Inflection: Function, Tasks, Role & Diseases

Flexion is one of the main movements of the human musculoskeletal system. It occurs in the spine and many extremity joints.

What is flexion?

Like many anatomical terms, the term flexion comes from Latin and describes bending in single joints or chains of joints, such as in the spine. Like many anatomical terms, the term flexion comes from Latin and describes flexion in single joints or joint chains. The definition takes place with the help of an analytical system, which describes movements on the basis of their sequence in an imaginary body plane and around an imaginary axis. Flexion and the opposite movement, extension, take place in the so-called sagittal plane, about an axis of rotation that runs transversely to the body and through the joint heads. In most cases, flexion is characterized by the fact that in the course of the movement the bones involved come closer together, so there is a reduction in angle. Except for the spine, flexion occurs in almost all extremity joints. In the arm, it occurs in the shoulder, elbow and wrist joints, as well as in the finger joints. In the leg, the situation is similar. Flexion exists in the hip, knee and ankle joints, as well as in the toe joints. The description according to the above pattern is not always unambiguous. Therefore, in order to achieve more clarity, additions have been added to the names in the wrist and ankle joints that define the direction of movement. At the foot one speaks then of plantar flexion, at the hand of palmar flexion.

Function and task

Flexion is involved in many functional movements that are important for everyday, occupational, and athletic activities. In the shoulder joint, it is an important component in lifting the arm, especially forward upward. This includes lunging movements in many sports as well as lifting and holding during overhead work. Flexion at the elbow is an important function when lifting heavy loads or bringing food and drink to the mouth. At the hand, strong muscular flexion activity occurs during fist closure, requiring all flexors. During walking, all joints that have flexion as a function are involved in the swing leg phase. The thigh is pulled forward upward in the hip joint and the lower leg is pulled backward upward in the knee joint. The faster these movements are performed, for example during sprinting, the greater the range of motion in both joints. Especially at the beginning of the lifting of the foot during running and walking, the ankles are also required. The ankle joint is actively pushed into plantar flexion, causing the heel to lift off. Subsequently, the flexing activity of the toe flexors causes the entire foot to come off the ground. Basically, the toes have the same functional capabilities as the fingers, they are just atrophied in most people because their flexor function is no longer used as actively. However, grasping, holding and guiding objects with the toes is quite possible with training. Flexion of the spine is required whenever we bend forward downward, for example to pick something up or to work in a stooped position. The overall movement results from a summation of the individual components. A small bending movement takes place in each vertebral joint, and all of them added together then result in the total range of motion. Flexion is also involved in many athletic activities. In gymnastics or high diving, for example, during the somersault, in martial arts during the skilled roll, in volleyball and handball during and after hitting or throwing the ball.

Diseases and ailments

Like all movements of the human body, flexion can be negatively affected by two basic factors. Either the muscles performing the movement are weakened or fail due to injury or disease, or the range of motion is compromised as a result of increased resistance in the connective tissues. Typical injuries that lead to reduced muscle activity and thus reduced flexion are strains, muscle fiber tears and muscle ruptures, but also bone fractures. To protect the site of injury and avoid pain, the body switches down muscle activity and movement is no longer performed or is performed only to a limited extent.If, for whatever reason, the possible ranges of motion are no longer utilized over a longer period of time, connective tissue structures in and around the muscle stick together and restrict mobility and flexion. Typical processes that can trigger processes of this kind are immobilization of a bone by plaster or other measures, but also degenerative changes such as osteoarthritis. In the spine, herniated discs that exert pressure on the exiting nerves often lead to a temporary rigidity of movement, lumbago. In this phase, no movements are possible, even flexion is blocked. If the executing muscles, the flexors, are not supplied with nerve impulses, they can no longer work and the associated movement cannot be performed. This often happens as a result of diseases and injuries in which the nerves that supply the flexors are damaged. The consequence is a complete or incomplete paralysis of the associated muscles. A typical mechanism of injury is paraplegia, in which the spinal cord is severed. All muscles below the area of supply fail. Many neurological diseases result in impaired muscle function and thus impaired range of motion. One example is amyotrophic lateral sclerosis, a severe but fortunately rare disease that causes ongoing paralysis of the entire skeletal musculature. Affected people, as the disease progresses, can no longer perform any movements, flexion, extension, or otherwise.