The inter- and intra-foot coordination dynamics of quiet standing postures
Open Access
- Author:
- Wang, Zheng
- Graduate Program:
- Kinesiology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 01, 2013
- Committee Members:
- Karl Maxim Newell, Dissertation Advisor/Co-Advisor
Karl Maxim Newell, Committee Chair/Co-Chair
Semyon Slobounov, Committee Member
John Henry Challis, Committee Member
David Russell Hunter, Special Member - Keywords:
- Foot coordination
Postural control
Quiet standing - Abstract:
- Human postural stance is inherently unstable and is a complex task involving the coordination and control of redundant degrees of freedom at each level of analysis (e.g., limbs, joints, muscles, etc.). In numerous investigations of the postural control system, it has been found that, the coordination and control of posture and balance is simplified by employing different strategies for postural stability. For example, strategies may utilize the ankle joint alone (i.e., inverted pendulum model), ankle-hip coordination (i.e., double inverted pendulum model) or multi-joint synergy (i.e., multi-linkage model). Even though the postural control mechanism has been comprehensively documented by investigations of EMG, kinematic and kinetic data, there are limited data on the investigation of the inter- and intra-foot coordination dynamics in quiet stance. The primary focus of this dissertation is on the center of pressure (COP) foot coupling under the varying mechanical and task constraints induced by different stances. We investigated: 1) how foot position and asymmetrical body weight distribution interact to influence postural control and inter-foot coordination; 2) the effect of foot position and orientation on the body weight distribution and the foot coordination dynamics of standing postures; and 3) the influence of a shortened support surface together with its orientation on the COP coordination in quiet stance. Three experiments were conducted that manipulated foot position, foot orientation and the base of support properties in quiet standing. The following conclusions have been reached from the analyses of the individual foot COPs and the coupling between COPs: 1) The time evolutionary properties of the inter-foot coordination dynamics revealed patterns of “stable” but “flexible” control of the postural system as a function of foot position and orientation. In particular, the staggered stance represents a “hybrid” blend of the properties of the side-by-side and tandem foot position in both linear and nonlinear analyses. 2) Foot position played a more important role than its orientation in channeling the inter- and intra-foot coordination dynamics. When the postural stance was challenged by the limitation of the base of support (side-by-side and tandem stances), the COPs in the unstable plane (inter-foot coordination) were predominantly involved in postural control. In contrast, when standing posture was not challenged by the support boundary (staggered stance), the COPs of the more loaded foot (intra-foot coordination) dominated postural stability. 3) When the shortened base of support was oriented along the horizontal axis, the four COP time series revealed a parallel contribution indicating an inter-dependence of the inter- and intra-foot coordination. When the shortened support area was positioned along the longitudinal axis, the COPs in the sagittal plane (inter-foot coordination) displayed a more significant contribution to postural stability. Multistability exists at different levels of the motor control hierarchy (Braun and Mattia 2010; Kelso 2012). The “phase wandering” of the inter-foot coordination dynamics presented in Experiment 1 reflects the multistability properties of the postural control system. The phase synchronization of the COPL—COPR coupling characterizes the capability of the self-organizing system to retain its intrinsic attractive states (i.e., stability) whereas the phase transition specifies the escape or de-affiliation tendencies of the system from an attractive steady state. Overall, our findings support the proposition that postural control is achieved through the foot coordination dynamics and the asymmetrical body weight distribution.