In partial fulfillment of the requirements for the degree of
Doctor of Philosophy in Applied Physiology
In the
School of Biological Sciences
Joelle Dick
Will defend her dissertation
MANAGING REDUNDANCY FOR STABLE TASK PERFORMANCE UNDER CONSTRAINTS
Friday, November 6th, 2026
12:00 PM
Applied Physiology Building (555 14th St.), Room 1253
Thesis Advisor:
Young-Hui Chang, Ph.D.
School of Biological Sciences
Georgia Institute of Technology
Committee Members:
Lewis Wheaton, Ph.D.
School of Biological Sciences
Georgia Institute of Technology
Boris Prilutsky, Ph.D.
School of Biological Sciences
Georgia Institute of Technology
Greg Sawicki, Ph.D.
Schools of Mechanical Engineering and Biological Sciences
Georgia Institute of Technology
Colin Grove, Ph.D.
Department of Rehabilitation Medicine
Emory University School of Medicine
ABSTRACT:
Human movement requires the nervous system to use motor and sensory redundancy to maintain stability and achieve task-specific goals. This redundancy provides flexibility to adapt movement strategies in response to changing internal, mechanical, and environmental constraints. Understanding how the nervous system uses this flexibility to maintain task performance is essential for understanding motor coordination and adaptation.
This dissertation investigates how the nervous system organizes movement variability and joint coordination in response to three distinct constraints: neuromuscular fatigue, increasing running speed, and altered gravity. Using uncontrolled manifold analysis and system identification techniques, three studies examine how changing task demands influence joint-level coordination and the stabilization of task-relevant variables.
The first study investigated running speed in non-amputees and unilateral transtibial amputee sprinters, showing that runners without a prosthesis shift from interjoint toward individual joint coordination at higher speeds, whereas runners with a prosthesis relied more on interjoint covariation. The second study examined lower-limb coordination during repetitive squatting revealing that kinematic coordination remained relatively consistent as fatigue progressed. The third study examined postural control following simulated hypogravity adaptation, revealing a significant reduction in whole-body center of mass sway without significant changes in joint moment variability or relative ankle-to-hip contributions.
Together, these findings suggest that the nervous system responds to changing physiological, mechanical, and environmental constraints by adjusting movement coordination and control. This dissertation highlights the importance of interpreting movement variability in relation to task-specific goals and provides insight into how the human motor system uses redundancy and flexible coordination strategies to maintain performance across diverse conditions.