While the locomotion performance of legged robots over flat terrain or known obstacles has improved over the past few decades, they have yet to equal the performance of their animal counterparts over variable terrain. This work analyzes a multi-legged reduced order model of cockroach locomotion on variable slopes which will be used as an inspiration for a future sprawled posture legged robot. The cockroach is modeled as a point mass, and each leg of the cockroach is modeled as a massless, tangentially rigid, linearly elastic spring attached at the center of mass. All of the springs are actuated to allow changes in energy to the system. This is accomplished by varying the force free length of each leg in a feed-forward manner without reliance on feedback to change the actuation scheme. Fixed points of the model are found using a numerical solver that varies the velocity and phase shift parameters while leaving all other parameters at fixed values selected to match true cockroach motion. Each fixed point is checked for stability and robustness representing how effective the model is at staying on the predetermined gait, and transport cost as a measure of how efficient this gait is. Stable and robust fixed points were successfully found for the range of heading angles encompassing those of representative cockroach motion at each slope. Cockroaches may select the gait used based on stability or efficiency. Thus, additional fixed points were found in combination with a search routine that varies the leg actuation parameters in order to optimize either stability or metabolic efficiency, gaining insights into why cockroaches use the gaits that they do. Optimized fixed points were found based on four different leg functional combination families depending on whether each leg pushes or pulls. Optimized fixed point gaits exist for every incline slope studied between level ground and vertical slopes, at a range of initial heading angles that encompass those typically used by cockroaches. The selected gaits using both a stability based and an efficiency based optimization on the modeled cockroach are very similar. Both are also similar to gaits used by real cockroaches. The forces generated by the model are qualitatively similar to the experimental forces. / Graduation date: 2012

We present a novel control strategy for running which is robust to disturbances, and makes excellent use of passive dynamics for energy economy. The motivation for our control strategy is based on observations of animals, which are able to economically walk and run over varying terrain and ground dynamics. It is well-known that steady-state animal running can be approximated by spring-mass models, but these passive dynamic models describe only steady-state running and are sensitive to disturbances that animals can accommodate. While animals rely on their passive dynamics for energy economy, they also incorporate active control for disturbance rejection. The same approach can be used for spring-mass walking and running, but an active controller is needed that interferes minimally with the passive dynamics of the system. We demonstrate, in simulation, how force control combined with a leg spring stiffness tuned for the desired hopping frequency provides robustness to disturbances on a model for robot hopping, while maintaining the energy economy of a completely passive system during steady-state operation. Our strategy is promising for robotics applications, because there is a clear distinction between the passive dynamic behavior of the model and the active controller, it does not require sensing of the environment, and it is based on a sound theoretical background that is compatible with existing high-level controllers for ideal spring-mass models. / Graduation date: 2012

Zusammenfassung Histomorphometrische Befunde am M. gluteus medius von Pferden ausgewählter deutscher Warmblutrassen - Selektionskriterium für die sportliche Veranlagung? (96 S., 11 Abb., 52 Tab., 131 Lit.) Zur Untersuchung histomorphometrischer Indizes wurden aus dem M. gluteus medius von Warmblut-Pferden ausgewählter deutscher Zuchtgebiete Bioptate entnommen. Insgesamt standen 64 zweijährige Hengste zur Verfügung. Die Biopsien wurden an einem definierten Punkt und bei einer immer gleichen Entnahmetiefe von 5 cm mit der Biopsiekanüle nach BERGSTRÖM (1962) durchgeführt. Eine Auswertung der Muskelproben erfolgte im Hinblick auf die Rassenzugehörigkeit, hinsichtlich Züchtung der Pferde für den Dressur- bzw. Springsport, mit Bezug auf das Körurteil sowie unter Berücksichtigung der Abstammung von verschiedenen väterlichen Blutlinien. Dazu kam die histochemische Methode der sauren Kreuzkombination nach ZIEGAN (1979) zur Anwendung, welche neben den physiologischen auch die biochemischen Eigenschaften der Muskelfasern berücksichtigt. Demzufolge wurde eine Differenzierung in die Fasertypen STO (slow-twitch-oxidative), FTO (fast-twitch-oxidative), Fasern des Intermediärtyps und FTG (fast-twitch-glycolytic) vorgenommen. Für diese Fasertypen wurde die relative Anzahl, die absolute und die relative Faserquerschnittsfläche sowie die Quotienten schnell-/langsam-kontrahierende Fasern (F/S), oxidative/glykolytische (Ox/G) Muskelfasern und FTO/FTG ermittelt. Zwischen Pferden verschiedener deutscher Warmblutrassen ließen sich signifikante Unterschiede im STO- (p< 0,001) und FTO-Faseranteil (p< 0,01) nachweisen. Warmblutpferde Trakehner Abstammung wiesen dabei mit 35,9 % den größten Anteil langsamer Muskelfasern (STO) und mit 33,8 % den geringsten Anteil schnell-kontrahierender, oxidativer Fasern (FTO) auf. Die gegensätzlichen Extremwerte bezüglich dieser beiden Fasertypen nahmen die Pferde des Zuchtgebietes Westfalen ein. Auch die absoluten Faserquerschnittsflächen langsam-kontrahierender Muskelfasern von Pferden verschiedener Rassen waren signifikant (p< 0,05) verschieden. Wiederum nahmen mit 2957 µm2 die Trakehner eine Spitzenposition ein. Im Vergleich der Werte der relativen Faserquerschnittsfläche von Pferden verschiedener Rassen wurde auch ein signifikanter Unterschied bei den FTG-Fasern deutlich (p< 0,01). Dressurpferde besaßen mit 26,6 % einen signifikant (p< 0,05) höheren STO-Faseranteil als Springpferde mit einem Wert von 21,9 %. Umgekehrt verhielt sich der prozentuale FTO-Faseranteil mit 46,7 % bei Spring- und 38,8 % bei Dressurpferden (p< 0,05). Die Werte der relativen Faseranzahl und der relativen Faserfläche wiesen einen Korrelationskoeffizienten von r=0,92 auf. Demzufolge bestanden zwischen Dressur- und Springpferden auch bei der relativen Faserquerschnittsfläche signifikante Unterschiede für STO- (p< 0,05) und FTO-Fasern (p< 0,001). „Gekörte Hengste“ hatten mit 20 % signifikant (p< 0,05) weniger langsam-kontrahierende Muskelfasern als „Nicht gekörte“ Hengste mit 25 %. Auch für die relative Faserquerschnittsfläche traf dieses Verhältnis signifikant (p< 0,05) zu. Es konnte weiterhin gezeigt werden, daß Nachkommen von verschiedenen väterlichen Blutlinien signifikant im STO- (p< 0,01) und FTO-Faseranteil (p< 0,001) sowie bezüglich der relativen Faserquerschnittsfläche von STO- (p< 0,001), FTO- (p< 0,01) und FTG-Fasern (p< 0,05) und hinsichtlich der absoluten Faserfläche der langsamen Muskelfasern (p< 0,05) voneinander abweichen. Aus den Ergebnissen konnten folgende Erkenntnisse gewonnen werden: 1. Die Befunde weisen auf eine enge Abhängigkeit der Muskelfasertypenkomposition des Pferdes von genetischen Faktoren hin. 2. Bereits zwischen Pferden anderer Rassen beobachtete Unterschiede hinsichtlich morphologischer Muskelindizes lassen sich auch bei Pferden verschiedener deutscher Warmblut-Pferderassen aufzeigen. 3. Pferde, die seit mehreren Generationen speziell für eine Nutzung im Springsport gezüchtet worden sind, besitzen einen höheren prozentualen FTO-Faseranteil. Dieser verleiht ihnen wahrscheinlich die Fähigkeit, in der Absprungphase ein enormes Maß an Kraft zu generieren. Dressurpferde haben Arbeit von vergleichsweise niedriger Intensität, aber langer Dauer zu verrichten. Daraus ergibt sich die Möglichkeit, die Muskelbiopsie bereits bei jungen Pferden als Selektionskriterium einzusetzen. 4. Die Ergebnisse der „Gekörten Hengste“ weisen auf eine Selektion zugunsten der Individuen mit hohem FTO- und dementsprechend niedrigem STO-Faseranteil hin, was auf einen Zusammenhang zwischen der Muskelfasertypenzusammensetzung und der Bewegungsqualität eines Pferdes hindeutet. / Summary Histomorphometric findings of the gluteus medius muscle of horses from selected german warm-blooded breeds - selection criterion for athletic ability? (96 p., 11 fig., 52 tables, 131 ref.) For examining the histomorphometric muscle indices biopsies were taken of warm-blooded horses descending from selected German breeds. Biopsies were taken at standardized depth of 5 cm from the left gluteus medius muscle of 64 two-year-old stallions using a BERGSTROEM biopsy needle (1962). Muscle samples were evaluated according to different breeds, the aptitude for dressage or show jumping, the possession of a breeding licence and the derivation of different paternal bloodlines. The histochemical method used was that described by ZIEGAN (1979), which considers the physiological as well as the biochemical properties of muscle fibres. Therefore muscle fibres were distinguished in STO, FTO, fibres of intermediate type and FTG. For these fibre the types relative number, absolute and relative cross-sectional fibre area as well as the quotient fast-/slow-twitch fibers, oxidative/glycolytic muscle fibers and FTO/FTG were determined. Between horses of different German warm-blooded breeds there were significant differences in the percentage of STO (p< 0,001) and FTO-fibres (p< 0,01). Trakehner horses had the highest percentage of slow-twitch fibres with 35,9 %, and the lowest percentage of FTO-fibres with 33,8 %. The other two extremes according to these fibre types occured in Westphalian horses. Absolute cross-sectional STO-fibre areas were also significantly different between horses of different breeds (p< 0,05). Again, the Trakehner horses were in the lead with 2956,89 µm2. Comparing the relative muscle fibre area of differently bred horses, FTG-fibres also turned out to be significantly different (p< 0,01) from each other. Dressage horses had with 26,6 % a significantly higher (p< 0,05) proportion of STO-fibres than show jumping horses with a percentage of 21,9 %. Show jumping horses had a higher percentage of FTO-fibres with 46,7 % than dressage horses with 38,8 % (p< 0,05). Expressing a high correlation of relative number and relative cross-sectional fibre area (r< 0,92), the latter criterion also turned out to be different for STO- (p< 0,05) and FTO-fibres (p< 0,001). Licenced breeding stallions showed a significantly (p< 0,05) lower proportion of slow-twitch fibres with 20 % than stallions without breeding permission with 25 %. This relation also turned out to be significant for the relative fibre area (p< 0,05) . Furthermore it was found that offsprings of different paternal bloodlines differ from one another according to the percentage of STO- (p< 0,01) and FTO-fibres (p< 0,001), according to relative cross-sectional fibre areas of STO- (p< 0,001), FTO- (p< 0,01) and FTG-fibres (p< 0,05) and according to absolute fibre areas of slow-twitch muscle fibres (p< 0,05). These results suggest following conclusions: 1. The findings show a high correlation between muscle fiber type composition and genetic factors in the horse. 2. Earlier observed differences in morphological muscle indices between different races of horses were also evident between horses of different german warm-blooded breeds. 3. Horses, which have been bred specifically for show jumping over numerous generations, possess a higher percentage of FTO-fibres. This probably enables them to generate an enormous amount of power in the moment of take-off. Dressage horses have to perform exercises of comparatively low intensity but long duration. Therefore the muscle biopsy is a usefull selection criterion in young horses. 4. The results from the licenced breeding stallions indicate selection in favour of individuals having a high percentage of FTO- and a low percentage of STO-fibers, which may be related to muscle fibre properties and the locomotor pattern of the horse.

Locomotion is an integral part of a whole range of animal behaviours. The basic rhythm for locomotion in vertebrates has been shown to arise from local networks residing in the spinal cord and these networks are known as central pattern generators (CPG). However, during the locomotion, these centres are constantly interacting with the sensory feedback signals coming from muscles, joints and peripheral skin receptors in order to adapt the stepping or swimming to varying environmental conditions. Conceptual models of vertebrate locomotion have been constructed using mathematical models of locomotor subsystems based on the neurophysiological evidence obtained primarily in the cat and the salamander, an amphibian with a sprawling posture. Such models provide opportunity for studying the key elements in the transition from aquatic to terrestrial locomotion. Several aspects of locomotor control using the cat or the salamander as an animal model have been investigated employing computer simulations and here we use the same approach to address a number of questions or/and hypotheses related to rhythmic locomotion in quadrupeds. Some of the involved questions are, the role of mechanical linkage during deafferented walking, finding inherent stabilities/instabilities of muscle-joint interactions during normal walking and estimating phase dependent controlability of muscle action over joints. Also we investigate limb and body coordination for different gaits, use of side-stepping in front limbs for turning and the role of sensory feedback in gait generation and transitions in salamanders.      This thesis presents the basics of the biologically realistic models of cat and salamander locomotion and summarizes computational methods in modeling quadruped locomotor subsystems such as CPG, limb muscles and sensory pathways. In the case of cat hind limb, we conclude that the mechanical linkages between the legs play a major role in producing the alternating gait. In another experiment we use the model to identify open-loop linear transfer functions between muscle activations and joint angles while ongoing locomotion. We hypothesize that the musculo-skeletal system for locomotion in animals, at least in cats, operates under critically damped condition.      The 3D model of the salamander is successfully used to mimic locomotion on level ground and in water. We compare the walking gait with the trotting gait in simulations. We also found that for turning, the use of side-stepping alone or in combination with trunk bending is more effective than the use of trunk bending alone. The same model together with a more realistic CPG composed of spiking neurons was used to investigate the role of sensory feedback in gait generation and transition. We found that the proprioceptive sensory inputs are essential in obtaining the walking gait, whereas the trotting gait is more under central (CPG) influence compared to that of the peripheral or sensory feedback.      This thesis work sheds light on understanding the neural control mechanisms behind vertebrate locomotion. Additionally, both neuro-mechanical models can be used for further investigations in finding new control algorithms which give robust, adaptive, efficient and realistic stepping in each leg, which would be advantageous since it can be implemented on a controller of a quadruped-robotic device. / This work is Funded by Swedish International Development cooperation Agency (SIDA). QC 20111110

Includes bibliographical references (leaves 276-2970. / xiii, 297 leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigations presented involve 18 hour to 5 day old South Australian merino lambs. Some twin lambs were available for comparative studies. Examines the relationship between the strength of ewe-lamb bond and the lamb's ability to follow the mother, the energy availability and usage in the lamb, particularly for locomotion, and the metabolic and cardiorespiratory responses to locomotion. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Sciences, 1992

Two experiments were undertaken. The objective of Experiment One was to identify the lower limb muscles that were most frequently active during the early period of a step turning task for further testing in Experiment Two. In Experiment Two participants undertook multiple trials of a step-turning task, 30 and 60° to the left and right of midline, at a self-selected pace in response to a visual cue. There were five objectives to Experiment Two. Firstly, to identify the predominant order in the onset of foot movement so that anticipatory muscle activity could be defined for this task. Secondly, to identify whether there is a consistent temporal order in movement onset between the head and the feet. Thirdly, to identify whether and how consistently anticipatory lower limb muscle activity is present bilaterally. Fourthly, to assess whether there is a consistent sequence in the onset of anticipatory muscle activity among muscles active in at least 80% of trials. The final objective was to identity whether there was a consistent temporal relationship in the onset of the anticipatory muscle activity present in at least 80% of trials, with the onset of head and foot movement. Study Design: A repeated measures design was used. Background: Anticipatory lower limb muscle activity in gait initiation and forward stepping studies has been reported to be consistently present, and associated with initial and important balance responses. Falls during turning are associated with a high incidence of hip fractures in the elderly population. The presence of anticipatory lower limb muscle activity turning has not been previously reported. Participants: There were five participants in Experiment One, and ten in Experiment Two. All were between 18 and 40 years of age and did not have neurological or musculoskeletal disorders, or severe visual loss. Results: In Experiment One, four muscles were consistently active bilaterally, during the early period of step-turning and were: tibialis anterior, gastrocnemius, biceps femoris and gluteus medius. In Experiment Two the ipsilateral foot moved before the contralateral foot in 68% of trials towards the left, and 79% of trials towards the right. The onset of head movement consistently occurred before the onset of foot movement during turns towards both directions. The percentage of trials in which the four muscles were active in an anticipatory manner was low bilaterally, ranging from 12 to 38% of trials. Objectives that involved the further analysis of muscles active in at least 80% of trials were unable to be completed. Conclusions: During a step-turning task young healthy adults predominantly move their ipsilateral foot before their contralateral foot. The consistent onset of head movement prior to that of the feet, indirectly suggests that the visual system might influence the temporal onset of the feet. The low levels of anticipatory muscle activity during step-turning suggest that the lower limbs are not involved with the initial balance responses for this task thus making it inherently different to gait initiation and forward stepping.

[Truncated abstract] In ecomorphological or ecophysiological studies, variation in `design? traits (e.g. size, morphology and physiology) is thought to determine variation in ecologically-relevant performance traits, which in turn determines fitness in a particular habitat (Arnold 1983). Thus, natural selection is thought to act most directly on intermediate traits such as measures of locomotory performance. This thesis examined this process in the closely related group of Australian varanids lizards (Squamata: Varanidae). Phylogenetically, varanids are divided into three major clades. Size (mass and snout-to-vent length) is strongly correlated with these three clades. Two clades, (Gouldii and Komodoensis) are large, while the third clade (Odatria) has a smaller body size. Thus, there is considerable variation in size for various species. Size varied for species by three orders of magnitude. Size is also related to two ecological characteristics, foraging mode and habitat openness. Widely-foraging species were larger than sit-and-wait strategists, while species from open habitats were larger than species from semi-open or closed habitats. However, given the tight link between size and phylogeny we cannot separate adaptation of size to ecological traits from that of phylogenetic patterns. Of interest throughout this thesis was how variations in design (e.g. morphology and physiology) were related to ecological characteristics. Since body size also influences many of these morphological and physiological characteristics it is often necessary to remove the effects of size. Three design traits were examined in detail: body dimensions, vertebral number and metabolic rates. …Curiously, no performance variable linked differences in size-free body dimensions to retreat sites. This suggests that there is either a direct link between design and ecology (e.g. dorso-ventral compression), or some unmeasured performance variable related to retreat site. Given that most performance traits are thought to involve kinematic movements of the hindlimb limb and pelvis, and these were not best related to retreat site, then a direct link between design and ecology with respect to retreat site seems possible. In summary, this thesis provides evidence not only for links between design and ecology mediated by locomotory performance traits, but also direct links between design and ecology, for Australian varanid lizards.

Licentiatavhandling (sammanfattning) Skara : Sveriges lantbruksuniversitet, 2005. / Härtill 2 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 4 uppsatser.

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniversitet, 2005. / Härtill 5 uppsatser.