As always, I liked your post – a great summary. Let me throw something out at you This has always confused me. As you stated, the muscle spindle lies within the muscle fibers (Intrafusal fibers) and act as a protective mechanism, activating the muscle to prevent it from being overstretched and causing damage. Like you said they record the changes in length and rate of change in length.
Then you have the GTO which also acts as a protective mechanism, measuring tension and rate of change in tension and when the tension becomes too great – inhibits the muscle.
So here we have 2 protective mechanisms, one protects the muscle by activating it while the other protects it by inhibiting it. Here’s my problem: it has never been explained to me why the muscle spindles become overactive due to poor posture. Furthermore, is it really the GTO overriding the muscle spindle? I’ve never found that in any physiology book. Lastly, what about muscular adhesions? What is mechanically/physiologically happening with adhesion and how does the process of SMR (or massage) release them?