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Table of contents
1. Introduction
I. Abstract
II. Optimal patterns of motor coordination
1. Feedback and feedforward control
2. Internal inverse models for feedforward control
3. Motor redundancy and the uncontrolled manifold
4. Stochastic optimal feedback control for redundant tasks
5. Adaptive control
6. Centralised knowledge
III. Where is the knowledge for motor control
1. Basic neuro-anatomy of motor control
2. Spinal organisation of movement
3. Learning and adaptation in spinal synergies
IV. Improvements in performance through the adjustment of body dynamics
1. How the way we move shapes our body
2. How much knowledge is necessary for motor control?
3. Adjustment of body mechanical properties for stability
V. Motivation and plan of the thesis
1. Motivation
2. Plan of the thesis
2. Postural adjustments for improving stability
I. Introduction
1. Muscular contraction response to a perturbation
2. Body mechanical properties
3. Interactions between body mechanical properties and sensorimotor feedback
II. Modelling results
1. Single inverted pendulum model of stance
2. Delayed feedback control of a single dimensional system
3. Generalisation to N dimensions
III. Discussion
1. Adjusting posture to decrease relative speed
2. Adjusting feedback gains to changed dynamics
3. Is immobility critical?
IV. Supplementary methods: Stability analysis
1. Propagation of exponential signals and derivation of the characteristic equation
2. Nyquist criterion
3. Application to our system
4. Simulations
V. Supplementary methods: Critical damping
1. Pade approximation
2. Generalisation of criticality
VI. Supplementary methods: generalisation to N dimensions
3. Mobility as the purpose of postural control
I. Abstract
II. Introduction
III. Adjustment of posture during stance
1. The standing posture allows for mobility
2. The standing posture is actively maintained
3. The standing posture is adjusted in anticipation of movement
4. Summary
IV. Adjustment of posture during voluntary movement
1. Initiation of voluntary movement
2. The ability to use one’s weight for movement requires practice
V. Balance requires mobility rather than immobility
1. Responding to external perturbations
2. Emergence over development and impairment with aging
VI. Discussion
1. Posture is adjusted in view of mobility rather than immobility
2. Mobility emerges through development and skill learning
VII. Supplementary methods
1. Limits to ankle torque
2. Horizontal acceleration of the CoM
4. Postural adjustments for mobility and immobility in aging
I. Introduction
1. Mobility in aging
2. Falls in aging and risk factors for falling
3. Clinical assessments of balance and mobility and prediction of fall risk
4. Laboratory based assessments of balance and mobility and prediction of fall risk
5. Postural adjustments
II. Methods
1. Protocol
2. Analysis
III. Results
1. Previously published results
2. Performance in the two tasks
3. Initial posture
4. Change in initial posture across tasks
5. Ankle stiffness
IV. Discussion
1. Adjustment of the initial position of the CoM
2. Adjustment of ankle stiffness
3. How to measure the adjustment of ankle stiffness
V. Supplementary methods
1. Success in the perturbation task
2. Position of the centre of mass
5. Discussion
I. Summary
II. Postural versatility
1. Adjustment of posture to the task
2. Postural allostasis
3. Fall risk in the elderly
III. Motor coordination
1. Redundancy in motor tasks
2. Change in coordination during learning
3. Postural modulation after learning
6. Appendix: Models of human stance
I. Ankle torque and body rotational momentum
1. Torques of the external forces
2. Lower leg muscle contraction changes the ground reaction torque
II. Double inverted pendulum model
1. Rotational momentum
2. Acceleration of the centre of mass
7. References
