In biomechanics, balance is an ability to maintain the line of gravity (vertical line from centre of gravity) of a body within the base of support with minimal postural sway. Sway is the horizontal movement of the centre of gravity even when a person is standing still. A certain amount of sway is essential and inevitable due to small perturbations within the body (e.g. , breathing, shifting body weight for one foot to the other or from forefoot to rearfoot) or from external sources (e.g.