For example, when you perform a bicep curl, the biceps will be the agonist as it contracts to produce the movement, while the triceps will be the antagonist as it relaxes to allow the movement to occur. The biceps contracts and raises the forearm as the triceps relaxes. The triceps contracts and lowers the forearm as the biceps relaxes. The following groups of muscles are antagonistic pairs:. To allow antagonistic pairs to work efficiently, other muscles called fixators assist by supporting and stabilising the joint and the rest of the body.
Some fixators also assist the agonist and act as a synergist. The trapezius muscle can act as a fixator when the biceps is flexing the elbow joint. The abdominals can act as fixators to stabilise the body for hip and knee movements.
In the preparation phase, when footballers prepare to kick a football, their hamstrings contract to flex the knee while the quadriceps lengthens to allow the movement. The hamstrings are the agonist and the quadriceps are the antagonist. 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. Table 2: Some of the Agonist and Antagonist muscles pair that results in different types of movement. Lengthening of the extensor digitorum to extend the fingers and the hand at the wrist Antagonist. What 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:. 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.
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. 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.
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. 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. The majority of muscles are grouped in pairs, with an antagonist to each agonist muscle.
Exceptions include those muscles such as sphincter muscles that act to contract in a way that is opposite to the resting state of the muscle.
Antagonist muscles act as opposing muscles to agonists, usually contracting as a means of returning the limb to its original, resting position.
During flexing of the forearm, the triceps brachii is the antagonist muscle, resisting the movement of the forearm up towards the shoulder. Synergist muscles act around a moveable joint to produce motion similar to or in concert with agonist muscles.
They often act to reduce excessive force generated by the agonist muscle and are referred to as neutralizers. Synergists are useful because they fix certain joints to allow a range of contractions, in contrast with the sheer power of an agonist contraction that limits the range of possible movements. During flexing of the forearm, the brachioradialis and brachialis act as synergist muscles, aiding the biceps brachii in pulling the forearm up towards the shoulder. The muscles of the rotator cuff are also synergists in that they fix the shoulder joint allowing the bicepps brachii to exert a greater force.
Flexing of the forearm by the biceps brachii : The biceps brachii is the agonist, or primer mover, responsible for flexing the forearm.
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