Form and exploration of mechanical stability limits in erect stance.

The stability limits of erect stance are described as a geometrical structure in a movement space. Mechanical properties and response latency, a neural property, are determining factors for the stability limits. Standing stability limits of adults and young children are compared, and a simple scheme is suggested by means of which infants can discover the stability limits as they learn to stand. The mechanics of different standing movements are discussed because their spatial temporal properties relate directly to their different stability limits. The combination of the stability limits for different movements gives a total set of stability limits, a different structure for adults than for children.