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.
Some of the body movements can be controlled at will, others cannot. The body has a motor program, which is the pattern of neural activities required to perform a movement. Learn more about this topic in this tutorial.
Find out the mechanisms involved in length-monitoring systems, alpha-gamma coactivation, and withdrawal reflex Read More. Skip to content Main Navigation Search. Dictionary Articles Tutorials Biology Forum. Table of Contents. Antagonistic Muscle biology definition : a muscle that opposes the action of another.
For example, when the triceps oppose the contraction of the flexing biceps by relaxing, the triceps would be regarded as the antagonistic muscle to the biceps whereas the biceps, the agonist muscle.
Compare: agonist muscle. 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. Doer of an action Agonist muscle. Antagonistic muscle. Opposition to action Agonist muscle. Responsible for returning bones to their original position Agonist muscle.
Pulling a door to open Isometric contraction. Isotonic contraction. Walking is an example of Isometric contraction. Send Your Results Optional. Your Name. To Email. Time is Up! Control of Body Movement Some of the body movements can be controlled at will, others cannot. Related Articles No related articles found See all Related Topics. Agonist refers to the doer of an action. Antagonist refers to the opposition to action. Stretching pulls on the muscle fibers and it also results in an increased blood flow to the muscles being worked.
Without a proper warm-up, it is possible that you may either damage some of the muscle fibers or pull a tendon. A pulled tendon, regardless of location, results in pain, swelling, and diminished function; if it is moderate to severe, the injury could immobilize you for an extended period. Recall the discussion about muscles crossing joints to create movement.
Most of the joints you use during exercise are synovial joints, which have synovial fluid in the joint space between two bones. Exercise and stretching may also have a beneficial effect on synovial joints.
Synovial fluid is a thin, but viscous film with the consistency of egg whites. When you first get up and start moving, your joints feel stiff for a number of reasons. After proper stretching and warm-up, the synovial fluid may become less viscous, allowing for better joint function. Skeletal muscle is enclosed in connective tissue scaffolding at three levels. Each muscle fiber cell is covered by endomysium and the entire muscle is covered by epimysium.
Fascicle arrangement by perimysia is correlated to the force generated by a muscle; it also affects the range of motion of the muscle. Based on the patterns of fascicle arrangement, skeletal muscles can be classified in several ways. What follows are the most common fascicle arrangements. Parallel muscles have fascicles that are arranged in the same direction as the long axis of the muscle Figure 2. The majority of skeletal muscles in the body have this type of organization.
Some parallel muscles are flat sheets that expand at the ends to make broad attachments. Other parallel muscles are rotund with tendons at one or both ends. Muscles that seem to be plump have a large mass of tissue located in the middle of the muscle, between the insertion and the origin, which is known as the central body.
A more common name for this muscle is belly. When a muscle contracts, the contractile fibers shorten it to an even larger bulge. For example, extend and then flex your biceps brachii muscle; the large, middle section is the belly Figure 3. When a parallel muscle has a central, large belly that is spindle-shaped, meaning it tapers as it extends to its origin and insertion, it sometimes is called fusiform. Figure 2. Muscle Shapes and Fiber Alignment.
The skeletal muscles of the body typically come in seven different general shapes. Figure 3. Biceps Brachii Muscle Contraction. The large mass at the center of a muscle is called the belly. Tendons emerge from both ends of the belly and connect the muscle to the bones, allowing the skeleton to move. The tendons of the bicep connect to the upper arm and the forearm. Circular muscles are also called sphincters see Figure 2.
We could also say that the antagonist is the main muscle that does the opposite of the action that it is resisting. For example, we could say that gluteus maximus is an antagonist of the primary hip flexor, iliopsoas because gluteus maximus is a hip extensor. Gluteus maximus is an antagonist of iliopsoas, which does hip flexion, because gluteus maximus, which does extension of the hip, resists or opposes hip flexion.
We describe muscles that work together to create a movement as synergists. For example, iliacus, psoas major, and rectus femoris all can act to flex the hip joint. All of these muscles together could be referred to as synergists for flexion of the hip joint. In real life, outside of anatomical position , we move our body in all kinds of creative and interesting ways.
While we need the main muscle, or agonist, that does an action, our body has a good support system for each action by using muscle synergists. Likewise, our body has a system for maintaining the right amount of tension at a joint by balancing the work of a muscle agonist with its antagonist.
Balance between a muscle agonist, its synergists, and its antagonist s is important for healthy movement and avoiding pain and injury.
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