APA Dictionary of Psychology

trembling of a body part that arises when the individual is engaged in directed voluntary activity and that increases as the movement progresses. Action tremors are classified into the following subtypes: Postural tremor occurs when the person maintains a position against gravity, such as holding the arms outstretched; kinetic tremor appears during movement of a body part, such as moving the wrists up and down; intention tremor is the trembling of a body part that arises near the conclusion of a directed, voluntary movement, such as touching a finger to one’s nose; task-specific tremor appears during the performance of highly skilled, goal-oriented tasks such as handwriting; and isometric tremor occurs during a voluntary muscle contraction that is not accompanied by any other movement. Compare resting tremor.