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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.

While the traditional dependent variables of motor skill learning are accuracy and consistency of movement outcome, there has been increasing interest in aspects of motor performance that are described as reflecting the ‘energetics’ of motor behaviour. One defining characteristic of skilled motor performance is the ability to complete the task with minimum energy expenditure (Sparrow & Newell, 1998). A further consideration is that movements also have costs in terms of cognitive ‘effort’ or ‘energy’. The present project extends previous work on energy expenditure and motor skill learning within a coordination dynamics framework. From the dynamic pattern perspective, a coordination pattern lowest on the 11KB model potential curve (Haken, Kelso & Bunz, 1985) is more stable and least energy is required to maintain pattern stability (Temprado, Zanone, Monno & Laurent, 1999). Two experiments investigated the learning of stable and unstable coordination patterns with high metabolic energy demand. An experimental task was devised by positioning two cycle ergometers side-by-side, placing one foot on each, with the pedals free to move independently at any metronome-paced relative phase, Experiment 1 investigated practice-related changes to oxygen consumption, heart rate, relative phase, reaction time and muscle activation (EMG) as participants practiced anti-phase, in-phase and 90°-phase cycling. Across six practice trials metabolic energy cost reduced and AE and VE of relative phase declined. The trend in the metabolic and reaction time data and percent co-contraction of muscles was for the in-phase cycling to demonstrate the highest values, anti-phase the lowest and 90°-phase cycling in-between. It was found that anti- and in-phase cycling were both kinematically stable but anti-phase coordination revealed significantly lower metabolic energy cost. It was, therefore, postulated that of two equally stable coordination patterns, that associated with lower metabolic energy expenditure would constitute a stronger attractor. Experiment 2 was designed to determine whether a lower or higher energy-demanding coordination pattern was a stronger attractor by scanning the attractor layout at thirty-degree intervals from 0° to 330°. The initial attractor layout revealed that in-phase was most stable and accurate, but the remaining coordination patterns were attracted to the low energy cost anti-phase cycling. In Experiment 2 only 90°- phase cycling was practiced with a post-test attractor layout scan revealing that 90°-phase and its symmetrical partner 270°-phase had become attractors of other coordination patterns. Consistent with Experiment 1, practicing 90°-phase cycling revealed a decline in AE and VE and a reduction in metabolic and cognitive cost. Practicing 90°-phase cycling did not, however, destabilise the in-phase or anti-phase coordination patterns either kinematically or energetically. In summary, the findings suggest that metabolic and mental energy can be considered different representations of a ‘global’ energy expenditure or ‘energetic’ phenomenon underlying human coordination. The hypothesis that preferred coordination patterns emerge as stable, low-energy solutions to the problem of inter-and intra-limb coordination is supported here in showing that the low-energy minimum of coordination dynamics is also an energetic minimum.

The complexity in human movement has provided a theoretical challenge for movement scientists to comprehend the underlying processes controlling joint movements in a functional and goal-directed manner. Although there has been an increase in research on examining coordination in multi-articular actions, it is still in its infancy. The aim of this thesis was to examine the acquisition of coordination of a discrete multi-articular movement action from the theoretical perspective of Dynamical Systems Theory. Specifically, four different studies examined key research questions raised about understanding the coordination and control of a lower limb multi-articular interceptive action. The thesis concludes with a brief discussion on the key findings and the implications for practitioners in physical education pedagogy relating to a games teaching approach. A discrete multi-articular kicking action with specific task constraints (kicking over a height barrier and to different target positions) was utilised as a research vehicle to examine differences in coordination between three groups of participants: skilled, intermediates and novices. From group analysis, it was determined that skilled and intermediate groups demonstrated a functional coordination mode involving a restricted range of motion at the proximal joints and a larger range of motion at distal joints, mimicking a 'chip-like action' in soccer. In contrast, large range of joint motions throughout the kicking limb were seen for the novice participants who demonstrated a 'driving-like action'. Analysis of ball trajectory data confirmed that novice participants were not able to successfully project the ball over the height barrier. Findings from this study suggested that the observed range of motion is dependent on skill level and task constraints. Functional foot speed at ball contact to various target positions demonstrated by skilled and intermediate players further highlighted the possibility of using a model of learning focusing on coordination to examine progression through the different stages of learning. A multiple single-participant design was further used to investigate coordination of skilled players to determine if refined differences could be present at the skilled level of performance. Although global similarities in terms of the use of a chipping action in projecting the ball was found, differences in foot position for the non-kicking foot and centre of mass displacement near ball contact emphasised that even skilled individuals can demonstrate different coordination solutions to meet the same task goal. Such an observation highlights the concept of degeneracy in the control and coordination of human movement and also provides the impetus to further examine coordination changes in novice learners as a function of practice using multiple single-participant analysis. From the study, individual learners demonstrated different progression trends in terms of joint motion changes while achieving the same task goal. Intra-participant analysis showed how the ball can be projected accurately across the height barrier with both a 'scooping' and a 'chipping' action. When referenced to a model of learning (Newell, 1985), foot speed at ball contact was functionally manipulated by the novice participants to target positions with varying height and accuracy constraints by later stages of learning. It was further suggested that the dynamics of the learner prior to practicing the task could influence the eventual kicking action that emerged. To further investigate learning from a dynamical systems perspective, key features like transitions between preferred movement patterns and role of movement patterns variability in effecting such transitions, were examined. It was determined through the use of cluster analysis procedures that increased movement pattern variability was not a pre-requisite for a transition between preferred movement patterns across participants. Informational and intentional constraints can have a role to play in effecting the search for pathways of change in movement patterns especially in discrete trial-based multi-articular actions. This thesis has contributed novel knowledge regarding examining coordination changes for a selected discrete multi-articular lower limb action. Focusing on investigating changes in coordination has enabled a detailed examination on the process of change with practice and referencing these changes to a model of learning based on concepts in dynamical systems theory. Specifically, a greater understanding of the role of movement pattern variability and transitions between preferred movement patterns using refined cluster analysis procedures was an advancement of previous work in this area of study. In addition, the empirical findings provided theoretical support for a pedagogical approach, Nonlinear Pedagogy, based on key concepts in dynamical systems theory. Future studies should continue to examine coordination in multi-articular actions to provide theoretical, experimental and practical implications for understanding human movement.

Les tests couramment utilisés pour évaluer le déficit sensori-moteur induit par une lésion du cerveau chez le rat posent problèmes en termes de sensibilité, d'objectivité et de quantification. Nous avons émis l'hypothèse selon laquelle l'analyse 3D de la cinématique de la locomotion constitue un paradigme expérimental approprié pour quantifier un tel déficit. Aussi, la locomotion a été étudiée lors d'une course sur tapis roulant (25 cm/s) muni ou pas d'obstacles (deux obstacles de 3cm de haut et 1,2 cm de large) à l'aide du système optoélectronique VICON. Le mouvement des quatre pattes a été simultanément enregistré avant et après induction d'une lésion unilatérale soit du striatum (mort d'origine métabolique des neurones striataux) soit du cortex cérébral (infarctus du cortex moteur) chez le rat adulte. Le laboratoire a précédemment montré que ces deux modèles de lésion conduisaient à une anomalie plus ou moins durable de la traversée d'une poutre étroite et surélevée, test classiquement utilisé pour évaluer la locomotion du rat. La première étude décrit pour la première fois la stratégie utilisée par le rat pour franchir un obstacle. Elle révèle que le franchissement s'accompagne d'une rupture complète du pattern locomoteur de base et que l'élévation des ceintures contribue de façon notable au passage de chacune des pattes au- dessus de l'obstacle. La seconde étude montre que la lésion du striatum s'accompagne d'un déficit locomoteur durable lors des deux modalités de course, l'anomalie portant sélectivement sur les pattes contralatérales à la lésion. Plus précisément, ces pattes présentent une flexion exagérée pendant la phase d'appui dont la durée est augmentée. Par ailleurs, lorsque que la patte antérieure opposée à la lésion conduit la manœuvre de franchissement, elle prend fréquemment appui sur l'obstacle suite à une initiation trop précoce de son élévation. Dans ce cas, la patte postérieure homolatérale franchit ou non correctement l'obstacle. L'ensemble de ces résultats suggère l'implication du striatum dans la programmation des mouvements guidés par la vue. La dernière expérience montre qu'aucune des modalités de locomotion n'est affectée par la lésion corticale, suggérant que le faisceau corticospinal n'est indispensable ni à la locomotion ni à son adaptation à l'environnement. En conclusion, notre travail montre que nos modalités d'enregistrement de la locomotion sont appropriées pour quantifier le déficit fonctionnel induit par une lésion du striatum, mais pas celui induit par une lésion du cortex moteur. Il serait intéressant de répéter les expériences lors d'une course volontaire, de manière à s'affranchir de la stimulation sensitive générée par le déroulement du tapis sous les pattes et d'étudier la réversibilité du déficit en cas de lésion partielle du striatum.

In the Everest valley of Nepal, because of the rugged mountain terrain, the ‘roads' are nothing more than dirt mountain footpaths. Most of the material is conveyed over long distances by professional porters who carry impressive burdens in a wicker basket supported by a strap looped over their head. We measured the body weight and loads carried by the Himalayan porters passing along the busy footpath to Namche Bazaar, the main market place of the Everest region. On average, the porters were carrying loads equivalent to 90% of their body weight on the last day of a 7-9 day trip covering a horizontal distance of ~100 km with >8000 m of total ascents and >6300 m of total descents. Interestingly, these porters adopt a specific rhythm of walking: they generally walk slowly and make very frequent rest stops using a T-stick or stone-platforms built along the trail to support the load during the pause. It has been shown that African women could carry head-supported loads more economically than Western subjects because they have developed a mechanical energy-saving strategy. Similarly, Nepalese porters could also have developed a mechanism to carry economically their very heavy loads. To test this hypothesis, we measured the energy consumption and the mechanical work done during level walking under different loading and speed conditions in the Nepali porters and in Western subjects. We compared these results to those of the African women. Nepalese porters carry loads at a lower cost than either the control subjects or the African women. For example, for a load equivalent to 60% of body weight, western Caucasian subjects increases their metabolic rate by 60%, the African women by 40% and the Nepalese porters by only 30%. Contrary to the African women who are taking advantage of the load to reduce the work performed, Nepalese porters do not modify their gait while carrying a load. Consequently, the mechanical work performed is not reduced as compared to control subjects walking at same speed-load combinations. Yet the Nepalese porters are the most economical load-carriers measured to date, particularly while carrying heavy loads at walking speeds slower than 1.4 m/s, but the exact mechanisms by which they save energy are still unknown. G. J. Bastien et al. Eur J Appl Physiol 94, 76 (2005); G. J. Bastien et al. Science 308, 1755 (2005); G. J. Bastien et al. J Exp Biol submitted.

This report documents our work in exploring active balance for dynamic legged systems for the period from September 1985 through September 1989. The purpose of this research is to build a foundation of knowledge that can lead both to the construction of useful legged vehicles and to a better understanding of animal locomotion. In this report we focus on the control of biped locomotion, the use of terrain footholds, running at high speed, biped gymnastics, symmetry in running, and the mechanical design of articulated legs.

Terrestrial animals encounter natural surfaces which comprise materials that can yield and flow such as sand, rubble, and debris, yet appear to nimbly walk, run, crawl, or climb across them with great ease. In contrast, man-made devices on wheels and treads suffer large performance loss on these surfaces. Legged locomotion thus provides an excellent source of inspiration for creating devices of increased locomotor capabilities on natural surfaces. While principles of legged locomotion on solid ground have been discovered, the mechanisms by which legged animals move on yielding/flowing surfaces 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. Granular media (e.g., sand) provide a promising model substrate for discovering the principles of legged locomotion on yielding/flowing surfaces, because they can display solid- and fluid-like behaviors, are directly relevant for many desert-dwelling animals, can be repeatably and precisely controlled, and the intrusion force laws can be determined empirically. In this dissertation, we created laboratory devices to prepare granular media in well-controlled states, and integrated biological, robotic, and physics studies to discover principles of legged locomotion on granular media. For both animals and bio-inspired robots, legged locomotion on granular surfaces must be achieved by limb intrusion to generate sufficient vertical ground reaction force (lift) to balance body weight and inertial force. When limb intrusion was slow (speed < 0.5 m/s), granular forces were independent of intrusion speed (dominated by grain-grain and grain-intruder friction) and generally increased with intrusion depth (due to granular hydrostatic pressure). Locomotor performance (speed) depended sensitively on limb kinematics, limb morphology, and the strength of the granular media, which together determined vertical force balance (or lack thereof). Based on these findings, we developed a granular resistive force theory in the sagittal plane as a general model for calculating forces during low-speed intrusions relevant to legged locomotion.

We study vertical jumping in a simple robot comprising an actuated mass spring arrangement. The actuator frequency and phase are systematically varied to find optimal performance. Optimal jumps occur above and below (but not at) the robot's resonant frequency f0. Two distinct jumping modes emerge: a simple jump which is optimal above f0 is achievable with a squat maneuver, and a peculiar stutter jump which is optimal below f0 is generated with a countermovement. A simple dynamical model reveals how optimal lift-off results from non-resonant transient dynamics.

This thesis presents a method for determining range of body motion for a walking machine with feet fixed on the ground. The darkling beetle was selected as the sample subject in this study. A closed form inverse kinematic solution is used to determine if a point in space is within range of body motion. An algorithm for tracing workspace boundary is also presented. The software, developed in Microsoft QuickC, has three main parts: (1) a module for searching the workspace contours and recording the contour points, (2) a plotting program for presentation of the workspace on the screen, (3) a module to determine ranges of roll, pitch and yaw for specified foot positions. The plotting program shows four views of the workspace, including front, top, and side views, and user specified axonometric projection. Body range of motion for a representative set of foot positions is presented and analyzed. Results are presented for normal resting height (10mm) and for 8mm and 12mm heights. Body range of motion for feet positioned for the alternating tripod gait is also presented. Ranges of roll, pitch and yaw have been determined and are discussed. / Graduation date: 1991