The Function of Abduction in the Body

Abduction is a term that simply means the movement of a body part away from the midline, or center of the body. It's often used along with—and frequently confused with—adduction, which means exactly the opposite: movement toward the midline of the body.

One easy way to remember the difference is to note that the root of abduction is "abduct," which means to take away (as in to kidnap) and that the first three letters of adduction are "add," which could be taken to mean to add to or bring together.

Both terms frequently are used by movement specialists such as exercise physiologists, physical therapists, fitness and yoga instructors, personal trainers, and kinesiologists, but it can be useful to understand the ways in which the ability to abduct certain body parts allows us to move and use our bodies effectively.

Here's a closer look at how abduction works in the body, with a special emphasis on abduction of the legs and its role in movement and mobility.

Body Parts Capable of Abduction

Abduction (and adduction) are movements that take place at the joints; any type of joint that facilitates lateral (side-to-side) movement can aid in abduction. There are several parts of the body that are capable of abduction. You're probably most familiar with hip abduction (which is discussed in detail below)—especially if you've ever used weight training machines, which often have a station specifically designed to work the muscles that abduct and adduct the legs.

These are the body parts that are capable of abduction and the muscles that are responsible for moving them:

Arms

Abduction of an arm means to lift it out to the side from the shoulder. The main muscles responsible for this movement are located on the shoulder: the deltoids and the supraspinatus—one of the four rotator cuff muscles in the shoulder.

Hands

Abduction of the hands is a little tricky to understand, as it's different from flexing (moving the back of the hand toward the top of the forearm) and extending the hand (bending it in the opposite direction, toward the underside of the forearm).

To understand abduction of the hand, imagine your arm by your side with your palm facing forward. Abduction of your hand in this position would happen at the radiocarpal joint of the wrist and would mean moving your entire hand away from your body in the direction of your thumb. The muscles involved in abducting the wrist are: extensor carpi radialis longus, extensor carpi radialis brevis, abductor pollicis longus and flexor carpi radialis.

Fingers

To abduct your fingers simply means to spread them apart. Although you aren't moving them away from the midline of the body, you are moving them away from each other. The muscle responsible for abducting the pinky finger is the abductor digit minimi of the the hand. Four muscles are involved in abducting the rest of the fingers; together they're called the dorsal interossei of the hand.

Thumb

This is the movement that brings the thumb to a 90-degree position perpendicular to the rest of the hand. If you were to hold your palm with all your fingers together and then move your thumb away from your index finger to create an "L" shape, you would be abducting your thumb. The muscles responsible for abduction of the thumb are the abductor pollicis brevis and abductor pollicis longus.

Toes

As with the fingers, abducting the toes means to separate them away from each other. The muscle that abducts the big toe is the abductor hallucis; the muscle that abducts the little toe is the abductor digiti minimi of the foot. As in the hand, a group of four muscles work together to adduct the three middle toes; they're called the dorsal interossei of the foot.

Legs

The abductor muscles of the legs are sometimes referred to as the hip abductors. There are six of them. The primary abductors of the hip are the gluteus maximus and the gluteus medius. They're often nicknamed the "glutes," and are the large muscles in the buttocks.

Also involved in hip abduction are the third glute, the gluteus minimus, and several other muscles in the region of the upper leg/hips/buttocks: the tensor fasciae latae, the sartorius, and the piriformis.

In addition to moving the leg away from the midline of the body, the hip abductors help to rotate the thigh in the hip socket and to stabilize the hip joint. The abductors attach from the pelvis to the femur (thigh bone). You use your hip abductors whenever you move from side-to-side—for example, when you swing one leg off the bed to get up in the morning and when you step into or out of the car.

When we sit for long periods, these muscles, along with others, can become weak and lead to certain types of pain, such as patellofemoral pain syndrome (sometimes called runner's knee, or PFPS) and iliotibial (IT) band syndrome. Keeping the abductor muscles strong and flexible is one key to preventing these problems.