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In case of tug of war the more people participate the more strength they represent. And in case of muscles - the longer it is, the greater the number of myosin heads bind to actin when muscles contract. So why doesn't length matter?

UPDATE:

Since I've found multiple answers that compare muscles to ropes, let me comment on why those explanations don't work for me. Ropes don't have "muscle" strength, they have tensile strength. So this analogy can only compare tensile muscle strength to tensile rope strength.

In the end I'm pretty sure I'll find out that tensile strength constraints the muscle strength. And that's probably going to be the reason why muscle strength doesn't grow with length - something does not allow it, otherwise it would get damaged.

But I'd like find out what exactly prevents further contraction. Is it mechanical receptors on the muscle cell which block deploarization? Mechanical receptors in tendons which send nervous signals (but then - do tendons get thicker in proportion with the muscle)? Something else?

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    $\begingroup$ Does this answer your question? Why is muscle force more dependent on cross-sectional area than on fiber length? $\endgroup$
    – kmm
    May 11 at 12:37
  • $\begingroup$ @kmm, I haven't seen that question, though I tried hard to look for it. Thanks for pointing out. But no, unfortunately there are no satisfying answers there :( $\endgroup$ May 13 at 8:12
  • $\begingroup$ @kmm, I've updated the question to explain why the rope analogy doesn't answer the question. $\endgroup$ May 13 at 8:44
  • $\begingroup$ To those who vote for closing: this site doesn't have an answer to my question. If you close it - someone else in the future will have to ask this question again. Otherwise no one will ever answer it. $\endgroup$ May 14 at 12:25
  • $\begingroup$ The close votes are for this question being a duplicate (which I think it is). Whether or not you find the answers here or on the other question satisfying does not change that this and the other question are basically asking about the same concept. $\endgroup$
    – kmm
    May 14 at 13:00
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It's simply that the fibers are arranged end-to-end. If you simplify this down and imagine a single muscle fiber you have actin and myosin like this:

ligament-|actin-myosin-actin-myosin-actin-myosin

If you think of this as a strand of cotton pulling on a weight (ligament). Each group only pulls along the length, so the strength is not multiplied, but rather related to the strength of the individual fibre.

In reality muscles are stacked into bundles, which are much stronger as all the fibers can contract pulling with the strength of the multiple ends. Like this:

         |actin-myosin
         |actin-myosin
ligament-|actin-myosin
         |actin-myosin
         |actin-myosin

This is like the multiple strands of cotton making up a rope, the strength comes from having lots of them distributing the load.

This is something called physiological cross-sectional area, which describes the strength of a muscle by estimating the cross-section of the muscle across its thickest part.

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The confusion I had is that I thought that myosin pulls on actin with a force which some how isn't the maximum possible. And if we were to add another sarcomere in a series - each myosin would have to work harder and together with the new sarcomere they would exert a greater force.

But this of course isn't how it works. Myosin doesn't have a notion of a varying strength, it's binary: it either attaches to actin or not. If we were to try to pull apart actin or myosin harder by their "tails" (by a neighbouring sarcomere) - actin would've started to "slip" from myosin. Therefore putting more sarcomeres in series would not make the muscle stronger - we'd simply add more "slipping".

The other possibility in a theoretical world would be to make actin and myosin strands longer and add more myosin heads (we'd have to reinforce lots of structures though). This way we could've made the muscle stronger by making it longer. But that's not how it works: a longer muscle cell merely means more sarcomeres in series.

Thanks @Bryan Krause for nudging me into the right direction in the comments.

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