Ppl have been posting pulling the feet back with the hamstrings for years - never seen anyone take exception. Flexorist?
OK, I'll play. I'm procrastinating on something that is going to keep me up all night. This will help rejuvenate my mind.
Let's assume a skier, during transition, pulls both feet back. Let's also assume the skier does not square up, stand tall to flatten both skis with equal weight on each foot. No. I want to talk about a dynamic performance turn. Several things happen.
--The old outside leg gets "shorter." The foot feels like it is moving backwards relative to the hip above it but it isn't. It's moving back relative to the knee, but forward relative to the hip. This pull-back requires shortening the leg by flexing at the hip and at the knee. The foot moves back in a semi-circle relative to the knee... it's as if it were on a pendulum hanging from the knee. But relative to its previous position under the hip, it moves forward.
--The old inside leg gets "longer" by extending at the knee and extending at the hip joint. This moves the foot back enough to get it behind the other foot.
--As these two things are happening, the skis flatten as a by-product and continue tipping onto new edges in one smooth movement. As the skis begin to point down the fall line, the new short inside leg ends up ahead of the new long outside leg despite the fact that it is getting pulled back. The skier experiences a strong pulling-back action while the nature of things wants that foot to slide forward.
Meanwhile, the glutes are instrumental in the new outside foot/ski pull-back. There is some hamstring involvement in pulling the knee back relative to the pelvis above, but the glutes take the prize for doing most of the work by pulling the knee back relative to the hip above it. Quads chime in to help open the knee.
The hamstrings are instrumental in the new inside foot/ski pull-back because the bend the knee. But so are the iliopsoas, because they flex the hip to bring the knee up toward the chest or armpit. The anterior tibialis does its thing to keep the new inside foot's heel down as it is sliding back. This foot pull-back is actually an active resistance to a passive slide-forward that wants to happen on its own.
Unless the skier wants to end up "shuffling" when pulling both feet back, this divergent way of doing it is necessary. So no, the hamstrings are not responsible for both feet/skis getting pulled back.
Would I ever ever talk like this during a lesson? No.