Accomplishments

Outstanding Researcher Award, National Center for Simulation in Rehabilitation Research
2018

Sarah Baskin Award for Excellence in Research, 1st Place Postdoctoral Fellow Category
2015

Craig H. Neilsen Foundation Postdoctoral Fellowship
2014 - 2016

NIH Loan Repayment Program Award, Rehabilitation Institute of Chicago
2012 – 2016

National Science Foundation Graduate Research Fellowship, UT Austin
2007 – 2010

Thrust 2000 Fellowship, UT Austin
2005 – 2006

Class of 1931 Engineering Scholar, University of Michigan
2001 – 2004

Affiliations

• American Society of Biomechanics
• IEEE Engineering in Medicine and Biology
• Biomedical Engineering Society

Courses

EGRB 491 Modeling and Simulation of Human Movement
Students learn why modeling and simulation techniques are needed to complement experimental approaches, and how to implement modeling and simulation techniques to understand human movement towards optimizing ability and rehabilitation after a musculoskeletal or neurologic injury.

EGRB 423 Rehabilitation Engineering and Prostheses
This course explores the principles and practices regarding the measurement and analysis of human movement towards the development of rehabilitation therapies, prostheses, and other assistive devices.

EGRB 203 Statics and Mechanics of Materials
The objective of this course is to understand the theory and application of engineering mechanics applied to the design and analysis of rigid and deformable structures.

Education

Northwestern University and the Rehabilitation Institute of Chicago
Postdoctoral
Physical Medicine and Rehabilitation

The University of Texas at Austin
Ph.D.
Mechanical Engineering

The University of Texas at Austin
M.S.E.
Mechanical Engineering

University of Michigan
B.S.E.
Mechanical Engineering

Research Focus

Musculoskeletal modeling and simulation to estimate biomechanical forces
There are many quantities we cannot measure with experimental techniques in human subjects during dynamic tasks of daily living. Musculoskeletal modeling and simulation analyses of human movement, however, can be used to estimate important quantities such as dynamic muscle and tendon forces, joint contact forces, and muscle mechanical work. These quantities provide valuable insight with regard to muscle function and the effect of neurologic impairments on task performance. Our research in modeling and simulation spans different patient populations (e.g., post-stroke and spinal cord injured patients) and different human movements, such as walking and wheelchair mobility activities.

Design interventions that promote neuroplasticity to improve function after neurologic injury
Our goal is to increase our understanding of factors that contribute to functional neuroplasticity, and to use that knowledge to direct rehabilitation. Our ultimate goal is to optimize neuromuscular function in individuals with sensorimotor deficits to improve their quality of life and independence, and we believe neuromodulation as an adjunct to physical rehabilitation has much promise in this regard.

Research Grants

Home-Based Immersive Virtual Reality and Spinal Stimulation for Upper Limb Rehabilitation in Tetraplegia
Department of Defense, Spinal Cord Injury Research Program
2022-07-31

Our goals are to develop and test a combined virtual reality and trans-spinal stimulation training as a home-based, upper limb intervention for individuals with tetraplegia. The intervention development is heavily informed by expert and lived experience input.

Virginia Consortium for Spinal Cord Injury Care
National Institute on Disability, Independent Living and Rehabilitation Research Spinal Cord Injury Model Systems
2021-08-31

The goal of this center is to enhance upper extremity function in persons with tetraplegia and to improve the equitable delivery, quality, and coordination of interdisciplinary spinal cord injury (SCI) rehabilitation across the healthcare continuum. Role: Co-Investigator

Quantification of Shoulder Pathology and Manual Wheelchair Propulsion in Children and Adults with Spinal Cord Injury using Advanced Biomechanical Modeling and Diagnostic Imaging
Eunice Kennedy Shriver National Institute of Child Health & Human Development
2019-06-30

The central hypothesis is that the variability of manual wheelchair propulsion is significantly greater in children than adults, which ultimately reduces overuse injuries of the shoulder and leads to decreased shoulder pain and pathology. The outcomes of this research could lead to improved wheelchair training guidelines, rehabilitation paradigms, prediction of injuries and development of novel interventions for the prevention of shoulder pathology and musculoskeletal disease. Role: Co-Investigator

Using Haptic Virtual Reality and Noninvasive Brain Stimulation to Restore Touch Perception Among Individuals with Complete Paraplegia
VCU Value and Efficiency Teaching and Research (VETAR) Award
2020-06-30

This project combines a novel virtual haptic interface with noninvasive brain stimulation (transcranial direct current stimulation) to promote touch sensation among individuals with paraplegia identified as having discomplete spinal cord injury using an imaging protocol.

Intermittent Theta Burst Stimulation to Promote Motor Re-education After Upper Limb Reconstruction in Tetraplegia
National Institutes of Health National Center of Neuromodulation for Rehabilitation
2017-06-30

Our goal is to determine whether purposefully increasing corticomotor excitability during motor re-learning as an adjuvant to physical rehabilitation after tendon or nerve transfer increases post-transfer strength and functional outcomes. Intermittent theta burst stimulation (iTBS) is a non-invasive brain stimulation technique that can increase corticomotor excitability. The purpose of this work is to determine the effect of iTBS on corticomotor excitability of the biceps in individuals with tetraplegia (with and without upper limb reconstruction) and nonimpaired individuals.

Selected Articles

Effect of intermittent theta burst stimulation on biceps corticomotor excitability in nonimpaired individuals
Neuroscience Letters
2021

Intermittent theta burst stimulation (iTBS) is a form of repetitive transcranial magnetic stimulation (TMS) that can increase corticomotor excitability in distal upper limb muscles, but the effect on the more proximal biceps is unknown. The study objective was to determine the effect of iTBS on corticomotor excitability of the biceps brachii in non-impaired individuals. Ten individuals completed three sessions, and an additional ten individuals completed one session in a secondary study; each session included sham and active iTBS. Resting and active motor thresholds (RMT, AMT) were determined prior to sham and active iTBS. Motor evoked potentials (MEPs) in response to single pulse TMS served as our measure of corticomotor excitability. Our results suggest that when RMTs are expected to be high when measured with biphasic stimulation, monophasic stimulation can better capture changes in MEPs induced by iTBS, and biphasic stimulation appears limited in its ability to capture changes in biceps MEPs in nonimpaired individuals. In both cohorts, increased corticomotor excitability after iTBS occurred when the biceps AMT:RMT ratio was high. Thus, the AMT:RMT ratio may be a predictive measure to evaluate the potential for iTBS to increase biceps corticomotor excitability.

Effect of low-cost transcranial magnetic stimulation navigation on hotspot targeting and motor evoked potential variability in the biceps brachii
Restorative Neurology and Neuroscience
2021

We implemented a navigated TMS system using a low-cost 3D camera system and open-source software environment programmed using the Unity 3D engine. MEPs were collected from the biceps brachii at rest and during voluntary contractions across two sessions in ten non-disabled individuals. Motor hotspots were recorded and targeted via two conditions: navigated and conventional. The low-cost system is a suitable alternative to expensive systems in tracking the motor hotspot between sessions and quantifying the error in coil placement when delivering TMS. Biceps MEP variability reflects physiological variability across a range of voluntary efforts, that can be captured equally well with navigated or conventional approaches of coil locating.

Assessing the effects of gait asymmetry: Using a split-belt treadmill walking protocol to change step length and peak knee joint contact force symmetry
Journal of Biomechanics
2021

Asymmetrical gait may affect important outcomes such as knee joint contact force (KJCF). A split-belt treadmill (SBTM) can be used to provoke changes in step length symmetry (SLsym) and may produce a similar response in KJCF symmetry (KJCFsym) between limbs. The purpose of this study was to explore the utility of employing a SBTM walking paradigm to alter KJCF and KJCFsym and to determine if changes in SLsym coincided with changes in KJCFsym. Results suggest a SBTM program may alter KJCF and KJCFsym between limbs. Furthermore, a comparison between baseline and post-adaptation may be more appropriate for evaluating the relationship between SL and KJCF.

Effect of biceps-to-triceps transfer on rotator cuff stress during upper limb weight-bearing lift in tetraplegia: A modeling and simulation analysis.
Journal of Biomechanics
2019

Rotator cuff stress during upper limb weight-bearing lifts presumably contribute to rotator cuff disease, which is the most common cause of shoulder pain in individuals with tetraplegia. Elbow extension strength appears to be a key determinant of rotator cuff stress during upper limb weight-bearing lifts since individuals with paraplegia who generate greater elbow extensor moments experience lower rotator cuff stress relative to individuals with tetraplegia. Biceps-to-triceps transfer surgery can increase elbow extension strength in individuals with tetraplegia. The purpose of this study was to determine whether active elbow extension via biceps transfer decreases rotator cuff stress during weight-bearing lifts in individuals with tetraplegia. A forward dynamics computational framework was used to estimate muscle stress during the lift. We found that limited elbow extension strength in individuals with tetraplegia, regardless of whether elbow strength is enabled via biceps transfer or is residual after spinal cord injury, results in muscle stresses exceeding 85% of the peak isometric muscle stress in the supraspinatus, infraspinatus, and teres minor. The rotator cuff stresses we estimated suggest that performance of weight-bearing activities should be minimized or assisted in order to reduce the risk for shoulder pain. Our results also indicate that biceps transfer is unlikely to decrease rotator cuff stress during weight-bearing lifts in individuals with tetraplegia.

Voluntary activation of biceps-to-triceps and deltoid-to-triceps transfers in quadriplegia
PLOS One
2017

The biceps or the posterior deltoid can be transferred to improve elbow extension function for many individuals with C5 or C6 quadriplegia. We compared voluntary activation during maximum isometric elbow extension following biceps transfer and deltoid transfer in three functional postures. Overall, individuals with a biceps transfer better activated their transferred muscle than those with a deltoid transfer. This difference in neural control augmented the greater force-generating capacity of the biceps leading to increased elbow extension strength after biceps transfer (average 9.37 N-m across postures) relative to deltoid transfer (average 2.76 N-m across postures) in our study cohort.

Posture-dependent corticomotor excitability differs between the transferred biceps in individuals with tetraplegia and the biceps of nonimpaired individuals
Neurorehabilitation and Neural Repair
2017

Following biceps transfer to enable elbow extension in individuals with tetraplegia, motor re-education may be facilitated by greater corticomotor excitability. Arm posture modulates corticomotor excitability of the nonimpaired biceps. If arm posture also modulates excitability of the transferred biceps, posture may aid in motor re-education. Our objective was to determine whether multi-joint arm posture affects corticomotor excitability of the transferred biceps similar to the nonimpaired biceps. We assessed corticomotor excitability using transcranial magnetic stimulation. Arm posture modulated corticomotor excitability of the transferred biceps differently than the nonimpaired biceps. Elbow extension strength was positively related and muscle length was unrelated, respectively, to motor-evoked potential amplitude across the arms with biceps transfer. Corticomotor excitability of the transferred biceps is modulated by arm posture and may contribute to strength outcomes after tendon transfer.

Withdrawal reflexes in the upper limb adapt to arm posture and stimulus location.
Muscle Nerve
2014

We examined the adaptability of withdrawal reflexes in response to nociceptive stimuli applied in different arm postures and to different digits. Reflexes were elicited at rest, and kinetic and electromyographic responses were recorded under isometric conditions, thereby allowing motorneuron pool excitability to be controlled. The withdrawal reflex in the human upper limb adapts in a functionally relevant manner when elicited at rest.

Muscle work is increased in pre-swing during hemiparetic walking.
Clinical Biomechanics
2011

Three-dimensional forward dynamics simulations of two representative hemiparetic subjects walking with different self-selected speeds (i.e., limited community=0.45 m/s and community walkers=0.9 m/s) and a speed and age-matched control subject were generated to quantify musculotendon (fiber and in-series tendon) work during paretic pre-swing. Total paretic and non-paretic fiber work were increased in both the limited community and community hemiparetic walkers compared to the control. Increased fiber work in the limited community walker was primarily related to decreased fiber and tendon work by the paretic plantar flexors requiring compensatory work by other muscles. Increased fiber work in the community walker was primarily related to increased work by the hip abductors and adductors. These results may partly explain the increased metabolic cost of hemiparetic walkers compared to nondisabled walkers at matched speeds.

Pre-swing deficits in forward propulsion, swing initiation and power generation by individual muscles during hemiparetic walking.
Journal of Biomechanics
2010

Using simulation analyses, we identified important deficits that limit walking ability in individuals post-stroke. Decreased paretic soleus and gastrocnemius contributions to forward propulsion and power generation were the primary impairments in a representative limited community walker compared to the control subject. In a representative community walker, paretic muscles had the net effect to absorb energy from the paretic leg during pre-swing in the community walker suggesting that deficits in swing initiation are a primary impairment. Rehabilitation strategies aimed at diminishing these deficits have much potential to improve walking function in these hemiparetic subjects and those with similar deficits.