Primary spinal cord injury (SCI) results from direct mechanical damage to the spinal cord. The resulting pathochemical and pathophysiological events, including oxidative stress and inflammation, lead to secondary injury. The ability to decrease secondary injury may lead to improved recovery. Increasing glutathione production after SCI leads to decreased secondary injury. Glutamine is an important precursor to glutathione following trauma. Skeletal muscle phenotype is strongly influenced by neuromuscular activity. SCI causes myosin heavy chain (MyHC) profiles to shift towards faster isoforms in slow muscles and slower isoforms in fast muscles. The hypothesis was that glutamine, as a precursor of glutathione, administration to SCI rats would lead to better functional recovery and a more preserved MyHC phenotype in locomotory muscles. <p> Rats were assigned to one of four groups; healthy, laminectomy only, untreated SCI, and SCI treated with an intraperitoneal injection of 1mmol/kg glutamine every 12 hours for one week after injury. SCIs were performed at T6 with a modified aneurism clip. Functional recovery was measured weekly using the Basso-Beattie-Bresnahan scale and the angle board method. Six weeks later, all rats were killed, and their extensor digitorum longus and soleus muscles excised and weighed. MyHC composition of the muscles was determined using SDS-PAGE.<p>The hypothesis that glutamine treatment following SCI would lead to better functional recovery and a more preserved MyHC profile was validated. Glutamine treated rats received significantly higher BBB scores (p<0.01) and angle board scores (p<0.001) than untreated SCI rats. Glutamine treatment also reduces muscle atrophy in the soleus muscle, but not the extensor digitorum longus (EDL). In untreated rats the soleus muscle accounted for significantly (p<0.001) less of the percentage of total body weight than the soleus muscle from glutamine treated rats. Finally, SCI rats with preserved functional abilities displayed a significantly better preserved MyHC profile compared to untreated SCI rats. In the soleus healthy rats contain 94% type 1 myosin, treated rats maintained 68% which was significantly (p<0.001) greater than 28% maintained by untreated rats. In the EDL healthy rats contain 55% type 2b myosin, treated rats maintained 32% which was greater than 26% type 2b myosin maintained by untreated rats.

We continually encounter different ground terrain such as slippery, compliant, uneven, rocky, and irregular terrain when walking, yet we know very little about how individuals safely negotiate this type of complex environment. Furthermore, we know little about how aging affects stability in these situations despite the increased risk of falls and fall-related injuries among older adults. Paramount to our comprehension of how individuals safely traverse challenging ground terrain is to understand how visual information is utilized as vision is the first line of defense for preparing for and/or avoiding potentially hazardous terrain or obstacles. Thus, the objective of this thesis was to provide a better understanding towards how individuals negotiate different ground terrain in the environment to maintain dynamic stability and prevent the occurrence of a fall. In particular, the role of vision and the effects of aging were investigated. Three studies focused on the role of vision while negotiating varying ground terrain while two studies examined stability across these surfaces. Two main conclusions can be drawn from the results of the three studies on the role of vision. First, regardless of age individuals fixate on highly task-relevant areas (i.e. surfaces eventually stepped on) in an on-line manner and by fixating approximately two steps ahead. Second, visual information from the lower visual field is important for negotiating varying ground terrain. This latter finding has implications for older adults who wear multi-focal glasses and suggests that these individuals should be cautious when wearing these glasses in complex environments. In terms of stability, the results suggest that young and older adults demonstrate greater instability when walking across varying unstable ground terrain compared to solid level ground. Older adults are particularly more unstable in the medial-lateral direction when negotiating the challenging terrain, which may explain the frequency of laterally directed falls and increased hip-fracture risk with advancing age. Interestingly, older adults appear more stable in the anterior-posterior direction; although, this can largely be explained by the cautious gait strategy (i.e. slower walking speed and shorter steps) adopted by these individuals. The results of the studies of my thesis provide valuable insight into how individuals safely negotiate different types of challenging ground terrain when walking. Importantly, this knowledge can serve as an initial step in attempting to reduce falling among those at risk.

A major function of the central nervous system (CNS) during locomotion is the ability to maintain dynamic stability during threats to balance. The CNS uses reactive, predictive, and anticipatory mechanisms in order to accomplish this. Previously, stability has been estimated using single measures. Since the entire body works as a system, dynamic stability should be examined by integrating kinematic, kinetic, and electromyographical measures of the whole body. This thesis examines three threats to stability (recovery from a frontal plane surface translation, stepping onto and walking on a compliant surface, and obstacle clearance on a compliant surface). These threats to stability would enable a full body stability analysis for reactive, predictive, and anticipatory CNS control mechanisms. From the results in this study, observing various biomechanical variables provides a more precise evaluation of dynamic stability and how it is achieved. Observations showed that different methods of increasing stability (eg. Lowering full body COM, increasing step width) were controlled by differing CNS mechanisms during a task. This provides evidence that a single measure cannot determine dynamic stability during a locomotion task and the body must be observed entirely to determine methods used in the maintenance of dynamic stability.

Bipedal locomotion is a challenging control engineering problem due to the non-linear dynamics and postural instability of the bipedal form. In addition to these challenges, some dynamical effects such as the ground reaction force are difficult to model accurately in simulation. To this end, it is essential to develop physical hardware to validate walking control strategies and gait generation methods. This thesis develops an on-line walking control strategy for humanoid robots and the electromechanical design of a physical platform for experimental validation. The first part of the thesis presents the development of a 14 degrees-of-freedom (DOF) lower body humanoid robot. The initial electromechanical design of the proposed system is derived from dynamic modeling of a general multibody system. Kinematic trajectories for the lower body joints are extracted from motion captured human gait data to form the preliminary design specifications. The drivetrain components are selected by analyzing the mechanical power requirements, torque-speed profiles, efficiency and thermal characteristics of actuators. The supporting mechanical chassis and power transmission system are designed to raise the center-of-mass (to reduce the swinging inertia of each leg) while minimizing the overall weight of the system. Refining the design of a complex multibody robotic system like the biped is an iterative process. The mechanical model of the system is transferred from Computer-Aided-Design (CAD) software to a dynamic simulator for analysis and the design is revised to improve performance. This iterative approach is necessary as small changes in the mechanical model can have significant impact on the overall dynamics of the system as well as implications for control design. A streamlined prototyping toolchain is developed in this thesis to extract the relevant kinematic/dynamic parameters of a mechanical system in CAD and automatically generate the equivalent system in a dynamic simulator. This toolchain is used to revise the electromechanical design and generate forward dynamics simulations. The second portion of this thesis develops a novel walking control strategy for on-line gait synthesis for 3D bipedal robots based on Wight's Foot Placement Estimator (FPE) algorithm. This algorithm is used to determine the desired swing foot position on the ground to \emph{restore} balance for a 2D bipedal robot. The FPE algorithm is extended to the general 3D case by selecting a suitable plane in the desired direction of motion. Complete gait cycles are formed by combining a finite state machine with the 2D FPE solution along the selected plane. Gait initiation is accomplished by computing state-dependent task space trajectories on-line to produce a forward momentum along the selected plane. A whole-body motion control framework (Jacobian-based prioritized task space control scheme) tracks the task space trajectories and generates the appropriate joint level command for each state. The joint level commands are tracked by local high gain PD controllers. This framework produces the desired whole-body motion during each state while satisfying higher priority constraints. Gait termination is accomplished by controlling the swing foot position to track the FPE point on the ground along the selected plane. The proposed control strategy is verified in simulation and experiments. A parallel hardware-in-the-loop (HIL) testing environment is developed for the physical lower body humanoid robot. The motion control framework and joint dynamics used in the proposed walking control strategy are verified through HIL experiments.

This thesis sets up terrain parameters and locomotion strategies of a hexapod robot walking on variable and discontinuous terrain. Walking on this kind of terrain is the greatest advantage of legged robots compared with wheeled robots. First, establish a randomly distributed parameterized terrain. Second, set up morphological parameters and dimension parameters of the robot. Third, build kinematic model and generate continuous gaits of the robot, including crab gaits and turning gaits. The locomotion strategy can determine every AEP ,PEP and stride depending on terrain. Finally, verify the strategy through computer programming and find shorter path by calculating if foothold is available in advance. Because of applying randomly distributed parameterized terrain, in addition to describing the terrain more comprehensively, the terrain parameters can be adjusted easily according to different needs. This research will bring about more applications and developments of legged robots.

Piezoelectric materials have been widely used in applications such as transducers, acoustic components, as well as motion and pressure sensors. Because of the material’s biocompatibility and flexibility, its applications in biomedical and biological systems have been of great scientific and engineering interest. In order to develop piezoelectric sensors that are small and functional, understanding of the material behavior is crucial. The major objective of this research is to develop a test system to evaluate the performance of a sensor made from polyvinylidene fluoride and its uses for studying insect locomotion and behaviors. A linear stage laboratory setup was designed and built to study the piezoelectric properties of a sensor during buckling deformation. The resulting signal was compared with the data obtained from sensors attached a cockroach, Blaberus discoidalis. Comparisons show that the buckling generated in laboratory settings can be used to mimic sensor deformations when attached to an insect. An analytical model was also developed to further analyze the test results. Initial analysis shows its potential usefulness in predicting the sensor charge output. Additional material surface characterization studies revealed relationships between microstructure properties and the piezoelectric response. This project shows feasibility of studying insects with the use of polyvinylidene fluoride sensors. The application of engineering materials to insect studies opens the door to innovative approaches to integrating biological, mechanical and electrical systems.

A discussion of the theory and methodology for creating believable quadrupedal locomotion for computer animation applications. The study focuses on a variety of issues related to producing realistic animal gait animations and includes a case study for rigging and animating the various gaits of a horse. Visualization of unnatural gaits for the horse will also be discussed and animated. The process of rigging involves setting up the character control system in a high-end 3d computer animation program such as Maya which is used extensively by the computer graphics industry.

Thesis (Ph. D.)--University of Chicago, Dept. of Organismal Biology and Anatomy, June 2001. / Includes bibliographical references. Also available on the Internet.

Reproduction de : Thèse de doctorat : Sciences du mouvement humain. Science de la vie et de la santé : Toulon : 2007. / Titre provenant du cadre-titre. Références bibliographiques f.138-152.

Thèse de doctorat : Sciences et techniques des activités physiques et sportives : Rennes 2 : 2007. / Bibliogr. f. 162-185. Annexes.