Everyday human activity provides for two types of activity: psychological and physical. Psychological activity includes intellectual work, communication, emotions; physical – the performance of mechanical work, movement. Psychological activity requires the activation of a limited number of body systems, mainly the higher levels of the nervous system. During physical activity, all systems of the body are activated, without exception, which, working together, create the conditions for performing a certain physical action. Arising much later in terms of evolution, mental activity controls the physical. The influence of physical activity on the activity of the human psyche is very limited.

During sports (if the physical load does not exceed the physiologically permissible), a number of adaptive processes occur in the human body that help it adapt to the conditions of regular exercise. If the degree of physical activity far exceeds the physical potential of a person, various health disorders can occur: overtraining, chronic fatigue, and various diseases. Lack of movement (hypodynamia) is also dangerous. Physical inactivity is considered one of the main factors (along with obesity, malnutrition and bad habits) of the occurrence of diseases of the cardiovascular system and diabetes.

Below we consider the main physiological aspects of physical activity and the changes that occur in the body with regular sports.

Changes in the musculoskeletal system
The main functional load in sports falls on the musculoskeletal system, that is, on the system of muscles, bones, joints, ligaments and tendons.

Muscles are the only motor element of the human body, and therefore any movement or work is the result of their contraction. We note right away that muscle contraction is the result of the coordinated work of the nerve centers, nerves and muscles, as such. Voluntary work of denervated muscles (muscles without nerves) is impossible. Any movement, regardless of its complexity and purpose, originates in the central nervous system (brain and spinal cord) in the form of activity of certain groups of neurons. The nerve impulse from these cells along the nerve trunks transmitted to the muscles and causes them to contract. An interesting fact is that during sports, it is not the muscles that “get tired” first, but the nerve cells that regulate their activity; this mechanism prevents muscle wasting. During training, therefore, not only muscles are trained, but also the nerve centers responsible for movement. One of the types of doping are psychostimulants that increase the activity of the nervous system, and thereby increase the physical (muscular) characteristics of the athlete.

Muscle training consists mainly in thickening the muscle fibers. Muscle mass is built up by increasing the amount of thickness of muscle fibers. The thickening of muscle fibers is accompanied by the synthesis of contractile elements – myofibrils. Myofibrils are like long protein filaments that can contract to absorb energy. The work of myofibrils depends entirely on the energy state of the cell, that is, on the amount of nutrients, oxygen, vitamins and minerals. Regular training leads to the growth of blood vessels in the muscles (this increases the supply of oxygen and nutrients to the muscles), as well as to an increase in the concentration of various enzymes in muscle cells, with the help of which energy is produced. As it became clear, not only proteins are necessary for muscle development, but also vitamins and minerals that contribute to the release of energy and muscle contraction (muscle contraction, for example, is impossible without calcium).

Bones in the human body play the role of support, protection and leverage. Muscles are attached to the bones by means of tendons or directly adhere to the bones, intertwining with the fibers of the periosteum (or rather, the shell of the bone). The closer the place of attachment of the muscle to the point of rotation of the bone (joint), the faster the movements at the other end of the lever will be performed and the less the force of movement will be. An example of such a mechanism is the shoulder muscle (biceps, triceps), which are attached immediately after the elbow joint (the place of their attachment can be felt if these muscles are slightly strained). On the other hand, the deltoid muscle attaches in the middle third of the shoulder and develops more strength.

Under the influence of training, the bones undergo significant restructuring. The process of bone renewal occurs constantly, while some parts of the bone are resorbed, while others are recovering. In athletes, the bones are rebuilt in accordance with the load. In this case, the lines of loads coincide with the lines of bone stiffness (concentration of bone substance). Therefore, regular exercise strengthens the bones.

Under the influence of physical activity, the ligaments and tendons thicken and become stronger. In trained people, the strength of the ligaments reaches such a value that, during injuries, a piece of bone with a ligament attached to it comes off, and the ligament itself remains intact.

Regular moderate exercise has a positive effect on the joints. The range of motion in the joint increases, the cartilage tissue thickens. Excessive physical activity can adversely affect the condition of the joints. Professional athletes often develop a disease such as osteoarthritis or osteochondrosis, in which the destruction of articular cartilage occurs.

For the normal development of bones, ligaments and joints during sports, it is necessary to provide the body with the necessary minerals and vitamins. Vitamin C stimulates the development of connective tissue, ligaments and tendons, and calcium and phosphorus give bone hardness.

Changes in the cardiovascular system
The cardiovascular system is designed to provide blood circulation and supply tissues with oxygen and nutrients. Regular exercise has a stimulating effect on the heart. At the same time, the muscles of the heart thicken a little and become more resilient. In trained people, the rhythm of the heart contraction (pulse) at rest slows down. This is due to the fact that a trained heart pumps more blood in one contraction than an untrained one.

The walls of the blood vessels of athletes become more elastic and resilient. The beneficial effect of sports on the veins of the legs is especially pronounced. When the muscles contract, the walls of the veins are compressed, thereby the blood from the veins is pumped faster to the heart. Moderate exercise helps prevent varicose veins and vein thrombosis in the lower extremities. The number of red blood cells in the blood of athletes increases, which improves the supply of oxygen to tissues.

Respiratory system changes
The lungs of trained people are significantly different from those of non-athletes. Firstly, in the lungs of an athlete, the bronchi expand and additional alveoli (air sacs) open, thereby increasing the vital capacity of the lungs. Secondly, the lungs of a trained person are much better supplied with blood. Due to this, oxygen saturation of the blood increases, and, consequently, the supply of oxygen to all organs and tissues of the body.

Thanks to improved ventilation of the lungs, people involved in sports are much less likely to get sick with bronchitis and pneumonia.

Metabolic changes
Moderate physical activity has a beneficial effect on the metabolic processes in the body.

Protein metabolism in athletes is characterized by a positive nitrogen balance, that is, the amount of nitrogen consumed (mainly nitrogen is found in proteins) exceeds the amount of nitrogen excreted. Negative nitrogen balance is observed during illness, weight loss, metabolic disorders. In people involved in sports, proteins are used mainly for the development of muscles and bones. While in untrained people – for energy (in this case, a number of substances harmful to the body are released).

The metabolism of fats in athletes is accelerated. Much more fat is used during physical activity, hence less fat is stored under the skin. Regular exercise reduces the amount of so-called atherogenic lipids, which lead to the development of a serious disease of the blood vessels – atherosclerosis.

The metabolism of carbohydrates during sports is accelerated. At the same time, carbohydrates (glucose, fructose) are used for energy, and are not stored in the form of fats. Moderate muscle activity restores tissue sensitivity to glucose and prevents the development of type 2 diabetes. To perform fast power movements (lifting weights), carbohydrates are mainly spent, but during prolonged non-strong loads (for example, walking or slow running), fats are consumed.

In general, moderate exercise has a general healing effect on the body. Regular physical activity is an important preventive measure against diseases of the cardiovascular system (hypertension, coronary heart disease, atherosclerosis), metabolic disorders (type 2 diabetes mellitus), diseases of the musculoskeletal apparatus (osteochondrosis, arthrosis).

It should be noted that only moderate physical activity (comparable to a person’s physical abilities) has a beneficial effect on his health. Excessive physical activity is dangerous for the body and can lead to various diseases.

In general, sports are recommended for everyone. You just need to sensibly assess your abilities and choose a sport that will bring pleasure. It can be simple walking or cycling, slow running, swimming, aerobics, fitness. All forms of movement are useful, as long as they correspond to the physical abilities of the organism, and their performance brings pleasure.