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Physiology of labor


Physiology of labor is an integral part of occupational hygiene, which studies the physiological processes in the human body that occur during a particular labor activity. Based on the detected changes, measures are being developed to normalize physiological functions, prevent fatigue and increase efficiency.
Professional activity is characterized by the predominance of either movements or mental work. Proceeding from this, labor is divided into physical and mental, which, however, is conditional, since the nervous system is involved in muscle work, and mental labor is accompanied by a certain physical stress. Currently, in connection with the mechanization of production processes, the number of professions related to mental stress has increased, while physical activity has sharply decreased.
Physical work. Muscular activity is characterized by contraction and relaxation of working muscles, the formation of heat in them, increased metabolism and increased energy expenditure. The more intense the work, the more muscle groups involved in it, the higher the energy expenditure. If an adult engaged in light physical labor spends about 12,540 kJ (3,000 kcal) per day, then with hard work, energy consumption increases to 16,720–20,900 kJ (4,000–5,000 kcal), and sometimes more. At the same time, metabolism increases and blood circulation and respiration increase. In the body, changes occur in the composition of the internal environment, expressed in the development of acidosis, an increase in osmotic pressure and body temperature. In all these changes and in muscle contractions themselves, the central nervous system plays a leading role, which determines the formation of a new dynamic working stereotype that ensures the regulation and coordination of all physiological processes in the body.
In accordance with the latest official documents, labor activity in the field of physical labor is divided into three categories: light physical work - category I; moderate work - II category and heavy physical work - III category.
Light physical work (I category) is divided into
• a (energy consumption is up to 139 W) - work in a sitting position, accompanied by insignificant physical stress (professions in the field of control, instrumentation and mechanical engineering, watchmaking, sewing production, etc.);
• b (energy consumption 140–174 W) - work in a sitting position, standing, or associated with walking and accompanied by some physical stress (professions in the printing industry, supervisors, communication workers, etc.).
Work of moderate severity (category II) is divided into
• a (energy consumption 175-232 W) - work associated with constant walking, moving small (up to 1 kg) objects in a standing or sitting position and requiring a certain physical stress (profession in mechanical assembly shops of machine-building enterprises, spinning and weaving, etc.);
• b (energy consumption 233-290 W) - work related to walking, moving heavy loads (up to 10 kg) and accompanied by moderate physical stress (a number of professions in mechanized workshops of machine-building and metallurgical enterprises - foundry, welding, rolling, forging, etc.) .
Heavy physical work (energy consumption of more than 290 W, category III) - work associated with the constant movement and carrying of heavy loads (more than 10 kg) and requiring great physical effort (manual work in forge shops, foundries, auxiliary construction workers, etc.).
The process of muscle contraction goes through two phases - anaerobic, without oxygen consumption, and aerobic, with its consumption. Under the influence of pulses from the cerebral cortex, the muscles become excited and contract, which requires energy arising from the breakdown of adenosine triphosphoric acid (ATP) under the influence of actomyosin (muscle proteins of actin and myosin) into adenosine diphosphoric (ADP) and phosphoric acid as a result of which the energy of phosphate bonds of ATP is released. In the course of further transformations, ATP resynthesis occurs, which promotes the breakdown of creatine phosphate into creatine and phosphoric acid. The latter turns into hexose and then into lactic acid, on this the anaerobic phase of muscle contraction ends. In the second, aerobic phase, a small part of lactic acid is oxidized to carbon dioxide and water and excreted from the body, and the rest is restored to glycogen. The chemistry of muscle contraction is influenced by hormonal factors controlled by the central nervous system.
With hard physical work, a violation of the relationship between the oxygen demand and its actual consumption is possible, which leads to oxygen starvation and the accumulation of unoxidized decomposition products in the body. Under such conditions, prolonged and intensive work causes fatigue and reduced performance. The main cause of fatigue is the development of inhibition in the functional motor center of the cerebral cortex. The accumulation of acidic metabolic products in the muscles, metabolic disorders in the heart and brain, and hypoglycemia, which causes a disturbance in the normal course of nervous processes, can be of some importance.
Feeling tired is a physiological phenomenon. If it passes after a normal rest and working capacity on the next day is fully restored, then this does not go beyond the norm. If fatigue persists, we are talking about overwork, which is a pathology.
The fight against premature fatigue and overwork in the workplace is extremely important for the prevention of diseases, injuries and maintaining a normal level of performance. A major role in this regard is played by training. With an increase in the body’s fitness level, physical work is performed with less energy, which is explained by the development of certain motor skills and the ability to involve those muscle groups that are really necessary to perform these labor operations. Over time, automatism is developed in movements, which allows you to perform muscular work with less tension of forces, attention and will. As a result, workers with experience are less tired compared to newcomers, and the recovery period after work is shorter.
A positive favorable role is played by positive emotions resulting from a conscious attitude to work.
The speed of development of fatigue depends on the degree of dynamism of physical labor. Static work, expressed in prolonged muscle tension, causes more rapid fatigue than dynamic, accompanied by alternate contraction and relaxation. This is due to the fact that with static efforts, continuous pulses from the nerve endings in the tendons and muscles to the central nervous system and vice versa lead to more rapid depletion of the energy of the central nervous system, which in turn leads to the development of fatigue. In dynamic work, impulses arise only at the moment of muscle contraction, while relaxation does not exist. With significant static efforts, the onset of fatigue is facilitated by a decrease in the blood supply to tense muscles (A.N. Krestovnikov, M.E. Marshak).
Mental labor is not associated with any significant expenditure of energy, it depends on the fact that the mass of the nervous system makes up only 3% of the total body mass, and the main difference is that in mental labor the nervous energy is intensively consumed. An increase in total metabolism does not exceed 10-15%, although metabolic processes in the brain proceed very intensively. Changes in the blood are also insignificant and inconsistent: there is a slight decrease in the sugar content, an increase in the amount of organic phosphorus, cholesterol, creatine, and a decrease in alkaline reserves. Therefore, according to these indicators and energy expenditures, it is not possible to judge the intensity of mental work; for this, various subtle and complex methods are used to take into account physiological changes in the central nervous system (latent period of the motor reaction, attention span, electroencephalography, etc.).
Mechanization and automation of production, the introduction of control panels, automatic lines, electronic computers have made fundamental changes in the nature of the physiological reactions of workers, significantly increasing the role of neuropsychic and mental activity. Many professions in modern production are essentially becoming professions of mental labor. From dispatchers of airfields, railway stations, operators of control panels for power systems, automatic lines, they are required in a short time to cope with the large flow of information received, quickly respond to it and make the necessary decisions. In the conditions of production and conveyor production, an aggravating factor is the monotony of labor activity, which causes workers to worsen their mood, well-being and is one of the important causes of neuropsychic fatigue.
Mental labor is diverse, some types of it require creative thinking, others only stress of attention, development of speed of reactions to external stimuli. The emotional saturation of intellectual activity often masks fatigue and, along with a sense of satisfaction from work, imperceptibly leads to overwork.
Representatives of modern professions related to mental work are divided into the following 5 groups:
1) operator work - work related to the management of various production mechanisms and technological processes, characterized by great responsibility and high neuro-emotional stress;
2) the work of the administrative apparatus - the work associated with the management of enterprises and institutions, and the work of teachers. This work is associated with the processing of a huge flow of information, often in a time deficit mode, high personal responsibility for decisions made, and high neuro-emotional stresses;
3) the work of representatives of creative professions - scientists, writers, artists, architects, artists, designers, designers - requires a large amount of operational and long-term memory, the ability to concentrate, which leads to high neuro-emotional stress;
4) the work of medical workers - work requiring high personal responsibility in decision-making, often with a lack of time and information, contact with sick people and their relatives. This leads to high neuro-emotional stress, the danger of infection, stressful reactions in conflict situations;
5) work of pupils and students - work requiring stress of all types of memory, concentration of attention, ability to perceive and process a huge flow of information. It is accompanied by stressful reactions during the execution of control tasks, passing tests and examination sessions.
The main means of preventing fatigue and increasing labor productivity in both physical and mental activity are the proper organization of work and rest, a rational work schedule, the right working posture, the design of machines, tools, equipment, and the anatomical and physiological characteristics of the human body, mechanization and automation of production, the creation of favorable sanitary conditions at workplaces, the use of auxiliary recreational activities. The latter include occupational gymnastics, which is an effective form of outdoor activity during work. Its relevance is currently increasing due to a sharply reduced physical load in the conditions of modern mechanized production. The healing effect of gymnastics is expressed not only in relieving fatigue and improving the general state of health, but also in increasing working capacity and labor productivity.
The main form of production gymnastics conducted directly at workplaces is physical breaks in the form of a specific set of physical exercises, compiled in accordance with the characteristics of professional work. Such exercises are selected that can affect mainly the development of certain systems and functions of the body, especially important in this particular case. Physical breaks lasting 5-7 minutes are carried out when the first signs of fatigue appear (S.A. Kosilov, A.A. Minkh, I.V. Muravov, etc.).

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Physiology of labor

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