Postural sway, in terms of human sense of balance, refers to horizontal movement around the center of gravity. This sway is essential due to the many large and small changes in the center of gravity due to functions such as walking and breathing. For a person to maintain balance requires coordination of input from multiple sensory systems including the vestibular, somatosensory, and visual systems. The vestibular sense controls equilibrium and directional information as it relates to head position and is related to middle ear. The somatosensory system senses information from skin and joints (pressure and vibratory senses) along with spatial position, movement relative to the support surface, and movement/position of different body parts relative to each other. The visual system works by reference to the verticality of body and head motion and spatial location relative to objects. These systems together coordinate to allow us to maintain balance: the more balanced the less postural sway.