A Moment of Science

Why Are Some People Double-Jointed?

Can you bend your thumb backwards until it touches your wrist? If you join your hands behind your back, can you lift them over your head without letting go?

sculpture's hands

Photo: justaslice (Flickr)

Are you double-jointed?

Can you bend your thumb backwards until it touches your wrist? If you join your hands behind your back, can you lift them over your head without letting go?

If you can, you might be what some people call “double-jointed.” But, A Moment of Science wonders, how could anyone have double joints?

Range Of Motion

Double-jointed people don’t really have two joints. Any joint, such as the thumb joint or the shoulder, can be called “double-jointed” if the tendons and ligaments surrounding the joint allow a wider range of motion than is usual.

Joints are created whenever 2 adjacent bones meet. They have fibrous bands of connective tissue called ligaments that stabilize the joint. Connective tissues also form the tendons that join the bones to the muscles.

Ligaments and tendons usually restrict the movement of the joint, but in some people, these normally restrictive tissues can be quite flexible and allow the extra movement we call “double-jointed.” Practice can increase a joint’s natural flexibility just the way stretching can increase your muscles’ flexibility.

Flexibility

While flexible joints are very useful to contortionists, some joints can become so loose that they are unstable. This allows the bones of the joint to slip out of their sockets and can be very damaging.

Strengthening the muscles around the joint can stabilize it and still allow you to show off your trick joint at parties.

Stay Connected

What is RSS? RSS makes it possible to subscribe to a website's updates instead of visiting it by delivering new posts to your RSS reader automatically. Choose to receive some or all of the updates from A Moment of Science:

Support for Indiana Public Media Comes From

About A Moment of Science

Search A Moment of Science