But we base a lot of our riding on theories and science, and if the science of horse physiology says what we are believing is wrong, then that is something to pay attention to. I've also read the sustainable dressage site for years and learned many things and thought a lot about the ideas listed on there. Some I feel are correct, others I've learned may be incorrect.
I think you need to have both the "feel" and experience of riding, along with the knowledge of scientific facts. In my job, we say "don't treat the numbers." The numbers are a clue that something is wrong, but since instruments are sometimes inaccurate, the measurements have to be supported by what you see and what you've learned from experience. If you can't say for certain the numbers are wrong, then you must go by the numbers. If you can support what you are doing with what you see plus the numbers, then you can be certain everything is right.
The theories I've read must be supported by science, otherwise they must be wrong. My husband is a scientifically minded guy (non-horse person) and also an athlete who has studied human anatomy and physiology. A few years ago, I came home from a dressage lesson all excited and began to explain to him about the circle of muscles. He said, "That makes no sense." I told him I must be explaining it wrong, so I went and read about it more in depth and then tried to explain it to him again. He told me that muscles don't work that way, that it didn't make sense based on the laws of physics, and that horse people were deluding ourselves if that was what we thought was happening.
If it is correct that horses need their head and neck in a certain position to have a strong back and to move athletically, we will see that supported by evidence. The studies will show this is the case. When we ride our horses, we will see their muscles developing better and that they can perform more athletically when they are moving with their neck held lower and the nose just in front of vertical.
What I've seen instead is that horses have better muscle development and perform better athletically when they are allowed to use their head and neck freely based on their particular anatomy. No matter how long you train them, they don't at some point begin to naturally carry themselves in a certain aesthetically pleasing way because that's the easiest and most efficient way to do it (I've been told this would happen from dressage instructors). Instead, when trained athletically they learn to carry themselves in a way that is most efficient for their body type and structure, as long as the rider and tack don't interfere.
In education I conducted experiments myself, which were then reviewed. I had to learn physiology, kinesiology and biology. Only in my job, when I had to put what I learned into practice, then and only then, could I discern what was reality and what needed to remain in textbooks and studies. In a way it was very mentally liberating because it meant it was okay to think for myself.
In any "study" How many of the horses they tested were post legged? What were the ratios of the cannon to the fetlock? What breed were they? Were any of them cow hocked and to what degree? Any sickle hocked, pigeon toed, **** footed? What was the ratio of the neck to the barrel to the croup in the horses they tested? Were any of them paddlers? How big was their head as a percentage of body weight? Were their croups level with their withers? Did they have shark fin withers or mutton withers? Where did the neck tie into the chest? What was the width of the pelvis in comparison to the shoulders? How much prior training did they have? Any pasture puffs? What environment; plains, stall, mountains, hills did they spend most of their time in? Were they shod or barefoot? How tall were the horses? What was their leg length in comparison to their overall height? How old were they? Did any of them ever have any injuries? Where do their tails tie into the croup?
On this we appear to agree: Form follows function. It is why equestrians often get caught up in using certain breeds for certain things and look for "good" conformation. That result did not come about because of any study, but because of results. A TWH for instance does not move like an Arabian and forcing it to do so may not only be an exercise in futility (experience), but dangerous to the long term well being of the animal (science).
All of those things listed above can have an effect on the measurements and also be confounding factors if not otherwise accounted for in the results. That is where our own assessment of a particular situation (feel) needs to kick in. Your horse’s conformation and listening to what the horse is telling you will dictate how best to obtain a particular result or if that result is even possible.
My point is that “Science” needs to be taken with a grain of salt, never as absolute predicate for your action.