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0ANATOMICAL AND PHYSIOLOGICAL FEATURES OF THE MUSCULOSKELETAL SYSTEM AND CARDIORESPIRATORY SYSTEM IN YOUNG SCHOOL-AGE CHILDREN
Seydakova G.S.
Medical Institute of Karakalpakstan, Nukus, Uzbekistan https://doi. org/10.5281/zenodo. 13882513
Abstract. The condition of the musculoskeletal system is one of the key indicators of health in children and adolescents. The age of 7-12 years, which coincides with the start of school education, is an important stage of late childhood when growth processes and changes in the morphological and functional structure of all organs and systems continue actively. During this period, the development of all components of the musculoskeletal system is completed. The growth and development of the cardiovascular and respiratory systems are closely linked to the morphological formation of the musculoskeletal system. In young school-age children, the development of the thoracic cavity continues, along with its gradual ossification. The cardiorespiratory system, being one of the key functional systems of the body, plays a crucial role in adapting to various external influences, reflects the course of recovery processes, and is one of the first to respond to excessive physical loads.
Functional postural disorders in schoolchildren are quite common, and despite significant attention to this issue from scientists, doctors, and educators, a definitive solution has not yet been achieved. The identified characteristics of the influence of postural disorders on the growing organism and their widespread prevalence highlight the importance of developing objective quantitative methods for assessing postural status, as well as the need to expand the range of studies on the musculoskeletal system.
Keywords: school-age children, physical development, musculoskeletal system, cardiorespiratory system.
Introduction. The health of children and adolescents is a vital resource for society and represents a pressing issue in modern conditions, requiring in-depth and comprehensive analysis. The condition of the musculoskeletal system is considered one of the key indicators of the health of the younger generation. School age is a period of intense growth and maturation of bone tissue, during which the so-called "peak bone mass" accumulates, which, according to modern understanding, reflects the maximum development of the skeleton.
The growth and development of children occur unevenly: phases of rapid growth are followed by periods of slowdown, and quick changes in functions are replaced by stages of gradual improvement. At each stage of ontogenesis, unique characteristics and properties of individual systems of the body are formed.
Objective of the Study. To provide an overall characterization of the anatomical and physiological features of the musculoskeletal system and the cardiorespiratory system in young school-age children based on data from current scientific research.
The beginning of school education coincides with a key stage of late childhood (ages 712), characterized by active growth and significant morphological and functional changes in all organs and systems [2,34]. During this period, the development of all elements of the
musculoskeletal system continues, particularly its main axis—the spine. The spinal column, which is a complex anatomical and biomechanical structure, consists of 34 vertebrae and possesses high strength, stability, and flexibility. These properties allow it to perform numerous vital functions both at rest and during movement. Some of the most significant functions include providing the body with its main shape and supporting body weight in an upright position [5,7]. Additionally, the spine serves a cushioning and protective role, reducing the negative impact of mechanical loads during walking, running, jumping, and other activities on sensitive tissues, such as the spinal cord and internal organs [1,22].
The formation of the natural curves of the spine, its growth, and the process of ossification occurs gradually [6,13]. The most active growth is observed in the first three years of life, then at ages 7-9, and during puberty. The lumbar region of the spine grows the fastest, followed by the sacral and coccygeal regions. The most pronounced increase in the height of the lower thoracic vertebrae is noted around the age of 10 [3,26]. Even minor disturbances in the metabolism of the cartilage tissue of the spine can negatively affect the growth and differentiation of tissues, which can potentially lead to organic changes and the development of pathological deformities such as scoliosis or lordosis [8].
Children aged 7-10 exhibit significant spinal mobility, which is related to the larger sizes of intervertebral discs and their elasticity. According to some researchers, the growth and development of the spine are completed by around 17-20 years of age [20,31]. Thanks to the mobility between individual vertebrae, the spinal column can change its shape during various movements. Anatomically, movements of the spine can occur around three axes: around the transverse axis (flexion and extension), around the sagittal axis (rotations to the left and right), and also rotations around the longitudinal axis. The greatest flexion and extension are observed in the cervical and lumbar regions, while the least mobility is characteristic of the thoracic region. Lateral movements are most pronounced in the thoracic and lumbar regions, while circular movements are most pronounced in the cervical region. These functional features are determined by the shape, size, and structure of the vertebrae in different regions of the spine [16,29,33].
The spine is capable of withstanding significant static and dynamic loads, which is reflected in its anatomical structure. Thus, the mass of the vertebral bodies increases from the cervical to the lumbar region [7,14]. In young school-age children, a stable structure of the vertebrae is already forming, but it is not yet fully strengthened. The process of ossification of the connective and cartilaginous elements of the vertebrae begins. Independent points of ossification appear on the upper and lower parts of the vertebrae, as well as at the ends of the spinous processes [6,21,30]. At the same time, some areas, such as the scapulae and clavicles, still retain a cartilaginous structure in children [9]. This makes the spine particularly sensitive to deforming influences. During this period, improper postures, excessive physical loads, and undue labor can lead to functional and persistent postural disorders.
As it is known, in the vertical position, the spine does not form a straight line. A normally formed spine creates four physiological curves that help maintain balance and cushion impacts during movement. The main curvatures are located in the sagittal plane: two of them curve forward, forming cervical and lumbar lordoses, while two curve backward, creating thoracic and sacral kyphoses. The prominence of these physiological curves varies at different age periods in both children and adults, indicating the presence of age-related changes [27,38]. A interdependence between different sections of the spinal column has also been established.
According to V.A. Tyichinin [11,25], an increase in one of the curvatures may lead to changes in the others.
The curves of the spine in the sagittal plane are formed during the child's growth and the emergence of new functional capabilities. Cervical lordosis begins to develop at two months of age when the baby attempts to hold their head up. The thoracic curve forms at 6-7 months when the infant starts sitting, while the lumbar curve appears when they learn to stand [10,19]. It is believed that cervical and thoracic curves are fully formed by age 7, while the lumbar curve develops later [26,34]. Some researchers argue that the final formation of the physiological curves of the spine occurs by 15-16 years of age [4,15], while others claim that this process is completed only by 20-25 years [7,13].
The maintenance of proper body statics, meaning normal natural curves of the spine, is ensured not only by the anatomical features of the skeleton but also by the normal functioning of the joint-ligamentous and neuromuscular apparatus. Muscles play an important role in maintaining the vertical position of the spine and executing movements [21,29]. In young school-age children, there is uneven development of muscle mass: first, the large muscles of the trunk, shoulder girdle, and lower extremities develop, followed by the smaller muscles. In children aged 8-10 years, an increase in the thickness of muscle fibers and the number of myofibrils is observed; however, their strength is still insufficient, and the tone of the flexors predominates over that of the extensors. This leads to difficulties for children in maintaining an upright back position during prolonged sitting [8,12]. Thus, through the ligamentous apparatus and numerous muscles of the back, anterior abdominal wall, shoulder girdle, and pelvic girdle, individual vertebrae are united into a single organ of support and movement—the spinal column. It supports the weight of the entire body in an upright position, provides for various movements, shapes the torso, and influences postural condition [3,23].
Children's spine, compared to that of adolescents and adults, has a high degree of mobility and physiological instability. This is primarily due to the still not fully formed physiological curves, the constantly changing muscle tone during growth, and the lack of physical training in most children. Consequently, the mobility, stability, and endurance of a healthy spine in children are interdependent qualities that can be improved through a rational physical education system [1,28].
Effective motor function in humans depends not only on the condition of the spine but also on the proper formation and development of the arch of the foot [2,36]. The anatomical and physiological features of children are such that the arch of the foot is poorly developed in early childhood and forms later when the child begins to walk. The main changes in the arch of the foot occur during school years and are particularly active between the ages of 6 and 10 [4]. The formation of the arches is usually completed by ages 11-12, while the complete development of the foot occurs by ages 16-18 [18]. The children's foot, compared to that of an adult, is relatively short and narrower in the heel area. There is noted heterochrony in the development of individual structural elements (length, width, height of the foot) and the entire foot as a whole in relation to other parts of the skeleton [9,24]. The most significant changes in foot length are observed in girls after age 7 and in boys after age 9. Although by age 7, the average foot parameters in boys exceed those of girls [17,21].
The foot, serving as an organ of support and movement, is subject to significant loads (gravitational force and ground reaction force); therefore, one of its key functional qualities is its
resistance to these loads. This stability is ensured by a certain tone in the muscular and ligamentous apparatus. Normally, the functional endurance of the foot is characterized by the absence of fatigue and pain, as well as the absence of progressive lowering of the arch under normal loads throughout the day [35].
The foot has two arches: the longitudinal and the transverse. Both arches are reinforced by muscles and ligaments. When the muscles relax, the body's load falls on the ligaments, compressing the arches of the foot and causing the foot to become flat. Typically, the arch of the foot is classified as normal, flattened, or flat. Some researchers also identify an intermediate state known as "pre-flattened," which lies between normal and flattened [26,37]. In some children, the process of forming the arch of the foot may halt at one of the stages, which is one of the reasons for the high percentage of schoolchildren suffering from flat feet [8,36].
The musculoskeletal system, along with the functional capabilities of the cardiovascular, respiratory, nervous, and other body systems, plays an important role in the adaptation of the body to various environmental conditions.
The cardiopulmonary system, being one of the most important functional systems of the body, ensures its adaptation to various influences, reflects the dynamics of recovery processes, and is the first to respond to inadequate physical loads [1].
The size and mass of the heart increase due to the thickening of the heart muscle walls and the enlargement of the organ's volume, which occurs both as a result of natural growth and through regular physical exercise. These changes contribute to an increase in the power and performance of the heart muscle [17].
The process of morphological formation of the musculoskeletal system is closely related to the development of the respiratory system. In early school age, the development of the thoracic cage and its gradual ossification continue [4,28]. With age, children exhibit an increase in vital lung capacity (VLC), respiratory volumes, and reserve lung capacity. This is explained by age-related changes in the length and position of the ribs in 7-8-year-olds, which leads to a lowering of the front part of the thoracic cage. As a result, the ability to change its volume during breathing significantly increases, affecting the nature of breathing. Previously, it was predominantly "abdominal" or "thoraco-abdominal," but from this age onward, the intercostal muscles begin to play a leading role in the organization of inhalation and exhalation [30,35].
In children aged 8-10, sexual differences in breathing patterns become apparent: boys predominantly develop a diaphragmatic type of breathing, while girls develop a thoracic type. The increase in the longitudinal dimensions of the thoracic cage promotes the development of the organs within the thoracic cavity, and the morphological changes create favorable conditions for the functioning of the lungs [24,32].
The human respiratory system demonstrates both quantitative and qualitative changes at different age periods, which are associated with the continuous development of morphological structures and functional restructuring of external respiration [3,31]. In early school age, an increase in lung volume, differentiation of lung tissue, and active expansion of the bronchial tree are observed. The anatomical increase in the number and volume of alveoli, as well as their diameter, leads to a constant increase in vital lung capacity (VLC) and its fractions [34].
As the body grows and develops, not only do the VLC and its components change, but also the ratio between them. However, data on these indicators vary. Some researchers [19] believe that both volumes are approximately equal, constituting about 42-45% of the VLC. At the same time,
other authors [28] argue that the reserve inspiratory volume (RIV) exceeds the reserve expiratory volume (REV). I.I. Shmykov and Yu.M. Perelman [17,23] note that the increase in the REV occurs earlier, completing by 12-13 years in girls and by 10-11 years in boys.
Numerous studies show that age-related changes in static lung volumes depend on age, sex, chest circumference, and level of physical fitness [7,19].
An increase in volumetric breathing rates shows a certain periodicity associated with the development of respiratory musculature and changes in lung and chest elasticity. According to research data [5,15], volumetric rates significantly increase during the age periods from 5 to 7 and from 12 to 14 years. S.O. Soook [18] asserts that vital lung capacity (VLC) experiences the greatest increase between the ages of 3 and 5 years (increasing from 910 to 1280 ml) and from 10 to 12 years (from 2040 to 2800 ml). A noticeable increase in maximum ventilation of the lungs (MVL) is observed in girls at age 13 and in boys at age 12 [33].
A.N. Barkan and N.G. Mizinova [38] note not only age-related changes but also a constant increase in volumetric and speed indicators throughout the academic year. Gender differences in key indicators of external respiration, according to research [26,30], begin to manifest at ages 7-8, usually being higher in boys. With age, the differences in lung volumes decrease, while forced expiratory volume (FEV1), expiratory speed indicators, and MVL increase.
One of the features of children in early school age is the frequent and shallow nature of breathing [34]. It is believed that the respiratory rate (RR) decreases with age, leading to more complete breathing. However, some authors do not note a significant impact of age and gender on these indicators [26]. Frequent and shallow breathing is explained by the low efficiency of lung ventilation and insufficient diffusive capacity of the lungs in children and adolescents: in younger school-aged children, 1 liter of oxygen is extracted from 29-30 liters of air.
The efficiency of external respiration function and the blood transport function in children is relatively low, meaning that their oxygen regimes are less intense than in adults. This indicates the presence of high reserves for improving the economy of breathing with age and increasing fitness levels [16].
Thus, the uneven growth and maturation of individual lung structures, along with the imperfection of neurohumoral regulation of breathing, lead to functional instability and determine the high sensitivity of the respiratory system in younger school-aged children to negative factors [18,21].
One of such factors is the educational process, during which children spend a large part of their time in a sitting position, accompanied by postural-static tension. This position has both advantages and disadvantages. From the perspective of energy expenditure, the sitting position is more advantageous compared to standing, as it implies a larger base of support and a lower center of gravity, creating more favorable conditions for maintaining body balance [2,17].
However, sitting leads to the flattening of lumbar lordosis and the exacerbation of thoracic kyphosis, which hinders the normal functioning of the cardiovascular and respiratory systems, as well as several internal organs [1,26]. The sitting posture significantly affects respiratory function. Even a slight forward lean of the torso impedes diaphragmatic and ribcage breathing, while the chest experiences compression [10]. Vital lung capacity decreases, especially in a forward-leaning sitting position, which is the primary working posture for most children.
Lung ventilation also significantly impacts the functioning of the muscles of the musculoskeletal system. Exhalation generally has a relaxing effect on skeletal muscles, while
inhalation activates their work. Maximum extension of the thoracic region is only possible with complete exhalation, whereas for the lumbar and cervical regions, this occurs with complete inhalation, and vice versa [31]. According to this author, the diaphragm and abdominal cavity, with well-developed abdominal muscles, can provide support for the spine from the front, but this support is lost with improper breathing patterns. This also leads to overloading of the cervical region, as accessory respiratory muscles are engaged, disrupting the symmetry of ribcage movements.
It should be noted that prolonged sitting leads to a deterioration of several hemodynamic indicators, although to a lesser extent than standing. Studies show that prolonged sitting can cause blood stagnation in the joints and muscles [7,11]. Moreover, working in this position can result in pain in the cervical and lumbar regions, as well as in the shoulder muscles [6,23]. According to research, the pressure on the intervertebral discs while sitting is 35% higher than that of a person in a standing position [12,27]. In situations where the back is rounded, the adverse effects become even more pronounced [8,29].
Conclusion: In summary, the majority of changes in the cardiovascular and respiratory systems in children with postural disorders are functional in nature. Functional postural disorders in school-aged children are extremely common, indicating that 27-30% of children already arrive at school with spinal issues. This also highlights the emergence and development of this pathology throughout the entire school period. It becomes evident that despite significant attention to the problem of posture from scientists, doctors, and educators, it is currently not feasible to consider this issue resolved.
The identified features of postural disorders in growing organisms and their prevalence necessitate the development of objective quantitative methods for assessing postural conditions, as well as the expansion of research into the musculoskeletal system.
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