The different sensorial systems involved in the postural control form a super system preserving the static and dynamical equilibrium of a standing human being, motionless or moving. Now, the human posture captors are endowed with conditions that are sufficient to constitute a dynamical system. Then, we can show that: (i) generic properties of dynamical systems may be applied to the postural system, (ii) we may benefit from conceptual justifications to postural interactions experienced at a clinical level. Moreover, concerning the issue of the multi-causal chain in posturology, it is possible to infer and characterize a certain number of generic properties relative to these postural interactions. From this theoretical grounding, based on the knowledge of dynamical systems, it appears licit to introduce the concept of Non-linear Postural Dynamics (NPD). In a first part of this paper, the bases and foundations of NPD are presented, while the second part deals with different possible modes of NPD. Indeed, because the postural system is comparable to the structure of a dynamical system, it turns out that the former, natural seat of non-linear interaction dynamics, exhibits four dynamical modes and only four, "solutions" to the whole postural system. These four modes are as follows: (1) the quasi-linear mode, (2) the stationary mode, (3) the non-linear convergent mode, and (4) the chaotic mode. The present paper is devoted to the definition and articulation of these postural dynamic's modes. A codification of the clinical elements of their recognition should constitute a logically indispensable sequel. However, by their very constitutive principles themselves, some of these modes call for a functional multi-disciplinary approach. As a consequence, in the search for therapeutic protocols, not blindly but rather built on the interplay of various medical fields relative to posture and its physio-dynamical equilibrium, it is necessary to identify in a first step, and as surely as possible, the postural mode in which the patient stands. (C) 2010 Elsevier Masson SAS. All rights reserved.
