Movements Permitted by Synovial Joints
Intact skeletal muscles are attached to bones by tendons that span joints. When a muscle contracts, one bone moves in relation to another bone.
Angular movements increase or decrease the joint angle
between the bones of a joint:
Flexion decreases the joint angle. Flexion of the elbow moves the forearm toward the upper arm; flexion of the knee moves the lower leg toward the upper leg. Dorsifle:xion is flexion of the foot upward, as when you stand on your heels; plantar flex'ion is flexion of the foot downward, as when you stand on your toes. Extension increases the joint angle. Extension of the flexed elbowtstraightens the arm so that there is a 18° angle at the elbow. HyPerextension occurs when a portion of the body parts are extended beyond 1800. It is possible to hyperextend the head and the trunk of the body.
Abduction is the movement of a body part laterally away from the midline. Abduction of the arms or legs moves them to the side, away from the body.
Adduction is the opposite of abduction. It is the movement of a body part toward the midline. For example, adduction of the arms or legs moves them back to the sides, toward the body.
Circular movements occur at ball-and-socket joints:
Rotation is the movement of a body part around its own axis, as when the head is turned to answer "no" or when the arm is twisted one way and then the other.
Supination is the rotation of the lower arm so that the palm is upward; pronation is the opposite-the movement of the lower arm so that the palm is downward.
Circumduction is the movement of a body part in a wide circle, as when a person makes arm circles. If the motion is observed carefully, one can see that, because the proximal end of the arm is stationary, the shape outlined by the arm is actually a cone.
Inversion and eversion are terms that apply only to the feet. Inversion is turning the foot so that the sole is inward, and eversion is turning the foot so that the sole is outward.
Elevation and depression are the lifting up and down, respectively, of a body part, such as when you shrug your shoulders.
Movements at joints are broadly classified as angular and circular.
