If you have been around physical therapists, whether you’ve received treatment or been present while another has been working with a therapist, you have probably heard them refer to extension of a body part.
Many people get confused between the terms “flexion” and “extension”. But to clear up any misunderstandings, extension means to straighten, or move to the rear of the body.
In the photo above, you’ll see that one leg is straightened and it’s moving toward the rear of the body relative to the other leg. The straight leg is extended. But, extension doesn’t necessarily mean a body part is actually straight or moved completely to the rear. Extension is the movement itself and it doesn’t matter what position your body is in, whether seated, lying down, or standing.
For instance, if you clench your fist, the fingers are flexed to the limit and cannot flex any further. If you open your hand just a little, you are extending your fingers simply because you’re not actively flexing them.
Likewise, when you are getting up from a sitting position, but not quite standing erect, your hips and knees are said to be extending because they are moving toward a more straightened position and toward the rear of the body.
Your trunk and neck can also be extended. Standing erect with shoulders back is considered trunk extension. If you were to look up to the sky and arch your trunk backwards, you would be going further into neck and trunk extension.
Keep in mind that extension is generally the opposite of flexion.