Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 86-88). Also available on the World Wide Web.

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This thesis studies the effects of morphological factors of hexapod robots on their locomotion stability. In particular, an offset model for such robots is proposed. The stability margin as well as the error margin are used to indicate the stability of the hexapod robot, as it walks with different gaits in arbitrary directions. Two hexapod gaits are compared, which are the symmetric gait and the metachronal gait. The former is an artificial gait and the latter, on the contrary, is a natural gait which can be observed in many multiped animals. As we investigate advantages and disadvantages of the two gaits, we find that the stability of a hexapod robot can be enhanced by increasing the offset value. This is particularly true for a robot moving in the X and oblique directions with a symmetrical gait. However, altering the offset is less useful for metachronal gaits. In general, a hexapod robot moves most stably in the Y direction with a symmetrical gait, whereas it is most stable in the X direction with a metachronal gait.

Background: Though numerous studies have compared overground and treadmill walking there still exists a significant debate about whether the two modes of walking are equivalent. The present study provides a comprehensive evaluation of overground and treadmill walking at matched speeds and increasing treadmill speeds. Walking performance was compared in healthy adults, in people with stroke and between the groups. This is important to know because any differences may have implications for gait training in both groups. Methods: Ten healthy adults (50-73 years) and ten subjects with stroke (54-80 years) walked at their self-selected speed overground which was matched on a treadmill. Temporal parameters, angular kinematics and vertical ground reaction forces were recorded during walking once subjects were in steady state as determined from their heart rate and oxygen uptake, both of which were also recorded. Belt speed was then increased 10% and 20% above matched speed and steady state recordings obtained. Speed related adjustments were also evaluated and compared between the two groups of subjects. Results: For healthy adults, step, stride, and joint angular kinematics were similar for both modes of walking. Small reductions in double support time and decreased push-off force were evident on the treadmill. For subjects with stroke, step, stride, and stance times were longer when walking overground but the degree of symmetry was comparable for both surfaces. Kinematic data revealed interlimb asymmetry was more pronounced for all lower limb joint excursions during overground walking and vertical forces were higher. In comparison to healthy adults, stroke subjects walked with lower cadence, shorter strides, lower stance time, and smaller lower limb joint excursions than their healthy counterparts. When compared with overground walking the metabolic requirements of treadmill walking for healthy adults and subjects with stroke however were about higher by 23% and 15% respectively. All temporal-distance parameters, hip joint excursion, F1 and F2 forces and metabolic costs showed main effects of speed. An interaction between speed and group indicated that oxygen consumption increased at a greater rate in stroke than healthy subjects. Conclusions: The findings suggest that, although overground and treadmill gait patterns are similar for each group of subjects, people with stroke adopt a more symmetrical kinematic walking pattern on the treadmill that is maintained at faster belt speeds. Although there are differences in gait patterns between healthy and stroke subjects, both groups respond to the challenge of increased walking speed in the same way. One important difference is the abnormal elevation of energy demands associated with treadmill walking at faster speeds in stroke. Clinically, this warrants consideration as it may lead to premature fatigue and undesirable cardiorespiratory challenge in this group of individuals. / Thesis (Ph.D, Rehabilitation Science) -- Queen's University, 2009-08-27 06:41:19.999

Feature extraction is the most critical step in any human gait recognition system. Although gait is a dynamic process yet the static body parameters also play an important role in characterizing human gait. A few studies were performed in the past to assess the comparative relevance of static and dynamic gait features. There is, however, a lack of work in comparative performance analysis of dynamic gait features from different parts of the silhouettes in an appearance based setup. This dissertation presents a comparative study of dynamic features extracted from legs, arms and shoulders for gait recognition. Our study partially supports the general notion of leg motion being the most important determining factor in gait recognition. But it is also observed that features extracted from upper arm and shoulder area become more significant in some databases. The usefulness of the study hinges on the fact that lower parts of the leg are generally more noisy due to a variety of variations such as walking surface, occlusion and shadows. Dynamic features extracted from the upper part of the silhouettes posses significantly higher discriminatory power in such situations. In other situations these features can play a complementary role in the gait recognition process. We also propose two new feature extraction methods for gait recognition. The new methods use silhouette area signals which are easy and simple to extract. A significant performance increase is achieved by using the new features over the benchmark method and recognition results compare well to the other current techniques. The simplicity and compactness of the proposed gait features is their major advantage because it entails low computational overhead.

Feature extraction is the most critical step in any human gait recognition system. Although gait is a dynamic process yet the static body parameters also play an important role in characterizing human gait. A few studies were performed in the past to assess the comparative relevance of static and dynamic gait features. There is, however, a lack of work in comparative performance analysis of dynamic gait features from different parts of the silhouettes in an appearance based setup. This dissertation presents a comparative study of dynamic features extracted from legs, arms and shoulders for gait recognition. Our study partially supports the general notion of leg motion being the most important determining factor in gait recognition. But it is also observed that features extracted from upper arm and shoulder area become more significant in some databases. The usefulness of the study hinges on the fact that lower parts of the leg are generally more noisy due to a variety of variations such as walking surface, occlusion and shadows. Dynamic features extracted from the upper part of the silhouettes posses significantly higher discriminatory power in such situations. In other situations these features can play a complementary role in the gait recognition process. We also propose two new feature extraction methods for gait recognition. The new methods use silhouette area signals which are easy and simple to extract. A significant performance increase is achieved by using the new features over the benchmark method and recognition results compare well to the other current techniques. The simplicity and compactness of the proposed gait features is their major advantage because it entails low computational overhead.

This thesis investigates walking patterns in healthy young people and in people with an increased risk of falling, and determines the physiological contributions to walking stability. First, a review of the relevant literature on techniques for assessing walking stability, age-related changes in balance and gait, and the contributions of vision, vestibular function, peripheral sensation and strength was undertaken. In response to a critical analysis of these findings, a new technique and protocol for the assessment of walking stability was developed. This involved measuring and analysing head and pelvis accelerations while subjects walked on a level surface and an irregular surface. Gait patterns were studied in 30 young healthy subjects and two groups known to be at increased risk of falling - 100 subjects over the age of 75, and 30 subjects with diabetic peripheral neuropathy. A series of vision, sensation, strength, reaction time and balance tests were also undertaken to identify subjects??? physiological abilities and risk of falls. Acceleration patterns of the head and pelvis differed according to physiological risk of falling, particularly when walking on the irregular surface. Those with a high risk of falling walked with a reduced velocity, cadence and step length, and exhibited less rhythmic acceleration patterns at the head and pelvis. Gait patterns were significantly associated with leg strength, peripheral sensation and reaction time. It is concluded that subjects with a high physiological risk of falling exhibit characteristic patterns of walking that indicate an impaired ability to control the movement of the pelvis and head, which may predispose to loss of balance.

Breeding success in the broiler chicken has been accompanied by gait problems which are detrimental to productivity and welfare. Although these gait issues have not been reported to the same extent in Pekin ducks, there is concern that such problems will manifest if the duck continues on its current selection trajectory. In order to understand how changes in morphology due to selection have affected gait in both species, divergent lines were objectively assessed for gait using a pressure platform (12 birds per line at three, five and seven weeks of age). The broiler chicken was compared to the slower growing layer chicken and the Pekin duck to its slower growing ancestor, the mallard. Two breeding lines of Pekin duck were also assessed. After gait assessment, the leg bones (femur and tibiotarsus) were scanned by computed tomography to measure morphological changes which have occurred due to selection for high growth and meat yield. Results were analysed by ANOVA, accounting for age and sex. During walking, heavy lines walked at a slower velocity, displayed a wider stance and spent more time supporting their mass on both feet than their lighter conspecifics, strategies which are likely to improve balance. The foot angle while walking differed between lines; all duck lines rotated their feet internally whereas the layer chickens’ feet were aligned with the direction of travel. Conversely the broiler chicken rotated its feet externally by seven weeks of age. Morphologically, the main differences were between species. Duck lines reached adult leg size earlier than chickens, which may be a response to differing adaptive environments prior to domestication. This early cessation of bone growth in ducks may provide more opportunity for the bones to remodel to handle the loads imposed on them. Lower levels of porosity and a unique cortical architecture observed in ducks endow relatively greater bone strength. Bone curvature also differed between species; the tibiotarsus curved more laterally in ducks than in chickens and may be a swimming adaptation that hinders locomotion on land in the modern production bird. In order to improve the objectivity of selection for better gait in poultry, the genetic parameters of gait components selected on the basis of results in this thesis were estimated using a linear mixed model in a population of Pekin ducks of known pedigree. As they are a simpler measure, similar or improved heritability estimates were estimated for these gait components when compared with the standard commercial gait score which is based on a subjective view of walking ability. Intense selection for economic traits has altered gait in similar ways in both species. To improve gait in poultry, greater breeding success may be achieved by focussing on those components of gait which have changed through selection, rather than using a subjective overall visual gait score. Furthermore, in both species, adaptations for pre-domesticated life may have affected the ability with which the selected lines have accommodated their gait to other morphological changes associated with increasing body mass.

The human ankle joint is hypothesized to be a primary controller of support, propulsion and steering during locomotion. A series of experiments were initiated to understand ankle plantarflexor muscle kinematics and kinetics in normal and pathological gait, and to define the specific locomotor demands of community ambulation. Additional experiments were then conducted to quantify the effects of walking speed on plantar pressures and centre of mass motion, to illuminate the role of the ankle in acceleration and deceleration during walking, and to examine how humans alter their kinematics and kinetics to turn. The results of these experiments provide support for the hypothesis that the ankle joint is important in a wide range of locomotor movements beyond walking straight ahead at constant speed. The ankle appears instrumental in adapting to different walking speeds, altering both the pressures on specific regions the plantar surface and the motion of the centre of mass across a range of speeds. The ankle also has subtle kinetic changes that appear to modulate acceleration and deceleration during single limb stance. For turning, the ankle plays a role during slowing into the turn and accelerating after the turn, but mediolateral shears appear to alter the trajectory of the body to negotiate a corner and the external hip rotators appear to rotate the trunk toward the new direction of travel. This work extends our understanding of the ankle in functionally relevant gait activities beyond simple straight-ahead walking at constant speed. The published papers included in this supporting statement have been cited by 180 different subsequent peerreviewed publications, suggesting that this work has had some impact on the field.

Background: Youth sports participation has numerous positive mental and physical health benefits. In young athletes, injuries result in millions of emergency room visits and millions of dollars spent every year offsetting many of the positive benefits gained by participation in sports. An increase in traumatic injury rates has been found to occur during the year of peak height growth (PHV), with a subsequent increase in risk of overuse injury in the years immediately following. This may be the result of changes to movement coordination around the time of adolescent growth spurts, a phenomenon called adolescent motor awkwardness (AMA). Though this phenomenon is well known to parents and coaches of young athletes, scientific research into its causes, symptoms, and timeline remains sparse. Minimal scientific evidence exists to quantify the impact of AMA on specific areas of movement coordination (ex. gait) and muscle performance, as well as its relation to growth spurts. Equally as poorly understood are the potential causes of motor disruptions during this period. As adolescents experience a wide variety of alterations to body size, proportions, and composition during puberty, there are many factors which could lead to disruptions to movement coordination. Additionally, there are substantial differences which arise in body proportions and composition between the sexes during puberty, yet any between-sex-group differences in the timeline, causes, or specific changes to movement coordination have not yet been explored. Purpose: The purpose of this dissertation was threefold: 1) To understand how gait stability changes with age and height during adolescence, and how these changes differ between the sexes (aim 1; chapter 2); 2) To understand the immediate effects of physical growth on gait smoothness during adolescence (aim 2; chapter 3); 3) To understand how peripheral fatigue affects gait smoothness during adolescence, and to understand how physical growth impacts muscular fatigability (aim 3; chapter 4). Participants: Sixty-Seven individuals (n=34 female, n=33 male) participated in the first study session to obtain Harmonic Ratio (HR), age, height, and fatigue data for aims 1 and 3. A subset of 46 participants (n=20 female, n=26 male) returned to participate in a second study session to obtain growth rate, HR, and fatigue data for aims 2 and 3. Methods: The testing protocol used in both sessions was identical. Trigno sensors were adhered to the participants skin at four locations determined by manual palpation: C7, L5, and the right and left rectus femoris. Once sensors were secured, participants completed a 15-minute treadmill warm-up in which their self-reported preferred walking speed was obtained. Following the warm-up, participants completed two 9-minute treadmill walking trials at three set speeds: 70% (slow walking speed; SWS), 100% (preferred walking speed; PWS), and 130% (Fast Walking Speed; FWS) of preferred walking speed. The walking trials were separated by a 10-minute leg-focused fatigue protocol. During each walking trial, accelerations of the upper (C7) and lower (L5) trunk were recorded in three planes of motion: Anterior-Posterior (AP), Medio-Lateral (ML), and Vertical (V). Harmonic Ratios were calculated from these acceleration signals. Prior to beginning each walking trial (i.e., pre-fatigue and post-fatigue) surface electromyography (sEMG) of the right and left rectus femoris was obtained during a 10-second sustained maximal contraction. Median frequency (Fmed) of this sEMG signal was used to calculate muscular fatigue level before and after the fatiguing protocol. Descriptive statistics were calculated for both the first session group and the second session subgroup. To accomplish aim 1, relationships between age, height, and HRs were assessed using multiple linear regression models with Holm-Bonferroni correction. Gait and anthropometric characteristics were compared by sex using independent sample t-tests. To accomplish aim 2, associations between growth rate and HRs were assessed through multiple linear regression adjusted for age and height. To accomplish aim 3, pre- and post- fatigue HRs were compared within subjects using paired t-tests. The association between muscular fatigability and growth rate was assessed using linear regression. Results: In aim 1, male and female groups differed significantly in height, age, and gait speeds. HRs improved with age for females at C7AP at all speeds pre-fatigue and at C7V in SWS and PWS post-fatigue. Males’ HRs increased with age during FWS pre-fatigue at C7V, C7AP , and L5ML . Females had a significant negative association between height and HR post-fatigue at C7V during both SWS and PWS, and at C7AP during FWS. In aim 2, male and female groups differed significantly in height, but not in age, growth rate (GR), walking speeds, or average HRs. When accounting for age and height, GR over a four-month period was a significant linear predictor of smoothness of trunk motion only for females during fast walking at L5AP. In aim 3, Females showed a significant effect of fatigue at SWS and at PWS on smoothness of motion of the lower trunk. Males showed a significant effect of fatigue during FWS at C7 in all planes of motion. Conclusions: These findings overall suggest substantial sex differences in changes to smoothness of trunk motion during gait in adolescents and in the effects of fatigue on trunk smoothness. In aim 1, several HRs improved with age in both sexes, but benefits were eliminated with fatigue in males. Aim 2 suggests that physical growth does not have immediate impacts on HR in adolescence. The results of aim 3 show substantial differences between the sexes in how muscular fatigue impacts gait stability. Males were most affected by fatigue at the upper trunk, particularly at FWS, while females were most affected by fatigue at the lower trunk at PWS. / Physical Therapy