The analysis of three-dimensional and complex motion sequences of human gait and therefore the most important question of kenesiology ”why are we falling?” is the essence of this paper. The gerontology and its science of movement is currently limited to simple and one-dimensional methods and models. An extensive literature research shows the latest state of research of the three common methods to determine the stability of human gait. To assess the margin of stability, local stability and orbital stability it is shown, how those methods are applicable to evaluate the subject’s ability to recover from any disturbences of the subject’s gait. Based on this assessment and the method’s advantages and disadvantages a new method will be derived that allows spatial analysis of dynamic instability of linear and non-linear human gait. A motion capture system and the timed up and go test serve as a basis for this new method and will be explained. A numerical approximation to optimise the number of markers within a marker-set of a motion capture analysis and its maximum correlation with the full-body-marker-set will be given. This simplification is very helpful for further clinical or scientific research. To validate the new method a trial with subjects will be shown and discussed. New appreciable variables and snapshots of specific situations during the gait offer new and different interpretations of the human gait. The new method is the most applicable and appropriate assessment of human gait and the individual development of the human gait while aging, as well as to detect and prevent falling and associated injuries. Especially directional change of a non-linear gait become assessable with the new method.