The term extension is used in anatomical nomenclature to describe movement. It refers to one of the main movements of the human body.
What is extension?
Extension, in German Streckung, like its opposite movement, flexion, occurs in many extremity joints and at the spine. Extension, in German Streckung, occurs, like its countermovement, flexion, in many extremity joints and at the spine. The original definition of the terms in anatomical nomenclature was based on the model of embryonic posture. Accordingly, extension is defined as the movement leading out of this position. Extension movements occur in the major extremity joints, above in the shoulder and elbow, below in the hip and knee, and in the toe and finger joints. Extension of the spine occurs as a single movement in the vertebral joints of each segment. However, descriptions and documentation often describe the overall motion or behavior of a segment of motion. The lumbar spine and cervical spine are physiologically already in an extension position at rest, which is called lordosis. With one exception, the range of motion of extension is less than that of flexion in all joints. The metatarsophalangeal joints alone can be extended more than flexed. In the knee and elbow joints, active extension is not possible in many people; often only the zero position is achieved.
Function and task
Extension is involved in the stance leg phase in all involved joints of the lower extremity, although in different subphases and with different function. While the toes are elevated right at the beginning when the foot is planted, the knee joint does not reach full extension until the middle and the hip joint at the end of the movement sequence. When jumping or overcoming a height, the activity of the extensor muscles in the hip and knee joints is significantly increased. With the Musculus glutaeus maximus, the Musculus quadriceps femoris and the Triceps surae, 3 of the strongest muscles of the human body are available for this purpose. In the free chain, extension activities in the knee can be observed during kicking or kicking movements, as in martial arts and soccer, respectively. Accentuated extensions of the hip joint occur frequently in ballet and floor gymnastics. On the arm, extension plays an important role in stabilization requirements and in free movements. Support activities in front of the body, such as when bracing at a table or on the thighs, primarily require active extension in the elbow. A typical strength exercise for this is the push-up. When supporting behind the body, shoulder extension is also switched on. The corresponding exercise form in sports is dips in different variations of execution. In functional anatomy, the return from a flexion position is often called extension. On the arm, there are many movement sequences in sports and in normal everyday life that are characterized precisely by these components in the elbow and shoulder joint. Smash strokes in volleyball, overhead strokes in tennis, throws in handball, or return movements in all types of swimming involve simultaneous extension in the shoulder and elbow as important elements. Extension of the finger joints is important as a counter process to closing the hand. In order to be able to grip or work on something purposefully, the fingers must be opened beforehand. The finger joints are also extended during lunging movements before a punch. Extension of the spine is an important component of straightening the trunk, as in lifting heavy loads. Free extension can be observed in some sports such as gymnastics, ballet, swimming, and high diving.
Diseases and complaints
Degenerative diseases such as osteoarthritis can basically affect all joints. Typically, this condition tends to occur where loads are applied, such as in the hip and knee joints and the spine. Extension can be affected by several arthritic processes. On the one hand, shrinkage of the joint capsule occurs in the course, which directly restricts extension. On the other hand, the pain that occurs leads to a protective behavior that results in weakening and shortening of the muscles. In this case, the range of motion is negatively affected both actively and passively. The limited extension in the hip joint has a direct effect on the gait pattern.Any kind of muscle loss can also limit extension. Usually, activities that are performed against gravity are affected first, such as when straightening up from a stooped or squatted position or when holding the legs in a standing position. Muscle wasting can be the result of inactivity or disease. Muscular dystrophies and amyotrophic lateral sclerosis fall into this range. Specific neurological diseases and damages can have negative influences on the regular function of the extensors. In multiple sclerosis, correct, targeted movement and stability are affected, among other things. Coordination and stability problems occur as a result, especially in walking and standing. A lesion of the femoral nerve leads to partial paralysis of the quadriceps femoris muscle, severely affecting stability in standing and walking. The same problem can occur in the upper extremity if the radial nerve is damaged by a fracture of the humerus. Among other things, this supplies the triceps brachii muscle, the main extensor in the elbow. If this muscle fails, the elbow can only be rudimentarily extended, and supporting loads are no longer possible. Supraspinatus tendon syndrome is a specific disorder in the shoulder joint that particularly affects extension. The supraspinatus muscle is a shoulder muscle that belongs to the rotator cuff. Its tendon runs in a narrow space between the acromion and the joint head. Repetitive pressure loads can cause irritation of the muscle. This often painfully limits return of the arm, especially in combination with internal rotation.
