My first introduction to rider biomechanics and Mary Wanless' theories was many years ago. I rode with a wonderful dressage trainer for a while, who introduced me to some of the upper level movements on her retired PSG horse, and who also introduced me to the books Centered Riding by Sally Swift and The Natural Rider by Mary Wanless. The ideas in Centered Riding seemed to resonate with me more at the time, since I was still doing a lot of jumping, but as the years have passed I have moved to riding dressage most of the time and bought more and more of Mary's books and found them to be frustrating, because some concepts and exercises I could not "get", yet helpful, because some of the exercises and ideas worked immediately.
Let me explain: I totally believe in Mary's hypothesis about talented versus untalented riders, about how some of the best riders cannot explain what they do with their bodies because they have no idea what they do bio-mechanically, and that a lot of what are considered horse training problems have a lot more to do with bad rider biomechanics than a truly resistant horse. The frustration for me came not with believing in Mary's theories, but in implementing and interpreting them on my own without eyes on the ground. With two small children, a farm to maintain, and not much spare time, I have been able over time to gradually improve my riding and biomechanics but have felt slightly stuck around first level, while feeling that I was this close to moving on to more complex riding.
Being able to view rider biomechanics videos in the past year on YouTube has helped bring in some big break throughs though, and as EP said, I have a lovely, happy horse with a swinging back and good rider alignment and basic symmetry. The next step is to work on having a correct first level horse with a bit of bounce to his step, a little more bending of the hind end joints, and a little more "tone". All of this should come about by my having better "bear out", "tone", and some slight seat adjustments at the canter.
I am excited to have "eyes on the ground", even if it is by video consultation, and I encourage anyone struggling with improving their dressage riding to explore Mary Wanless via books, DVDs, and YouTube. She has so many interesting ideas about learning, horse training, and development of a good riding seat.