Function of the musculature

It’s interesting how little we do with our musculature. Movement is so normal for us that we only think about it when we can no longer move. A relatively harmless, but very impressive reason for the temporary loss of our mobility is lumbago.


How movement comes about

Our muscles are surprisingly simple in principle and have one thing in common: they can only tense up and relax. In technical terms, muscle tension is called contraction and relaxation.

Muskulöser Mann Schwarz/WeißIn the following, I will explain the function of the muscles by means of the elbow flexor, the so-called musculus biceps humerus. In strength sports, very impressive specimens of this muscle can often be admired – but this is only on the side. Imagine a standing person holding a weight, e.g. a dumbbell in his hand, his arm hanging down relaxed. The person now moves the dumbbell to the shoulder and back by bending and stretching the elbow. This exercise is called “biceps-curl” in weight training. It is named after the muscle that mainly performs this movement: the biceps brachialis.

Only through the interplay of contraction and relaxation of one and/or more muscles/muscle groups and their arrangement, a rotational movement (rotation) in the joints is created.
All movements of the body result from a combination of this muscle work of one and/or more muscles/muscle groups!</block rate>

Muscle types

Humans have 3 different types of musculature. The 3 muscle types are named as follows because of their appearance:

Transverse striated muscles

This type of muscle makes up the largest part of our muscle mass and forms the skeletal muscles, which are responsible for all movements in space.

Smooth muscles

This type of muscle is found in the intestines and is responsible, for example, for peristalsis in the intestine. The esophagus and stomach also consist of smooth muscles.

heart muscles

In technical jargon called Myocard. Very specialized muscle cells that have to work tirelessly around the clock to keep blood circulation going. For endurance training, not only the heart muscles are important, but also the cross-striped muscles, which are responsible for our movement.

The function and types of the individual muscle fibers are described in the article muscle fiber types are described.


Motor units

To trigger a contraction of the skeletal muscles it is necessary to excite the corresponding nerves. Since these nerves (= neurons) ultimately control the muscles through their activity, these nerves are also called motoneurons. A motoneuron does not innervate a single muscle fiber, but always a group of muscle fibers = motor unit. See also Henneman size principle.

Man with 6-pack

The 3 Contraction Types


The length of the muscle remains constant and the tension changes.


Describes the change in length at constant tension.


The tension and length of the muscle change simultaneously.

The smaller the load (force), the greater the speed of an (isotonic) contraction. The maximum speed is developed with an unloaded muscle. In an isometric contraction, the maximum force or tension is developed. Light loads can, therefore, be lifted faster than heavy ones.


The way the skeletal muscles work

Three types of muscle work can be distinguished.

Human SkeletonConcentrated

Also positive – dynamic. Contraction and relaxation alternate under stress, e.g. when climbing stairs or climbing mountains.


Also negative – dynamic. In this case, braked muscle stretching (braking work to prevent falls) alternates with load-free contraction, e.g. when going downstairs.


Also holding work, e.g. standing still or holding something. In practice, many activities combine two or even all three types of work.


Agonist – Antagonist – Synergist

How the muscles (groups) work together.


“Gambler.” Is the muscle that performs a defined function in interaction (synergism) with its opponent (antagonist). The muscle works concentrically. In the case of an extension of the knee joint, this is mainly the quadriceps femoris muscle.


“Opponents.” Is the muscle that counteracts the function of the agonist. In the case of an extension of the knee joint, this is essentially the ischiocruralis and acts in the direction of knee flexion. The muscle works eccentrically.

Functional pair

Agonist and antagonist together form a so-called “functional pair”.


“Employees.” Interaction; the harmonious interaction of muscles/muscle groups.


Sense and benefit of agonist – antagonist – synergist


The main function of the knee joint is flexion and extension. The m.quadriceps femoris is mainly responsible for extension. The ischiocruralis is responsible for flexion.

When the knee is stretched, the quadriceps muscle tightens, shortens and thereby causes an extension in the knee joint. At the same time, however, the ischiocrural muscle must become longer so that an extension can take place in the knee joint. Here, the quadriceps is the player (agonist) and the m. ischiocruralis the opponent (antagonist).

The opposite is true for knee flexion. Here the ischiocruralis shortens and is, therefore, the agonist. In return, the m.quadriceps lengthens and becomes the antagonist.



Coordination is one of the 5 basic motor skills of humans, summarized also called condition.

In general, we understand coordination as the coordination of different activities with each other, the improvement of the interaction, the interaction, as well as the order under consideration of several aspects.

The physiology/sport physiology understands coordination as the harmonious interaction of muscles, more precisely motor and sensory processes.

With regard to our musculature, a distinction is made between two types of coordination:


Describes the orderly interaction of the muscle fibers within a muscle. (Compare the Henneman Size Principle!


Describes the orderly interaction of several muscles and/or muscle groups with each other.

Two further terms are often used in connection with the above-mentioned types of muscular coordination:

Reciprocal innervation (RI)

This means that with a selective, appropriate tension of the agonist (player), a direct relaxation of the antagonist (opponent) takes place.

Post Isometric Relaxation (PIR)

After an isometric tension, the muscle relaxes more than before its tension. This effect is often mentioned in the stretch exercises.


Muscle chains

There are two types of so-called muscle chains. As the name suggests, several muscles/muscle groups work together like a chain. An example of this is shown here using the knee joint.

Open Muscle Chain

Knee extension in a sitting position. The lower leg makes a circular arc, so it is “open” because it moves freely in space.

Closed muscle chain

Squats from a standing position. Here the feet are firmly placed on the floor. Only the knee bends and stretches.


Active and passive muscle insufficiency

The natural limits of muscle function: Every human being has a certain physiological (= natural) active and passive muscle insufficiency, which can be very well influenced by physical training.

Active muscular insufficiency

In a concentric contraction, the muscle never contracts 100%. It always remains a remainder. This remainder is the active muscular insufficiency.

Passive muscular insufficiency

The limit of “stretchability” of a muscle is called passive muscular insufficiency. This can be very well influenced by daily stretching.


One- / multi-joint muscles

Muscles can span only one joint but also several joints.

Single-jointed musculature

Muscle that only spans one joint and moves it. The vastus medialis, intermedius and lateralis muscles only span the knee and make a knee extension in this joint.

Multi-jointed musculature

Muscle that spans several joints and moves them. The m. rectus femoris spans the hip joint and knee. It makes a flexion in the hip joint and an extension in the knee joint.

This post is also available in: German

William C. Hilberg
As an author, Mr. Hilberg has published several papers on health issues that have gained international recognition. He is close to nature and loves the seclusion and activity as a freelance journalist. In his function as editor William C. Hilberg manages the entire content of PENP. Our team greatly appreciates his expertise and is proud to have him on board.