Neural mechanisms determining temporal muscle activity patterns during postural control are not well understood. We hypothesize that a feedback control mechanism can predict both temporal extensor muscle EMG and CoM kinematics (acceleration, velocity, and displacement) during postural perturbations before and following peripheral neuropathy to group I afferents induced by pyridoxine intoxication. We introduce a feedback model for analyzing temporal EMG patterns that decomposes recorded electromyogram (EMG) signals into the sum of three center of mass (CoM) feedback components. EMG and CoM kinematics during postural responses due to support surface translations were measured before and 14 days after somatosensory loss in cats. We successfully predicted EMG before and after peripheral neuropathy by modeling a standing cat as an inverted pendulum and decomposing temporal EMG patterns using a simulation with time delayed feedback loop of CoM kinematics. This model accounts for over 60% of the total temporal variability of recorded extensor EMG patterns. Feedback gains for acceleration, velocity and position necessary to predict EMGs before and after sensory loss were different. For intact animals, more that 90% of the initial burst of EMG were due to CoM acceleration feedback, while later portions were due entirely to velocity and position feedback. After peripheral neuropathy, the initial burst was absent and the acceleration gain was significantly reduced when compared to the acceleration gain of intact animals for extensor muscles (p lt 0.05). By successfully decomposing EMG into three kinematic gains, a quantitative comparison of temporal EMG patterns before and after peripheral neuropathy is possible. The reduction of acceleration gain in sensory loss cats suggests that group I afferents provide necessary information that is used as acceleration feedback.

Marfan syndrome, affecting approximately one out of every 5,000 people, is characterized by abnormal bone growth, ectopia lentis, and often-fatal aortic dilation and dissection. The root cause is a faulty extracellular matrix protein, fibrillin-1, which associates with elastin in many tissues. Common carotids from wild-type controls and mice heterozygous for the mgR mutation, the most commonly used mouse model of Marfan syndrome, were studied in a biaxial testing device. Mechanical data in the form of pressure-diameter and force-stretch tests in both the active and passive states were collected, as well data on the functional responses to phenylephrine, carbamylcholine chloride, and sodium nitroprusside. Although little significant difference was found between the heterozygous and wild-type groups in general, the in vivo stretch for both groups was significantly different from previously studied mouse vessels. Although the two groups do not exhibit significant differences, this study comprises a control group for future work with mice homozygous for mgR, which do exhibit Marfan-like symptoms. As treatment of Marfan syndrome improves, more Marfan patients will survive and age, increasing the likelihood that they will develop many of the vascular complications affecting the normal population, including hypertension and atherosclerosis. Therefore, it is imperative to gather biomechanical data from the Marfan vasculature so that clinicians may predict the effects of vascular complications in Marfan patients and develop appropriate methods of treatment.

Hindlimb unloading is a widely used model for studying the effects of microgravity on a skeleton. Hindlimb unloading produces a marked loss in bone due to increased osteoclast activity. Electrical muscle stimulation is being investigated as a simulated resistive exercise countermeasure to attenuate this bone loss. I sought to determine the relationship between strain measured at the antero-medial aspect of the proximal diaphysis of tibia and plantar-flexor torque measured at the ankle during electrical muscle stimulation as an exercise countermeasure for hindlimb unloading in rats. A mathematical relationship between strain and torque was established for the exercise during a 28 day period of hindlimb unloading. The strain generated during the exercise protocol is sufficient to attenuate bone loss caused by hindlimb unloading. Twelve six-month old Sprague-Dawley rats were implanted with uni-axial strain gages in vivo on the antero-medial aspect of the proximal diaphysis of the left tibia. Strain and torque were measured during electrical muscle stimulation for three time points during hindlimb unloading (Day 0 (n=3), Day 7 (n=3), Day 21 (n=3)). Peak strain decreased from 1,100 strain at the beginning of the study to 660 strain after 21 days of hindlimb unloading and muscle stimulation. The peak strain rate measured during muscle stimulation was 10,350 strain/second at the beginning and decreased to 6,670 strain/second after 21 days. The changes in strain are not significant, but the underlying trend in strain values may indicate an increase in bone formation due to the electrical muscle stimulation countermeasure. A mathematical model that relates measured strain to peak eccentric torque during muscle stimulation was created to facilitate estimation of strain for future studies of electrical muscle stimulation during hindlimb unloading.

The purpose of this study is to quantify the dynamic mechanical properties of human cervical ligaments following whiplash. Cervical ligaments function to provide spinal stability, propioception, and protection during traumatic events to the spine. The function of cervical ligaments is largely dependant on their dynamic biomechanical properties, which include force and energy resistance, elongation capability, and stiffness. Whiplash has been shown to injure human cervical spine ligaments, and ligamental injury has been shown to alter their dynamic properties, with potential clinical consequences such as joint degeneration and pain. In this study we quantified the dynamic properties of human lower cervical ligaments following whiplash and compared their properties to those of intact ligaments. Whiplash simulation was performed using biofidelic whole cervical spine with muscle force replication (WCS-MFR) models. Next, ligaments were elongated to failure at a fast elongation rate and peak force, peak elongation, peak energy, and stiffness values were calculated from non-linear force-elongation curves. Peak force was highest in the ligamentum flavum (LF) and lowest in the intraspinous and supraspinous ligaments (ISL+SSL). Elongation was smallest in middle-third disc (MTD) and greatest in ISL+SSL. Highest peak energy was found in capsular ligament (CL) and lowest in MTD. LF was the stiffest ligament and ISL+SSL least stiff. These findings were similar to those found in intact ligaments. When directly comparing ligaments following whiplash to intact ligaments in a prior study it was found that the anterior longitudinal ligament (ALL) and CL had altered dynamic properties that were statistically significant, suggesting that whiplash may alter the dynamic properties of cervical ligaments. These findings may contribute to the understanding of whiplash injuries and the development of mathematical models simulating spinal injury.

Techn. Univ., Diss.--Chemnitz, 2004. / Literaturverz. S. 141 - 151.

Thesis (Ph.D.)--Virginia Commonwealth University, 2009. / Prepared for: Dept. of Mechanical Engineering. Title from title-page of electronic thesis. Bibliography: leaves 98-106.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references. Also available in print.

Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Haj-Ali, Rami; Committee Member: White, Donald; Committee Member: Will, Kenneth; Committee Member: Yavari, Arash; Committee Member: Yoganathan, Ajit. Part of the SMARTech Electronic Thesis and Dissertation Collection.

As of 2005, there were over 1.5 million amputees living in the United States, more than 548,000 of them with upper extremity involvement. The total number of amputees is projected to rise to at least 2.2 million by 2020. Unfortunately, full functional use of upper extremity prosthetic devices is low. Knowledge gained regarding the cortical systems active in amputees performing motor tasks may reveal atypical motor control strategies that contribute to these issues. Substantial evidence demonstrates a strong dependence on left parietofrontal cortical areas to successfully plan and execute tool-use movements and pantomimes. It was previously unclear how this network functioned in users of prostheses. The hypothesis of this dissertation is that in order to optimally engage the typical parietofrontal network during action imitation with a prosthetic device, the action being imitated should be performed by a matching prosthesis. Also, that greater engagement of the parietofrontal network will result in increased ability to perform tool-use movements. First, this dissertation showed that when imitating motor tasks performed by intact actors, prosthesis users exhibit lower engagement of the parietofrontal action encoding system. This network is crucial for motor adaptation. Left parietofrontal engagement was only observed when prosthesis users imitated matched limb prosthesis demonstrations, which suggests that matched limb imitation may be optimal to establish motor representations. Next, intact subjects donned a fictive amputee model system (FAMS) to simulate the limb movement that transradial amputees experience. Matched limb imitation in FAMS users yielded better movement technique compared to mismatched imitation. Finally, the longitudinal effects of a matched limb training paradigm on the cortical action encoding activity and motor behavior in FAMS users were investigated. Matched limb imitation subjects showed greater engagement of the parietofrontal network and better movement technique compared to those trained with mismatched limb. This dissertation has clinical relevance as it supports the notion that matched limb imitation could play an important role in the performance of motor tasks using a prosthetic device. These findings could be used to inform the development of improved rehabilitation protocols that may lead to greater functional adaptation of prosthetic devices into the lives of amputees.

Understanding possible variations in muscle activation patterns and its functional implications to movement control is crucial for rehabilitation. Inter-/intra-subject variability is often observed in muscle activity used for performing the same task in both healthy and impaired individuals. However, the extent to which muscle activation patterns can vary under specific neuromuscular conditions and differ in function are still not well understood. Current musculoskeletal modeling approaches using optimization techniques to identify a unique solution cannot adequately address such questions. Here I developed a novel computational framework using detailed musculoskeletal model to reveal the latitude the nervous system has in selecting muscle activation patterns for a given task regarding neuromechanical constraints. I focused on isometric hindlimb endpoint force generation task relevant to balance behavior in cats. By identifying the explicit bounds on activation of individual muscles defined by biomechanical constraints, I demonstrate ample range of feasible activation patterns that account for experimental variability. By investigating the possible neuromechanical bases of using the same muscle activation pattern across tasks, I demonstrate that demand for generalization can affect the selection of muscle activation pattern. By characterizing the landscape of the solution space with respect to multiple functional properties, I demonstrate a possible trade-off between effort and stability. This framework is a useful tool for understanding principles underlying functional or impaired movements. We may gain valuable insights to developing effective rehabilitation strategies and biologically-inspired control principles for robots.