Time for our Workout Of The Month. Each month we take a look at something fitness related and break it down in a way that you can understand it so that you can apply it to your life. Some months we take a look at a specific workout and break it down – other times we’ll take a look at the latest fitness research and separate fact from fiction. This month we’ll be talking about one of everyone’s favorite things: muscle.  Last month we broke down what a muscle looks like.  This month, we’re taking a look at how a muscle does the things that it does.  

What’s In A Muscle Review

This is the view of a muscle cell under the microscope. The black lines represent the Z-Line: the space between one muscle cell and another.

Last month we took a look at some simple muscle anatomy and broke down what’s in a muscle.  The muscle is made up of three different layers:  an outer layer, a middle layer and an inner layer.  All layers come together at the end of the muscle to form thick  connective tissue that will either connect to other muscles or bones.  The inner layer of a muscle fiber is where most of the magic happens.  In the inner layer, energy is made and stored and where movement happens.  The inner layer is where nerve endings and capillaries that supply oxygen to the muscles are.  Part two in muscle anatomy takes place where part one left off:  how does a muscle contract?  

How Does A Muscle Contract?

The majority of muscle contraction takes place on the inner layer of the muscle fibers.  It’s in this layer that a muscle receives its signal from the brain to move.  It’s also in this layer that the muscle cells have a rich blood supply and abundant mitochondria.  Mitochondria are cells which are responsible for producing energy.  They’re like the power plant of the cell.

Components Of Muscle Contraction

  • Sarcomere:  The functional unit of muscle found in the inner layer which produces contraction.
  • Myofilaments:  The portion of muscle cell contains even smaller muscle cells called filaments.  There are two different kinds of filaments, thin and thick.  Thin filaments contain actin and thick filaments contain myosin.  Actin and myosin are two different proteins responsible for “pulling” muscle cells closer together to make a contraction.
  • Z-Line:  A small space in the cell where one sarcomere ends another begins.

The Sliding Filament Theory

The two important things here are the red and the blue.  They both represent a myofilament.  The myofilaments come together to make the muscle contract.  


The sliding filament theory is the current accepted proposal of how a muscle contracts.  Let’s say that you wanted to lift a bag of groceries or a forty-five pound dumb-bell.  This is the order of events that would take place:

  1.  You think of lifting the weight in your hands and your brain sends a signal to your muscle.
  2. In the inner layer of the muscle, the sarcomere gets the message from the neuron.
  3. The myofilaments communicate with each other through different cell transmitters.
  4. The different components of myfilaments pull closer together shortening the z-lines between all sarcomeres.
  5. All the sarcomeres pull all laywers of the muscle together resulting in a muscle contraction.

BOOM!  That’s muscle contraction in a nutshell.

Muscle Contraction Summary

Muscles are incredible organs.  They do incredible things and at times are responsible for super human strength.  It takes an intricate timing of neurons, electrolytes, and specialized cells to come together to make a muscle contract.  Our muscles can do three types of contractions:  isometric, eccentric, and concentric.  Each type of contraction can be used for specific reasons.  Each type of contraction can also be used to help you get the most of your workouts.

Read About Different Types Of Muscle Contractions To Get The Best Of Your Workout

1. Clark, M., Corn, R., Lucett, S. “Muscle Contractions.” NASM Essentials Of Personal Training. National Academy Of Sports Medicine. Baltimore: Lippincott Williams & Wilkins. 2008. Print. 31-34.

2. Sherwood, Lauralee. Fundamentals of Physiology. Third Edition. Thomson Brooks/Cole. 2006. Print. 204-210.