Dynamometry is the measurement of muscle strength. The tension developed by one or another muscle group is a functional characteristic of the motor analyzer and is considered as an indicator of general physical development. When studying the strength of muscle tension, indicators of the strength of the arms, legs, fingers and deadlift strength are distinguished (i.e., the strength of the muscles that extend the torso in the hip joints), etc. In psychophysiology, the measurement of hand strength and deadlift strength is most often used. The study of endurance under static muscle tension is of particular interest due to the fact that it is present in all muscle activity and occupies a fairly large place in it. To assess static muscular endurance, a special version of the dynamometer technique is used. In the process of measuring the strength of muscle tension, the asymmetry coefficient (AC) is calculated. In general form, its value is determined by the following formula:
Where Vn - Right hand indicator, kg; Vn - indicator of the left hand, kg.
In practice, the method of determining the muscle strength of the hand is used as a test to establish the level of general physical development of a person. For this purpose, muscle strength of both arms is measured before and after work. A comparison of the ratio of muscle strength of the right and left arms before and after the work load indicates a change in the involvement of bilateral regulation in the human body under the influence of load.
CHAPTER2. METHODS RESEARCH PSYCHOMOTOR ORGANIZATIONS
The average statistical indicators of strength (in kilograms) of the hands and back strength for the student age group are given in Table. 2.16.
Table 2.16. Average statistical indicators of hand strength and back strength for the student age group, kg
To measure arm muscle strength and deadlift strength, a manual knee spring dynamometer and a deadlift dynamometer are used. When taking measurements, it is necessary to comply with a number of conditions and, above all, the constancy of the subject’s posture. When measuring hand strength, the subject sits on a chair; the arm for which measurements are being taken is extended forward, bent at the elbow joint; free hand on knee.
Instructions. Squeeze the dynamometer spring with your hand as hard as possible.
The measurements are repeated 3 times for the right and left hands, both before and after the load. After this, the deadlift force is also measured before and after the load.
Instructions. Stand on the lower jaws of the dynamometer. Using a chain, adjust the dynamometer to suit you, that is, so that the measuring part of the device is at the level of your kneecaps. Grasping the upper branches with both hands, pull them up as much as possible, while straightening your torso.
Then the subject performs 20 squats, after which the experimenter measures the strength of each arm 3 times, and measures the back strength once.
Processing of the results is as follows:
1) calculate the average values (M) of the strength of the right and left hands;
2) calculate the asymmetry coefficient (KA) for arm strength using the formula:
Analyzing the data obtained, compare them with the average values.
In table 2.17-2.19 presents age standards for muscle strength indicators published by different authors.
Table 2.17. Arm strength of teenagers 14-17 years old
METHODS FOR STUDYING PSYCHOMOTOR ACTIVITIES IN A COMPREHENSIVE STUDY OF HUMAN PERSONS
|
38 or more |
59 or more |
Note. Data obtained by N. A. Grishchenko.
Table 2.18. Dynamometry of the right arm (in kilograms), average values
|
Ast, Years | ||
Note. Data provided by Rudik.
Table 2.19. Age-related changes in manual strength in men and women
|
Age, Years |
Quantity |
The power of the right |
Left power |
Quantity |
The power of the right |
Left power |
|
Subjects |
Hands |
Hands |
Subjects | |||
CHAPTER 2. METHODS RESEARCH PSYCHOMOTOR ORGANIZATIONS
End of table. 2.19
|
Age, Years |
Quantity |
The power of the right |
Left power |
Quantity |
The power of the right |
Left power |
|
Subjects |
Subjects | |||||
|
51 and older |
Note. Data presented by E. P. Ilyin.
But not ordinary ones, which are used in industry, but special ones - medical ones. Medical dynamometers include a wrist dynamometer, also called a hand dynamometer, and a backbone dynamometer. In this article we will tell you how measurements are carried out using these devices.
So let's start with the wrist dynamometer. This device is intended to determine the compressive force of the muscles that flex the fingers of both human hands, as well as to diagnose the condition and function of the hands of both healthy people and those recovering from injuries. The hand dynamometer is used by doctors who engage in physical therapy; in addition, the dynamometer is used in law enforcement agencies, the armed forces and the Ministry of Emergency Situations. Strength measuring devices are indispensable for the training of professional athletes. As an example of a hand dynamometer, we can cite such devices as: mechanical DC and electronic DMER.
Hand dynamometer DC.
Taking isometric strength measurements using a dynamometer does not require much time, and the measurement process does not tire the subject. To obtain accurate absolute results, it is necessary for the patient to maintain a certain body position and the angle of individual joints. Let the person being examined extend his arm with the hand dynamometer and move it to the side perpendicular to the body. The free hand, at the same time, should be relaxed and lowered down. After which, on command, he will have to squeeze the wrist dynamometer as hard as he can. The dynamometer measurement can be taken alternately with both hands several times, with the best result for each hand being selected.
Drawing conclusions based on the absolute results of the measurements can only be made dynamically, when the previous results were recorded in a special diary. Otherwise, since the results of measurements made using a dynamometer are influenced by factors such as age, sex of the subject, as well as height and weight, more objective indicators should be used. The most objective indicator of strength will be the so-called relative magnitude of muscle strength. This is due, in addition to the listed factors, to the fact that during training, the growth of absolute strength indicators is closely related to the growth of a person’s muscle mass, and, as a consequence, to his weight.
To determine the relative hand strength, you need to multiply the absolute readings in kilograms obtained by measuring with a hand-held dynamometer by 100 and divide by the athlete’s body weight. For men who do not engage in sports, this figure should be 60-70, and for women 45-50.
Deadlift dynamometry, carried out using a deadlift dynamometer, is, one might say, a comprehensive measurement of the strength qualities of an athlete, since almost all major muscles are involved in such a study. The deadlift exercise using a dynamometer should be used in all dispensary-type sports and recreational institutions. As an example of a deadlift dynamometer, we can cite the DS-200 and DS-500.
Dynamometer Stanovoy DS-200
Deadlift dynamometry involves the use of a deadlift dynamometer - a device that looks like a regular foot expander, which consists of a handle, a footrest placed under your feet, a cable and a measuring device with a sensor and a reading device. The subject must pull the handle towards himself and up as hard as he can, while keeping his legs straight at the knees.
The relative value of the deadlift force is calculated in exactly the same way as in manual dynamometry, however, here the index values should be several times higher. For example:
If the index is less than 170, then the relative strength index is low.
- From 170 to 200 - below average.
- 200 - 230 - average.
- 230 - 260 - above average.
- If more than 260, then it is considered high.
An increase in relative strength indicators, both manual and deadlift, usually indicates an increase in muscle strength, and, consequently, an increase in muscle mass as a percentage.
Indications from such measurements are used in neurology when examining diseases that may be accompanied by muscle weakness, for example, myasthenia gravis, multiple sclerosis with limb weakness, as well as various consequences of stroke.
Separately, we should highlight a type of study called dynamography, in which indicators of the strength and speed of muscle contraction are recorded on a graph. As the name suggests, the essence of this method is that the readings are recorded graphically over time (over time). Often, dynamography is associated with any exercises or circumstances, the effectiveness of which needs to be measured.
In children, there are also average dynamometry indicators, which are considered to be the norm. Average values vary depending on the gender, height, and age category of the subject. Measurements of right hand strength and back strength are usually carried out for children aged eight to 18 years in two stages, with a short break for rest. Thus, the norms for indicators of right hand strength for boys are:
- From 13 to 18.5 kg - for ages 8-11 years.
- 21.6 - 37.6 kg - 12-15 years.
- 45.9 - 51 kg - 16-19 years.
For girls, the norm ranges from:
- 9.8 - 17.1 kg - for ages 8-11 years.
- 19.9 - 28.3 kg - 12-15 years.
- 31.3 - 33.8 kg - 16-19 years.
Concluding the article, let's just say that dynamometry is an important element of anthropometry, which has found its application in physiology, sports medicine, and sports hygiene. Thanks to the indicators of absolute and relative strength, the degree of physical development of a person is assessed.
In the literature there are descriptions of various positions of subjects when measuring muscle strength (standing, lying, sitting). The absolute muscle strength significantly depends on the starting position when measuring: for example, the strength of the hip extensors measured while standing and lying down has a difference of up to 20%.
When measuring muscle strength, the following rules must be observed:
1) the best time for taking measurements is the first half of the day, 2.5-3 hours after eating;
2) warm-up is necessary for 10-15 minutes without weights;
3) the ambient temperature must be from + 18 to + 22°:
4) the position of the subject is vertical;
5) mandatory fixation of the proximal joints and maintaining a constant position of the distal joints;
6) the shoulder of application of force should be constant for all subjects, since in all cases it is not the force that is measured, but the moment of muscle force;
7) the angle between the dynamometer and the link (thigh, lower leg) must be straight;
8) when studying the relationship between muscle strength and technical parameters of movements, it is advisable to carry out measurements taking into account individual working angles;
9) the cuff to which the dynamometer is attached must be at least 5 cm wide to eliminate the pain component;
10) measuring strength after training and the day after competition is not advisable, except for special studies;
11) when comparing the strength of flexor and extensor muscles acting on one link, it is necessary to make measurements with strict consideration of the initial state of the muscles (their stretch);
12) it is advisable to measure muscle strength throughout the entire range of motion every 10° for large joints and 5° for small ones.
Measuring force according to the method of A. V. Korobkov et al. is carried out on a measuring machine, which allows you to achieve the isolated action of a certain muscle group. The machine consists of a metal frame tightly mounted on six legs. A vertical stand with a transverse movable bar moves along the frame, to which the sensor is attached during the experiment. Inside the frame there is a wooden platform with a headrest on one side and a bar for resting the legs on the other. The frame is equipped with straps that ensure immobility of the thing being measured. The starting position of the subject for all measurements is lying on his back or stomach. The disadvantage of the method is that measurements are taken without taking into account the condition of the muscles. their elongation, as well as the ability to measure only if there is a right angle between the proximal and distal links. There is no way to measure muscle strength during pronation and supination.
Measuring muscle strength according to the method of B. M. Rybalko is carried out using a special device consisting of a support board with belts, which is fixed on the gymnastic wall and serves as a support and fixation for the subject during measurement; a stand that makes it possible to fix the foot during measurement and strengthen the dynamometer; a bracket attached to the gymnastics stand and serving as an upper support for the dynamometer. The initial position of what is being measured is vertical. The disadvantages of the method are the same as for the method of A.V. Korobkov; advantages - portability of the device.
The technique developed at the Department of Anatomy of the Smolensk State Institute of Physical Culture (R. N. Dorokhov, Yu. D. Kuzmenko, Ya. S. Tatarinov, M. I. Shutkov) allows you to measure muscle strength over the entire amplitude of possible movement in the joints. The stationary version of the measuring device consists of a supporting frame 2.5 m high, one side of which has the shape of a semicircle, along which blocks are located, creating the ability to measure muscle strength in any position of the limb while maintaining the mandatory condition - the position between the limb and the dynamometer is 90°. In the center of the frame there is a vertical support to strengthen the subject.
It has an additional support bar for fixing the knee joint, a platform with a reinforced slalom boot, which allows you to completely eliminate movement in the ankle joint of the supporting leg, and a platform for supporting and fixing the torso. The support device rotates freely around a vertical axis. This allows you to measure muscle strength when moving around the sagittal and frontal axes. When measuring the strength of the trunk muscles, a fixing device for the pelvis and lower extremities with a varying height of the reinforcing platform is installed in the center of the support frame instead of the support vertical. Two reversible electric motors are also mounted on the support frame, which make it possible to measure muscle strength during overcoming and yielding types of work using cables and a dynamometer. The advantage of this method is that it is possible to measure muscle strength in specific working angles with great accuracy during movements in all joints without exception during overcoming, holding and yielding muscle work. Disadvantage: cumbersome.
A portable version of the support device for measuring muscle strength (R. N. Dorokhov, Yu. D. Kuzmenko) is a parallelepiped connected from pipes, three sides of which have metal jumpers located at equal intervals, which allow, if necessary, to set the desired position of the test subject using chains part of the body, that is, measure muscle strength in any state (extension). The fourth side is equipped with a movable frame with belts and support brackets, with the help of which the subject is secured in the desired position, eliminating additional movements. The support brackets and frame can be adjusted to any height of the subject, which is very important when taking measurements in schools. In order to maintain constant strength of the shoulder muscles, frame-type devices have been manufactured that are put on the body link whose strength is being studied.
Advantages - the ability to disassemble the device and easily transport it, the ability to measure force in the “working angles”.
Skeletal muscle fibers are divided into fast and slow. The speed of muscle contraction varies and depends on their function. For example, the calf muscle contracts quickly, and the eye muscle contracts even faster.
Rice. Types of muscle fibers
IN fast muscle fibers the sarcoplasmic reticulum is more developed, which contributes to the rapid release of calcium ions. They are called white muscle fibers.
Slow muscles are constructed from smaller fibers and are called red fibers because of their reddish color due to their high myoglobin content.
Rice. Fast and slow muscle fibers
Table. Characteristics of three types of skeletal muscle fibers
|
Index |
Slow oxidative fibers |
Fast oxidative fibers |
Fast Glycolytic Fibers |
|
The main source of ATP formation |
Oxidative phosphorylation |
Glycolysis |
|
|
Mitochondria |
|||
|
Capillaries |
|||
|
High (red muscles) |
High (red muscles) |
Low (white muscles) |
|
|
Glycolytic enzyme activity |
Intermediate |
||
|
Intermediate |
|||
|
Fatigue rate |
Slow |
Intermediate |
|
|
Myosin ATPase activity |
|||
|
Shortening speed |
Slow |
||
|
Fiber diameter |
|||
|
Motor unit size |
|||
|
Motor axon diameter |
Muscle strength
The strength of a muscle is determined by the maximum amount of load it can lift, or by the maximum force (tension) it can develop under isometric conditions.
Single muscle fiber capable of developing a force of 100-200 mg. There are approximately 15-30 million fibers in the body. If they acted in parallel in the same direction and at the same time, they could create a voltage of 20-30 tons.
Muscle strength depends on a number of morphofunctional, physiological and physical factors.
Calculation of muscle strength
Muscle strength increases with increasing area of their geometric and physiological cross-section. The physiological cross-section of a muscle is the sum of the cross-sections of all muscle fibers along a line drawn perpendicular to the course of the muscle fibers.
In a muscle with parallel fibers (for example, the sartorius muscle), the geometric and physiological cross-sectional areas are equal. In muscles with oblique fibers (intercostal) the physiological cross-sectional area is larger than the geometric area and this helps to increase muscle strength. The physiological cross-section and strength of muscles with a feathery arrangement of muscle fibers, which is observed in most muscles of the body, increase even more.
In order to be able to compare the strength of muscle fibers in muscles with different histological structures, the concept of absolute muscle strength is used.
Absolute muscle strength- the maximum force developed by the muscle, calculated per 1 cm 2 of physiological cross-section. The absolute strength of the biceps is 11.9 kg/cm2, the triceps brachii muscle is 16.8, the gastrocnemius muscle is 5.9, and the smooth muscle strength is 1 kg/cm2.
where A ms is muscle strength (kg/cm2); P is the maximum load that the muscle can lift (kg); S is the physiological cross-sectional area of the muscle (cm2).
Strength and speed of contraction, muscle fatigue depends on the percentage of different types of motor units included in that muscle. The ratio of different types of motor units in the same muscle varies from person to person.
The following types of motor units are distinguished:
- slow, non-fatiguing (red), they develop a small force of contraction, but can remain in a state of tonic tension for a long time without signs of fatigue;
- fast, easily fatigued (white in color), their fibers develop great contraction force;
- fast, relatively resistant to fatigue, developing a relatively large force of contraction.
In different people, the ratio of the number of slow and fast motor units in the same muscle is determined genetically and can vary significantly. The greater the percentage of slow fibers in a person’s muscles, the more adapted it is to long-term, but low-power work. Individuals with a high content of fast, strong motor units in their muscles are able to develop greater strength, but are prone to fatigue quickly. However, we must keep in mind that fatigue depends on many other factors.
Muscle strength increases with moderate stretching. One explanation for this property of muscle is that when the sarcomere is stretched moderately (up to 2.2 μm), the likelihood of more connections between actin and myosin increases.
Rice. Relationship between contractile force and sarcomere length
Rice. The relationship between muscle strength and its length
Muscle strength depends on the frequency of nerve impulses, sent to the muscle, synchronizing the contraction of a large number of motor units, preferentially involving one or another type of motor units in the contraction.
The strength of contractions increases:
- when more motor units are involved in the contraction process;
- when synchronizing the contraction of motor units;
- when more white motor units are involved in the contraction process.
If it is necessary to develop a small force, slow, non-fatiguing motor units are activated first, then fast, fatigue-resistant ones. If it is necessary to develop a force of more than 20-25% of the maximum, then fast, easily fatigued motor units are involved in the contraction.
At a voltage of up to 75% of the maximum possible, almost all motor units are activated and a further increase in strength occurs due to an increase in the frequency of impulses sent to the muscle fibers.
With weak contractions, the frequency of sending nerve impulses along the axons of motor neurons is 5-10 impulses/s, and with a strong contraction force it can reach up to 50 impulses/s.
In childhood, strength increases mainly due to an increase in the thickness of muscle fibers, which is associated with an increase in the number of myofibrils in them. The increase in the number of fibers is insignificant.
When training muscles in adults, an increase in their strength is associated with an increase in myofibrils, and an increase in their endurance is due to an increase in the number of mitochondria and the production of ATP due to aerobic processes.
There is a relationship between the strength and speed of muscle contraction. The greater the length of a muscle, the greater the speed of muscle contraction (due to the summation of the contractile effects of sarcomeres). It decreases with increasing load. A heavy load can only be lifted by moving slowly. The maximum contraction speed achieved during human muscle contraction is about 8 m/s.
Muscle power is equal to the product of muscle force and the rate of shortening. Maximum power is achieved at an average speed of muscle shortening. For the arm muscles, maximum power (200 W) is achieved at a contraction speed of 2.5 m/s.
The force of contraction and muscle power decrease as fatigue develops.
Human muscular strength is the ability to overcome external resistance or counteract it through muscular effort.
There are about 600 muscles in the human body. Muscles make up 42% of body weight in men; for women - 35%; in old age - 30%; among athletes - 45-52%. More than 50% of the weight of all muscles is located on the lower extremities, 25-30% - on the upper extremities; 20-25% - in the area of the torso and head.
Muscle strength is determined using dynamometers and the maximum weight of the barbell lifted (gravity). For example, the average hand muscle strength measured using a dynamometer is 30-35 kg for women and 40-45 kg for men. For athletes, this figure is 1.5-2.0 times higher.
There are mainly 2 types of human muscle strength:
- · absolute
- · relative
Human muscles are characterized by 2 operating modes:
- dynamic
- · static
In the dynamic mode, in turn, there is a yielding mode, when the length of the muscle increases during muscle tension, and an overcoming mode, when the muscle shortens during work.
Development of human muscle strength
Strength as a physical quality of a person
The physical quality of a person “strength” can be defined as his the ability to overcome or counteract external resistance through muscular effort. One of the most significant aspects that determine muscle strength is the mode of muscle operation. In human physiology, there are two forms of muscle contraction - dynamic and static.
The dynamic form manifests itself in two types of work: 1) if the external load is less than the tension developed by the muscle, then it shortens, performing overcoming work; 2) if the external load is greater than the tension of the muscle, then the muscle under its action is stretched, lengthened and thus produces inferior work.
If the external load is equal to the tension developed by the muscle, and its length does not change, then such muscle work is called isometric. This is a static form of contraction. To measure muscle strength, two concepts have been introduced: absolute strength and relative strength. Absolute strength is all the force exerted by a person in any exercise without taking into account the weight of the muscles or the entire body. For example: the greatest weight of the barbell with which an athlete managed to get up from a squat serves as an indicator of the absolute strength of the leg muscles. You can measure the strength of the muscles - flexors or extensors of the elbow, knee joints, the strength of the extensor muscles of the torso. Relative strength is the strength a person exhibits in any exercise per 1 kg of body weight. Relative strength increases if absolute strength increases without a noticeable increase in the exerciser’s body weight.
The amount of external resistance or load determines the speed of muscle contraction. With very small loads the muscle contracts quickly, and with very large loads it contracts slowly. It has been established that the ability to demonstrate strength in movements of different speeds and durations is little interconnected. There are four types of sports movements in which the strength qualities of an athlete are manifested:
- a) movements that require maximum or close to them efforts are called actual power movements;
- b) movement where it is necessary to exert significant force in a short period of time is called speed-strength;
- c) movements that are performed with extreme speed with very little external resistance are called high-speed;
- d) static and cyclic exercises of a strength and speed-strength nature, performed for a long time, require the manifestation of strength endurance;
Morphological basis of muscle strength is the content of contractile proteins in the muscle fiber, the thickness of the muscle fibers. The manifestation of muscle strength also depends on the type of muscle fibers - fast and slow. If there are more fast-twitch fibers in the muscles, a person is able to develop maximum power in fast speed-strength movements and perform explosive work. The predominance of slow motor units makes it possible to maintain muscle tension for a long time. The strength endurance of such people is higher than that of people of the explosive type.
Biochemical basis of muscle strength is the efficiency of energy metabolism and plastic function of the protein, improvement of the contractile actomyosin complex, the activity of enzymes that accelerate ATP resynthesis, and hormonal regulation. Maximum muscle strength during systematic exercise increases due to an increase in the absolute (anatomical) diameter of the muscles, as well as due to the physiological reserves of mobilization of neuromuscular (motor) units involved in work.
Muscle strength depends on many factors. All other things being equal, it is proportional to the cross-section of the muscles (Weber's principle). Its maximum possible contraction, shortening, other things being equal, is proportional to the length of the muscle fibers (Bernoulli's principle).
Structure of human strength abilities
In the pedagogical characterization of a person’s strength abilities, the following varieties are distinguished.
- 1. Maximum isometric (static) strength- an indicator of the strength exhibited when holding maximum weights or resistance with maximum muscle tension for a certain time.
- 2. Slow dynamic (press) strength, manifested, for example, during the movement of objects of large mass, when speed is practically unimportant, and the applied forces reach maximum values.
- 3. Speed dynamic force characterized by a person’s ability to move large (submaximal) loads with an acceleration below maximum in a limited time.
- 4. "Explosive" force- the ability to overcome resistance with maximum muscle tension in the shortest possible time.
- 5. Shock absorption force characterized by the development of effort in a short time in a inferior mode of muscle work, for example, when landing on a support in various types of jumps, or when overcoming obstacles in hand-to-hand combat, etc.
- 6. Strength endurance determined by the ability to maintain the necessary power characteristics of movements for a long time. Among the types of endurance for power work, endurance for dynamic work and static endurance are distinguished. Endurance to dynamic work is determined by the ability to maintain performance when performing professional activities associated with lifting and moving heavy objects, with long-term overcoming of external resistance. Static endurance is the ability to maintain static efforts and maintain a sedentary body position or stay in a room with limited space for a long time.
- 7. Power Agility- the ability to switch from one mode of muscle work to another if necessary, the maximum or submaximal level of manifestation of each strength quality. It manifests itself where there is a shifting mode of muscle work and unforeseen situations of activity (wrestling, rugby, etc.). To develop this ability, which depends on coordination abilities, a special focus of training is needed.
The focus of an exercise on a particular strength ability is determined by the components of the load and depends on: 1) the type and nature of the exercise; 2) the magnitude of the burden or resistance; 3) the number of repetitions of the exercise or the time of isometric muscle tension; 4) speed of movement; 5) the pace of the exercise.
Modes of muscle work
It is important to take into account the noted modes of muscle work, because they have different effectiveness in training. In special studies, attempts were made to determine the effectiveness of inferior, overcoming, statistical and combined modes of muscle work in strength training. It was found that the overcoming mode is more effective than the inferior and static mode, but the most effective is the combined one.
It is also known that previous static muscle tension has a positive effect on subsequent dynamic work, sometimes increasing its effectiveness by 20%. Therefore, static power elements should be planned before dynamic ones.
Methods and means of developing strength
In practice, the following methods of strength training are common:
- maximum effort method
- repeated effort method
- · dynamic force method
- · method of static forces
- electrical stimulation method
- · method of biomechanical stimulation
When comparing dynamic and statistical methods of strength development, it is necessary to note the following
When the muscles work dynamically, there is sufficient blood supply. The muscle functions as a pump - when relaxed, it fills with blood and receives oxygen and nutrients.
During static effort, the muscle is constantly tense and continuously presses on the blood vessels. As a result, it does not receive oxygen and nutrients. This limits the duration of muscle work.
Therefore, the problem of physical and functional development of arm muscles is relevant.
Determination of muscle strength using dynamometry
One of the indicators of the physical development of the body is muscle strength.
An assessment of a person's strength qualities is determined by the method of hand dynamometry, which allows one to determine maximum muscle strength, an indicator of strength, the level of muscle performance and an indicator of its decline.
When measuring the position of the joints, the parameters of the bone levers that transmit muscle force also change. Finally, after changing the relative position of body parts, fibers of other muscles are additionally included in the act of contraction.
Muscle strength refers to the maximum manifestation of voluntary effort that a muscle group can develop under certain conditions. These conditions are largely determined by the interest of the person being examined or the ability to perform maximum effort. Usually a specific group of muscles contracts at the same time, so it is difficult to accurately determine the work of each muscle in the total manifestation of force. In addition, bone levers are involved in muscle action.
Measuring isometric strength does not require much time and does not tire the subject. Here the strength is expressed in one cyclic maximum contraction. However, several factors can affect the measurement result. Thus, the isometric tension developed by each muscle fiber depends on its relative length and the duration of stimulation. When measuring the position of the joints, the parameters of the bone levers that transmit muscle force also change. Finally, after changing the relative position of body parts, fibers of other muscles are additionally included in the act of contraction.
Given these circumstances, when measuring isometric strength, it is necessary to strictly observe certain body positions and the angle of the corresponding joints. Failure to comply with this rule can lead to significant errors. The strength of identical muscle groups varies from person to person.
First, isometric strength is proportional to the cross-sectional area of the muscle. If we assume that the geometric shape of muscles is the same in people of different heights, then strength is measured in proportion to the square of linear dementia (height). Therefore, a 20% increase in height results in a 44% increase in strength. This gives certain advantages to tall people when moving heavy objects with their hands, throwing sports equipment, etc. However, when overcoming their own body weight (for example, when doing pull-ups on a bar, etc.), they have no advantage, since body weight increases in proportion to the cube of height.
Secondly, isometric strength varies by gender and age. Sex differences are little pronounced before puberty. However, strength indicators in adult women are 30-35% lower compared to men. This is partly due to differences in height. But after appropriate correction, strength indicators in women on average are only 80% of muscle strength indicators in men. Adult men reach maximum isometric strength around the age of 30, and then strength decreases.
