Flexor and extensor muscles: features, structure and examples

Muscle imbalances are quite common in people, even world-class athletes. The muscles on the front of the thigh (quadriceps) are quite often stronger than the muscles on the back of the thigh. And the upper trapezius muscles tend to be stronger than the lower trapezius muscles. The anterior deltoids are stronger than the posterior deltoids. As a rule, they develop the muscles that a person sees and they are located in front. The shoulder is a classic example of a body part that people try to develop first. It's no surprise that 30% of all strength training injuries occur in the shoulder joint.

The shoulder muscles can be divided into two groups:

Flexors and extensors and these include the deltoid muscle, supraspinatus and infraspinatus muscles, teres minor and major muscles, subscapularis muscle. The deltoid muscle has the most complex and diverse functions. The deltoid muscle consists of three bundles
The anterior deltoid muscle is located in the front of the shoulder, the lateral deltoid muscle is located in the middle of the shoulder, and the posterior deltoid muscle is located in the back of the shoulder.

Data from a study of bodybuilders showed that the strength of the anterior deltoid muscle could be 5 times greater than that of ordinary people. And the lateral deltoid muscles could be 3 times stronger. At the same time, oddly enough, the rear deltoid muscles were only 15% stronger.

The muscle imbalance between the front and rear deltoids can be partly explained by the emphasis on exercises that target the front deltoids and the lack of exercises that target the rear deltoids.

Coordinated work of the shoulder muscles allows you to perform the necessary movements and maintain stability of the shoulder joint. A disruption in the interaction of the muscles that stabilize the shoulder with the muscles that perform movements is called a muscle imbalance of the shoulder. This disorder creates problems with movement, since the muscles responsible for movement are stronger than the muscles responsible for stability and this leads to instability.

In most cases, muscle imbalance can occur due to repetitive movements. The most common is excessive strengthening of the internal rotator muscles of the shoulder accompanied by poor development of the external rotator muscles. The internal rotator muscles are strengthened with chest exercises and back exercises, but the external rotator muscles are rarely worked. This leads to rotator cuff imbalance and damage to both the rotator cuff muscles and tendons. This imbalance can be corrected with specific exercises to strengthen the external rotation muscles.

What are the muscles that act oppositely called?

Human musculature is designed in such a way that many muscles have “brothers” that perform completely opposite work: at the moment when one muscle tenses, the opposing one relaxes, and vice versa.

These muscles - flexors and extensors, which control the movement of the human body or individual limbs in space, are called antagonists. This is exactly how a person makes movements - thanks to a control system strictly coordinated by the brain and the coordinated work of the muscles that move the skeleton.

How do they work?

The brain sends an impulse to the nerve endings of a muscle, such as the biceps of the arm, and it contracts, bending the arm. The triceps - the extensor of the arm - is relaxed at this moment, since the brain gave the corresponding signal to it.

Flexor and extensor muscles, that is, antagonists, always work harmoniously, mutually replacing each other, but sometimes they can work simultaneously, maintaining a motionless, that is, static position of the body in space. A striking example of such work is the well-known plank pose, in which the body hangs motionless above the floor, resting only on the hands and toes. Most of the main flexors and extensors of the muscles in this position do exactly half of the work required for them, as a result, the body maintains this position. If a person does not strain, say, the abdominal muscle, then it becomes difficult for his back, since under the pressure of gravity the lower back begins to sag and sag. Arms lowered down along the body are completely relaxed antagonist muscles, and an outstretched arm in front of you at shoulder level is synchronous work of both muscle groups.

What determines the quality of movement?

The quality of the flexor and extensor muscles depends on several factors:

The amplitude of movement mainly depends on the length of muscle fibers and the factors restraining them, for example, muscle spasm or post-traumatic scar greatly reduces the range of movement, and elasticity and good blood flow, on the contrary, significantly add amplitude to muscle work. That is why it is important to warm up the body well with dynamic movements before training in order to saturate the muscles with blood.
The strength of a muscle depends on two aspects: the amount of leverage that the muscle uses, and directly the number and thickness of the muscle fibers that make it up. For example, lifting a 10 kg weight using the entire length of your arm is easy (large lever), but lifting it with just your hand will be more difficult. The same is true with the number of muscle fibers: a muscle that is 5 cm in diameter is several times stronger than one that is only 2 cm thick.
All muscle movements are controlled by the somatic nervous system, therefore all body movements, especially the coordinated actions of the flexor and extensor muscles, depend on the speed and quality of its work.

If an athlete knows about the correct functioning of muscles, his training becomes more conscious and therefore correct, the level of efficiency increases significantly with less energy expenditure.

Assessment of the strength and speed capabilities of the knee extensor and flexor muscles

V. N. Seluyanov, V. A. Rybakov, M. P. Shestakov

Chapter 3. Monitoring the level of physical fitness of a skier

3.3. Assessment of the strength and speed capabilities of the knee extensor and flexor muscles

When assessing the speed-strength capabilities of alpine skiers on a bicycle ergometer, the MAM indicator is obtained - maximum alactic power, which indirectly evaluates both the level of strength readiness and muscle composition. To separately assess these properties of the muscular system, testing should be carried out on force-measuring devices.

Measurement of strength and speed of muscle tension was carried out using an isokinetic BIODEX device.

The maximum moment in extension and flexion of the knee joint was measured in isometric mode.

As a result, we obtained estimates of the maximum moment of force, the gradient - the rate of increase of the moment of force and the rate of increase of force (k).

The rate of increase in strength depends on the ability to simultaneously recruit all motor units and hereditary endowment (proportion of fast muscle fibers), therefore, speed-strength fitness standards take into account both sides - relative strength and the speed of its manifestation. The combination of these two abilities determines the level of speed-strength fitness of the skier.

In table 1, 2 present the results of the survey.

Table 1.

Strength capabilities of the knee extensor and flexor muscles.

Extensors		Flexors
Surname	Weight, kg	Mmak, N*m	Mmax/weight, N*m/kg	Mmak, N*m	Mmax/weight, N*m/kg
R-a_L.	58	211	3,64	102	1,76
S-na_A.	59	230	3,91	76	1,29
A-va_I.	58	194	3,34	75	1,29
Sh-va_M.	63	219	3,48	95	1,51
R-va_E.	59	175	2,97	87	1,47
To you.	67	231	3,45	121	1,81
Mr._D.	65	225	3,46	76	1,17
P-va_E.	50	186	3,72	48	0,96
P-va_O.	60	220	3,67	73	1,22
Ch-va_M.	71	205	2,89	78	1,1
From you.	72	289	4,01	87	1,21
Zh-va_A.	64	231	3,61	82	1,28
K-va_E.	71	236	3,32	81	1,14
Zh-ov_M.	72	333	4,63	139	1,93
S-ts_K.	83	365	4,4	133	1,6
G-ev_A.	69	333	4,83	126	1,83
P-v_E.	86	336	3,91	98	1,14
X-ov_A.	79	402	5,09	148	1,87
K-ov_A.	67	279	4,16	92	1,37
U-v_D.	88	462	5,25	166	1,89
S-x_A.	75	363	4,85	126	1,68

Note: Mmax is the maximum moment at the joint, Mmax/mass is the maximum relative moment at the joint.

Table 2.

Speed capabilities of the flexor and extensor muscles of the knee joint.

Surname	Weight	Extensors		Flexors
J, N*m/s	K1=J/Mmak, 1/s	J, N*m/s	K2=J/Mmak, 1/s	k1/k2,
R-a_L.	58	428	2,03	183	1,8	1,1
S-na_A.	59	628	2,72	196	2,6	1,1
A-va_I.	58	207	1,23	197	2,6	0,5
Sh-va_M.	63	411	2,1	187	2	1,1
R-va_E.	59	183	1,04	145	1,7	0,6
To you.	67	654	2,92	245	2	1,4
Mr._D.	65	329	1,46	221	2,9	0,5
P-va_E.	50	377	2,6	175	3,6	0,7
P-va_O.	60	527	2,4	243	3,3	0,7
Ch-va_M.	71	177	0,87	144	1,9	0,5
From you.	72	463	1,6	231	2,7	0,6
Zh-va A.	64	302	1,44	203	2,5	0,6
K-va_E.	71	187	1,45	150	1,9	0,8
Zh-ov_M.	72	398	1,31	339	2,4	0,5
S-ts_K.	83	667	1,88	454	3,4	0,6
G-ev_A.	69	580	1,74	335	2,7	0,7
P-ev_E.	86	1242	4,24	383	3,9	1,1
X-v_A.	79	917	2,28	529	3,6	0,6
K-v_A.	67	245	0,88	304	3,3	0,3
U-v_D.	88	1629	3,53	732	4,4	0,8
S-x_A.	75	753	2,07	446	3,5	0,6

Note: J is the gradient or rate of increase of the moment, k1 and k2 are the rate of increase of the moment of force

Table 3.

Standards for strength and speed readiness of the knee joint extensors of alpine skiers (men).

Points	0	1	2	3	4	5
K1<1	<5,0	<5,5	<6,0	<6,5	<7,0	<7,5
K1=1-2	<4,5	<5,0	<5,0	<6,0	<6,5	<7,0
K1=2-3	<4,0	<4,5	<5,0	<5,5	<6,0	<6,5
K1=3-4	<3,5	<4,0	<4,5	<5	<5,5	<6,0
K1>4	<3,0	<3,5	<4,0	<4,5	<5,0	<5,5

Table 4.

Standards for strength and speed readiness of the knee joint extensors of alpine skiers (women).

Points	0	1	2	3	4	5
K1<1	<4,0	<4,5	<5,0	<5,5	<6,0	<7,0
K1=1-2	<3,5	<4,0	<4,5	<5,0	<5,5	<6,5
K1=2-3	<3,0	<3,5	<4,0	<4,5	<5,0	<6,0
K1=3-4	<2,5	<3,0	<3,5	<4,0	<4,5	<5,0
K1>4	<2,0	<2,5	<3,0	<3,5	<4,0	<4,5

Women

A-ova - has low

the indicator of muscle speed capabilities is 1.23, therefore, with a relative strength of 3.34 N*m/kg, it receives
a zero rating
for strength readiness.

Mr. - has a low

the muscle speed capability indicator is 1.46, therefore, with a relative strength of 3.46 N*m/kg, it receives
a zero
strength fitness rating.

Zh-ova - has low

the indicator of muscle speed capabilities is 1.44, therefore, with a relative strength of 3.61 N*m/kg, it receives a score of
one
strength fitness point.

Quantity - has low

the indicator of muscle speed capabilities is 1.45, therefore, with a relative strength of 3.32 N*m/kg, it receives
a zero rating
for strength readiness.

Quantity - has average

the indicator of muscle speed capabilities is 2.92, therefore, with a relative strength of 3.45 N*m/kg, it receives a score of
one
strength fitness point.

P-va - has average

the indicator of muscle speed capabilities is 2.4, therefore, with a relative strength of 3.67 N*m/kg, it receives a score of
two
strength fitness points.

P-va - has average

the indicator of muscle speed capabilities is 2.6, therefore, with a relative strength of 3.72 N*m/kg, it receives a score of
two
strength fitness points.

R-va - has low

the muscle speed capability indicator is 1.04, therefore, with a relative strength of 2.97 N*m/kg, it receives a score of
zero
strength fitness points.

Ro-va - has an average

the indicator of muscle speed capabilities is 2.03, therefore, with a relative strength of 3.64 N*m/kg, it receives a score of
two
strength fitness points.

S-va - has low

the indicator of muscle speed capabilities is 1.6, therefore, with a relative strength of 4.01 N*m/kg, it receives a score of
two
strength fitness points.

S-na - has average

the indicator of muscle speed capabilities is 2.72, therefore, with a relative strength of 3.91 N*m/kg, it receives a score of
two
strength fitness points.

Ch-va - has very low

the indicator of muscle speed capabilities is 0.87, therefore, with a relative strength of 2.89 N*m/kg, it receives a score of
zero
strength fitness points.

Sh-va - has an average

the indicator of muscle speed capabilities is 2.1, therefore, with a relative strength of 3.48 N*m/kg, it receives a score of
one
strength fitness point.

Men

G-ev - has low

the indicator of muscle speed capabilities is 1.74, therefore, with a relative strength of 4.83 N*m/kg, a score of
one
strength fitness point is received.

F-v - has low

the indicator of muscle speed capabilities is 1.31, therefore, with a relative strength of 4.63 N * m / kg, it receives a rating of

strength fitness point

K-ov - has a very low

the indicator of muscle speed capabilities is 0.88, therefore, with a relative strength of 4.16 N*m/kg, it receives a score of
zero
strength fitness

P-ev - has a high

the indicator of muscle speed capabilities is 4.24, therefore, with a relative strength of 3.91 N*m/kg, it receives a score of
two
strength fitness

S-ts - has average

the muscle speed capability indicator is 1.88, therefore, with a relative strength of 4.4 N*m/kg,
score is zero
.

C-x - has average

the indicator of muscle speed capabilities is 2.07, therefore, with a relative strength of 4.85 N*m/kg, it receives a score of
two
strength fitness

X-v - has average

the indicator of muscle speed capabilities is 2.28, therefore, with a relative strength of 5.09 N * m / kg, it receives a score of
three
strength fitness points.

U-v - has a high

the indicator of muscle speed capabilities is 3.53, therefore, with a relative strength of 5.25 N * m / kg, it receives a score of
three
strength fitness

Thus, natural talent for competitive activity in alpine skiing requires the manifestation of strength in the shortest possible periods of time; of the examined athletes, the following have such talent:

- men - two, average - three more.

Consequently, at present, non-informative indicators are taken as a criterion for selecting a team. Russian skiers at the international level occupy places far from the first hundred, which means that they need to progress. Only physically gifted athletes who are capable of learning technical actions on difficult courses of international competitions can progress. In this regard, selection for national teams should be carried out not only according to the results of competitions, but also according to laboratory testing data. It is possible that athletes who occupy places in the second ten are more physically and coordinationally gifted compared to the winners. They do not have results for objective reasons (equipment, trainer qualifications, training conditions, etc.), and when they find optimal conditions for training, they can progress quickly.

2.3

3.1

3.2

3.3

4.1

4.2

4.3

Table of contents

Examples of antagonist muscles

The simplest examples of flexor and extensor muscles:

The femoral biceps and quadriceps are the flexor and extensor muscles of the leg, or more precisely the hip. The biceps is located at the back, attached to the ischium at the top and bottom, turning into a tendon, adjacent to the femur in the area of the knee joint. And the quadriceps is an extensor, located on the front side of the thigh, attached by a tendon to the knee joint, and the upper part is attached to the pelvic bone.
The biceps and triceps are the flexor and extensor muscles of the arm, located between the elbow and shoulder joints and attached to them by powerful tendons. They are the main muscles that form the shoulder and control the vast majority of flexion and extension movements of the arm.

You can often notice that if there is an overly active extensor muscle, then, as a result, the flexor muscle will be in a passive state, that is, not sufficiently developed, which creates inadequate body movements with a greater loss of energy than in harmoniously trained people (yogis are an example of this) .

MUSCLES OF THE FOREARM

The forearm in its normal state is club-shaped with a flattened anterior and posterior surface. In the upper part of the forearm there are, for the most part, the belly of the muscles, in the lower part, mainly their tendons. In muscular people, the shape of the forearm can change to a large extent due to muscle contraction. A thin and narrow lower forearm indicates a weaker skeleton. The tendons of the superficial muscles appear quite clearly. The muscle ridges and grooves of the forearm are more noticeable the more muscular a person is and the less body fat he has.

From an anatomical point of view, the muscles of the forearm are divided into three groups. Some of them are responsible for wrist movements, while others are responsible for finger movements. In front, on the side of the palm, there is a group of flexors. On the opposite side are the extensors. The third group of muscles is located in the area of the thumb.

Muscles that flex the arm at the wrist joint:

Palmaris longus muscle
Flexor carpi radialis
Flexor carpi ulnaris

Muscles that flex the fingers:

Flexor digitorum superficialis
Flexor digitorum profundus
Flexor pollicis longus.

Of the muscles on which the outline of the forearm depends, mention should be made of the pronator teres, which has the shape of an oblong, not particularly convex roller, located on the inside of the cubital fossa. The pronator is involved in two movements of the forearm - flexion and pronation (internal rotation) along with the following muscles: flexor carpi radialis, palmaris longus, flexor digitorum superficialis, flexor carpi ulnaris. The pronator starts from the inner condyle of the humerus and is attached in the wrist to the phalanges of the fingers from the palmar surface of the hand. The above muscles form elongated muscle ridges, which are noticeable when the hand is bent at the wrist towards the palm and little finger.

Muscles that extend the arm at the wrist joint:

Extensor carpi radialis longus
Extensor carpi radialis brevis
Extensor carpi ulnaris

Muscles that extend the fingers:

Extensor digitorum
Extensor pollicis longus
Extensor pollicis brevis
Extensor index finger

The extensors are located on the back of the forearm. Covered only by thin skin, they are clearly visible in muscular people. The prominent muscles primarily include the extensors of the little finger and index finger, the extensor carpi ulnaris, the abdomen of which is especially clearly visible along the edge of the ulna. In addition, the same group of muscles includes the long and short extensors of the thumb and its long abductor muscle. All of the above muscles make it possible to bend the hand towards its back, move the hand towards the thumb and little finger, and extend the fingers. Other muscles are grouped near the radius. The extensor carpi brevis and longus muscles are clearly visible when clenching your hands into a fist, when they contribute to the dorsiflexion of the hand at the wrist, which, in turn, allows the flexors to clench the fingers more tightly into a fist.

Muscles that turn the hand palm up:

Arch support
Biceps

Muscles that turn the hand palm down:

Pronator teres
Pronator quadratus

Another example of antagonist muscles

The rectus abdominis and longitudinal muscles along the spine, along with the lumbar muscle, are also prominent representatives of the flexors and extensors of the body, and they are the most global, because thanks to their coordinated and uninterrupted work, the human body takes on various positions in space: from a vertical position of the torso to bending in an arc or, on the contrary, bending back.

And if a person is working to correct posture: eliminate kyphosis, correct scoliotic curvature, or remove hyperlordosis in the lower back, he needs not only to work on the spinal extensors and lumbar muscles, but also to actively pump the abdominal muscles, in particular the longitudinal abdominal muscle.

Pectoral muscles and diamond backs

These two couples also belong to the antagonists, although they are often unfairly classified in other categories. The relationship between spasm of the pectoral muscles and the passive rhomboid muscles of the back has repeatedly become an area of research for physical and yoga therapists, kinesiologists and rehabilitation specialists. The pectoralis major and minor muscles are shaped like a fan. They are located on the front of the chest, originate in one bundle at the collarbones, the lower one - at the upper abdominal wall and are attached to the crests of the humerus. Spasm of the pectoral muscles can be determined not only by the person’s stoop, but also by the position of his arms, lowered along the body. His arms from the shoulder and down to the hand will be turned inward, that is, the hands will face back with the palms.

The rhomboid muscles are located between the shoulder blades, controlling their work together with the trapezius, which, in turn, directly depend on the freedom of the shoulder muscles, in the area of which there is already an attachment of the pectoral muscles. As a result, a person works on stooping, loading the back muscles, but in fact he first needs to get rid of hypertonicity of the pectoral muscles, then work the extensor and flexor muscles of the neck, which will give freedom to his posture.

Treatment

The most effective treatment for shoulder muscle imbalance is exercise therapy. The exercise program allows you to strengthen weakened muscles and relax muscles that are constantly tense. In addition to exercise therapy, it is possible to use physical procedures that help reduce pain. Massage can reduce muscle spasms and improve blood circulation in the muscles. Changing posture during work is of great importance in the treatment of muscle imbalance in the shoulder muscles, especially if the patient’s work involves prolonged sitting.

Typically, treatment for muscle imbalance is conservative. But in cases where the muscle imbalance is severe and has led to complications (such as instability), then arthroscopic surgery is performed to improve the stability of the shoulder joint.