Fitness Vocabulary

The Difference Between Concentric, Eccentric, & Isometric Muscle Contractions

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Fitness terms can get confusing.

The idea for this post came to me in the middle of a Body Pump class. As do many of my writing ideas.

Instructors often make reference to different types of muscle contractions during the workout, with little to no explanation, leaving newbies to fend for themselves. In this case, the instructor was hyperfocused on repeating the word “eccentric.”

So I began to wonder, how many in the class aren’t sure what that is?

Now it’s not necessarily the fault of the instructor, they aren’t required to give you a full dissertation on each word. But I encourage you to learn as much as you can about your fitness activities to get the most out of your workouts and prevent injuries.

Plus, it’s no fun to awkwardly smile and nod when you have no idea what someone just said. Don’t let the lingo bring you down! Strengthen your fitness vocabulary and get the most out of your workout!

This post focuses on three types of muscle contractions: concentric, eccentric, and isometricand why you should care.


Muscles are made of soft tissue, arranged in fibers, that contract (shorten) and relax (lengthen) to produce movements.

Tendons connect muscle to bone. Tendons have receptors that communicate with the brain and spinal cord to relay information. They produce movement by telling the muscle to contract or relax. 

Muscles have fixed endpoints. There is only so much length to contract and relax. This is important to explain these three types of muscle contractions. (And why workouts can’t really lengthen your muscles.)

Muscle contractions scheme demonstrating different types of muscle contractions with arm cross section and fitness weight lifting exercise movement. Concentric, eccentric and isometric contraction types diagram.
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Concentric contractions are often the easiest muscle movements to conceptualize.

During a concentric contraction, the muscle shortens when the fibers overlap, and the two endpoints move closer together.

The most simple example is a concentric contraction of the biceps muscle. When you bend your elbow and bring your hand close to your shoulder, you are performing a concentric contraction of the biceps. In weight training, this would be the concentric phase of a biceps curl.


When a muscle is loaded while lengthening and controlling a movement, this is an eccentric contraction.

Using the same example from the biceps, controlling the lowering of your hand (or weight) from your shoulder would be an eccentric contraction of the biceps. 

Eccentric training can help improve functional strength, which mimics the demands of real-life activities. Eccentrics are also useful in the treatment of tendinopathy by reducing the load on the tendon.


If you look up the definition of eccentric, the pronunciation sounds like IK-cen-trick, such as when referring to a personality trait. However, in the medical and fitness world, you will almost always hear it pronounced like EE-sen-trick when referring to muscle contractions.

Go ahead, google a few videos and see.

I can’t actually find a dictionary supporting this version, so you might just have to accept it, like how everyone says coupon differently. I did find full-blown arguments in online forums over it though. Someone in science may have forgotten to contact the dictionaries…

Cartoon image of a woman doing a single leg deadlift with a kettle bell to illustrate eccentric hamstring muscle contraction.
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A muscle contracts isometrically while holding a static position.

Back to the biceps example, holding a tray would demonstrate an isometric contraction of the biceps. You are engaging the muscle, but there is no change in range of motion. Planks are another example of isometrics on a full-body scale.

More complex or compound movements (for example a squat where multiple joints and muscle groups are involved) will have components of all three throughout the body at various points during the movement.

Although isometrics sound easy, some people have great difficulty performing them, especially when asked to isometrically contract a muscle on demand, say an abdominal brace.

Isometrics can be great for improving body awareness and decreasing stress because they require you to isolate your focus on one muscle and engage it without moving. Isometric contractions can help build a mind-body connection.

Isometric muscle contractions also play a role in stabilization. The Bar Method, one of my favorite fitness classes, focuses a lot on isometrics. If you think isometrics are easy, try a Bar Method class and enjoy your soreness the next day!


Studies show focusing on different types of muscle contractions during weight training could lead to improved muscle function and support for functional activities. Varying your strength training can help prevent injuries.


It’s essential to understand what you’re doing to get the most out of your workout and avoid injury.

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O’Neill S, Watson PJ, Barry S. WHY ARE ECCENTRIC EXERCISES EFFECTIVE FOR ACHILLES TENDINOPATHY?. Int J Sports Phys Ther. 2015;10(4):552‐562.

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