There are about 650 muscles in the human body. These fulfill different tasks. One part of them is responsible for the movements we perform with arms, legs and other parts of the body.
The muscles of our extremities are important for this. Another part takes over the supporting function and makes sure that we do not sink down into ourselves. This function is mainly performed by the trunk muscles, i.e. abdominal muscles and back muscles.
In order to perform these functions, many muscles need to work together. Thus, for a certain movement, often not just one muscle is responsible alone, but several muscles together. The interplay of several muscles allows, on the one hand, greater force development with the same function of the acting muscles and, on the other hand, finer force coordination when exerting force in two different directions.
Agonist
The word agonist means “the doer”. In medicine and anatomy, respectively, the muscle is called an agonist, which performs a certain function, i.e. it acts. It is also colloquially called “player”.
Antagonist
When a movement is performed, one muscle must always be actively tensed. In addition, there is always a muscle that is passively stretched as a result of the movement. This muscle is called an antagonist or opponent.
When the agonist moves, the antagonist is stretched. Often the antagonist is the reason why a movement can only be performed to a certain extent, such as when stretching the leg backwards. Here, among other things, the hip flexors prevent further stretching. The antagonist also has the function of executing the corresponding counter movement.
Example
Suppose we want to bend our arm in the crook of our arm. In this case the biceps as the executing muscle is the agonist. It is the muscle whose contraction causes the arm to bend.
During this movement, the triceps on the other side of the arm is stretched. The triceps also has the task of stretching the arm again if we want to. During the stretching movement, the terms are then reversed. Then the triceps is the executing muscle, i.e. the agonist, and the biceps is passively stretched and acts as an antagonist, which can perform the counter movement (in this case, flexion).
