Human bipedal locomotion is characterized by a habitual heel-strike (HS) plantigrade gait, yet the significance of walking foot-posture is not well understood. To date, researchers have not fully investigated the costs of non-heel-strike (NHS) walking. Therefore, we examined walking speed, walk-to-run transition speed, estimated locomotor costs (lower limb muscle volume activated during walking), impact transient (rapid increase in ground force at touchdown) and effective limb length (ELL) in subjects (n=14) who walked at self-selected speeds using HS and NHS gaits. HS walking increases ELL compared with NHS walking since the center of pressure translates anteriorly from heel touchdown to toe-off. NHS gaits led to decreased absolutewalking speeds (P=0.012) and walk-to-run transition speeds (P=0.0025), and increased estimated locomotor energy costs (P<0.0001) compared with HS gaits. These differences lost significance after using the dynamic similarity hypothesis to account for the effects of foot landing posture on ELL. Thus, reduced locomotor costs and increased maximum walking speeds in HS gaits are linked to the increased ELL compared with NHS gaits. However, HS walking significantly increases impact transient values at all speeds (P<0.0001). These trade-offs may be key to understanding the functional benefits of HS walking. Given the current debate over the locomotor mechanics of early hominins and the range of foot landing postures used by nonhuman apes, we suggest the consistent use of HS gaits provides key locomotor advantages to striding bipeds and may have appeared early in hominin evolution.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

The circuit of recurring inhibition between motor neurons and Renshaw cells in the spinal cord has been known for around 70 years, though no determined function has been outlined as of yet. Renshaw cells are thought to be part of the central pattern generator in the spinal cord establishing them as an important part of the animal’s locomotive properties. In this study we aimed to investigate the role of Renshaw cells in locomotion with the help of optogenetics and electrophysiology. Halorhodopsin was inserted into the genome of mice and driven to expression with Cre recombinase in Renshaw cells. The spinal cord of P3 mice was extracted and by inducing fictive locomotion with appropriate neurotransmitters we could inhibit the Renshaw cells in action with a green laser, opening the halorhodopsin channels for Cl- ions. In previous experiments where the ability of Renshaw cells to release inhibitory neurotransmitters was inactivated, no effect was observed in either behavioral experiments or electrophysiological experiments. In a system where the effect of Renshaw cells was knocked out acutely with optogenetics there was no discernible change in fictive locomotion cycle length, frequency or amplitude. Nor was there an effect on alternation. The access of light to the Renshaw cells area might have been limited during the experiment considering the angle of light delivery and strength of the laser. Furthermore, the maturity of Renshaw cells at P3, the exclusive ability of the marker used to target Renshaw cells and the observed nature of neonatal inhibitory neurons acting as excitatory neurons could all be called into question about whether they contributed to these results or not.

Cellular networks are required for a variety of processes in complex organisms. Caenorhabditis elegans is a useful model to gain insight into the gene regulatory networks that assemble cellular networks. Mutations in a variety of genes can affect the sinusoidal locomotive pattern of C. elegans. We isolated the mutant jd1500 from a standard genetic screen looking for mutants in C. elegans that exhibit asymmetric locomotive patterns. The two aims of this study were to: 1) identify the gene and characterize its role in the gene regulatory network and 2) characterize the cells affected by the mutation. We reasoned that jd1500 likely disrupts the proper balance between dorsal and ventral body wall muscle contractions. By using three-point genetic mapping, we predicted the locus of jd1500 between -9.42 and -11.73 centimorgans of the X chromosome. Our results implicate the embryonic, cholinergic DB motor neurons as likely cellular targets of the mutation.

We present work to transfer decentralized neuromuscular control strategies of human locomotion to powered segmented robotic legs. State-of-the-art robotic locomotion control approaches, like centralized planning and tracking in fully robotic systems and predefined motion pattern replay in prosthetic systems, do not enable the dynamism and reactiveness of able-bodied humans. Animals largely realize dexterous segmented leg performance with leg-encoded biomechanics and local feedback controls that bypass central processing. A decentralized neuromuscular controller was recently developed that enables robust locomotion for a simulated multi-segmented planar humanoid. A portion of this controller was used in an active ankle-foot prosthesis to modulate ankle torque during stance, enabling level and inclined ground walking. While these results suggest that the neuromuscular controller is a promising alternative control method for both fully robotic systems and powered prostheses, it is unclear if the controller can be transferred to multi-segmented robotic legs. The goal of this thesis is to investigate the feasibility of controlling a multi-segmented robotic leg with the proposed neuromuscular control approach, which may enable robots and powered prostheses to react to locomotion disturbances dynamically and in a human-like way. Specifically, work in this thesis investigates two hypotheses. Hypothesis one posits that the proposed decentralized swing-leg controllers enable more robust foot placements into ground targets than state-of-the-art impedance controls. Hypothesis two posits that neuromuscular swing-leg control enables more human-like motion than state-of-the-art impedance control. To transfer neuromuscular controls to powered segmented robotic legs, we use a model-based design approach. The initial transfer is focused on neuromuscular swing-leg controls, important for maintaining dynamic stability of both fully robotic systems and powered prostheses in the presence of unexpected locomotion disturbances, such as trips and pushes. We first present the design of RNL, a three segment, cable-driven, antagonistically actuated robotic leg with joint compliance. The robot’s size, weight, and actuation capabilities correspond to dynamically scaled human values. Next, a highfidelity simulation of the robot is created to investigate the feasibility of transferring neuromuscular controls, pre-tune hardware gains via optimization, and serve as a benchmark for hardware experiments. An idealized version of the swing-leg controller with mono-articular actuation, as well as the neuromuscular interpretation of this controller with multi-articular actuation is then transferred to RNL and evaluated with foot placement experiments. The results suggest that the proposed swing-leg controllers can accurately regulate foot placement of robotic legs during undisturbed and disturbed motions. Compared to impedance control, the proposed controls achieve foot placements over a range of ground targets with a single set of gains, which make them attractive candidates for regulating the motion of legged robots and prostheses in the real-world. Furthermore, the ankle trajectory traced out by the robot under neuromuscular control is more human-like than the trajectories traced out under the proposed idealized control and impedance control. In parallel to this control transfer, a synthesis method for creating compact nonlinear springs with user-defined torque-deflection profiles is presented to explore methods for improving RNL’s series elastic actuators. The springs use rubber as their elastic element, which, while enabling a compact spring design, introduce viscoelastic behavior in the spring that needs to be accounted for with additional control. To accurately estimate force developed in the rubber, an empirically characterized constitutive rubber model is developed and integrated into the series elastic actuator controller used by the RNL test platforms. Benchtop experiments show that in conjunction with an observer, the nonlinear spring prototype achieves desired behavior at actuation frequencies up to 2 Hz, after which spring behavior degrades due to rubber hysteresis. These results show that while the presented methodology is capable of realizing compact nonlinear springs, careful rubber selection that mitigates viscoelastic behavior is necessary during the spring design process.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

A prática do alongamento muscular é comum durante as rotinas de aquecimento para a corrida, com a crença de que tal atividade pode prevenir lesões e/ou melhorar o desempenho. Evidências experimentais indicaram que de forma aguda o alongamento estático pode prejudicar, melhorar ou não influenciar no desempenho de corridas de longas distâncias. Da mesma forma, evidenciou-se que o alongamento dinâmico pode melhorar ou não interferir no desempenho da corrida subsequente. No entanto, são escassos os dados relacionados à biomecânica da corrida em função destes estímulos. Portanto, o objetivo deste trabalho foi o de dimensionar os efeitos agudos do alongamento estático e do alongamento dinâmico sobre as variáveis biomecânicas da corrida relacionadas ao desempenho e à sobrecarga mecânica externa. 32 corredores amadores participaram do estudo (20 homens e 12 mulheres; 31,5 ± 4,9 anos; 1,7 ± 0,1 metros; 68 ± 10,8 kg). Os corredores participaram de três sessões experimentais para a avaliação biomecânica durante 15 minutos de corrida em esteira numa velocidade constante. A velocidade de corrida foi individualizada e correspondente à velocidade média da última prova de 10 km de cada participante. Foram feitas aquisições do comportamento da força de reação do solo no eixo vertical (esteira Mercury® Med, H/P/Cosmos Sports & Medical GMB) e da atividade muscular (TeleMyoDTS) do reto femoral, do vasto lateral, do bíceps femoral, do gastrocnemio lateral e do tibial anterior, bem como de parâmetros espaço temporais como o tempo de apoio, a frequência e o comprimento de passos, em quatro momentos distintos: momento 1- entre 0 e 1 minuto de corrida, momento 2 - entre 4 e 5 minutos de corrida, momento 3 - entre 9 e 10 minutos de corrida e momento 4 - entre 14 e 15 minutos de corrida. Em cada sessão de avaliação, os voluntários foram submetidos a um protocolo de exercícios de alongamento distinto, sendo eles: alongamento estático para os membros inferiores, alongamento dinâmico para os membros inferiores e alongamento estático para os membros superiores. Em cada um dos dias, foram executados 5 exercícios distintos, com um volume total de estímulo de 60 segundos para cada grupamento muscular. Os resultados não evidenciaram influência significativa do alongamento estático ou do alongamento dinâmico sobre as variáveis biomecânicas da corrida avaliadas neste estudo. Observou-se somente efeitos principais de momento, evidenciando uma diminuição no primeiro pico da força de reação do solo no momento 4 em comparação com o momento 2 (p = 0,011), um aumento no comprimento e uma diminuição na frequência de passos (p < 0,05) nos momentos 3 e 4, e uma menor intensidade de atividade muscular do bíceps femoral e do gastrocnêmio lateral na fase de apoio a partir do momento 2 (p < 0,05), independentemente do tipo de exercício de alongamento utilizado. Com base nestes resultados é possível concluir que a utilização de até 60 segundos de alongamento, estático ou dinâmico, para os membros inferiores não foi capaz de influenciar significativamente o comportamento muscular e os parâmetros dinâmicos durante uma corrida na esteira em velocidade constante submáxima / Stretching is a common practice during warm up routines for running, with the belief that it could prevent against injuries or improve performance. Literature suggests that static stretching can impair, improve or cannot influence on subsequent long-distance running performance. On the same way, it has been shown that dynamic stretching can improve or do not influence running performance. However, data about the acute effects of stretching on running mechanics are rare. Therefore, the objective of this study was to assess the acute effects of static and dynamic stretching on running mechanics related to performance and to mechanical overload. 32 amateur runners volunteered to this study (20 men, 12 women; 31,5 ± 4,9 years; 1,7 ± 0,1 meters; 68 ± 10,8 kg). The runners underwent on three experimental sessions to assess running mechanics for 15 minutes of constant speed running on a instrumented treadmill. The speed was correspondent to the average speed of the last 10 km race performance of each volunteer. Ground reaction forces (Mercury® Med, H/P/Cosmos Sports & Medical GMB) data were collected, and electromyographic activity were assessed (TeleMyoDTS) of rectus femoral, vastus lateral, biceps femoral, lateral gastrocnemius and tibialis anterior during trials. Step frequency and step length were also assessed. These parameters were assessed in four different moments: moment 1 - between 0 and 1 minute of test; moment 2 - between 4 and 5 minutes of test; moment 3 - between 9 and 10 minutes of test; moment 4 - between 14 and 15 minutes of test. At each session, the volunteers underwent a different protocol of stretching exercises: static stretching for lower limbs; dynamic stretching for lower limbs; and static stretching for upper limbs. There were 5 different exercises for lower limbs, with a total volume of 60 seconds for each muscle. The results did not show any significant influence of static or dynamic stretching on running mechanics. It was only observed a moment main effects, showing a decrease in the first peak of ground reaction forces at time 4 compared to moment 2 (p = 0,011), an increase on step length and a decrease on step frequency (p < 0,05) at moments 3 and 4, and a decrease on electromyograph intensity of biceps femoral and lateral gastrocnemius during stance phase from the moment 2 to the end of the test. With these results, is possible to conclude that the use up to 60 seconds of static or dynamic stretching for lower limbs was not able to significant influence the neuromuscular behavior and the dynamic parameters during a treadmill running at a constant submaximal speed

The hydrodynamics of three different shark heads: Eusphyra blochii (Winghead shark), Carcharhinus acronotus (Blacknose shark) and Sphyrna tiburo (Bonnethead shark) were investigated. Force transducer measurement was used to explore how the cephalofoil (wing-shaped head) affects maneuverability and efficiency. As the dynamic behavior of maneuvering wings differs from that of the steady state motion, experiments have been conducted to simulate: 1) steady-state (no yaw motion) constant velocity swimming, 2) constant forward velocity with yawing motion of the head and 3) turning maneuvers. Different range of velocities, angle of attack, yaw frequency and yaw amplitude were tested. Drag and lift coefficients were calculated and compared. The lift coefficient of Winghead shark is much higher compared to the other sharks. The lift-to-drag ratio showed that the Winghead shark has a hydrodynamic advantage compared to Blacknose shark and Bonnethead shark. / by Julien Barousse. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

Posthatchling green (Chelonia mydas) and loggerhead (Caretta caretta) turtles overlap ecologically but differ morphologically. This study compared hydrodynamic stability between the two species during swimming to test for functional differences in body shape. Flipper movement paths, four stability measures (yaw, pitch, heave, and sideslip), and the relative positions of the centers of buoyancy and gravity were compared between species. Both centers of buoyancy and gravity lie in the anterior body; their positions relative to one another differed with species, but showed no functional consequences. Neither species demonstrated substantial yaw, sideslip, or pitch. Both experienced upward heave with the flippers' downstroke and downward heave with the upstroke; however phase relationships differed between these limb and body motions. No differences were found between the two species. Despite obvious morphological differences, loggerheads and green turtles were similarly stable during swimming, suggesting that the species use different mechanisms to achieve stability. / by Erin Dougherty. / Thesis (M.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

A locomoção representa um marco motor, e está dialeticamente relacionada a processos cognitivos e sociais no bebê, sendo investigada no campo como importante aspecto do seu desenvolvimento. Frequentemente, é articulada à maior capacidade de explorar o ambiente, direcionar-se a objetos/pessoas de interesse e engajar-se mais ativamente em interações. No entanto, os trabalhos têm forte tradição experimental e apontam à necessidade de aprofundar a compreensão dos fatores sociais e contextuais envolvidos no desenvolvimento da locomoção. Além disso, quando considerados os processos relacionais, enfoca-se fundamentalmente o papel do adulto. Deste modo, entendendo-se: que o desenvolvimento é biologicamente-cultural, contendo tanto elementos filogenéticos, como socioculturais; que a análise da aquisição da locomoção enquanto processo de transformação no tempo em contextos naturalísticos, permite apreender sua dinamicidade e complexidade; e, que há crescente inserção de bebês em instituições de educação infantil coletiva, contexto no qual o par de idade é um importante parceiro relacional, traçou-se por objetivo investigar o entrelaçamento dos processos de engajamento com parceiros de idade e o desenvolvimento da locomoção. Com base na perspectiva da Rede de Significações, foram conduzidos estudos de caso múltiplos através da análise do banco de imagens de uma creche hospitalar. Três bebês foram acompanhadas ao longo de quatro meses, em três sessões semanais de 30 minutos. A análise se dividiu em três etapas: 1) acompanhamento do percurso desenvolvimental de cada sujeito-pivô mês a mês; 2) mapeamento e identificação das ocorrências de locomoção em momentos de interação com o par; e, 3) seleção e análise microgenética de episódios. Observou-se que dentro do que o contexto da creche possibilita, a locomoção foi coconstruída em forma de fluxo, através de pequenos deslocamentos produzidos na interação com o outro que com o tempo passam a tornar-se mais frequentes - trazem outras formas de locomoção que vão para além dos marcos do engatinhar, andar e cruising. Deste modo, entende-se que o par pode tanto assumir o papel de impulsionador como dificultador do desenvolvimento locomotor. Ademais, em muitos episódios interativos, a locomoção se deu em situações mediadas por objetos, ou marcadas pela expressividade emocional atrelada a movimentos de aproximação ou afastamento que geravam ou evitavam o contato corporal entre as crianças. Isso permitiu a evidência de processos como a atenção conjunta e a empatia, aqui não com o adulto, mas com o outro bebê, recolocando a necessidade de discutir o desenvolvimento das habilidades relacionais, locomotoras e cognitivas em processos interacionais com o par de idade. / Locomotion is considered a major milestone, and it is dialectically related to infants cognitive and social processes. It has been investigated in the field as an important aspect of development. Often, infants locomotion is articulated to the greater ability to explore the environment and to refer to objects / persons of interest as well as to engage more actively in interactions. However, most studies have strong experimental tradition and indicate the importance of additional understanding in regards to social and contextual factors interrelated in the locomotor development. Furthermore, when studies consider the relational processes involved, they seem to focus primarily to the adults role. Thus, in light of: human development being considered biologically-cultural, provided that it integrates both phylogenetic and socio-cultural elements; that naturalistic observation and analysis of locomotion onset as a process of transformation throughout time allows the grasping of its dynamics and complexity; and, given that there is increasing participation of infants in collective educational institutions, the context in which the peer is indicated as an important relational partner, this study aimed to investigate the intertwining of peer-interaction engagement processes and the development of locomotion. Based on the Network of Meanings perspective, multiple case studies were conducted pertaining to a image database of a hospital daycare. The participantes were three babies whose development was followed for a four-month period through three weekly 30-minute recording sessions. The analysis was divided in three steps: 1) monthly mapping of overall development from each participant; 2) mapping and identification of occurrences of locomotion in situations relating peer-interaction; and 3) microgenetic selection and analysis of episodes. Considering the daycare context, locomotion was co-constructed as a flow through small displacements produced in interaction with other infants which becomes more frequente over time. Hence, various means of locomotion take place, other than the traditional milestones of crawling, walking and cruising. It has also been observed that other infants may assume the role of stimulating or hindering locomotor development. Moreover, in many interactive episodes, locomotion occurred in situations mediated by objects, or involved emotional expressiveness linked to approaching or escaping movements, causing infants either to seek or avoid body contact among themselves. This allowed the evidence of processes such as joint attention and empathy, not here in adult-infant relationships, but in infant-peer interaction. Such findings indicate the need of further investigating the development of relational, locomotor and cognitive skills in interaction processes involving infant-peers.