The second section of When 2 Spines Align delves in the bio-mechanics of the horse and how horses work. It covers how horses balance, how the horse's weight distribution changes with correct training, impulsion and engagement, leverage for collection, transitions, and half halts. This sounds, by my description, like a zillion other books about dressage training but it's really not, and I feel like this book has consolidated a lot of different concepts I have learned over the years and made a cohesive whole picture. That picture is the ideal, classically trained, correctly ridden dressage horse.
Concepts are covered such as, the horse in natural balance through highly collected dressage and how shaping, connection, and correct half halts, lead to collection. Half halts are explained in the best, most effective way I have ever encountered. The difference between thrust, reach, and engagement are explained and the correct timing of all the aids are detailed. Shaping the horse for straightness is covered in depth, and the progression of all of these concepts from a horse in natural balance through collected balance is looked at in detail. I feel like this is the best and easiest to understand explanation I have ever gotten for how a horse goes from "green" to "trained" in basic collection and why correct connected work leads to a correct collected, but happy horse.
There are, in this second section, several chapters laying out all the principles of how the horse's body works and how the rider's power lines and aids influence the correct work. Every chapter has exercises at the end to work on the concepts detailed in that particular chapter and basically test the correctness of the riding and training. This use of exercises at the end of every chapter to show the correctness of the work is genius. No thinking you have the concept while tooling around incorrectly. All in all, again, I highly recommend this book to any aspiring or active dressage rider. It is easy to understand, explains both correct riding AND correct progression of training, and is very sympathetic to the horse and making him content in his work.
Coming soon, a review of section three: how two spines meet in balance.