Human Anatomy (with the fundamentals of dynamic and sports morphology) - Ivanitsky M. F. 2008

Morphological support for mass physical culture and sports (sports morphology)
Adaptation of movement execution systems to physical loads

The Skeletal System

Functional Characteristics of bone growth. The fundamental principle regarding the functional determinism of bone growth was formulated back in the last century by P.F. Lesgaft, who wrote that a bone increases in size all the more significantly the greater The activity of the Muscles surrounding it. Based on the data accumulated over the past century, this principle can now be refined and expanded.

1. Bone growth is stimulated by pulsating mechanical loads that alternate in intensity and action. This is characteristic of loads associated with Muscle contraction (arising when a muscle contracts and ceasing when it relaxes). Static loads produce a similar effect when their intensity varies.

2. The mechanisms of longitudinal and transverse bone growth differ. The Cells that form new Bone tissue—osteoblasts—are located at the boundary of two media: bone and Cartilage for longitudinal growth, and bone and Connective Tissue for transverse growth.

The relative displacement of these media apparently triggers the impulse for osteogenesis. How does this happen? Muscle contractions cause tension in the periosteum, into which tendons are woven, shifting it relative to the bone tissue. Mechanical loads transmitted to the bone create stress within it, leading to the relative Displacement of the two contacting media (bone and cartilage, bone and connective tissue). In this way, perichondral (via cartilage) and periosteal (via the periosteum) Bone Formation is activated.

3. Mechanical loads affect the longitudinal and transverse dimensions of bones to varying degrees. The former are genetically more deterministic than the latter. Therefore, mechanical loads have a greater impact on bone growth in thickness and width than in length.

4. As mechanical loading increases up to a certain level, bone formation is enhanced; if this level is exceeded, osteogenic activity decreases (Fig. 186).

5. The optimal level of mechanical load depends on individual CHARACTERISTICS OF THE reaction norm.

Such are the basic functional regularities of bone growth. Based on them, it is easy to understand the mechanisms of skeletal changes in athletes caused by mechanical loads. These changes stem from two main sources: first, muscle contractions cause the periosteum to shift relative to the bone; second, when a limb collides with an obstacle (such as pushing off the ground during a jump or a boxer hitting a heavy bag, etc.), in accordance with Newton's third law of action and reaction, stresses arise in the bone that propagate from the point of impact toward the trunk.

Functional features of Bone Structure. Changes in bone tissue under mechanical loading strengthen the Skeleton as a mechanical structure and increase its durability. The primary role here is played by subperiosteal bone growth mechanisms. Their activation and the resulting thickening of the bone make it more resistant to bending and torsion. It is a known principle of mechanics that a large-diameter hollow Column Supports a greater load than a solid-core support of a small diameter without a cavity. A similar adaptation to static loads is observed in the Appendicular Skeleton of strength-sport athletes. The formation of tuberosities at muscle attachment sites improves their mechanical leverage (increasing the lever arm). The enlargement of epiphyses increases the contact area of bones within joints and facilitates the Shock absorption of mechanical impacts.

The adaptation of bone to mechanical loads is also manifested in its internal architecture. The strengthening of the diaphysis is facilitated by the thickening of its wall through the formation of new compact bone. This can occur from the inside—along the marrow cavity—or from the outside—via the periosteum. The second option is more biomechanically sound, as bone strength increases through an expanded outer diameter and a thickened compact layer while the marrow cavity remains unchanged (or even enlarges). The first option may occur as a compensatory mechanism under conditions where periosteal bone formation is delayed. In areas subject to particularly heavy mechanical loads, the compact substance acquires a layered structure. The strengthening of cancellous bone is manifested by the thickening of its trabeculae and its transformation from fine- or medium-meshed into coarse-meshed.

Human bone tissue contains A large number of microscopic bone tubes—osteons. Adapting to prevailing mechanical conditions, the bone undergoes remodeling, during which newly formed osteons alter their diameter and orientation.

Characteristic skeletal changes occur As a result of athletic training, with earlier onset of training leading to more pronounced alterations.

Skull. General hypertrophy of an athlete's body musculature increases mechanical stress in the bones and causes generalized skeletal changes. For example, judokas exhibit an increased HEAD circumference, greater longitudinal and transverse head diameters, and larger facial dimensions compared to non-athletes. This is driven by Changes in the skull itself, primarily within the spongy layer, whereas the outer and inner tables undergo virtually no remodeling.

Upper extremity. The humerus undergoes significant changes in strength-sport athletes, such as weightlifters and wrestlers. In weightlifters, the shape of its diaphysis approaches a cylinder (although some athletes retain the original shape during prolonged sports training) due to the expansion of the distal diaphysis. The difference in width between the middle and lower thirds of the bone is 3.8 mm in non-athletes, compared to only 0.6 mm in weightlifters. The widening of the diaphysis is associated with the thickening of the compact layer, which acquires a layered structure. Along the lateral margin of the bone, the delamination of the compact substance begins more proximally than along the medial margin. This is presumably due to the greater range of motion in the radiocarpal joint (two axes of rotation) compared to the humeroulnar joint (one axis).

The transverse dimensions of forearm bones are altered to a greater extent in athletes than their longitudinal dimensions. During gymnastics and wrestling, transverse dimensions increase predominantly in the ulna, whereas in sports games and boxing, they increase primarily in the radius. In boxers and gymnasts, the head of the radius reaches its maximum dimensions. In boxers, forearm muscle contractions are prolonged, leading to the reinforcement of the ulna as the site of muscle origin. In gymnasts, the BONES OF THE hand experience alternating stresses that are transmitted mainly to the radius (the ulna has a smaller contact area with the Carpal Bones).

A comparison of the hands of acrobats, swimmers, weightlifters, and archers reveals that hand length is greatest in swimmers and shortest in weightlifters. This lengthening and shortening occurs primarily in the metacarpus. Under predominantly dynamic impacts on the hand (volleyball, boxing, swimming), it is mainly the longitudinal dimensions of the bones, their heads, and bases that change. For instance, the second and third Metacarpal bones bear the brunt of the load in boxers. Their heads widen, but begin to narrow under excessive stress. Predominantly static loads (in gymnastics, weightlifting, wrestling) mainly alter the bone diaphysis: it widens, and the compact substance thickens, sometimes at the expense of the marrow cavity, which may narrow. Elongation of the metacarpal bones has been observed, even after the epiphyseal plates at the distal end have ossified. Longitudinal growth of these bones continues via the articular cartilage. Furthermore, the proximal ends of the metacarpal bones experience tension and compression during exercise, whereas the distal ends are subjected primarily to tension. Consequently, the proximal ends bear heavier loads than the distal ones.

Differences in the morphological changes of individual hand bone dimensions become apparent when analyzing the distribution of mechanical loads in boxers and gymnasts. In gymnasts, the load is applied to the metacarpal diaphysis (during floor support) or the proximal phalanx (during bar hangs), whereas in boxers, it affects the metacarpal head and the Base of the proximal phalanx. Therefore, boxers exhibit major changes in the epiphyses, while gymnasts show greater alterations in the diaphysis.

The elongation of the metacarpal bones in gymnasts has a distinct functional significance. As is known, the interosseous muscles lie between the metacarpal bones and account for half the strength of the finger flexors. A cumulative 1 cm elongation of the metacarpal bones leads to a 2 cm2 increase in the physiological cross-sectional area of the muscles and a strength gain of 20 kg (40 kg for both hands). For gymnasts, finger flexor strength is of paramount importance, as giant swings generate centrifugal forces exceeding the athlete's body weight by 3 to 4 times.

Lower extremity. In female gymnasts, the transverse and anteroposterior dimensions of the pelvis are smaller than in non-gymnast women. As a rule, the female pelvis is larger than the male pelvis. However, it was found that in female swimmers and team-sport athletes, the distance between the iliac crests and between the greater trochanters of the femurs is smaller than in male athletes of the same specialization. Pelvic bone growth depends on sex hormone levels in the Blood. Intensive muscular activity increases The production of Male Sex Hormones, which can influence pelvic dimensions.

Distinct differences are observed in the dimensions of the acetabulum and the femoral head across various sports. For instance, the diameter of the acetabulum and femoral head in soccer players is large and increases with athletic proficiency, whereas in gymnasts, it is smaller and decreases as their proficiency grows. Soccer players are characterized by relatively large anteroposterior and transverse dimensions of the femoral diaphysis. However, these dimensions reach their maximum values in weightlifters and hammer throwers. The width of the distal femoral epiphysis between the epicondyles is greatest in soccer players and cyclists. The cross-section of the femoral diaphysis and its compact layer is largest in long jumpers. The characteristic bilateral asymmetries are further amplified, with these dimensions being significantly greater in the take-off leg than in the swing leg.

Cyclists exhibit markedly more massive Femur and Tibia bones. Along the edges of the femur, the compact substance is hypertrophied relatively evenly, whereas in the bones of the lower leg, this hypertrophy is uneven and depends on the athlete's specialization: in track cyclists, the compact layer thickens more markedly on the anterior surface of the tibia (middle third) and the posterior surface of the Fibula (lower third); in road cyclists, compact bone thickening is characteristic in the middle third of the leg along contacting borders (in this case, contractions of the anterior leg muscles are prolonged and require greater structural support).

Among the Metatarsal Bones, the first metatarsal has the thickest compact layer, whereas the second through fourth metatarsals show negligible changes.

Bone Articulations

The shape of bone articulations is determined by both inherited traits and mechanical factors, among which movement plays the dominant role. This is confirmed by the formation of new (false) joints at bone fracture sites, where one bone fragment constantly rubs against another. The contacting surfaces are thereby polished, resulting in the formation of a joint.

Specialized training can lead to significant changes in joint mobility and shape. For instance, the ellipsoidal radiocarpal joint in rhythmic gymnasts tends to become more spheroidal, allowing for a greater range of motion. Basketball and handball players exhibit a total mobility across four movements in the radiocarpal joint exceeding 200°, whereas gymnasts and rowers show lesser values. In the former group, the joint is more congruent with an elongated ellipsoidal head, while in the latter, the degree of articular surface conformity is lower and the head is more convex.

Gymnasts develop a flattening of the acetabulum, which creates a difference in the curvature of the articular surfaces and increases mobility in the hip joint. Spinal flexibility can also be developed to an exceptional degree, reaching an "extreme manifestation" in contortionists performing the "snake woman" circus act.

In athletes of certain specializations, joint mobility is actually reduced. For example, compared to gymnasts, soccer players' hip joints adapt to prioritize enhanced static stability at the expense of mobility. This is necessary to ensure pelvic ring stability during the single-support phase when kicking the ball. Soccer players also demonstrate a smaller passive range of motion in the knee joint. In strength-oriented sports (such as weightlifting and wrestling), decreased mobility and increased static reliability in the ankle joint are achieved through the flattening of the talar trochlea. Observations of track-and-field athletes, weightlifters, gymnasts, swimmers, soccer players, and handball players have revealed that the lowest spinal flexibility is characteristic of swimmers and weightlifters.

Studying the topography of joint mobility in athletes across various disciplines is of both theoretical and practical interest. For instance, when selecting children for swimming sports schools (SDYUSSH), considerable emphasis is placed on shoulder and hip joint mobility. In artistic gymnastics Selection, a diagnostically significant factor is that the leading national gymnasts exhibit a total (cumulative) joint mobility (in the hip, shoulder, and spine) exceeding 900°, compared to over 750° for 10-year-old gymnasts, and over 650° for non-athletic 10-year-old children.

A comparison of the total magnitude of flexion and extension in the shoulder, hip, and ankle joints among athletes from different sports showed that this value decreases in the following order: for the shoulder joint — in handball players, non-athletes, cross-country skiers, and cyclists; for the hip joint — in handball players, cross-country skiers, cyclists, and non-athletes; for the ankle joint — in cyclists, cross-country skiers, handball players, and non-athletes.

The amplitude of flexion-extension movements in the shoulder and hip joints was highest in handball players and lowest in cyclists, which is attributable to the specific riding posture of cyclists. Conversely, the greatest mobility in the ankle joint was observed in cyclists and the lowest in handball players.

Muscular System

Adaptive changes in athletes' muscles are studied using biopsy data. Training loads exert a selective influence on microscopic muscle components. For example, cycling on a ergometer for one hour a day, four days a week over a period of five months at 75–90% of $\text{VO}_2\text{max}$ increases the proportion of type I (slow-twitch) fibers. During dynamic exercises (such as running and swimming), these fibers undergo greater hypertrophy than type II (fast-twitch) fibers. Blood supply shifts exhibit the opposite pattern: blood capillaries proliferate more extensively around type II fibers, which is explained by their initially poorer capillary supply. Moderate exercise recruits reserve capillaries, whereas high-intensity exercise stimulates the formation of new ones. It is hypothesized that muscular adaptation to physical loads occurs primarily through type II fibers. Women exhibit the same muscle fiber types as men, albeit with a smaller diameter, and possess a higher count of fibers with aerobic METABOLISM/26.html">Energy Metabolism (type I).

Absolute muscle strength is subject to significant individual variation. The strength of a muscle or muscle group relative to the cross-sectional area of its fibers defines its specific strength. Age- and sex-related Variability in specific strength is relatively small, although individual differences are likely hereditary in nature.

The topography of muscle strength in individuals across various sports specializations is of considerable practical interest. Examples include data on the strength of the forearm flexors (FF), forearm extensors (FE), shoulder flexors (ShF), shoulder extensors (ShEx), trunk extensors (TE), thigh flexors (TF), leg extensors (LE), and FOOT flexors (FFl) in non-athletes, handball players, cyclists, and cross-country skiers, with muscle groups listed in order of decreasing strength¹¹.

Non-athletes: TE - TF - FFl - LE - ShEx - TF - FF - ShF - FE — SG.

Handball players: TE - FFl - TF - LE - ShEx - TF - ShF - FF - FE - SG.

Cyclists: TE - TE - TF - LE - ShEx - TF - ShF - FF - SG - FE.

Cross-country skiers: TE - FFl - TF - LE - ShEx - ShF - TF - FF - SG - FE.

Athletes demonstrate relatively greater foot flexion strength compared to non-athletes, with this metric being especially high in cyclists. The aforementioned specialists differ in the ratio between leg flexion strength and forearm extension strength. However, one key characteristic unites them: the total strength of flexor muscles is consistently lower than that of extensors. In wrestlers, the flexor-to-extensor strength ratio is approximately 1:1.1–1.5 for the arm and forearm, 1:3.4–3.5 for the trunk, 1:3 for the thigh and leg, and 1:4 for the foot; in weightlifters, it is 1:4.2 and 1:5.2 for the thigh and leg; in hammer throwers, 1:5 and 1:4; in high jumpers, 1:3.9 and 1:4; and in swimmers, 1:2.7 (for both thigh and leg).

Polydynamometry, which outlines the topography of muscle strength, should replace isolated measurements of grip strength and back strength, as the latter fail to adequately assess an athlete's comprehensive strength capabilities.

¹¹ A double line indicates a shift in muscle ranking by two positions, and a single line by one position, compared to non-athletes.

Muscular development can be indirectly estimated through limb girths (perimeters). However, in wrestlers, the correlation between the strength of muscles acting on the elbow and knee joints and the perimeters of the arm and thigh did not exceed 0.5–0.6, respectively. This is because limb girth is determined not only by muscular development, but also by bone diameter and subcutaneous fat deposition.