Human Anatomy (with the Fundamentals of Dynamic and Sports Morphology) - Ivanitsky, M. F. 2008

Special Dynamic Morphology
Anatomical characteristics of rotational body movements. Preliminary remarks

Rotational Movements of the body can occur around both Abstract axes (vertical, frontal, and sagittal) and material axes of rotation (such as a gymnastic bar). Examples of rotational movements around a material axis include giant swings in gymnastics, while movements around an abstract axis include saltos, pirouettes, rolls, and various flips. Such rotational movements are most frequently encountered in gymnastics, figure skating, diving, and other sports.

To perform a rotational movement, the applied force must not be directed parallel to the axis of rotation or through the body's center of mass (COM), but rather at a certain distance from it, creating a torque. This torque is equal to the product of the force magnitude and its moment arm (the shortest distance from the axis of rotation to the point of force application). The greater the torque, the higher the angular acceleration imparted to the body; therefore, the farther the point of force application is from the axis of rotation, the more effective its action.

As is well known, every body possesses inertia, which means that a certain force must be applied to bring it out of a state of rest or to change the direction of its motion. Any force that alters the position or movement of a body encounters resistance. In translational motion, this resistance is directly proportional to the mass of the body, whereas in rotational motion, it is proportional to the body's moment of inertia.

The moment of inertia of a body with respect to a specific axis of rotation is a quantity that characterizes the resistance the body itself offers to a force striving to rotate it around that axis. The radius of gyration relative to an axis of rotation is the distance from that axis to a point where the entire mass of the body is assumed to be concentrated. In rotational movements, the moment of inertia and the torque of an applied force play roles analogous to those played by body mass and applied force in translational movements. Thus, the moment of inertia of a rotating material point is directly proportional to its mass and the square of its radius: M=mr², where M is the point's moment of inertia, m is the body mass, and r is the radius. The moment of inertia of an entire body can be represented as the sum of the moments of inertia of all its points — Σmr². The moments of inertia of different points of a body are not uniform and depend on the point's position relative to the axis of rotation: the farther a point (or body segment) is from the axis of rotation, the greater its resistance to motion.

The moment of inertia of the entire body relative to the longitudinal axis in the attention stance is approximately 1.2 kg/m²; in a single-leg stance in the gymnastic scale (“arabesque”) it is 8 kg/m² relative to the vertical axis. For a person in a prone position, this moment relative to the vertical axis passing through their COM is 17 kg/m².

When performing various rotational exercises, athletes attempt to alter the moment of inertia of the entire body or a specific limb. For instance, when executing a pirouette, pulling the limbs closer to the body's longitudinal axis can reduce the total moment of inertia by approximately a factor of 7, and by about a factor of 3 when performing a salto.

If the moment of inertia decreases by a factor of 3, the angular velocity increases by the exact same factor, and vice versa (meaning the body accelerates or decelerates its rotation). A standing back salto serves as a prime example of such rotational body movements.

Standing back salto

This is a complex acyclic rotational movement that involves pushing off from a supporting surface, airborne flight with rotation around a free axis, and a subsequent landing.

All movements during a salto can be divided into 4 phases: the first is preparatory, the second is push-off (takeoff), the third is flight, and the fourth is landing. In turn, the flight phase comprises takeoff, tucking, rotation, and body extension. The HEAD jerk sometimes described during a salto originates from the movement initiated during the push-off. Thanks to this motion, the inertia of the head's mass is utilized to increase the push-off force. Thus, the head jerk is not an independent movement during flight, but rather a continuation of the action begun during the takeoff. This explanation follows logically from the general premise that independently executing a head jerk mid-flight would otherwise induce a motion opposite to the one the athlete intends to perform during the salto.

Phase One: Preparatory. The initial body position for executing a salto is a semi-squat (similar to a standing long jump). This phase involves plantarflexion at the ankle joint, flexion at the knee and hip joints, and trunk flexion. The arms are slightly bent at the elbows and extended at the shoulders.

Since the positioning of the lower limbs and trunk is largely determined by gravity, the working Muscles are the antagonists of those responsible for the respective joint movements: the plantar flexors, knee extensors, and hip extensors. Performing first yielding and then isometric (holding) work, they remain in a stretched state, which promotes the generation of elastic deformation forces within them, preparing these muscles for the overcoming (concentric) work In the second phase.

Phase Two: Push-off. In this phase, plantarflexion occurs at the ankle and FOOT joints. This is driven by the Muscles of the SOLE OF THE foot, along with the posterior and lateral Muscle groups of the lower leg. Of primary importance are the triceps surae (especially the soleus muscle), the tibialis posterior, the flexor hallucis longus, the flexor digitorum longus, and the peroneal muscles. Knee extension is performed by the quadriceps femoris, predominantly its femoral heads (the vastus medialis, vastus lateralis, and vastus intermedius). Hip extension is produced by the muscles located on the posterior aspect of the hip (gluteus maximus, posterior fibers of the gluteus medius and minimus), and partly by the posterior and medial hamstring and adductor muscle groups (semitendinosus, semimembranosus, biceps femoris, and adductor magnus).

In the upper extremities, the muscles that ensure forearm flexion and shoulder extension are active, while on the trunk, the spinal extensors are engaged (primarily the erector spinae and transversospinalis muscles).

Phase Three: Flight. This phase involves tucking and rotating the body around its transverse axis. During the tuck, the lower limbs are flexed at the Hip and knee joints, the feet are extended, the upper limbs are lowered, and the head is tilted back. These movements involve the antagonists of the muscles that worked during the second phase.

Foot extension is produced by the anterior muscle group of the lower leg (tibialis anterior, extensor hallucis longus, extensor digitorum longus); knee flexion

— by the posterior thigh muscle group and partly the calf muscles (biceps femoris, semitendinosus and semimembranosus, gracilis, sartorius, gastrocnemius, and popliteus); hip flexion by the iliopsoas, rectus femoris, sartorius, tensor fasciae latae, and partly the pectineus muscles; lowering of the shoulder girdle and the entire arm by the lower part of the trapezius, the lower slips of the pectoralis minor, subclavius, as well as the latissimus dorsi and pectoralis major muscles. Simultaneously, trunk flexion occurs in the thoracic and lumbar regions.

The tuck reduces the body's moment of inertia, contributing to an increase in angular velocity. Toward the end of the third phase, body extension begins, accompanied by an increase in the moment of inertia and a decrease in angular velocity. Extension occurs in the JOINTS OF THE lower limbs (except the ankle), the upper limbs are lowered, and the spinal Column straightens out. The group of muscles extending the lower limb at the knee and hip joints while flexing it at the ankle includes the plantar foot muscles, the posterior and lateral lower leg muscles, the anterior thigh muscles, and the posterior hip joint muscles. The lowering of the upper limbs occurs predominantly under METABOLISM/18.html">The Influence of gravity.

Phase Four: Landing. In this phase, complete extension of the lower limb joints does not occur, as the limb acts as a spring mechanism to absorb the Shock of the impact. Shock absorption is achieved through the yielding (eccentric) action of the muscles involved in body extension. Complete lowering of the upper limbs and full extension of the trunk also do not occur. These PARTS OF THE body largely perform balancing work, bringing the body into a position where the trajectory of the COM passes within the support area at the moment of landing; otherwise, a fall will ensue.

Thus, performing a back salto requires a brief yet highly energetic Muscle contraction at the moment of takeoff. During the body tuck, as well as during extension and landing, the muscular effort is less intensive.

Precise coordination of the entire body's movements is essential for the successful execution of this exercise. This is only possible when the athlete has a keen sense of their body — that is, when the motor analyzer, As a result of systematic training, finely perceives peripheral stimuli, and in response to these afferent stimuli, precise and coordinated impulses are sent to the active part of The Musculoskeletal System, namely the muscles.

Executing a salto is easier the smaller the body's moment of inertia is relative to the transverse axis passing through its COM. Therefore, individuals with shorter stature find it easier to perform a salto than those who have the same mass but are taller. In taller individuals, even with a maximum body tuck, the moment of inertia remains relatively large.

Since performing a salto demands considerable muscular exertion, it is typically accompanied by a breath-holding maneuver (Valsalva effect). However, due to the brief duration of the movement, this does not have a noticeable negative impact on the Organism. Furthermore, prior to executing the exercise — immediately before the squat — the athlete takes a few deep breaths, and at the moment of push-off, accompanied by the raising of the arms, the chest expands and an inhalation occurs. Consequently, the exhalation is somewhat delayed and is usually performed only after landing. The tuck phase is favorable for exhalation, but athletes generally do not have time to utilize it for this purpose. Because the trunk straightens and the arms are raised upward during the push-off and ascent phases, the inhalation occurs not through the descent of the Diaphragm, but rather via chest expansion caused by the elevation of the Ribs. The descent of the diaphragm is also hindered by the stretching of the abdominal wall muscles during takeoff and ascent.

The standing back salto helps improve jumping ability, coordination, and movement precision, and serves as an effective exercise for training the vestibular system.

Dynamic Morphology is one of the most crucial sections of educational and scientific anatomy, extending far beyond The Scope of sports alone. The art of choreography, ballet, and pantomime demands perfect bodily mastery from the performer. Optimizing movements and enhancing their expressiveness require theoretical reflection from the standpoint of dynamic morphology.

Work at a machine tool or an assembly line often consists of specific movements repeated in a particular sequence and brought to the point of automatism. The intensification and rationalization of labor, along with occupational safety concerns, require a scientific substantiation of the body positions and movements of workers from the perspective of dynamic morphology and ergonomics.

The Development of new industrial and consumer equipment is typically preceded by an ergonomic analysis of human capabilities and, consequently, also requires their interpretation from the standpoint of dynamic morphology.

Sports, the arts, labor processes, and daily life involve a complex of both natural and non-standard motor actions, the mastery of which helps reduce fatigue and increase human performance levels. Proficient control of one's body is only possible with a certain amount of knowledge in the field of dynamic morphology. However, it should be borne in mind that not only the musculoskeletal system, but the entire organism with its regulatory and support systems is influenced by motor activity. One of the sections of modern morphology—sports morphology—is dedicated to the examination of these issues.