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Circumduction is a kind of joint action which produces a circular, or more accurately, a conical movement of the limb extending from that joint. Circling the arm at the shoulder joint is an example of circumduction. Though several of the condyloid joints, including elliptical joints such as those at the wrist and base of the fingers, are described as being capable of circumduction, in reality they can only produce a diamond-shaped movement consisting of flexion and extension, abduction, and adduction. These are, respectively, front, back, and side-to-side movements. Only the ball-and-socket joints — those found at the hip and shoulder — are truly capable of circumduction, or 360 degrees of movement.
The mechanism at the ball-and-socket, or spheroid, joint that allows circumduction is the shape of the bones in the joint. On the top of the bone in the attaching limb is the head, a ball-shaped structure that inserts into a round cavity or socket on the bone receiving the limb. In the hip joint, called the acetabulofemoral joint, the head of the femur or thigh bone inserts into a cavity in the pelvic bone called the acetabulum. This cavity is actually made up of three adjacent bones: the ischium, the ilium, and the pubis.
Because circumduction of the hip joint is the result of a combination of movements, several muscle groups are needed to circle the leg. Bringing the leg forward, or flexion, utilizes the hip flexor muscles — among them the iliopsoas muscles, the rectus femoris of the quadriceps, and the tensor fasciae latae (TFL) of the upper thigh. Abducting the leg, or raising it to the outside, recruits the hip abductors, including the TFL as well as the gluteus medius and minimus in the side of the hip. Extending the leg, or bringing it behind the body, activates the gluteus maximus, hamstrings, and adductor magnus muscles. Finally, adducting the leg, or bringing it to the inside, requires the action of the hip adductors: the adductor brevis, adductor longus, adductor magnus, pectineus, and gracilis, which are all found on the inner thigh.
In the shoulder joint, the glenohumeral joint, the ball of the humerus bone in the upper arm inserts into a cavity in the shoulder blade known as the glenoid fossa. Of any joint in the body, the glenohumeral joint is capable of the greatest range of motion. Like the hip joint, many muscle groups are required to make circumduction possible. Flexion of the arm is achieved via the pectoral muscles in the chest as well as the anterior deltoid in the shoulder, whereas extension requires the posterior deltoid as well as the latissimus dorsi and teres major. Abduction is the result of contracting the supraspinatus, a rotator cuff muscle, and the deltoid; adduction, on the other hand, is accomplished by the pectorals, latissimus dorsi, and teres major, among others.
It is easy for most humans to move their arms or legs in all different directions because of the wonderful make-up of our joints. The hard part is finding a way to do this with our technology.
Scientists have been studying how various creatures move to try and duplicate it with robots and someday, maybe even for prosthetic arms or legs for people in need of replacement limbs.
The truth is even though it looks easy, it is harder than it looks. Even under the best of conditions and with the best of equipment, scientists still have a hard time making robots move with the grace and ability most people do every day.
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