Movement of a limb in a specific direction is referred to as its:

The concept of movement of a limb in a specific direction is best captured by the term "joint action." This term relates to the way joints function to produce movement in the body, as each limb's motion is typically a result of the actions taken at one or more joints. Essentially, every movement involves a change in position of the limb, which occurs through the coordinated actions of the joints.

Joint action encompasses various types of movements – including flexion, extension, abduction, and adduction – that are all executed in specific planes and directions. This is crucial to understanding how limbs can articulate and adapt during various physical activities. Factors such as muscle engagement, joint structure, and overall biomechanics contribute to effective joint actions during movement.

The other terms listed, while they pertain to movement and kinetics, do not specifically describe the directional aspect of limb movement in relation to joint mechanics. For example, planar movement refers more to the overall pathway of movement in anatomical planes, linear velocity deals with speed in a straight line rather than directional specificity, and direction of rotation addresses how an object turns around an axis, rather than the movement of limbs in particular directional pathways defined by the joints. Therefore, "joint action" is the term that most accurately encompasses the concept