Monthly Archives: February 2012

Muscles: How they work!

This is the first physiology post we’ve had so please hang on for some scientific language.  We’ll do our best to translate while still indulging our pent- up inner nerd.  We will start with the structure of muscle tissue and how it works.  Some of you are saying to yourself “hang on dude, I SLEPT through health class.  This is boring.”  WRONG!  That deadlift you just did, yup it was muscle tissue that produced the force to lift it.  That Kale salad you’re munching on?  Yeah, muscles did the chopping and they are doing the chewing too.  No muscle, no movement.  That’s why muscles are cool and why they are worth understanding.

Before going into how muscles create force we have to describe their structure.  Muscles are like onions… they have layers…

A brief overview from smallest to largest:

  1. Filaments. Individual strands of protein. These are the basic building blocks.
  2. Myofibrils. Think of this as the smallest unit that can do anything.  It is made up of bunch of filaments overlapping each other.  Each segment of overlapping filaments is like a car of a train, and the myofibril is the train as a whole.
  3. Fibers. Hundreds to thousands of these myofibrils are bundled together inside each individual muscle fiber.  A muscle fiber is the same thing as a muscle cell.
  4. Motor unit. Lots of fibers are grouped together and all connected to the same nerve.  They are essentially all wired to the same “on/off” switch.  All the fibers in a motor unit fire together, though not all motor units in a muscle necessarily fire all at the same time
  5. Muscle. We made it! Something recognizable!  A muscle is a bundle of bundles of muscle fibers.  There are a lot of muscle fibers in a muscle.
  6. Muscle groups. As we know from our experience using our bodies to do work, muscles don’t work in isolation. Muscles function together in groups, with multiple muscles working together to accomplish movement. Some of our favorite muscles are really groups of muscles.  For example the quadriceps are not one muscle but four (Quad; it’s a give- away.  That’s about the extent of the Latin we know.)
  7. Kevin Bacon. Just kidding, we need at least 3 more steps to get to KB.
  8. Muscular system. Every muscle in your body.

Ok, enough technical stuff, lets talk about how these pieces come together to produce movement.  Introducing… the Sliding Filament Theory!  Lets go back to the smallest of our structures, the filaments.  There are actually two main kinds of filaments.  One is thin, and is covered in attachment sites.  The second is thick and is made up of a crap ton of hook shaped proteins that like to attach to the first type of filament.  When your muscle is relaxed they overlap only a little.  When it is stimulated to contract the heads of the thick filament bend, acting like a ratchet pulling the thin filaments closer together.  This effectively shortens the length of each individual segment of the myofibril by a few nano-meters.  Remember though, that there are thousands of these small segments in a long sequence on each myofibril.  Each muscle fiber is a bundle of thousands of myofibrils.  There hundreds to thousands of muscle fibers in every muscle.  The cumulative effect of billions of these tiny hooks latching onto tiny filaments is a shortening of the length of a muscle; in other words, a muscle contraction.

So that’s the story on muscles.  Muscles perform all the awesome things we do with our bodies.  From the smallest building block to the whole body in motion every piece is perfectly designed to do its job: move.  There is a lot of technical terminology in this post, but no, there won’t be a quiz.  This information is there for those of you who are curious about how your body does the incredible things we ask it to.  Knowing only makes what we are able to do that much cooler.