Index
They are those who act together with the agonists to make a move.
Muscles are described using unique anatomical terminology according to their actions and structure.
Types
There are three types of muscle tissue in the human body: skeletal, smooth, and cardiac.
Skeletal muscle
Skeletal skeletal muscle, or “voluntary muscle,” is primarily attached to bone with tendons. Skeletal muscle allows movement of the bones of the human skeleton and maintains posture.
Soft muscle
Smooth muscle tissue is found in parts of the body where it transmits action without conscious intention.
Most of this type of muscle tissue is found in the digestive and urinary systems where it works by pushing food, chyme and feces forward in the former and urine in the latter.
Elsewhere, smooth muscle can be found within the uterus, where it helps facilitate birth, and the eye, where the pupillary sphincter controls the size of the pupil.
Cardiac muscle
The heart muscle is specific to the heart. It is also involuntary in its movement, and it is also self-excited, it contracts without external stimuli.
A synergistic muscle is a muscle that works in concert with another muscle to generate movement. They act on mobile joints.
Synergistic muscles help neutralize the extra movement of the agonists (muscles) to ensure that the force generated works within the desired plane of motion.
They stabilize muscle movements and keep them even. By working synergistically, the muscles also reduce the amount of work they need to do, which can improve endurance.
Synergistic muscles are also sometimes part of a group of fixators and are essential to facilitate the fixation action.
It becomes essential to use these fixatives to fix some of the joints so that others can be moved effectively. For example, the fixation of the wrists during the complete flexion of the fingers when clenching the fist.
Synergistic action
Synergistic muscles perform, or help perform, the same set of joint motion as agonists. Synergistic muscles act on mobile joints.
Synergists are sometimes referred to as “neutralizers” because they help neutralize, or neutralize, the extra movement of the agonists to ensure that the force generated works within the desired plane of motion.
Muscle fibers can only contract up to 40% of their fully stretched length. Therefore, the short fibers of the pennate muscles are more suitable when power is required rather than a range of contraction.
This limitation in the range of contraction affects all muscles, and those that act on several joints may be unable to shorten enough to produce the full range of motion in all simultaneously.
Active insufficiency, for example, the fingers cannot flex fully when the wrist is also flexed.
Similarly, opposing muscles may be unable to stretch enough to allow such movement to occur (passive insufficiency).
For these two reasons, it is often essential to use other muscles, called fixators or synergists, in this type of action to fix certain joints so that others can move effectively, for example, fixation of the wrist during full flexion of the joints. fingers in clenching fist.
Synergists are muscles that facilitate the fixing action.
There is an important difference between a collaborative synergistic muscle and a true synergistic muscle.
A true synergistic muscle is one that only neutralizes an unwanted joint action, while a helping synergist is one that neutralizes an unwanted action but also helps with the desired action.
Muscle roles and types of contraction
It is vital to understand the different types of contractions that a muscle can perform. It will help you ensure that your program designs are specific to your clients’ capabilities and goals, and keep them safe with good technique.
Muscle contractions are classified according to the movements they cause and, in terms of physical form, we are mainly interested in the following three types of contractions:
Concentric contraction: Any contraction in which the muscle shortens under load or tension is known as a concentric contraction.
For example, the quadriceps muscles in the thigh contract concentrically (shorten) during the upward phase of the squat movement (in the direction of the arrow), as can be seen in the adjacent image.
Eccentric Contraction : Muscles not only “shorten” but can also lengthen under load or tension. An eccentric contraction refers to any contraction in which the muscle lengthens under load or tension.
So in the squat exercise, the quadriceps muscles eccentrically contract (lengthen) in the downward phase of the movement (the opposite direction of the arrow), as can be seen in the adjacent image.
Isometric Contraction – Muscles don’t actually need to move (shorten or lengthen) to contract or develop tension.
An isometric contraction refers to any contraction of the muscles where little or no movement occurs.
If during the squat the person stopped moving at a certain point (say halfway) and held that position for 10 seconds, the quadriceps muscle would contract isometrically, it would still be under load / tension but no movement would occur.
Many skeletal muscles contract isometrically to stabilize and protect active joints during movement.
So while the quadriceps muscles contract concentrically during the upward phase of the squat, and eccentrically during the downward phase, many of the deeper muscles in the hip contract isometrically to stabilize the hip joint during the movement.
Concentric and eccentric are also terms used to describe the phase of a movement. The concentric phase is the phase of the movement that is overcoming gravity or load, while the eccentric phase is the phase that resists gravity or load.
So for push-ups the concentric phase is the upward phase where gravity is overcome, and the eccentric phase is the downward phase where gravity is resisted.
What roles do skeletal muscles play during movement?
In addition to anatomical movement terms, which describe the movement performed by a muscle, a unique terminology is used to describe the action of a set of muscles.
When completing movements such as walking or squatting, there are many different muscles involved to complete the movement smoothly and effectively.
They achieve this as each adopted the appropriate type of contraction (concentric, eccentric or isometric) and have their own specific role that they play during the movement.
There are four different roles that a muscle can fulfill during movement, these roles are:
Agonists and antagonists
Agonist and antagonist muscles refer to muscles that cause or inhibit movement.
Agonist muscles cause movement through their own activation. For example, the triceps brachii contracts, producing a shortening contraction, during the upward phase of a push-up (elbow extension).
During the lowering phase of a push-up, the same triceps brachii actively controls elbow flexion while producing a lengthening contraction.
It remains the agonist, because while resisting gravity during relaxation, the triceps brachii continues to be the main motor or controller of joint action.
Agonists are also known as “prime movers” as they are the muscles considered primarily responsible for generating or controlling a specific movement.
Another example is the dumbbell elbow curl. The “elbow flexor” group is the agonist, shortening during the lifting phase (elbow flexion).
During the descent phase, the “elbow flexor” muscles lengthen, leaving the agonists because they control load and movement (elbow extension).
For both the raising and lowering phase, the “elbow extensor” muscles are the antagonists. They lengthen during the dumbbell lifting phase and shorten during the dumbbell lowering phase.
Here it is important to understand that it is common practice to name a muscle group (eg elbow flexors) based on the joint action they produce during a shortening (concentric) contraction.
However, this naming convention does not mean that they are only agonists during shortening. This term typically describes the function of skeletal muscles.
The antagonist muscles are simply the muscles that torque the joint opposite the agonist muscles. This pair can help control a movement.
The opposing torque can slow down the downward movement, especially in the case of a ballistic movement.
For example, during a very fast discrete (ballistic) movement of the elbow, such as throwing a dart, the triceps muscles will be activated very briefly.
And hard (in a ‘burst’) to rapidly accelerate the extension movement at the elbow, followed almost immediately by an activation ‘burst’ in the elbow flexor muscles that decelerates the movement of the elbow to a quick stop .
To use an automotive analogy, this would be similar to pressing the accelerator pedal quickly and then pressing the brake immediately.
Antagonism is not an intrinsic property of a particular muscle or muscle group; it is a role that a muscle plays depending on which muscle is currently the agonist.
During slower joint actions involving gravity, as with the agonist muscle (mentioned above), the antagonist muscle can shorten and lengthen.
Using the above example of the triceps brachii during a push-up, the elbow flexor muscles are the antagonists in the elbow during the upward phase and the downward phase of the movement.
During the dumbbell curl, the elbow extensors are the antagonists for the raising and lowering phases.
Agonist-antagonist pairs
Antagonist and agonist muscles often come in pairs, called antagonistic pairs. When one muscle contracts, the other relaxes.
An example of an antagonistic pair is the biceps and triceps; contract: the triceps relaxes while the biceps contracts to lift the arm.
“Reverse movements” require antagonistic pairs located on opposite sides of a joint or bone, including the abductor-adductor pairs and the flexor-extensor pairs.
These consist of an extensor muscle, which “opens” the joint (by increasing the angle between the two bones) and a flexor muscle, which does the opposite by decreasing the angle between two bones.
However, muscles do not always work this way: sometimes agonists and antagonists contract at the same time to produce force, according to the Lombard paradox.
Also, sometimes during a joint action controlled by an agonist muscle, the antagonist will be slightly activated, naturally.
This normally occurs and is not considered a problem unless it is excessive or uncontrolled and disturbs the control of joint action. This is called agonist / antagonist coactivation and serves to mechanically stiffen the joint.
Not all muscles are paired in this way. An example of an exception is the deltoid.
Neutralizing action
A muscle that fixes or retains a bone so that the agonist can carry out the intended movement is said to have a neutralizing action.
A famous good example of this is the hamstrings; the semitendinosus and semimembranosus muscles perform knee flexion and internal knee rotation, while the biceps femoris performs knee flexion and external knee rotation.
In order for the knee to flex while not turning in either direction, all three muscles contract to stabilize the knee as it moves in the desired manner.
Compound muscle
Composite or hybrid muscles have more than one set of fibers that perform the same function, and they are generally supplied by different nerves for different sets of fibers.
For example, the tongue itself is a muscle made up of various components, such as longitudinal, transverse, and horizontal muscles with different innervated parts that have different nerve supply.
Synergist : The synergist in a movement is the muscle (s) that stabilize a joint around which the movement occurs, which in turn helps the agonist to function effectively.
Synergistic muscles also help create movement. In the bicep curl, the synergistic muscles are the brachioradialis and brachialis that help the biceps create movement and stabilize the elbow joint.
Fixator : The fixator in a movement is the muscle (s) that stabilizes the origin of the agonist and the joint that the origin encompasses (moves) to help the agonist work more effectively.
In the bicep curl, these would be the rotator cuff muscles, the “guardians of the shoulder joint.” Most of the fixator muscles are found working around the hip and shoulder joints.
Shape
Insertion and origin
The insertion and origin of a muscle are the two places where it is anchored, one at each end. The tissue of the accessory is called an enthesis.
The origin of a muscle is the bone, typically proximal, which has a greater mass and is more stable during a contraction than the insertion of a muscle.
For example, with the latissimus dorsi muscle, the site of origin is the torso, and the insertion is the arm. When this muscle contracts, the arm normally moves because it is less massive than the torso.
This is the case when gripping objects lighter than the body, as in the typical use of a lateral extraction machine. However, this can be reversed, as in a chin-up where the torso moves up to meet the arm.
The insertion of a muscle is the structure to which it adheres and tends to move due to the contraction of the muscle. This can be a bone, tendon, or subcutaneous dermal connective tissue.
The attachments are usually connections of the muscle through the tendon with the bone. The insertion is a bone that tends to be distal, have less mass and greater movement than the origin during a contraction.
Muscle fibers
Muscles can also be described by the direction the muscle fibers move.
Spindle muscles have fibers that run parallel to the length of the muscle and are spindle-shaped. For example, the pronator teres muscle of the forearm.
Unipended muscles have fibers that run the entire length of a single side of a muscle, like a feather. For example, the fibularis muscles.
The bipennate muscles consist of two rows of oblique muscle fibers, oriented in opposite diagonal directions, that converge on a central tendon.
The bipennate muscle is stronger than the unipennate muscle and the fusiform muscle, due to a larger physiological cross-sectional area.
The bipenic muscle shortens less than the unipenic muscle, but develops more tension when it does, resulting in greater power but less range of motion.
Pennate’s muscles generally tire easily as well. Examples of biped muscles are the rectus femoris muscle of the thigh and the stapedius muscle of the middle ear.
Condition
Hypertrophy and atrophy
Hypertrophy is an increase in muscle size due to an increase in the size of individual muscle cells. This usually occurs as a result of exercise.
