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

General Dynamic Morphology
Morphokinetic Analysis of the Upper Extremity

The primary Movements of the upper extremity during physical education and sports activities are as follows:

1. Pulling an object toward the torso (e.g., pulling an oar in rowing).

2. Pushing an object away from the torso (such as in shot putting, bench pressing, etc.).

3. Executing strikes and punches (e.g., hitting an opponent in boxing).

4. Swinging movements to increase the radius of rotation and the speed of an object (in discus or javelin throwing).

5. Movements associated with weight-bearing and support Functions (such as in a handstand or a support on parallel bars).

6. Bringing the torso closer to or moving it away from the support surface (when pulling up or lowering oneself on a pull-up bar or rings, or during push-ups).

7. Locomotor movements (in swimming, where the upper limb is used to propel the body against the surrounding medium; and during walking, running, and jumping, which involve the progressive locomotion of the entire body).

The most vital part of the upper extremity—serving as its grasping and holding organ—is the hand. Its high mobility is due to the significant number of "degrees of freedom" it possesses. The three main JOINTS OF THE upper limb alone—the shoulder, elbow, and wrist joints—provide the hand with a total of seven "degrees of freedom," which exceeds the requirements for unrestricted hand mobility within its sphere of action. Movements of the hand, like those of the entire upper limb, are characterized by coordination, precision, speed, and diversity (Fig. 164).

Two potential points of support are distinguished in the functioning of the upper extremity. First, the upper limb may be fixed at its proximal end while the distal segment remains mobile (this option is utilized in the majority of movements where the torso is relatively stationary). Second (though less frequently used), the hand can be fixed while the torso moves relative to it (as in pull-ups and certain other movements). In the first case, the Muscles operate with a proximal, or upper, support, whereas In the second case, they operate with a distal, or lower, support.

The mechanical operation of the motor apparatus (bones, joints, and muscles) of the upper extremity varies depending on the specific primary movement being performed.

1. When drawing an object toward the torso, the Water/144.html">Origin of the upper limb muscles serves as their fixed point, i.e., the proximal end; thus, they operate with an upper support. The movement involves flexion at the elbow joint, flexion (and occasionally extension and abduction) at the wrist joint, and, for most movements, extension and adduction of the shoulder. Consequently, the active muscles during these actions are those that flex the forearm and hand, and extend and adduct the arm. In the joints—primarily the wrist—the pressure of one bone against another is reduced. In addition to the ligament apparatus, muscles play a major role in stabilizing the wrist joint.

2. When pushing an object away from the torso, the linear distance between the proximal and distal ends of the upper extremity increases, accompanied by extension at the elbow joint and flexion at the shoulder and wrist joints. The muscles operating during this movement are the flexors of the shoulder, extensors of the forearm, and flexors of the hand and fingers. Simultaneously, the shoulder girdle moves forward or upward, involving the corresponding Muscle groups. During this movement, the pressure between opposing articular surfaces within the joints of the upper extremity increases.

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Fig. 164. Involvement of the hand in various occupational and everyday tasks (after E. P. Danilova)

3. When executing strikes, the movements of the upper extremity can be quite diverse. For instance, a straight right punch in boxing is biomechanically similar to pushing an object away from the torso. The hand, with fingers curled into a fist, delivers the blow primarily through the heads of the Metacarpal bones and the dorsal surface of the proximal Phalanges. In addition to the Muscles of the Upper Limb—specifically the triceps brachii and pectoralis major—the muscles of the shoulder girdle, particularly the serratus anterior, play a crucial role in these movements.

4. During swinging movements (in various throwing disciplines), the arm is kept straight. A preliminary backward swing (the wind-up) increases the degree of stretch in the Muscles responsible for moving the shoulder girdle forward and executing movements in the shoulder and other joints of the arm itself. This pre-stretched state of the muscles enhances the amplitude of their subsequent shortening due to the elastic recoil forces generated within them. The upper limb itself serves to increase the radius of Rotation of the projectile (javelin, discus) relative to the torso. As a result, the centrifugal force acquired by the body during rotation around the vertical axis passing through the torso increases. The primary upper extremity muscles involved in throwing are those that drive the shoulder girdle and humerus forward.

5. When the upper extremity is used as a support organ (e.g., during a handstand—Fig. 165—or a support on parallel bars), it is maintained in a straightened position, primarily through flexion at the Shoulder and Elbow joints and extension at the wrist joint. The entire body weight is transmitted to the supporting surface through the BONES OF THE upper limb. In this position, the bones undergo compression along their longitudinal axes, and the joints likewise experience vertical compressive forces. The active muscles are the extensors of the forearm (triceps brachii and anconeus) and the flexors of the fingers and hand, which protect the wrist and hand joints from excessive hyperextension. Conversely, when the upper limb functions as a support organ during a hang from a pull-up bar or parallel bars, the finger flexors are predominantly in a contracted state, while The primary function of the remaining muscles is to protect the joints of the upper limb from traction and prevent the Separation of their articular surfaces. In this position, the bones of the upper limb bear a load not of compression, but of tension.

6. Bringing the torso closer to or moving it away from the hand is performed with a distal support of the upper extremity. Examples include pulling up and lowering oneself in a hang from a bar, or performing push-ups. Notably, two consecutive opposing movements, such as pulling up and lowering, are performed by the exact same muscles. The difference in their action lies in the fact that during a pull-up, the muscles perform overcoming (concentric) work, whereas during descent, they perform yielding (eccentric) work. The active force during the descent is the weight of the entire body, while the muscles regulate the movement produced by this force. If the forearm flexors were to relax while hanging with bent arms on a bar, the body would drop even without muscle intervention.

During a pull-up, the active muscles are the forearm flexors, shoulder extensors, and shoulder adductors. In a push-up, the primary muscles under tension are the triceps brachii and shoulder flexors (anterior part of the deltoid muscle, pectoralis major).

An analysis of THE POSITION OF the upper limb muscles relative to the axes of rotation in the joints reveals that various options for muscle attachment are possible. This is of great consequence for the movement of any given link. The closer a muscle's attachment point is to the joint, the smaller its leverage (torque), but the greater the speed of movement of that body segment.

The same principle applies to all muscles of the upper extremity, especially those attaching to the humerus that originate from the torso (such as the pectoralis major and latissimus dorsi). If they attach more distally on the humerus, their leverage and, consequently, the force with which they can adduct the arm will be greater than if their attachment point were located more proximally. At the same time, the range of motion of the shoulder during abduction in the former case will be somewhat smaller than in the latter.

Fig. 165. Handstand

7. Locomotor movements associated with the Displacement of the body in space are also facilitated by the upper extremity. This applies primarily to progressive movements in swimming. The arm stroke contributes to the propulsion of the body through the aquatic environment. In this case, the upper limb acts as a lever whose moving fulcrum is the water itself.

Regarding the locomotor function of the upper extremity during walking and running, the arm reduces the rotational component of the whole-body movement through its swinging motion in the anteroposterior direction. This locomotor function of the upper extremity is discussed in greater detail on page 463. During jumping, the upper extremity also acts as a locomotor organ. In this case, swinging the arms upward helps utilize the mass of the upper extremity to propel the entire body upward, as detailed on page 479.

When viewing the upper extremity from the front, it can be observed that in the supinated state of the forearm, there is an outward-opening angle between the arm and the forearm. As a rule, this angle is smaller in women than in men.

In anatomy, it is standard practice to study the upper extremity with the forearm in the supinated position, where its bones lie parallel to each other. However, in a relaxed body posture with the arms hanging down, the palms face toward the body rather than forward—meaning they are in a pronated, and in some individuals even hyperpronated, position. This characteristic posture of the upper extremity during a relaxed stance is due to the higher muscle tone of the pronators compared to the supinators. The forearm, hand, and especially the fingers are also typically somewhat flexed in a relaxed posture, which can be attributed to the higher muscle tone of the flexors compared to the extensors.

Regarding the arrangement of the Muscles surrounding the elbow joint, it is known that the forearm flexors are stronger than the extensors. This can be related to the fact that in most cases, gravity or some other form of resistance works against the action of the forearm flexors, whereas gravity typically assists forearm extension. The layout of the muscles in the upper extremity is such that the "effective component" of the flexors and extensors is greater than that of the pronators and supinators. This is explained not only by the more frequent use of flexion movements around transverse axes compared to rotational movements around longitudinal axes, but also by the fact that the moment of inertia of the entire upper extremity with respect to the transverse axes of rotation in the joints is significantly greater than the moment of inertia with respect to the longitudinal axes (see p. 481). This also explains the marked superiority of such muscles as the biceps brachii, brachialis, and triceps brachii over the pronator teres, pronator quadratus, and supinator of the forearm.

A well-known compensation for the lesser Development of the forearm pronators and supinators is provided by the coupled movements of the arm and the Pectoral Girdle. For example, when forced pronation or supination of the forearm is performed, particularly against resistance, the humerus does not remain stationary (this is clearly visible from the position and displacement of its distal end). As a result, not only does pronation or supination of the entire upper extremity occur if the elbow joint is extended, but abduction or adduction of the arm also takes place if the forearm is flexed.

The same holds true for coupled movements in the region of the scapula. If the position of the scapula—specifically its inferior angle—is observed during forced rotational movements of the forearm, its alternating medial and lateral displacement is easily noticed. Evidence for these observations is provided by studying movements in fencing (lunges, thrusts), swimming (breaststroke), and gymnastic exercises on the pommel horse, among others.

The hand played an exceptionally vital role in the Evolution of the human species, and it plays an equally crucial role in the life of every individual. It is no coincidence that since antiquity, philosophers and scientists have paid close attention to The Significance of the hand. Anaxagoras (5th century BC) believed that "man is intelligent because he has hands." Lucretius Carus (1st century BC) wrote: "Our hands serve us as helpers, on the right and on the left, so that with their aid we may accomplish what life requires." And Galen (2nd century AD) wrote: "In compensation for his nakedness and lack of natural weapons, man was given the hand. Just as he was endowed with reason, the highest of all faculties, he surpassed animals by possessing the hand—that tool of all tools." F. Engels provided a scientific foundation for The Role of labor in Human Evolution, pointing out the highly refined development of the hand, "which is not only The Organ of labor, but also its product."