The interaction of the neuromuscular mechanisms ensuring optimal stability of human standing posture is not fully clarified. To explain this problem in the present study, we focused on identifying a human posture control system based on the assessment of center-of-gravity (COG) trajectory characteristics during the erect posture. Towards this aim, a transdisciplinary multilevel grey-box model of standing posture control has been proposed and then verified experimentally. Trajectories of COG during quiet stance were assessed in a large group of young healthy subjects, known for the most stable posture. Additionally, the impact of visual input on the COG output was analyzed to assess the robustness of the control. We assumed that in physiological conditions human erect posture can be efficiently stabilized by the ankle joint muscles mainly. Respiratory and circulatory rhythms disturb the COG positioning which results in its random oscillations in the vicinity of the setpoint. Observed in young healthy individuals, the spatiotemporal characteristics of the COG oscillations support the notion that the human standing posture is maintained by a dedicated linear time-invariant control system.