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

This thesis examines the influence on range-of-motion of beetle body of changes in leg segment parameters. From beetle's leg orientation, influence of the following leg segment parameters are investigated: coxa length, coxa twist and body-coxa joint. Kinematic equations are derived for legs of the beetle. Roots of quartic polynomials obtained while solving the kinematic equations are found by using the Bairstow (1966) numerical method. Inverse kinematic solutions are obtained for each leg and used to determine whether a point is within the body range of motion or not. An algorithm developed by Mason (1957) and Cordray (1957) for tracing closed boundaries is used to find ranges of motion of the body and feet. Changes in body range of motion caused by alteration in leg segment parameters are complex and not easy to explain. Similarities between changes in body range of motion and foot range of motion are observed. A great deal more work is necessary to fully understand the importance of observed changes. / Graduation date: 1992

Objectives: To describe the relationship between sensorimotor function and walking in incomplete SCI. Methods: 25 subjects were assessed using Lower Extremity Motor (LEMS) and Pinprick (LEPS) scores, and 7 walking measures: FIM-Locomotor Score, Assistive Device Score, Walking Index for SCI, 10-metre Walk Test (10mWT), Timed Up and Go (TUG), Six-Minute Walk Test (6MWT) and Walking Mobility Scale. Results: Walking and sensorimotor function varied between subjects. Walking measures significantly correlated with LEMS and individual leg muscles but not LEPS. 21/22 ambulatory subjects had LEMS threshold>20. Non-ambulatory subjects didn’t achieve threshold. Not all subjects completed all walking measures: 10mWT: n=19; TUG: n=14, 6MWT: n=13. Most walking measures were significantly related. 10mWT and 6MWT were highly correlated. Subjects walking0.95 m/s didn’t reach predicted 6MWT. Conclusion: Lower extremity strength is important for walking and should be further examined with other factors in a range of subjects across different measures to fully understand these relationships.

Objectives: To describe the relationship between sensorimotor function and walking in incomplete SCI. Methods: 25 subjects were assessed using Lower Extremity Motor (LEMS) and Pinprick (LEPS) scores, and 7 walking measures: FIM-Locomotor Score, Assistive Device Score, Walking Index for SCI, 10-metre Walk Test (10mWT), Timed Up and Go (TUG), Six-Minute Walk Test (6MWT) and Walking Mobility Scale. Results: Walking and sensorimotor function varied between subjects. Walking measures significantly correlated with LEMS and individual leg muscles but not LEPS. 21/22 ambulatory subjects had LEMS threshold>20. Non-ambulatory subjects didn’t achieve threshold. Not all subjects completed all walking measures: 10mWT: n=19; TUG: n=14, 6MWT: n=13. Most walking measures were significantly related. 10mWT and 6MWT were highly correlated. Subjects walking0.95 m/s didn’t reach predicted 6MWT. Conclusion: Lower extremity strength is important for walking and should be further examined with other factors in a range of subjects across different measures to fully understand these relationships.