As a former dancer of the Balanchine style, I feel qualified to comment mainly on the technical aspects of this style, which is fabulous from a choreographic standpoint, but which often has adverse effects on the dancers' bodies (if you are trained in the style; obviously, dancing a few Balanchine ballets a season won't give you shin splints).
Now, I do not know what SAB/NYCB were like while Balanchine was alive. I don't know how much the style has been distorted over the years, or if it has been kept the same, technically. One thing I notice a great deal is that Balanchine dancers tend to have incredibly tense arms and hands. From my experience, I believe that this is a result of excessive emphasis on speedy leg- and foot-work and a certain amount of neglect of the upper body. As far as I know, Balanchine did want the hands to be placed in that rounded claw position, with fingers poking out every which way, and I do understand that he wanted a more informal port de bras. I have always found it interesting, though, when someone comments that Balanchine hated mannerisms, because Balanchine dancers have the most mannered port de bras I have ever seen. The flowery use of the wrists is especially offensive, aesthetically.
In addition to having almost incorrigible mannerisms in the arms, I find that dancers of this style also tend to have poor posture, caused by excessive emphasis on having the weight too far forward. Never, in all my years at SAB, did I ever once hear a teacher say, "Shoulders back." The result? Dancers with rounded shoulders and heads that jut forward, staring out into the audience blankly.
Now for the legs and feet. Balanchine was said to have liked the look of winged feet, so at SAB, everyone dances on feet that are so pronated as to be injurious. This gave me--and many others--injuries in the ankles, knees, hips, and even back. The physical therapist's room at SAB is filled to the brim with dancers needing help for their lower legs. This is aggravated by jumping, or in fact doing any sort of plie with the heels off the floor. Yes, it allows for a deeper plie, but there is such a tiny amount of the foot on the floor that the plie is hardly worth anything at all. To jump well, it is necessary to push off from the heels--not by placing weight solely on the heels, of course, but by using them to help push off for the jump. If one plies with ones heels down, there is more area of the foot on the ground to contribute to the force necessary for a high jump. Without the heel one the ground, one is essentially jumping from ones toes.
Plies without heels on the floor have consequences besides that of a smaller jump. The achilles tendon can tighten and even snap because it is not being stretched of fully used. This causes tendonitis. And because jumping with no heels on the floor places an enormous amount of strain on the tiny muscles along the shin, shin splints often result, as well.
Returning to the upper body, so many Balanchine-style dancers hold an amazing amoung of tension in the backs of their necks. With the shoulders, upper back and arms carrying tension, and the head simply staring straight ahead, pressure is focused on the back of the neck. I think that this, too, can be the result of having the weight so far forward: the body is leaning so far to the front that the upper-back and neck muscles try their utmost to pull back to keep the dancer from toppling over.
Well, I could go on forever on this topic, but I don't want to put the board to sleep with in-depth technical analyses of every step in the Balanchine book

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CygneDanois