I am trying to conceptually understand this relationship. One thing that's not helping is I keep hearing the phrase "the resting length" of muscle. It's using the word "THE" as if there is one resting length. This phrase implies that the length stays the same no matter how bent my elbow is at rest (if I use the bicep as an example). At rest, I would think the length is shorter if bring in my forearm towards my bicep versus if I straightened out my arm.