There is a word, tonus (tonus - the elastic tension of living muscles, arteries, etc. that facilitate response to stimuli;) with elastic being the important word, and I think of it as positive tension. I first heard it in relation to doing yoga and it really helped me envisage the degree of "positive tension" we are looking for.
When I teach new people I tell them to first tense up as much as they can, be completely ridgid.
Then to become so relaxed that they are floppy, heavy and ungainly.
Then I ask them to hold them selves in self carriage, with a feeling of immense pride in themselves.
If they go too far towards tension they start to become ridgid and fluid movement is lost and following the horse would be difficult and of course the same goes if they become too relaxed.
Anybody who has been at all afraid on a horse knows how difficult it is to keep anxiety from translating into tenseness in the body.
And the same goes for the horse. So we can see that awful ridgid, stiff look of a horse that is tense and anxious. Or the totally relaxed horse dozing in the sunshine with its herd mates, lower lip droopy, ears flopped out to the sides. Then there is the proud stallion prancing for his mares. (in a natural situation of course
) This is tonus and can never come if there is fear, pain (or
anticipation of fear or pain) but can only come from a horse full of confidence and we know at AND all the things necessary for a horse to have true confidence.
I truly believe that a bitted horse, if not in discomfort/pain in the moment will alway have the anticipation of discomfort/pain and therefore can never have that confidence that allows for pure movement with no negative tension. So we can put forth technical arguements until the cows come home but if the bit negates confidence in the first place...... well as Josehpa says, we just dont have that problem
Colette