About

Katherine Saul is a Professor in the Department of Mechanical and Aerospace Engineering at NC State University, where she also serves as the Director of Graduate Programs. Her research interests include dynamics and neural control of the musculoskeletal system, upper limb biomechanics, orthopaedic rehabilitation, computational dynamic simulation of movement, and musculoskeletal imaging. She directs the Movement Biomechanics Lab (MoBL), which investigates the relationship between musculoskeletal structure and function in the upper limb, utilizing MR imaging, strength assessments, functional testing, and computational simulations to study upper limb function and neuromuscular control in both healthy and impaired populations. At the undergraduate level, she teaches Engineering Dynamics (MAE 208). Outside of her academic work, Dr. Saul enjoys spending time with her family, traveling, being outdoors, and quilting.

Research topics

• Computer Science
• Anatomy
• Physical medicine and rehabilitation
• Physics
• Medicine
• Engineering
• Biology
• Simulation
• Psychology
• Cell biology
• Neuroscience
• Mathematics
• Physiology
• Structural engineering

Selected publications

• Cosimulation of glenohumeral contact mechanics and multibody dynamics

  Computer Methods in Biomechanics & Biomedical Engineering · 2026-01-05 · 1 citations

  articleSenior authorCorresponding

  glenohumeral joint motion and contact mechanics remains challenging. This study evaluated feasibility of co-simulation of glenohumeral contact and dynamics using best available anatomical and biomechanical data. We augmented an existing shoulder model to include joint contact, passive stabilizers, and three additional translational degrees of freedom. Anthropometric scaling and Monte Carlo analysis were used to examine how subject-specific factors affect joint mechanics during scaption. Model predictions aligned with experimental data, with height and shoulder strength emerging as key predictors. These findings support the utility of co-simulation modeling and highlight importance of individual variability in shoulder loading.

  PublisherDOI

• Cosimulation of glenohumeral contact mechanics and multibody dynamics

  Figshare · 2026-01-01

  articleOpen accessSenior author

  Direct measurement of <i>in vivo</i> glenohumeral joint motion and contact mechanics remains challenging. This study evaluated feasibility of co-simulation of glenohumeral contact and dynamics using best available anatomical and biomechanical data. We augmented an existing shoulder model to include joint contact, passive stabilizers, and three additional translational degrees of freedom. Anthropometric scaling and Monte Carlo analysis were used to examine how subject-specific factors affect joint mechanics during scaption. Model predictions aligned with experimental data, with height and shoulder strength emerging as key predictors. These findings support the utility of co-simulation modeling and highlight importance of individual variability in shoulder loading.

  PublisherDOI

• Cosimulation of glenohumeral contact mechanics and multibody dynamics

  Figshare · 2026-01-01

  articleOpen accessSenior author

  Direct measurement of <i>in vivo</i> glenohumeral joint motion and contact mechanics remains challenging. This study evaluated feasibility of co-simulation of glenohumeral contact and dynamics using best available anatomical and biomechanical data. We augmented an existing shoulder model to include joint contact, passive stabilizers, and three additional translational degrees of freedom. Anthropometric scaling and Monte Carlo analysis were used to examine how subject-specific factors affect joint mechanics during scaption. Model predictions aligned with experimental data, with height and shoulder strength emerging as key predictors. These findings support the utility of co-simulation modeling and highlight importance of individual variability in shoulder loading.

  PublisherDOI

• The effect of elbow posture on biceps function at the shoulder in brachial plexus birth injuries: A computational sensitivity analysis

  Clinical Biomechanics · 2026-01-30

  articleSenior author
  PublisherDOI

• Utilizing Reinforcement Learning to Overcome the Challenge of Muscle-Specific EMG Placements for Musculoskeletal Modeling

  IEEE Transactions on Biomedical Engineering · 2026-01-01

  article

  OBJECTIVE: Electromyography (EMG)-driven musculoskeletal (MSK) models are widely used in biomechanics and rehabilitation, but they require muscle-specific (MSp) EMG recordings, which can be difficult to obtain from surface electrodes (sEMGs). This study aims to develop a novel framework to drive a MSK model using non-muscle-specific (NMSp) EMG recordings. METHODS: The key innovation is a reinforcement learning (RL)-based solution that can train a policy to estimate MSp excitations for MSK model control inputs without precise sEMG placement. To validate the method, ten able-bodied individuals and one individual with a transradial amputation participated. NMSp EMGs were recorded simultaneously with intended wrist and hand motion. These data were used to validate how accurately the NMSp EMG-driven MSK model estimates joint motion via our new framework offline. In a second visit, an online evaluation of this framework was conducted as the participants performed a virtual posture matching task. RESULTS: Offline and online performance showed that the RL estimated neural excitations yielded higher or equivalent motion estimation accuracy, compared to MSp EMG recordings, when driving the same MSK model. RL estimated versus actual neural excitations recorded from MSp EMG were similar in terms of co-contraction level and flexion/extension timing. CONCLUSION: Using RL can be an alternative to MSp EMG placement to obtain muscle signals needed to drive MSK models. SIGNIFICANCE: Our RL-based approach is a novel, effective solution to map NMSp EMG recordings to MSp neural excitation. This method may broaden future applications of MSK models when recording MSp EMG is difficult.

  PublisherDOI

• Bone Mineralization and Metabolism are Altered in a Rat Model of Brachial Plexus Birth Injury

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-05-27 · 1 citations

  preprintOpen access

  Brachial plexus birth injury (BPBI) is a common nerve injury incurred during a difficult childbirth when the brachial plexus nerve bundle is excessively stretched, resulting in functional arm impairment in 30-40% of those affected. Injury can present in two different locations, modeled in rats as postganglionic and preganglionic neurectomies. Osseous deformities are present following both injury types. However, the underlying factors behind these deformities are not fully understood. While past studies have explored muscle structure and altered mechanical joint loading as factors, bone metabolism, muscle composition, and muscle-bone crosstalk have not been fully explored. Using postganglionic and preganglionic BPBI rat models and a disuse model, bone metabolism, muscle composition, and muscle-bone crosstalk were explored. Dynamic histomorphometry and similar methods were used to characterize humeral growth and humeral growth plate activity to understand bone metabolism, muscle fibrosis was analyzed to assess muscle composition, and FGF-2 quantification was performed to assess muscle-bone crosstalk. Postganglionic injury portrayed more changes in the humeral diaphyseal region than preganglionic and displayed reduced bone metabolism on the endosteal surface while preganglionic displayed reduced bone metabolism on the periosteal surface. However, only preganglionic showed significantly lower growth plate activity. In regards to fibrosis, both injury types showed fibrosis in the biceps but only preganglionic showed fibrosis in the subscapularis. The limb disuse model did not show fibrosis. Additionally, preganglionic had an increased production of FGF-2 signaling more so in the subscapularis. Overall, deformities from postganglionic injury may be from bone formation and bone resorption while deformities from preganglionic injury are likely from an overall reduction in bone growth that is not solely from limb disuse. The fibrosis and FGF-2 signaling alterations seen are not likely to be the direct cause of osseous deformity and the drivers behind the alterations are likely different between postganglionic and preganglionic injuries.

  PublisherOA PDFDOI

• Assessing sensitivity of predictive shoulder simulations to uncertain soft tissue properties

  Journal of Biomechanics · 2025-12-08 · 2 citations

  articleOpen accessSenior author

  Accurate modeling of glenohumeral joint mechanics requires reliable representations of passive structures such as ligaments and articular cartilage, yet these tissue properties are un-available in vivo on a subject-specific basis. This study evaluated how variability in ligament and cartilage properties propagates to joint-level outcomes. Using a validated musculoskeletal shoulder model and two Monte Carlo simulation frameworks, we independently varied glenohumeral ligament (stiffness and slack length) and cartilage (elastic modulus and thickness) parameters to predict secondary kinematics and joint contact mechanics during scaption. Regression analysis revealed that ligament slack length, particularly for the anterior and middle glenohumeral ligaments (A-IGHL and MGHL), had the most significant influence across outcomes. Articular cartilage properties also contributed significantly to contact mechanics, reinforcing their role as key contributors to load distribution. These findings are especially relevant for modeling pathological conditions such as osteoarthritis and surgical intervention such as joint replacement and ligament reconstructions, where cartilage and ligament structure and properties are altered. This work underscores the importance of accounting for soft tissue variability in subject-specific shoulder simulations and highlights targets for advancing in vivo characterization methods.

  PublisherDOI

• Changes in Glenohumeral Musculoskeletal Development Following Brachial Plexus Birth Injury

  2025-01-13

  preprintOpen accessSenior author

  Brachial plexus birth injury (BPBI), one of the most common nerve injuries in children, often leads to impaired shoulder development, resulting in sustained postural and bone deformity and muscle weakness. Despite the substantial long-term consequences, clinical consensus is lacking for what BPBI treatments are optimal in terms of timing and approach, primarily because BPBI sequelae are complex, involving stunted muscle growth, muscle denervation, and limb disuse that can disrupt glenohumeral joint development. Injury can occur as nerve rupture (postganglionic injury) or nerve avulsion (preganglionic injury), which have distinct musculoskeletal consequences yet are often treated similarly clinically due to their similar initial presentations and the inability of existing methods to distinguish between them. Most of our clinical knowledge about the musculoskeletal detriments in the shoulder comes from studies in nerve rupture patients. Knowledge is generally lacking for the specific effects of injury location on the development and progression of muscle and bone deficits following BPBI. A better understanding of the distinct effects of postganglionic and preganglionic BPBI is important for developing more effective and targeted treatments. More studies are needed to elucidate differences between nerve rupture and nerve avulsion and the particular factors driving glenohumeral deformity development. This paper reviews current knowledge about clinical musculoskeletal deformity development in the shoulder following BPBI, as well as additional insights gleaned from animal and computational models, and identifies key gaps that need to be addressed in future studies to inform better approaches for mitigating and preventing glenohumeral deformity in these patients.

  PublisherOA PDFDOI

• Changes in Glenohumeral Musculoskeletal Development Following Brachial Plexus Birth Injury

  Journal of Orthopaedic Research® · 2025-06-08

  reviewOpen access

  Brachial plexus birth injury (BPBI), one of the most common nerve injuries in children, often leads to impaired shoulder development, resulting in sustained postural and bone deformity and muscle weakness. Despite the substantial long-term consequences, clinical consensus is lacking for what BPBI treatments are optimal in terms of timing and approach, primarily because BPBI sequelae are complex, involving stunted muscle growth, muscle denervation, and limb disuse that can disrupt glenohumeral joint development. Injury can occur as nerve rupture (postganglionic injury) or nerve avulsion (preganglionic injury), which have distinct musculoskeletal consequences yet are often treated similarly clinically due to their similar initial presentations and the inability of existing methods to distinguish between them. Most of our clinical knowledge about the musculoskeletal detriments in the shoulder comes from studies in nerve rupture patients. Knowledge is generally lacking for the specific effects of injury location on the development and progression of muscle and bone deficits following BPBI. A better understanding of the distinct effects of postganglionic and preganglionic BPBI is important for developing more effective and targeted treatments. More studies are needed to elucidate differences between nerve rupture and nerve avulsion and the particular factors driving glenohumeral deformity development. This paper reviews current knowledge about clinical musculoskeletal deformity development in the shoulder following BPBI, as well as additional insights gleaned from animal and computational models, and identifies key gaps that need to be addressed in future studies to inform better approaches for mitigating and preventing glenohumeral deformity in these patients.

  PublisherOA PDFDOI

• The effects of hip abductor fatigue on gait instability in older adults

  Journal of Neurophysiology · 2025-09-12

  articleOpen access

  Fatigue is a critical factor governing muscle force responsiveness and, thereby, capacity to respond to balance challenges. Mediolateral stability is crucial for older adults to safely navigate their daily environments and disproportionally requires active control; the hip abductors are the key muscles that regulate lateral foot placement and mediolateral stability. This research study draws a mechanistic link between hip abductor fatigue and its compromising effect when called upon to preserve lateral stability in older adults.

  PublisherDOI

Recent grants

• Upper limb kinematics and muscular compensation during activities of daily living in older adults with rotator cuff impairment

  NSF · $198k · 2013–2016

• Parallel Development of Bone and Muscle Impairments Following Neonatal Brachial Plexus Injury

  NIH · $399k · 2016–2019

Frequent coauthors

• Anthony C. Santago

  Mitre (United States)

  23 shared

• Johannes F. Plate

  University of Pittsburgh

  23 shared

• Dustin L. Crouch

  Knoxville College

  21 shared

• Meghan E. Vidt

  Penn State Milton S. Hershey Medical Center

  21 shared

• Zhongyu Li

  Northeast Agricultural University

  18 shared

• Derek G. Kamper

  14 shared

• Wendy M. Murray

  13 shared

• Anthony P. Marsh

  Southeast Louisiana Veterans Health Care System

  12 shared

Labs

• Movement Biomechanics Lab (MoBL)PI

Education

• PhD, Mechanical Engineering

  Stanford University

  2005

• MS, Mechanical Engineering

  Stanford University

  2002

• ScB, Mechanical Engineering

  Brown University

  2000