Confusion about length-tension relationship of muscle

[sodium.dioxid]

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.

 

[SW VandeCarr]

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.

The ideal resting length of muscle is the length from which it can develop its greatest isometric tension and it's not necessarily the most "relaxed" length although it's close. For the biceps of the arm, the length of the muscle from its origins in the shoulder area to its insertion in the radius of the forearm doesn't change that much between maximum flexion and maximum extension. That's because the insertion point is very close to the fulcrum of the system at the elbow joint. The insertion is just distal (toward the hand) to this joint on the radius bone of the forearm. The biceps muscle is a bit shorter in flexion than it is in extension from its origins to its insertion.

http://www.mc3cb.com/pdf_ap_lecture_s6/C11_3_length_tension_and_whole_muscle_behavior.pdf