Balance/stabilityis maintained as long as the footprint of the center of gravity (COG)/center ofbody weight is inside the base of support/support area.
All people experience swaying of the center of body weight. Imbalance occurs whenthe COG sways beyond the base of support as illustrated in the attachment. Since the footprint of the center of body weight is much closer to the rear edge ofthe base of support (because most of the body weight is on the heels), most incidents of imbalance occur when center of body weight sways beyond the rearborder of the base of support.
Humanbeing has three bio systems responsible for imbalance alerting – vision, vestibular and proprioceptive. Young people have sensitive bio systems that are able to detect imbalance at an early stage and they succeed to regain balance by slight movements of the body. However, when imbalance is already developed, people instinctively move a leg backward to regain balance. This “backward step” or sometimes called “compensatory step” is illustrated in the attachment.
Old people, however, because ofdegraded sensing bio systems detect imbalance with a delay, when it is already developed, and because of slow reflexes, they are not able to perform the backward step in time and they fall. Incidentally, the fall can occur in any arbitrary direction. In other words: the reason for the fall is the backward sway of theCOG, whereas the result can be a fall in any direction.