Gary, I saw this on TV, when they were showing one of the women's races at Loveland.
In the "intermission' they would show the training routines of different team members. I'm not sure of what the progression was. I do have a hidden suspicion that elite skiers have a naturally more active transverse abdominal muscle, that enables them to stabilize well in most situations.
I just found an AWESOME book on this subject. Its called Strength Ball Taining, by peter twist and Lorne Goldenberg. Not only does it contain some of the best stability and medicne ball exercises I have ever seen, it has some excellent content about the kinesiology of core trainig.
To paraphrase a bit of it, they speak of the body's speed center, which is comprised of the transverse abdominal muscle, the lower back, the hip flexors and extensors, the abductors and adductors, and the gluteals. In any sport, these muscles iniate, assist, and and stabilize all movement. Something to consider when training for core strength.
I'm sure most of you know this, but prior to performing any balance challenged exercises, it is important to "set"the transverse abdominal muscle. This can be done by drawing the navel upward and inward, almost as if you are being given a heimlich maneuvor. Its actually a good idea to do this 10x a day, holding the contraction for about 10 seconds. It does not matter what position you are in when you are doing it or even if you are simply walking around. Practicing this will make you more used to using your deeper abs most of the time.
Although this topic is core strength, keep in mind that in skiing, as in most sports, everything is related. Many people start to have trouble when they begin learning pole plants, either because they have poor core stabilty, lack of scapular stability, or most probably, both. On page 75 of Strength ball training, there is an interesting exercise. "Hug" the ball in front of you. Your arms . Assume an athletic ready position. Have a partner try to slap the ball in different directions, as you try to maintain your position.
I will have AC put up an Amazon link to this book!