Antagonistic Muscle n., plural: antagonistic muscles [ænˈtæɡənɪst ˈmʌsəl] Definition: a muscle that opposes the action of another What does the term “antagonistic” mean? As the name suggests, the word antagonistic means working opposite to the “agonist” or the “primary doer”. In biology, “antagonistic” describes an action or substance that interferes or inhibits the physiological process. In anatomy, the word antagonistic is used to describe a muscle, particularly one that works opposite to the action of the primary muscle. The muscle that works in the opposite direction as that of the primary muscle or agonist muscle, which is engaged in some activity. So which muscles are agonist and antagonist? The primary muscle that carries out the movement is known as the agonist muscle or the primer muscle. How about the antagonistic muscles? What are they? In contrast to agonist muscles, the muscle that acts in the opposite direction to that of the agonist or the primer muscle is known as the antagonistic muscle. These antagonistic muscles also balance the tension at the joint by resisting the movement carried out by the agonist muscles. Let us understand the difference between an antagonist muscle and an agonist muscle in Table 1.
Biology definition: Examples of agonist and antagonist muscles pair are shown in Table 2.
Muscle ContractionWhat is a muscle action? Muscle action is the transformation in the bodily part that may result in movement and it is due to a muscular contraction. Now, there are different types of contraction movements that can occur in the muscles. Contraction of muscle implies the generation of tension in the muscle and not necessarily the shortening of the muscles. Muscle contraction can occur in the following ways:
Muscle action (definition): the transformation in the body or in a bodily organ or alteration due to the functioning of the muscle. Essentially, muscle contraction that results in the movement of the particular body part is known as a muscle action. Read: Muscle Contraction Mechanisms – Biology Tutorials Our body is made up of multiple levers that need to coordinate in order to carry out the body’s efficient movement. The function of the muscles is to transmit the force to the bones via the tendons. As a result, the required body part moves to carry out the intended action. This process is known as muscle contraction. So basically, contraction of the muscles brings two bones closer to each other. This is also known as the flexing of the muscles that results in the movement of the bones. However, this contraction of the muscle cannot place the two bones back into their original position, i.e., away from each other. Thus, another muscle group acts in the opposite direction to bring the bone back to its original position. This group of muscles is known as antagonistic muscles. Thus, one group of muscle, i.e., primer or the agonist muscle contracts, enabling the movement of the bone; the antagonistic muscles, then, act in opposite or complementary direction to take the bone back to its original position. Accordingly, to carry out any movement, the main muscle, or the agonist muscle, contracts and shorten in length. Synergistically, antagonistic muscles work in complementary or the opposite direction, i.e., relaxes, to efficiently complete the action of the primer muscle. Thus, when the agonist or the primer or agonist muscle contracts, the antagonistic muscle relaxes to complete the movement. In summary, the complementary action of agonist and antagonist muscles is the prerequisite for any action to be carried out efficiently. This further implies that the muscle works in pairs wherein one muscle group takes up primer or agonist roles while the other functions as an antagonist. Some of the commonly used terms to describe the complementary movements are:
For the efficient working of the muscles, fixators assist by providing support and stabilize the joint and the rest of the body. The fixators that assist the agonist are known as a synergist, thus when primer muscle contracts, the synergistic muscle simultaneously contracts. Synergists or synergistic muscles are also sometimes referred to as neutralizers as these muscles help reduce the extra movement induced by the agonist muscle, thus maintaining the working plane of the agonist muscles. For example, for flexing the elbow joint using biceps, the trapezius muscle acts as a fixator while stabilizing the whole body for the lower abdominal movement, i.e., hip and knee movement, the abdominals act as fixators. The combination and coordination of four categories of the skeletal muscles, i.e., agonist, antagonist, synergist, and fixator, carry out any movement in the body. Take note that the antagonism of a muscle is not a fundamental or predetermined property of a muscle; it is a role undertaken by the muscle complementary to the current agonist muscle. Let us understand this with an example. Imagine a player who is about to take a kick at a soccer ball. Prior to kicking the ball, the knee flexes. The hamstrings contract while the quadriceps relax or lengthen in order to carry out the movement. In this example, the hamstrings take the agonist’s role while the quadriceps serve the role of the antagonist. See Figure 2. Next, when the player has completed kicking the ball, the knee extends. This also results in quadriceps contracting while hamstrings, relaxing. In this case, the quadriceps become the agonist while the hamstrings are the antagonist in this movement. See Figure 3. The Function of Antagonistic MusclesThe antagonistic muscles serve two essential functions of the body:
Any movement in the body is the result of the coordination of action between agonist and antagonist muscles. The co-activation of these two sets of muscles is critical. Our understanding of the concept till now makes it clear that the co-activation of the antagonistic muscle provides resistance to the action of the agonist muscle. In simpler terms, this resistance is called the stiffness of the joint. A certain level of stiffness to the joint or the resistance to the movement is critically essential to maintaining joint stability under varying load conditions. Thus, the activation of the antagonistic muscles is pertinent for carrying out any body movement. Examples of Antagonistic MusclesAntagonistic muscle that is paired with an agonist muscle is referred together as antagonistic pairs. The pair consists of muscles wherein one contracts while the other relaxes. Some of the antagonistic pairs are as follows:
Now let’s see a few examples of antagonist muscles to understand better the action of a pair of muscles to aid a movement. In order to extend the leg at the knee, the quadriceps femoris, which is a combination of four muscles in the anterior part of the thigh, acts as an agonist or primer muscle when activated. Simultaneously, a set of antagonistic muscles — the hamstrings in the posterior part of the thigh — become activated to aid this movement. Contrarily during the flexing of the leg at the knee, the hamstrings contract and act as agonist muscles while the quadriceps femoris relax and lengthen to aid the movement and act as an antagonistic muscle. From the above discussion so far, it is evident that every muscle has an opposing muscle group for it to function appropriately and keep the body in a balanced condition. The opposing or antagonistic pairs include:
Try to answer the quiz below to check what you have learned so far about antagonistic muscles. References
©BiologyOnline.com. Content provided and moderated by Biology Online Editors. |