By contracting, muscles pull on bones and allow the body to move. Muscles can only contract. They cannot actively extend, though they can move or relax back into the non-contracted neutral position. Therefore, to move bones in opposite directions, pairs of muscles must work in opposition
I believe it's likely the effect of the diagnosis.
A phrase to describe a negative feedback loop could be: self-regulating (though I'm not sure the exact word you're looking for).
