Research of muscle strength

The strength of the muscle is a quantitative measure that expresses the ability of the muscle to contract during counteraction to its external force, including gravity. Clinical research of muscle strength first of all reveals its decrease. A preliminary, tentative evaluation of muscular strength begins with finding out whether the subject can carry out active movements in all joints and whether these movements are carried out in full.

Having discovered the limitations, the doctor makes passive movements in the appropriate joints in order to exclude local injuries to the musculoskeletal system (muscular and joint contractures). Restriction of passive movements in the joint, caused by osteoarticular pathology, does not exclude that the patient can be reduced muscle strength. At the same time, the absence or restriction of active voluntary movements with the full amount of passive movements in the waking and cooperating with the doctor patient indicates that the cause of the disorder is most likely the pathology of the nervous system, neuromuscular junctions or muscles.

The term " paralysis " (plegia) means a complete absence of active movements due to a violation of the innervation of the corresponding muscles, and the term "paresis" - the reduction of muscle strength. Paralysis of the muscles of one limb is called monoplegia, paralysis of the lower facial muscles, hands and feet on the same side of the body - hemiplegia; paralysis of the muscles of both legs - paraplegia, paralysis of the muscles of all four limbs - tetraplegia.

Paralysis / paresis can be the result of the defeat of both the central (upper) and peripheral (lower) motor neuron. Accordingly, two types of paralysis are distinguished: peripheral (flaccid) paralysis occurs due to damage to the peripheral motor neuron; central (spastic) - as a result of the defeat of the central motor neuron.

The defeat of the central motoneuron (for example, in cerebral stroke ) affects the muscles of the extremities to varying degrees. On the arm, the abductors (abductors) and extensors (extensors) predominantly suffer, and flexors (flexors) on the leg. To defeat the pyramidal system at the level of the inner capsule (where the axes of the Betz pyramidal cells are located very compactly), the pathological posture of Wernicke-Mann is characterized: the patient's arm is bent and brought to the trunk, and the leg is unbent and, when walking, is diverted so that the foot moves along the arc ("the hand asks, the foot mows").

In the pathology of the peripheral motor neuron, each lesion level (involving the anterior horns of the spinal cord, spine nerve root, plexus or peripheral nerve) has a characteristic type of distribution of muscle weakness (myotome, neurotic). Muscular weakness is not only neurogenic: it occurs in the primary lesion of muscles (myopathy), and in the pathology of the neuromuscular synapse ( myasthenia gravis ). The defeat of the joint can be accompanied by a significant restriction of movements in it due to pain, so with pain syndrome judging of muscle weakness and the presence of neurological pathology should be carefully.

Evaluation of muscle strength

To assess muscle strength, the patient is asked to perform a movement that requires the contraction of a certain muscle (muscle), fix the posture and hold the muscle in the maximum contraction position, while the researcher tries to overcome the resistance of the subject and stretch the muscle. Thus, in the study of muscle strength in clinical practice, most often guided by the principle of "tension and overcoming" : the doctor counteracts the patient's exerted muscle and determines the degree of effort required for this. In turn, examine different muscles or groups of muscles, comparing the right and left sides (so it is easier to identify a slight muscle weakness).

It is important to follow certain rules of the survey. So, when assessing the strength of the muscles that take the shoulder, the doctor must stand in front of the patient and resist resistance to movement with one hand only (but not bend over the sitting patient, putting pressure on the patient's hand with the entire body mass). Likewise, when evaluating the strength of the finger flexor, the doctor uses only his finger, equivalent to the tested one, but does not apply the power of the whole hand or the hand as a whole. It is also necessary to make corrections for the child or the elderly patient. The strength of the muscles is usually assessed in points, most often on a 6-point system.

Criteria for assessing the strength of muscles on a 6-point system

Score	Muscle Strength
0	Muscle reduction is absent
1	Visible or palpable contraction of muscle fibers, but without locomotor effect
2	Active movements are possible only when the action of gravity is removed (the limb is placed on the support)
3	Active movements in full volume under the action of gravity, a moderate decrease in force with external counteraction
4	Active movements in full volume under the action of gravity and other external counteraction, but they are weaker than on the healthy side
5	Normal muscle strength

When examining the neurological status, it is necessary to find out the strength of the following muscle groups.

• Neck flexors: m. Sternodeidomastoideus (n. Accessories, C ₂ -C ₃ - items cervicales).
• Extensors of the neck: mm. Colli profundi (C ₂ -C ₄ - nn cervicales.).
• Shrugging: m. Trapezius (n. Accessories, C ₂ -C ₄ - n. Cervicales).
• Shoulder: m. Deltoideus (C ₅ -C ₆ - n axillaris.).
• Flexion of the supine arm in the elbow joint: m. Brachii biceps (C ₅ -C ₆ - . N musculocutaneus).
• Extension of the arm in the elbow joint: m. Brachii triceps (C ₆ -C ₈ - . N radialis).
• Extension in radiocarpal joint: mm. Extensores carpi radialis longus et brevis (C ₅ -C ₆ - n. Radialis), m. Extensor carpi ulnaris (C ₇ -C ₈ - n. Radialis).
• Contrasting the thumb of the brush: m. Opponens pollicis (C ₈ -T ₁ - p. Medianus).
• Lead of the little finger: m. Abductor digiti minimi (C ₈ -T ₁ - n. Ulnaris).
• Extension of the main phalanges of the II-V fingers: m. Extensor digitorum communis, m. Extensor digiti minimi, m. Extensor indicis (C ₇ -C ₈ - n. Profundus n. Radialis).

• Flexion of the hip in the hip joint: m. Iliopsoas (L ₁ -L ₃ - n.femoralis).
• Leg extension in the knee joint: m. Quadricepsfemoris (L ₂ -L ₄ - n.femoralis).
• Flexion of the leg in the knee joint: m. Biceps femoris, m. Semitendinosus, m. Semimembranosus (L ₁ -S ₂ - n. Ischiadicus).
• Extension (back flexion) of the foot in the ankle: m. Tibialis anterior (L ₄ -L ₅ - n. Peroneus profundus).
• Plantar flexion of the foot in the ankle: m. Triceps surae (S ₁ -S ₂ - n. Tibialis).

The above muscle groups are assessed using the following tests.

• Neck bend - a test to determine the strength of the sternocleidomastoid and stair muscles. The patient is asked to tilt (but not extend) his head to the side, and his face turn to the side opposite to the inclination of the head. The doctor opposes this movement.
• Neck extension is a test that allows to determine the strength of the extensors of the head and neck (a vertical portion of the trapezius muscle, belt muscles of the head and neck, muscles, lifting blades, semi-oval muscles of the head and neck).

The patient is asked to tilt his head back, opposing this movement.

Shrinking the shoulders - a test that determines the strength of the trapezius muscle. The patient is offered to "shrug", overcoming the opposition of the doctor.

Leaching of the shoulder is a test to determine the strength of the deltoid muscle. The patient withdraws the shoulder horizontally at the doctor's request; The hand is recommended to bend at the elbow joint. They resist the movement, trying to lower his hand. It should be borne in mind that the ability of the deltoid muscle to hold the shoulder in the allotted position is disturbed not only with the weakness of this muscle, but also when the functions of the trapezius, anterior dentate and other muscles stabilizing the shoulder girdle are impaired.

Bending of the supine arm in the elbow joint is a test designed to determine the strength of the biceps brachii muscle. The biceps arm muscle participates in flexion and simultaneous supination of the forearm. To examine the function of the biceps muscle of the shoulder, the doctor asks the subject to suppress the wrist and flex the arm at the elbow joint, resisting this movement.

Extension of the arm in the elbow joint is a test used to determine the strength of the triceps brachialis muscle. The doctor becomes behind or on the side of the patient, asks him to unbend his arm at the elbow joint and prevents this movement.

• Extension in the wrist joint is a test that helps determine the strength of the radius and elbow extensors of the hand. The patient unbends and leads the brush with straightened fingers, and the doctor prevents this movement.
• Contrasting the thumb of the hand is a test to determine the strength of the muscle that opposes the thumb. The subject is offered to firmly press the distal phalanx of the thumb to the base of the proximal phalanx of the little finger of the same hand and resist the attempt to unbend the main phalanx of the thumb. Use and test with a strip of thick paper: offer to squeeze it between the I and V fingers and experience the force of pressing.
• Leading the little finger is a test to determine the strength of the muscle that removes the little finger. The doctor tries to bring to the rest of the fingers the withdrawn little finger of the patient in spite of his resistance.
• The extension of the main phalanges of the II-V fingers is a test used to determine the strength of the common extensor of the fingers of the hand, the extensor of the little finger and the extensor of the index finger. The patient unbends the main phalanges of the II-V fingers of the hand, when the middle and the nail are bent; the doctor overcomes the resistance of these fingers, and the other hand fixes his wrist joint.

Hip flexion in the hip joint is a test that allows to determine the strength of the iliac, large and small lumbar muscles. Ask the sitting patient to bend the hip (bring him to the stomach) and at the same time, by resisting this movement, act on the lower third of the thigh. You can examine the strength of the hip flexion and in the patient's position lying on the back. To do this, he is offered to lift his straightened leg and hold it in this position, overcoming the pressure down the palm of the doctor, resting against the mid-thigh of the patient. The decrease in the strength of this muscle is attributed to the early symptoms of the defeat of the pyramidal system. Leg extension in the knee joint is a test for determining the strength of the quadriceps femoris muscle. The study is carried out in the patient's position lying on the back, the leg is bent in the hip and knee joints. Ask him to unbend his leg, raising his lower leg. At the same time, they bring a hand under the patient's knee, holding his hip in a half-bent position, with the other hand applying pressure on the lower leg downwards, preventing its extension. To test the strength of this muscle of the patient sitting on a chair, ask to unbend the leg in the knee joint. One hand is resisting this movement, the other - palpating the contracting muscle.

• Bending of the leg in the knee joint is a test necessary to determine the strength of the muscles of the hamstring (ischiocular muscles). The study is carried out in the patient's position lying on the back, the leg is bent in the hip and knee joints, the foot is in tight contact with the couch. Try to straighten the patient's leg, after giving him the task not to tear off the foot from the couch.
• Extension (back flexion) of the foot in the ankle is a test that helps determine the strength of the anterior bolepeter's muscle. The patient lying on his back with his legs straight, is asked to pull his feet toward him, somewhat bringing the inner edges of the feet, while the doctor is resisting this movement.
• Plantar flexion of the foot in the ankle is a test used to determine the strength of the triceps muscles of the lower leg and the plantar muscle. The patient, lying on his back with his legs straight, makes the plantar flexion of the feet, despite the opposition of the doctor's palms, which put pressure on the feet in the opposite direction.

More detailed methods for studying the strength of individual muscles of the trunk and extremities are described in the manuals on topical diagnostics.

The above methods of assessing muscle strength are advisable to supplement with some simple functional tests intended to test the function of the entire limb to a greater extent than to measure the strength of individual muscles. These tests are important for revealing a slight muscle weakness, which is difficult for a doctor to notice when fixing attention on individual muscles.

• To identify weakness in the muscles of the shoulder, forearm and the wrist, the patient is asked to squeeze the doctor as much as possible three or four fingers and try to release his fingers during the shake. The test is carried out simultaneously on the right and left hand to compare their strength. It should be borne in mind that the force of shaving depends more on the preservation of the muscles of the forearm, so when the small muscles of the hand are weak the handshake can remain quite strong. It is possible to accurately measure the force of brush compression using a dynamometer. The brush compression test allows us to reveal not only the weakness of the arm muscles, but also the phenomenon of the myotonia of the action, observed with such hereditary neuromuscular diseases as dystrophic and congenital myotonia. After a strong compression of his brush into a fist or a strong pressing of someone else's hand, the patient with the phenomenon of myotonia can not quickly release his brush.
• To reveal weakness in the proximal parts of the legs, the examinee should get out of the squatting position without the help of the hands. Children should observe how they rise from sitting on the floor. For example, with Duchenne's myodystrophy the child resorts to auxiliary techniques when getting up ("self-climbing").
• To identify weakness in the distal parts of the legs, the patient is offered to stand up and be like heels and "toes".
• The central (pyramidal) paresis of the hands can be identified by inviting the patient with closed eyes to hold their arms straight with almost touching palmar surfaces slightly above the horizontal level (Barre's test for upper limbs). The hand on the side of the paresis begins to descend, while the wrist is bent in the wrist joint and rotated inwards ("pronator drift"). These postural disorders are considered to be very sensitive signs of the central paresis, allowing it to be detected even when a direct study of muscle strength does not reveal any disturbances.
• In patients with suspected myasthenia gravis it is important to establish whether weakness in the muscles of the head, trunk and extremities during exercise is increasing. To do this, they stretch their hands in front of them and look at the ceiling. Normally, a person can be in this position for at least 5 minutes. Use and other muscle fatigue provoking tests (squats, loud count to 50, re-opening and closing eyes). Most objectively, myasthenic fatigue can be detected using a dynamometer: the force of compression of the hand is measured in a fist, then the patient quickly performs 50 intensive compressions of both hands into a fist, after which the dynamometry of the brushes is again performed. Normally, the compression force of the brushes remains practically the same before and after this series of brush compression into the fist. In myasthenia gravis, after a physical strain on the muscles of the hand, the force of compression of the dynamometer decreases by more than 5 kg.

[1], [2], [3]