Postural coordination patterns and surface of support dyanmics
Open Access
- Author:
- Ko, Ji Hyun
- Graduate Program:
- Kinesiology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 31, 2014
- Committee Members:
- Karl Maxim Newell, Dissertation Advisor/Co-Advisor
John Henry Challis, Committee Member
David A. Rosenbaum, Committee Member
Semyon Slobounov, Committee Member - Keywords:
- Postural control
moving platform
principal component analysis
collective variable - Abstract:
- The degrees of freedom problem (DFs) (Bernstein, 1967) has been interpreted as the central issue in motor control. It has been primarily investigated by focusing on the peripheral mechanical and physiological component levels (e.g., muscles, joints, etc.) in a variety of movement contexts. The analysis of these component DFs is important but it is distinct though related to the analysis of the dynamical (also called active or functional) DFs of the coordination and control of the motor output. The dynamical DFs provide information about how the very many component level DFs are organized and how the state of the organization of the system dynamics changes under certain constraints (e.g., environmental, organism, and task). The experimental paradigm used was a sinusoidally translating support surface to drive the organization of the individual DFs (e.g., joint) in the control of upright standing balance. It was used to address the questions of how the organizational properties of the postural control system, beyond the level of joint kinematic description, change during a moving surface of support balance task. In addition, the organization of postural coordination problem provides insight on the additional question of how the postural system constrains the many redundant DFs to a collective variable or a set of variables to realize task demands. Experiment 1 found by principal component analysis that the number of dynamical DFs of the postural coordination pattern was reduced from three to two as the average velocity of the support surface induced by a combination of frequency (0.2, 0.6, and 1.0 HZ) and amplitude (9, 16, and 23 cm) increased producing different contribution of each joint motion to the organization of the postural coordination pattern. Experiment 2 addressed the question of how the organizational properties of coordination patterns change as a function of the continuous scaling of frequency (0.2 Hz to 1.3 Hz) of the support surface in a trial. In addition, we investigated whether the postural system organizes a particular modal solution or a set of solutions to preserve the postural stability as a function of practice. The findings showed that practice induced 3 dynamical DFs at the lower frequencies and 2 dynamical DFs at the higher frequencies of the support surface. Relative phase analysis revealed that the anti-phase pattern of the ankle-hip coordination held at the higher frequencies and contributed to change in the dynamical DFs of the postural coordination patterns. Experiment 3 examined whether the coordination of COM-COP in the space level (Bernstein, 1996) exhibits a phase transition in movement coordination to the continuous scaling (0 to 3 Hz or vice versa) of the support surface dynamics. The results showed that the support surface dynamics induced a non-equilibrium phase transition of the COM-COP pattern including dynamic characteristics such as a critical fluctuations and hysteresis. Conversely, the ankle-hip coordination, in the level of muscular-articular synergies (Bernstein, 1996), transitioned earlier than the COM-COP with no change in the associated dynamical phenomena. Overall, the findings reveal that sinusoidally translated dynamics of the support surface maps redundantly though preferentially to a small set of qualitatively different postural coordination patterns. The organization of the coordination patterns that emerge in joint space is influenced by a particular adaptive solution to maintain postural stability under the broad range of the support surface constraints. Lastly, the COM-COP coordination that is at the level of space rather than that of synergy is a candidate collective variable of the multi-segmental whole body system acting on a redundant postural task.