Author ORCID Identifier

https://orcid.org/0000-0001-9699-721X

Semester

Summer

Date of Graduation

2025

Document Type

Dissertation (Campus Access)

Degree Type

PhD

College

School of Medicine

Department

Not Listed

Committee Chair

Sergiy Yakovenko

Committee Member

Valeriya Gritsenko

Committee Member

Loren Rieth

Committee Member

James W. Lewis

Committee Member

Marco Capogrosso

Abstract

Movement is the most sophisticated function arising from the cooperation between body and mind. Yet, the central nervous system (mind) faces the challenge of coordinating complex movements in a highly dimensional musculoskeletal system (body), known as the motor redundancy problem. To address this problem, we designed a neural network solution to computationally solve the inverse kinematics problem using raw motion capture recordings, as described in Chapter 2. Another solution to the redundancy problem can be observed through the reduced dimensionality of the neural control space, a concept known as muscle synergies or motor primitives. Although various mathematical methods applied to differently structured datasets obtain low-dimensional control space solutions, their neuromuscular or biomechanical underpinnings are unclear. Therefore, in Chapter 3, we investigate the link between muscle synergies and limb dynamics (forces) through two components: 1) a gravity component for supporting the limb against gravity and 2) a dynamic component for propelling and orienting the hand. We further examine these two components in the context of stroke. Poststroke, the outputs from the primary motor cortex to motoneurons are disrupted in patterns unique to individuals. While each stroke is different, common patterns of abnormal muscle activations are frequently observed. In Chapter 4, we find how gravity and dynamic components are differentially affected during the sub-acute and chronic stages of stroke recovery and how this knowledge can inform personalized rehabilitation using neuromuscular electrical stimulation. Chapter 5 focuses on the surface neuromuscular electrical stimulation to reduce rapid muscle fatigue, improve non-linear “all-or-none” recruitment of muscle fibers, and alleviate pain and paresthesia – critical factors for the long-term application of electrical stimulation. There, we leverage a phase-shifted stimulation approach, in which pulses of electrical current alternate between two or more electrode pairs. This approach minimizes fatigue, discomfort, and sensory issues while enabling more effective control of muscle contractions. By combining these approaches, we aim to develop a closed-loop stimulation system to support the hemiparetic arm against gravity and assist in the rehabilitation of reaching and grasping movements, as discussed in the final chapter.

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