An abductor muscle is any muscle which moves a body part away from the body’s midline or sagittal plane — the artificial division separating the body vertically into right and left halves. This type of movement is known as abduction. Abductor muscles are found throughout the human body, from obvious locations like the outer thigh to less expected places, such as the eyeball. They work in cooperation with adductor muscles, which move body parts back toward the midline.
The most basic movement of many body parts would be impossible without the work of an abductor muscle. Lifting one’s hand at the wrist, for instance, is dependent upon two of these muscles: the flexor carpi radialis and the extensor carpi radialis longus. The length of these muscles reveals the complexity of this seemingly simple abduction; both begin at the humerus, or funny bone, and terminate at the metacarpals, or upper bones of the hand. Raising one’s arm so that it is perpendicular to the torso is another example of abduction. In this case, two muscles of the shoulder, the deltoid and the supraspinatus, are responsible for the motion.
Generally, the term abductor muscle is commonly associated with the hip area, a place of frequent and sometimes painful injuries for runners and other types of athletes. The so-called "hip abductor" actually comprises a system of muscles — the gluteus medius, the gluteus minimus, the tensor fasciae latae, and the piriformis – that work together to abduct the thigh at the hip joint. Injury most commonly occurs in this area when the repetitive abduction of the femur, or thigh bone, causes inflammation of the local bursa sac — a fluid-filled pocket that acts as a cushion between bone and tendon. Various factors, such as wearing inadequately supportive shoes, training too frequently, or running on uneven surfaces, can contribute to this type of injury. Weakness of an abductor muscle in the hip area is often to blame for pain in other areas of the leg, such as the knee and the ankle.
Exercises to strengthen the hip abductor muscles can help reduce the chance of leg injury arising from physical activity. Many of these exercises utilize a resistance band — a thin circle of stretchable material that is anchored at one end around a stationary object. The foot is inserted at the other end and repeatedly lifted outward, or abducted, strengthening the hip muscles over time. People who experience lingering pain in the abductor muscles, or have difficulty abducting a limb or other body part, should consult a physician, who may prescribe a course of physical therapy.
