depending on the behavioral context. For example, knowing the position of the head relative to the environment is important in stabilizing vision, while knowing its position relative to the rest of the body is important in maintaining erect posture. Regulation of posture with respect to gravity is obviously important in maintaining postural equilibriumi, which may be defined as the state in which all forces acting on the body are balanced so that the body rests in an intended position(static equilibrium) or is able to progress through an intended movement without losing balance(dynamic equilibrium)
Postural control may have different goals under di ferent circumstances, such as longitudinal alignment of the whole body to maintain a steady, erect stance; remodeling of stance in preparation for a voluntary movement; shaping of the body for display purposes, as in dance; maintenance of balance, as on the gymnast's beam, or conservation of energy in a demanding task.
Different animals may use quite different postural strategies to achieve a steady stance in the face of gravity. Thus, as a result of sizedependent mechanics(allometry), the elephant mechanically locks its legs in line with the gravity vector to minimize the muscle forces supporting its heavy body. In contrast, small quad rupeds tense the muscles around flexed limb joints, thus permitting rapid responses to danger. (Tensing the muscles around flexed joints enhances. muscle stiffness, Since stiff muscle pairs mechanically resist change virtually instantaneously and hence well ahead of any active reflex response, opposition to unexpected perturbations is optimal.)