What do Motors and Muscles Have in Common?

Posted by on Sep 27, 2013 in Exercise Science, Review Topics | 0 comments

I started this post a month ago, and it got hairy in a hurry.

I thought “hey, let’s start at the beginning and just do a quick post”.  Yeah things didn’t turn out that way.  It’s the images that take a while, and constructing a good analogy.
Section 1 Chapter 1 is titled: “Structure and Function of the Muscular, Neuromuscular, Cardiovascular, and Respiratory System.”

This chapter is a terrible intro into the science of strength and conditioning, but I understand why.  Starting with a chapter explaining how muscles work on microscopic level makes sense from an organization standpoint, but I can’t imagine the number of people who opened the book, read the first chapter, and set it on their shelf never to complete their CSCS.

You turn the page once and it’s immediately confusing.  I am not easily confused.  At least, as an electrical engineer, I like to think so….back in school I often had to deal with pretty abstract concepts.  But these pages take a while to absorb, so let’s break it down and hopefully elucidate what’s going on here…I think I finally have a good mental 3-d picture of what’s going on, I just need to associate these mental pictures with the term “H-zone” “I-band” and “A-band”.

We’ve been over motor-units and things of that nature, so if you don’t remember that…maybe review this post, and the ones before and after it.

This all comes down to how we can mentally picture two structural components of muscle: Actin & Myosin.  These are the two basic structural components & engines of what make muscles move.  Take a look in the book on page 6 and 7, and look at all the pictures they have drawn for actin and myosin.  Do this for 5 minutes and build up a visual, 3D understanding of what they look like.

Now let’s draw an analogy.

The Piston

In engineering, a lot of what we do is make approximations.  If you’ve ever taken calculus, a classic example is a Riemann sum.  What does this have to do with muscles?  Not much, except I think that a muscle fiber is a pretty good approximation of a piston or pneumatic cylinder.

piston-text3

 

Compare that with a simplified drawing of actin and myosin interacting in a muscle fiber:

ActinMyosin

 

It’s not too far of a leap:

piston-text2

Although instead of one muscle representing one cylinder, a single myofilament (which is just another subunit of a large muscle) is actually many many cylinders stacked around each other with many pistons operating at the same time.  Represented graphically:

muscle-analogy-resized

Think of it like this, the material that creates the cylinder is the metal material that normally surrounds the piston and creates an airtight seal.  Though in a muscle it’s not continuous, but represented by individual strands of actin.

It makes little sense (or at least I can’t think of a reason) to design a real life engine this way, because you simply take up more space.  Furthermore, it complicates how you get gas in & out of the chamber.  You might as well just have one big cylinder.

But in the case of a muscle, it makes a lot of sense because the driving force isn’t the rapid expansion of a gas, it’s the cross bridging of actin and myosin.  The more actin and myosin cross bridging, the greater the force.

 

What are M-lines, I-bands, A-bands, H-zones, Z-lines?

The motor analogy is pretty simple, and gives you a good idea of what a very small section of muscle looks like…but it very quickly breaks down and doesn’t work when we look at the bigger picture and try to describe different areas of the filament interaction.

I’ll save all that for the next post!

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