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What’s the Difference Between Abduction and Adduction? (Biomechanics)
Stephen Mraz | Jul 22, 2014
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In medicine and biomechanics, movements of limbs and other body parts toward or away from the center line of the body (a line that runs up and down the center of the human body) are termed adduction and abduction, respectively.
Adduction is the movement of a body part toward the body’s midline. So, if a person has their arms straight out at the shoulders and brings them down to their sides, it is adduction. For fingers or toes, adduction brings the digits toward the center of the hand or foot. For example, if a person has their fingers spread wide apart, bringing them together would be adduction. Closing arms to the chest or bringing knees together are other examples of adduction. Adduction of the wrist, moving a hand toward the body at the wrist when that arm is at the person’s side, is also called ulnar deviation. Any muscle that creates this type of motion is called an adductor.
For normal eyes (not cross-eyed, for example) when the right is adducted, it moves toward the center of the face and looks left. At the same time, the left eye is abducted, moving away from the midline of the face and looking left. So in people with normal eyes, when one eye is adducted, the other abducts.
Abduction is any motion of the limbs or other body parts that pulls away from the midline of the body. Swinging the hands from the side of the body up to the shoulder or higher is abduction. For fingers and toes, abduction spreads the digits away from the hand or foot’s centerline of hand or foot. Raising the arms laterally, to the sides and moving the knees away from the midline are some examples of abduction. Abduction of the wrist, moving the hand away from the body at the wrist when that arm is at the person’s side, is called radial deviation. Any muscle that creates this type of motion is termed an abductor.
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The wrist is a complex series of joints that are formed around the carpal bones and the radius and ulna (forearm bones). The wrist is capable of three sets of distinct movements
- Flexion and extension
- Supination and pronation
- Ulnar deviation (ulnar flexion) and radial deviation (radial flexion)
Flexion and extension
Flexion describes the movement of bending the palm down, towards the wrist.
Extension describes the movement of raising the back of the hand.
Supination and Pronation
Supination describes the movement of rotating the forearm into a palm up position.
Pronation describes the movement of rotating the forearm into a palm down position.
Ulnar Deviation and Radial Deviation
Ulnar deviation, otherwise known as ulnar flexion, is the movement of bending the wrist to the little finger, or ulnar bone, side. With the right hand this is the movement you use when hitting the Enter key.
Radial deviation, otherwise known as radial flexion, is the movement of bending the wrist to the thumb, or radial bone, side.
The Neutral Position
The neutral position of the wrist is that position where the wrist is in straight alignment with the forearm: no flexion, extension, radial or ulnar deviation. The wrist is at the mid-point between supination and pronation. This is commonly called the handshake position.
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