This paper presents a kinematic and dynamic model to predict the arm posture when high velocity or acceleration motion of the end-effector (hand) is required. Two measures, directional dynamic dexterity (DDD) and directional kinematic dexterity (DKD) are defined and applied to predict the human arm posture. It is shown that DDD predicts the postures in which the hand has a high acceleration and DKD predicts the postures in which hand adopts a high velocity. The results are verified by comparing the predicted postures with practical postures required in high acceleration and velocity applications.