustments to deal with unpredictable events as there is limited flexibility sideways with the body.

Jumping (Swing)
Appropriate to developing angulation and control of rotation we applied all of this to "pivoting". The sideslipping nature of pivoting provides the perfect context to develop both control of rotation and angulation. I introduced jumping to start the pivot in the air - a skill which is very useful in crud! The jump gets the legs more active increasing vertical motion - the swing of the front of the skis is helped by gravity and the "two footed" jump (mostly lower leg) helps to improve timing and swing of both skis simultaneously. A good pole plant downhill aided by angulation helps to set up a launching platform.

Solid Pole Plant/Support with Pivot
Neither Audrey nor Huw were managing to get any significant weight downhill onto the ski pole. I asked both to get more weight on the pole by starting to turn from a static position by lifting the downhill ski so that weigh fell onto the pole and the uphill leg. This permits a very strong and rapid pivot from the uphill ski. It also shows that with the body and pole in the right place you can go from holding the body strongly uphill  to pivoting downhill just by removing the support of the downhill ski.

We had a brief excursion through the La Daille trees. Huw baulked at the steepness of some of the bumps. The intention had been to use the bumps to provide a practical context for the work we had been doing - as bumps are formed by skiers using precisely those qualities.

Both feet below the body (close stance)
I explained that even visually the skis need to be kept below the centre of mass (with respect to the geometry of the mountain) to be able to start each pivot from the uphill edges of the skis.  During a pivot the skis always work on their uphill edges so there is always a breaking effect. The edges change when the ski points straight down the fall line. The actual dynamics are identical to any other turn but the feet and skis are kept below the skier so the effect is very different. Standing in a steep couloir you want your feet to stay below you even when you turn.  When facing downhill, adopting a seated stance gets the feet and knees downhill of the body - with the centre of gravity still passing through the feet. This stance - with the femurs less upright - also permits a rotation at the knee joint (cannot mechanically happen with an upright leg) and also more leverage for pivoting the skis.

Right from the start of the pivot the uphill foot has to roll onto its lower inside edge - with the uphill ski (turning ski) remaining on its upper outside edge. This feeling with the foot allows the adductor muscles to be actively used in assisting the pivot by pulling the front of the ski across into the turn - like spreading butter with a knife. 

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