Age anatomy of muscles
Last reviewed: 23.04.2024
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In the newborn skeletal muscles are relatively well developed, amounting to 20-22% of the total body weight. In children 1-2 years of age, the muscle mass decreases to 16.6%. At the age of 6 years, due to the high motor activity of the child, the mass of skeletal muscles reaches 21.7% and continues to increase. In women, the muscle mass is 33%, in men - 36% of body weight.
In the newborn, the muscle fibers in the bundles lie loose, the thickness of the beams is small - from 4 to 22 μm. In the future, muscle growth occurs unevenly depending on their functional activity. In the first years of the child's life, the muscles of the upper and lower limbs quickly grow. In the period from 2 to 4 years, long muscles of the back and a large gluteus muscle are growing strongly. Muscles that provide a vertical position of the body, intensively grow after 7 years, especially in adolescents 12-16 years. At the age of 18-20 years old the diameter of muscle fibers reaches 20-90 microns. In people 60-70 years of age, the muscles partially atrophy, their strength noticeably decreases.
Fascia in the newborn is weakly expressed, thin, loose, from the muscles are easily separated. Formation of the fascia begins with the first months of the child's life, which is interrelated with the functional activity of the muscles.
Muscles of the head, including mimic, in the newborn are thin, weak. The frontal and occipital abdomen of the cervical-frontal muscles are relatively well expressed, although the tendon helmet is weakly and loosely connected to the periosteum of the bones of the skull roof, which favors the formation of hematomas during birth trauma. Weak muscles are weak in the newborn. During the eruption of the milk teeth (especially the molars) they become thicker and stronger. During this period, there are relatively large accumulations of adipose tissue between the superficial and deep leaves of the temporal fascia above the zygomatic arch, between the temporal fascia and the temporal muscle, between this muscle and the periosteum. Outside the buccal muscle, the fatty body of the cheek is formed, which gives the person a rounded outline characteristic of the newborn and children of the first years of life.
The muscles of the neck of the newborn are thin, differentiate gradually. The final development they reach to 20-25 years. In newborns and children up to 2-3 years of age, according to the higher position of the neck borders, the triangles of the neck are slightly higher than in the adult. Characteristic for adults, the position of the triangles of the neck takes after 15 years.
The plates of the cervical fascia in the newborn are very thin, loose connective tissue in the interfascial spaces is small. The amount of it increases noticeably only to 6-7 years. From 20 to 40 years, the amount of loose connective tissue in interfascial spaces varies little, and after 60-70 years decreases.
From the muscles of the breast the age-specific features of the diaphragm are most pronounced. At the newborn and children under 5 years old it is located high, which is connected with the horizontal position of the ribs.
The dome of the diaphragm in the newborn is more convex, the tendon center occupies a relatively small area. As the lungs expand in the process of breathing, the convexity of the diaphragm decreases. In elderly people, the diaphragm is flattened. After 60-70 years in the muscular part of the diaphragm, signs of atrophy are revealed against the background of an increase in the size of the tendon center.
The newborn has poorly developed abdominal muscles. The weak development of muscles, aponeuroses and fascia promotes the formation of a convex abdominal wall in children under 3-5 years of age. Muscles and aponeuroses are thin. The muscular part of the outer oblique abdominal muscle is relatively shorter. In the inner oblique abdominal muscles, the lower fascicles are better developed than the upper ones, in boys a part of the bundles joins the seminal cord. The tendon ligaments of the rectus abdominis are located high and in early childhood are not always symmetrical on both sides. The superficial inguinal ring forms a funnel-shaped protrusion, more pronounced in girls. The medial leg of the aponeurosis of the outer oblique abdominal muscle is developed better than the lateral one, which is strengthened by bundles of a curved (recurrent) ligament. Mezhdozhkovye fibers in newborns are absent. They appear only in the second year of life. The lacunar ligament is well expressed. The transverse fascia is thin, the preperitoneal accumulation of adipose tissue is almost nonexistent. The umbilical ring of the newborn is not yet formed, especially in the upper part, in connection with which the formation of umbilical hernias is possible. In contrast to adults in newborns and children of the first years of life, the muscles of the forearm and lower leg are much longer than the tendon part of the muscular abdomen. On the back of the lower leg, the deep muscles represent a single muscular layer. The development of the muscles of the upper limb is faster than the development of the muscles of the lower limb. The mass of the muscles of the upper limb relative to the mass of the entire musculature in the newborn is 27% (in the adult 28%), and the lower limb - 38% (in the adult 54%).
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