2014 - 2016
2012 – 2016
2007 – 2010
2005 – 2006
2001 – 2004
Postdoctoral, Physical Medicine and Rehabilitation
Ph.D., Mechanical Engineering
M.S.E., Mechanical Engineering
B.S.E., Mechanical Engineering
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.
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.
CCTR Endowment Fund of Virginia Commonwealth University
The purpose of this research is to develop innovative methodology to reliably assess changes in nerve supply to muscle and indicate the location of the nervous system that is performing suboptimally. Neuromodulation techniques can then be targeted to cortical or subcortical locations of the nervous system that our new measures indicate.
National Institutes of Health National Center of Neuromodulation for Rehabilitation
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.
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.
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.
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.
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.
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.
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.
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.
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.
Post-stroke hemiparetic walking is typically asymmetric. Assessment of symmetry is often performed at either self-selected or fastest-comfortable walking speeds to gain insight into coordination deficits and compensatory mechanisms. However, how walking speed influences the level of asymmetry is unclear. This study analyzed relative changes in paretic and non-paretic leg symmetry to assess whether one speed is more effective at highlighting asymmetries in hemiparetic walking and whether there is a systematic effect of speed on asymmetry.