It is often assumed that more realism is always desirable. In particular, many techniques for locomotion in Virtual Reality (VR) attempt to approximate real-world walking. However, it is not yet fully understood how the design of more realistic locomotion techniques influences effectiveness and user experience. In the previous VR studies, the effects of interaction fidelity have been coarse-grained, considering interaction fidelity as a single construct. We argue that interaction fidelity consists of various independent components, and each component can have a different effect on the effectiveness of the interface. Moreover, the designer's intent can influence the effectiveness of an interface and needs to be considered in the design. Semi-natural locomotion interfaces can be difficult to use at first, due to a lack of interaction fidelity, and effective training would help users understand the forces they were feeling and better control their movements. Another method to improve locomotion interaction is to develop a more effective interface or improve the existing techniques. A detailed taxonomy of walking-based locomotion techniques would be beneficial to better understand, analyze, and design walking techniques for VR. We conducted four user studies and performed a meta-analysis on the literature to have a more in-depth understanding of the effects of interaction fidelity on effectiveness. We found that for the measures dependent on proprioceptive sensory information, such as orientation estimation, cognitive load, and sense of presence, the level of effectiveness increases with increasing levels of interaction fidelity. Other measures which depend more on the ease of learning and ease of use, such as completion time, movement accuracy, and subjective evaluation, form a u-shape uncanny valley. For such measures, moderate-fidelity interfaces are often outperformed by low- and high-fidelity interfaces. In our third user study, we further investigated the effects of components of interaction fidelity, biomechanics and transfer function, as well as designers' intent. We learned that the biomechanics of walking are more sensitive to changes and that the effects of these changes were mostly negative for hyper-natural techniques. Changes in the transfer function component were easier for the user to learn and to adapt to. Suitable transfer functions were able to improve some locomotion features but at the cost of accuracy. To improve the level of effectiveness in moderate-fidelity locomotion interfaces we employed an effective training method. We learned that providing a visual cue during the acclimation phase can help users better understand their walking in moderate-fidelity interfaces and improve their effectiveness. To develop a design space and classification of locomotion techniques, we designed a taxonomy for walking- based locomotion techniques. With this taxonomy, we extract and discuss various characteristics of locomotion interaction. Researchers can create novel locomotion techniques by making choices from the components of this taxonomy, they can analyze and improve existing techniques, or perform experiments to evaluate locomotion techniques in detail using the presented organization. As an example of using this taxonomy, we developed a novel locomotion interface by choosing a new combination of characteristics from the taxonomy. / Ph. D. / Virtual Reality researchers have been trying to develop natural travel techniques to allow users to physically walk and move in virtual environments rather than using unnatural methods such as joysticks. Using such techniques, the user can physically move or perform actions similar to walking to navigate through virtual environments. More natural travel methods can improve various parameters such as sense of presence and spatial understanding. However, the effects of increasing naturalness of walking on the user experience have not been known for years. In this dissertation, we have run four user experiments, performed a meta-analysis on the literature and developed a taxonomy to contribute a better understanding of how increasing levels of walking naturalness can affect user experience in Virtual Reality. Our findings can benefit designers and researchers in designing novel travel techniques, improve existing techniques or more in-depth understating of what to expect when employing a certain travel technique.

Gap crossing is a regular locomotor activity for arboreal animals. The distance between branches likely plays a role in determining whether an animal is capable of crossing a given gap, and what locomotor behavior it uses to do so. Yet, despite the importance of gap distance as a physical parameter influencing gap crossing behavior, the precise relationships between gap distance and movement kinematics have been explored in only a very small number of species. One particularly interesting group of arboreal inhabitants are the flying snakes (Chrysopelea). This species is able to use a dynamic "J-loop" movement to launch its glides, but it is not known whether it is also capable of using such jumps to cross smaller gaps between tree branches. This dissertation addresses this knowledge gap, and investigates the influence of gap distance on crossing behavior and kinematics in three closely-related species of snake: Chrysopelea paradisi, a species of flying snake, and two species from the sister genus, Dendrelaphis, neither of which can glide. Chapter 2 is a literature review of the biomechanics of gap crossing, specifically focusing on the role played by gap distance, and establishes the context for the rest of the work. Chapter 3 presents a detailed study of how increasing gap size influences the behavior and kinematics of gap crossing in C. paradisi, showing that this species uses increasingly dynamic movements to cross gaps of increasing size. Chapter 4 explores the same relationships between gap size and kinematics in D. punctulatus and D. calligastra, revealing remarkable similarities between the three species, suggesting the possibility that dynamic gap crossing may have evolved prior to gliding in this clade. Finally, chapter 5 addresses the role played by gap distance in limiting the non-dynamic, cantilever movements used by these species to cross small gaps, comparing observed stopping distances to those predicted by various torque-related limitations. / Doctor of Philosophy / To successfully cross a gap, an animal must be able to reach or jump from one side to the other. Animals who live in trees must do this quite frequently, as they live among the branches and there are often not connected paths from one place to another. But we don't know very much about how the distance between two structures (the "gap distance") affects the ways an animal moves between them. In this dissertation, I explore how gap distance changes the way a few special species of snakes cross a gap. The species I am studying are special because one species, the paradise tree snake, can glide. Because this 'flying' snake launches its glides by doing a big jump, it is possible that the snake can also jump between tree branches, but this question has never been examined before. We also don't know how the ability to do big jumps evolved, so I studied how distance affects the way two very closely related species of snake, the common tree snake and the northern tree snake, cross gaps. By looking at all of these species, we can understand more about what kinds of behavior are specific to the flying snakes, and which are present in related species. Finally, I also explore how gap distance limits the way the snakes cross gaps when they are not jumping. When the snakes do not jump, they have to hold themselves out straight off the end of a branch. This requires a lot of muscular effort, which means they can't go as far. The fact that the non-jumping behavior is distance-limited might help explain why the snakes need to jump. Altogether, the projects in this study help us understand how gap distance influences what behavior an animal chooses to cross the gap, and increases our knowledge of how flying snakes and their relatives cross gaps in particular.

Ce mémoire porte sur l'évaluation de la qualité du contrôle moteur suite à une entorse latérale de la cheville (ELC). La validité concomitante et discriminante de la variable indicatrice de performance (distance maximale atteinte) au Star Excursion Balance Test (SEBT) a été étudiée dans le premier volet de ce mémoire. Le deuxième volet a permis, pour sa part, de déterminer si les militaires avec ELC présentaient des altérations du contrôle moteur par le biais de variables de stratégies motrices globales et segmentaires. Nos résultats principaux démontrent 1) l'excellente validité concomitante et discriminante de la mesure principale au SEBT lorsqu'une procédure standardisée est utilisée et, 2) la présence d'altérations du contrôle moteur chez les militaires avec ELC. En conclusion, nos travaux supportent l'importance d'évaluer la qualité du contrôle moteur suite à une ELC avec un test tel le SEBT.

Parce qu'il est naturel et facile de marcher, il peut sembler que cet acte soit produit aussi facilement qu'il est accompli. Au contraire, la locomotion nécessite une interaction neurale complexe entre les neurones supraspinaux, spinaux et périphériques pour obtenir une locomotion fluide et adaptée à l'environnement. La région locomotrice mésencéphalique (MLR) est un centre locomoteur supraspinal situé dans le tronc cérébral qui a notamment pour rôle d'initier la locomotion et d'induire une transition entre les allures locomotrices. Cependant, bien que cette région ait initialement été identifiée comme le noyau cunéiforme (CnF), un groupe de neurones glutamatergiques, et le noyau pédonculopontin (PPN), un groupe de neurones glutamatergiques et cholinergiques, son corrélat anatomique est encore un sujet de débat. Et alors qu'il a été prouvé que, que ce soit lors d’une stimulation de la MLR ou pour augmenter la vitesse locomotrice, la plupart des quadrupèdes présentent un large éventail d'allures locomotrices allant de la marche, au trot, jusqu’au galop, la gamme exacte des allures locomotrices chez la souris est encore inconnue. Ici, en utilisant l'analyse cinématique, nous avons d'abord décidé d'identifier d’évaluer les allures locomotrices des souris C57BL / 6. Sur la base de la symétrie de la démarche et du couplage inter-membres, nous avons identifié et caractérisé 8 allures utilisées à travers un continuum de fréquences locomotrices allant de la marche au trot puis galopant avec différents sous-types d'allures allant du plus lent au plus rapide. Certaines allures sont apparues comme attractrices d’autres sont apparues comme transitionnelles. En utilisant une analyse graphique, nous avons également démontré que les transitions entre les allures n'étaient pas aléatoires mais entièrement prévisibles. Nous avons ensuite décidé d'analyser et de caractériser les contributions fonctionnelles des populations neuronales de CnF et PPN au contrôle locomoteur. En utilisant des souris transgéniques exprimant une opsine répondant à la lumière dans les neurones glutamatergiques (Glut) ou cholinergiques (CHAT), nous avons photostimulé (ou photo-inhibé) les neurones glutamatergiques du CnF ou du PPN ou les neurones cholinergiques du PPN. Nous avons découvert que les neurones glutamatergiques du CnF initient et modulent l’allure locomotrice et accélèrent le rythme, tandis que les neurones glutamatergiques et cholinergiques du PPN le ralentissent. En initiant, modulant et en accélérant la locomotion, notre étude identifie et caractérise des populations neuronales distinctes de la MLR. Définir et décrire en profondeur la MLR semble d’autant plus urgent qu’elle est devenue récemment une cible pour traiter les symptômes survenant après une lésion de la moelle épinière ou liés à la maladie de Parkinson. / Because it is natural and easy to walk, it could seem that this act is produced as easily as it is accomplished. On the contrary, locomotion requires an intricate and complex neural interaction between the supraspinal, spinal and peripheric neurons to obtain a locomotion that is smooth and adapted to the environment. The Mesencephalic Locomotor Region (MLR) is a supraspinal brainstem locomotor center that has the particular role of initiating locomotion and inducing a transition between locomotor gaits. However, although this region was initially identified as the cuneiform nucleus (CnF), a cluster of glutamatergic neurons, and the pedunculopontine nucleus (PPN), a cluster of glutamatergic and cholinergic neurons, its anatomical correlate is still a matter of debate. And while it is proven that, either under MLR stimulation or in order to increase locomotor speed, most quadrupeds exhibit a wide range of locomotor gaits from walk, to trot, to gallop, the exact range of locomotor gaits in the mouse is still unknown. Here, using kinematic analysis we first decided to identify to assess locomotor gaits C57BL/6 mice. Based on the symmetry of the gait and the inter-limb coupling, we identified and characterized 8 gaits during locomotion displayed through a continuum of locomotor frequencies, ranging from walk to trot and then to gallop with various sub-types of gaits at the slowest and highest speeds that appeared as attractors or transitional gaits. Using graph analysis, we also demonstrated that transitions between gaits were not random but entirely predictable. Then we decided to analyze and characterize the functional contributions of the CnF and PPN’s neuronal populations to locomotor control. Using transgenic mice expressing opsin in either glutamatergic (Glut) or cholinergic (CHAT) neurons, we photostimulated (or photoinhibited) glutamatergic neurons of the CnF or PPN or cholinergic neurons of the PPN. We discovered that glutamatergic CnF neurons initiate and modulate the locomotor pattern, and accelerate the rhythm, while glutamatergic and cholinergic PPN neurons decelerate it. By initiating, modulating, and accelerating locomotion, our study identifies and characterizes distinct neuronal populations of the MLR. Describing and defining thoroughly the MLR seems all the more urgent since it has recently become a target for spinal cord injury and Parkinson’s disease treatment.

4 Summary: Title: Intraindividual comparison of selected indicators of coordinating steps on the ice skating and in-line. Objective: Assessment of coordination relationship rate of the skating forward during ice hockey and inline skating. Methods: Surface electromyography combinated with kinematography analysis used synchronized video recording. Results: Kinesiological content of movement during ice skating and inline skating is not the same. The general stereotype of the skating step is significantly different from the walking stereotype. Key words: human locomotion, sport locomotion, phylogeny, ontogeny, surface electromyography, ice hockey skating, inline skating.

Locomotion is an innate behaviour that is controlled by different areas of the central nervous system, which allow for effectiveness of movement. The spinal cord is an important centre involved in the generation and maintenance of rhythmic patterns of locomotor activity such as walking and running. Interneurons throughout the ventral horn of the spinal cord form the locomotor central pattern generator (CPG) circuit, which produces rhythmic activity responsible for hindlimb movement. Motoneurons within the lumbar region of the spinal cord innervate the leg muscles to convey rhythmic CPG output to drive appropriate muscle contractions. Intrinsic modulators, such as acetylcholine acting via M2 and M3 muscarinic receptors, regulate CPG circuitry to allow for flexibility of motor output. Using electrophysiology and genetic techniques, this work characterized the receptors involved in cholinergic modulation of locomotor networks and the role and mechanism of action of a subpopulation of genetically identified cholinergic interneurons in the lumbar region of the neonatal mouse spinal cord. Firstly, the effects of M2 and M3 muscarinic receptors on the output of the lumbar locomotor network were characterised. Experiments in which fictive locomotor output was recorded from the ventral roots of isolated spinal cord preparations revealed that M3 muscarinic receptors are important in stabilizing the locomotor rhythm while M2 muscarinic receptor activation seems to increase the irregularity of the locomotor frequency whilst increasing the strength of the motor output. This work then explored the cellular mechanisms through which M2 and M3 muscarinic receptors modulate motoneuron output. M2 and M3 receptor activation exhibited contrasting effects on motoneuron function suggesting that there is a fine balance between the activation of these two receptor subtypes. M2 receptor activation induces an outward current and decreases synaptic drive to motoneurons while M3 receptors are responsible for an inward current and increase in synaptic inputs to motoneurons. Despite the different effects of M2 and M3 receptor activation on synaptic drive and subthreshold properties of MNs, both M2 and M3 receptors are required for muscarine-induced increase in motoneuron output. CPG networks therefore appear to be subject to balanced cholinergic modulation mediated by M2 and M3 receptors, with the M2 subtype also being important for regulating the intensity of motor output. Next, using Designer Receptor Exclusively Activated by Designer Drug (DREADD) technology, the impact of the activation or inhibition of a genetically identified group of cholinergic spinal interneurons that express the Paired-like homeodomain 2 (Pitx2) transcription factor was explored. Stimulation of these interneurons increased motoneuron output through the activation of M2 muscarinic receptors and subsequent modulation of Kv2.1 channels. Inhibition of Pitx2+ interneurons during fictive locomotion decreased the amplitude of locomotor bursting. Genetic ablation of these cells confirmed that Pitx2+ interneurons increase the strength of locomotor output by activating M2 muscarinic receptors. Overall, this work provides new insights into the receptors and mechanisms involved in intraspinal cholinergic modulation. Furthermore, this study provides direct evidence of the mechanism through which Pitx2+ interneurons regulate motor output. This work is not only important for advancing understanding of locomotor networks that control hindlimb locomotion, but also for dysfunction and diseases where the cholinergic system is impaired such as Spinal Cord Injury and Amyotrophic Lateral Sclerosis.

Understanding animal locomotion requires modeling the interaction of the organism with its environment. Locomotion within granular media like sand, soil, and debris that display both solid and fluid-like behavior in response to stress is less studied than locomotion within fluids or on solid ground. To begin to reveal the secrets of movement in sand, I developed models to explain the subsurface locomotion of the sand-swimming sandfish lizard. I developed a resistive force theory (RFT) with empirical force laws to explain the swimming speed observed in animal experiments. By varying the amplitude of the undulation in the RFT, I found that the range of amplitude used by the animal predicted the optimal swimming speed. I developed a numerical model of the sandfish coupled to a discrete element method simulation of the granular medium to test assumptions in the RFT and to study more detailed mechanics of sand-swimming. Inspired by the shovel-shaped head of the sandfish lizard, I used the simulation to study lift forces in granular media: I found that when a submerged intruder moved at a constant speed within a granular medium it experienced a lift force whose sign and magnitude depended on the intruder shape. The principles learned from the models guided the development of a biologically inspired robot that swam within granular media with similar performance to the lizard.

Locomotion of animals, whether by running, flying, swimming or crawling, is crucial to their survival. The natural environments they encounter are complex containing fluid, solid or yielding substrates. These environments are often uneven and inclined, which can lead to slipping during footsteps presenting great locomotor challenges. Many animals have specialized appendages for locomotion allowing them to adapt to their environmental conditions. Aquatically adapted animals have fins and flippers to swim through the water, however, some species use their paddle-like appendages to walk on yielding terrestrial substrates like the beach. Beach sand, a granular medium, behaves like a solid or a fluid when stress is applied. Principles of legged locomotion on yielding substrates remain poorly understood, largely due to the lack of fundamental understanding of the complex interactions of body/limbs with these substrates on the level of the Navier-Stokes Equations for fluids. Understanding of the limb-ground interactions of aquatic animals that utilize terrestrial environments can be applied to the ecology and conservation of these species, as well as enhance construction of man-made devices. In this dissertation, we studied the locomotion of hatchling loggerhead sea turtles on granular media integrating biological, robotic, and physics studies to discover principles that govern fin and flipper locomotion on flowing/yielding media. Hatchlings in the field modified their limb use depending on substrate compaction. On soft sand they bent their wrist to utilize the solid features of sand, whereas on hard ground they used a rigid flipper and claw to clasp asperities during forward motion. A sea turtle inspired physical model in the laboratory was used to test detailed kinematics of fin and flipper locomotion on granular media. Coupling of adequate step distance, body lift and thrust generation allowed the robot to move successfully forward avoiding previously disturbed ground. A flat paddle intruder was used to imitate the animal's flipper in physics drag experiments to measure the forces during intrusion and thrust generation.

The potential of the crural fascia to increase the articulation of the posterior thigh muscles through the in series connection of the structures, suggests that the crural fascia may influence the endpoint force direction of the muscles by partially redirecting the muscular force output. Furthermore, not only the in series connections should be considered but also how the parallel alignment of the crural fascia and the triceps surae may influence the force direction from the muscles. A redirection in force may, in turn, affect the intra-limb coordination or contribute to the selection of a task variable muscle activation pattern. The central objective was to evaluate the role of the synergistically located, posterior, distal musculature and connective tissue during locomotion. The central hypothesis was that the crural fascia would redirect the force output from the posterior thigh muscles to the endpoint and consequently increase propulsion within the limb. We selected to perform our studies in the spontaneously locomoting decerebrate cat, which allows us to investigate acute treatments applied to the hindlimb. The overall objective was accomplished by: (1) evaluating the role of the crural fascia during level walking; (2) determine the acute effect of denervating the triceps surae muscles and disrupting the crural fascia during level walking; and (3) evaluating the change in force direction output of selective stimulation of muscles in different limb configurations before and after complete fasciotomy. Our findings demonstrated that the crural fascia not only assists in propulsion but also acts to stabilize the distal limb. Furthermore, the acute denervation of the triceps surae resulted in a decrease in leg length and an increase in ankle yield during the weight acceptance phase of stance. This suggests that the conservation of the limb length as a task level variable is an adaptation rather than an immediate response.

The kinematic motor redundancy of the human legs provides more local degrees of freedom than are necessary to achieve low degree of freedom performance variables like leg length and orientation. The purpose of this dissertation is to investigate how the neuromuscular skeletal system simplifies control of a kinematically redundant system to achieve stable locomotion under different conditions. I propose that the neuromuscular skeletal system minimizes step to step variance of leg length and orientation while allowing segment angles to vary within the set of acceptable combinations of angles that achieves the desired leg length and orientation. I find that during human hopping, control of the locomotor system is organized hierarchically such that leg length and orientation are achieved by structuring segment angle variance. I also found that leg length and leg orientation was minimized for a variety of conditions and perturbations, including frequency, constrained foot placement, and different speeds. The results of this study will give valuable information on interjoint compensation strategies used when the locomotor system is perturbed. This work also provides evidence for neuromuscular system strategies in adapting to novel, difficult tasks. This information can be extended to give insight into new and different areas to focus on during gait rehabilitation of humans suffering from motor control deficits in movement and gait.