in anatomy, flexion Y extension they are opposing movements of approach and withdrawal in an anteroposterior direction. They are typical movements of the synovial joints, although they can also refer to movements of other joints and mobile parts of the body.
More precisely, flexion and extension are defined as angular movements made in sagittal plane relative to the median frontal plane . Next we will see what these anatomical planes are and later we will explain the differences between flexion and extension.
The sagittal plane and the frontal plane
All anatomical descriptions of the human body are made with respect to the planes and axes defined in the so-called anatomic position . In this position, the body is placed in a standing position, with the arms extended to the sides and rotated so that the palms of the hands face forward.
From this position, the sagittal plane it’s the plan perpendicular to the ground that cuts the body right half and left half . Any movement made in the anteroposterior direction is considered in the sagittal plane.
For example, if we are in the anatomical position, raising and lowering the leg in front of the body, bending and extending the knee, or bending and extending, are movements made in the sagittal plane.
In addition to the sagittal plane that cuts the body exactly in half ( midsagittal plane ), any plane parallel to it is also called the sagittal plane, so we usually speak of sagittal planes and not just one
For example, the movement of knee flexion and extension occurs in the sagittal plane (plane in an anteroposterior direction and perpendicular to the floor), but it does not occur in the midsagittal plane, it does not occur right in the middle of the body.
flexion and extension
You angular movements within sagittal planes They are called flexion and extension . This means that flexion and extension are movements that modify the angle between two articulated segments of the body and are performed in an anteroposterior direction.
THE flexion is the movement that the angle decreases and approaches the two distal ends of the articulated segments. THE extension It is the opposite movement increase the angle between the segments articulated and separated from each other.
For example, flexing and extending the elbow decreases and increases the angle between the forearm and upper arm, respectively.
Flexion movements are the result of contraction of one or more flexor muscles . The opposite movement, that of extension, is the consequence of the contraction of one or more extensor muscles .
For example, the flexion movement of the elbow is a consequence of the contraction of the biceps brachii, which unites the arm and the forearm, and the extension movement is a consequence of the contraction of the triceps brachii.
The flexor muscles act as agonists and the extensor muscles as antagonists, therefore, When the flexor muscles contract, the extensors extend. and vice versa.
Flexion and extension should not be confused with angular movements in other planes. For example, if we move the arm laterally away from the body, the angle between the two parts varies, but not in the sagittal plane, but in the frontal plane. In this case, we are not talking about flexion and extension, but about abduction and adduction .
There are other movements in the sagittal plane that, by convention, are defined as flexion and extension movements, although they are not angular movements.
For example, forward arm lift is defined as a flexion movement and backward as an extension movement, but they are produced by rotation of the shoulder joint, so they are not angular movements.
