What is the Definition of Extension?

Learn About Extension

Extension of the elbow joint.
Extension of the elbow joint. Halfdark/Getty Images

Extension refers to the bending or flexing of a joint so that the bones forming the joint are moved farther apart, or straightened. Extension is a physical position that decreases the angle between the bones of the limb at a joint. It occurs when muscles contract and bones move the joint into a bent position.

Typically, extension of a joint is limited to 180 degrees or less. In other words, that joint can basically be opened until it is straight.

Think of your arm or leg as an example, as these can be bent until they are virtually straight.

What is a Joint?

A joint is a physical point of connection between two separate bones. For example, the knee joint refers to the point of connection between the femur, or thigh bone, and the tibia, or shin bone. Joints also contain a variety of fibrous connective tissue such as ligaments, which connect the bones together and tendons which connect muscle to bone and cartilage, which covers the ends of bones and provides some cushioning.

Hyperextension

Just as it sounds, hyperextension is an extreme version of an extension. Hyperextension is an excessive joint movement in which the angle formed by the bones of a particular joint is opened, or straightened, beyond its normal, healthy, range of motion. Such a movement may potentially make that particular joint unstable, and in turn increase the risk and likelihood for dislocation or other potential injuries of the joint.

Flexion

The opposite of extension is flexion. Flexion is defined as the bending of a particular joint so that the bones that form that joint are pulled closer together. Flexion is a physical position that decreases the angle between the bones of the limb at a joint. It occurs when muscles contract and bones move the joint into a bent position.

During flexion, the angle between the bones of limb at a joint is decreased. Flexion typically occurs when muscles contract and the bones thus move the nearby joint into a curved position. In short, flexion shortens a joint angle and extension increases it.

Range of Motion of a Joint

A majority of the human body’s joints allow for movement. A few, like joints in the skull, do not allow for movement. Those joints that do allow for motion, such as the knee or ankle, have a predetermined range of motion. Think of range of motion as a spectrum of limits of how far an individual joint can bend. The range of motion is basically how far is each direction that joint can move or bend comfortably. The range of motion of a joint is usually measured in degrees. Each individual joint has a separate range of motion.

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