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. What exactly is a muscle and how does it help us move?

What’s In A Muscle?

I understand that there’s a significant portion of people out there that could care less about what exactly a muscle is made up of. What you care about is that when you ask your leg to move, it moves or when you ask your arm to pick up a weight (or beer), it does that also. If you fit into that segment, that’s fine. You probably won’t be interested from this point out. But there’s a whole other segment of people, athletes, and gym rats that want to know more about their muscles so that they can get the most of their workouts. That’s who this article is for.

This is a pork tenderloin. Cooked on low heat with a dry spice rub it tastes delicious. The pork tenderloin is actually a muscle – the psoas major of the pig. We have one too. It’s in our ass. This particular muscle helps to flex our hips and stabilize our spine. Let’s slice that tenderloin in half. What you’re looking at are a bundle of muscle fibers that make up one large muscle.


Muscle Anatomy 101

One muscle is essentially broken down into a few different layers. Each layer is surrounded by smaller layers of muscle with connective tissue so that it forms one big muscle fiber  Don’t worry about the names.  I’ll tell you why they’re important.

Here you can see the three layers of the muscle that combine to form the tendon. The outer layer wraps all the other layers into smaller and smaller fibers.

The Outer Layer:

The outer layer of the muscle is called the epimysium.  This layer is made up of connective tissue that surrounds the entire muscle.  This layer separates the muscle from surrounding tissues and organs.

The Middle Layer:

The middle layer of muscle is called the perimysium.  This middle layer of muscle tissue divides the muscle into a series of smaller muscle compartments.  These smaller muscle compartments contain a bundle of muscle fibers of their own.  Inside these bundles of muscle fibers contain collagen, elastic muscle fibers, and blood vessels that supply each muscle strand.

The Inner Layer:  

The inner layer of muscle is known as the endomysium.  This layer surrounds each muscle fiber and is made up of a smaller network of muscle fibers.  This layer also contains the smaller blood vessels called capillaries that supply each individual muscle fiber.  This is where contraction happens, where energy is made, and where the neuromuscular junction is.  The neuromuscular junction is where your muscle gets the signal from your brain and spine to move.  The inner layer of the muscle is where the “magic happens.”

Why Muscle Anatomy Is Important

The three individual layers come together to combine and form the tendon.  The tendon is a strong network of a mix of muscle and premature bone cells.  These cells make a matrix that can withstand strong tensions during natural movement.  Tendons attach muscles to other muscles or muscles to bones.

The inner most layer of muscle is where the magic happens.  Inside the inner layer of muscle are something called satellite cells.  These satellite cells help to repair damaged muscle.

Why this is important to you:  When you workout and place a healthy amount of stress on muscle whether it’s through lifting weights, sprints, or some other type of activity micro-tears are created on your muscle fibers.  These micro-tears are what you feel the next day after a “good” workout.    These satellite cells within the muscles help to make you stronger.  If you’re placing enough stimulus on your muscles and getting enough protein, your muscles will also get bigger.

The inner layer of muscle fibers also contain cells called mitochondira and something called glycogen granules.  Embedded within these specialized cells and muscle fibers are also an intense network of capillaries.

Why this is important to you:  Mitochondira are your muscle’s energy makers.  They help sustain moderate to long-term energy levels.  Glycogen granules use stored sugar to help provide quick bursts of energy such as sprints.  The amazing thing about the cappilary network in muscles is that the capillaries are coiled around the muscle to allow for stretching and contractions.

These three components of muscle all come together to help you move.  Coming up in our next post, we’ll tell you what your muscles need to contract and how they do it.


1. Martini, F., Timmons, M., Tallitsch, R. Human Anatomy Fifth Edition. San Francisco: Pearson Education Inc. 2006. 237-241