Mechanical identification of layer-specific properties of mouse carotid arteries using 3D-DIC and a hyperelastic anisotropic constitutive model

The role of mechanics is known to be of primary order in many arterial diseases; however, determining mechanical properties of arteries remains a challenge. This paper discusses the identifiability of the passive mechanical properties of a mouse carotid artery, taking into account the orientation of collagen fibres in the medial and adventitial layers. On the basis of 3D digital image correlation measurements of the surface strain during an inflation/extension test, an inverse identification method is set up. It involves a 3D finite element mechanical model of the mechanical test and an optimisation algorithm. A two-layer constitutive model derived from the Holzapfel model is used, with five and then seven parameters. The five-parameter model is successfully identified providing layer-specific fibre angles. The seven-parameter model is over parameterised, yet it is shown that additional data from a simple tension test make the identification of refined layer-specific data reliable.Comment: PB-CMBBE-15.pd

Correlation of leg impedance and skin deformation during gait

Tese de mestrado integrado, Engenharia Biomédica e Biofísica (Engenharia Clínica e Instrumentação Médica) Universidade de Lisboa, Faculdade de Ciências, 2019O conhecimento da deformação da pele, juntamente com a cinética e cinemática do corpo humano, são essenciais no planeamento e desenvolvimento de dispositivos médicos em contacto próximo e frequente com a pele humana, fornecendo informações adicionais sobre as características únicas da marcha de cada indivíduo. A forma e intensidade como a pele estica e contrai tem especial atenção nas indústrias têxtil, cosmética e médica que pretendem garantir máxima ergonomia sem sacrificar a eficácia do produto. O planeamento de equipamentos médicos em contacto com o corpo humano (e.g. ortóteses, soft exoskeletons) é importante para garantir os sucessos de processos de reabilitação e a melhor adaptação possível ao paciente. A análise cinética do movimento caracteriza todas as forças que atuam sobre o corpo humano com o objectivo de provocar movimento, sendo as variáveis mais informativas a força de reação (GRF) e a evolução da trajetória do centro de pressão (CoP). Estas duas variáveis apresentam um padrão comum em todos os sujeitos saudáveis, permitindo facilmente a identificação de qualquer problema locomotivo quando os valores apresentam um desvio significativo – marcha patológica. A força de reação vertical apresenta um aspecto característico, com dois picos de intensidade relacionados com especificas etapas do ciclo de marcha: o primeiro pico na fase de apoio de peso, o segundo durante a fase de propulsão. Um pico adicional, por vezes registado no início da fase de apoio, encontra-se diretamente relacionado com o impacto do calcanhar e a forma como o peso é distribuído neste instante – este pico ocorre frequentemente em registos de andar sem calçado, onde não existe amortecimento causado pela sola. Na corrida, geralmente apresenta um pico único, com duração mais curta comparativamente ao andar. O centro de pressão caracteriza-se como a progressão da propagação do vetor da força de reação ao longo do pé, durante o movimento. A trajetória do centro de pressão apresenta uma progressão essencialmente retilínea, com ligeiros desvios quando ocorre a transição de peso do calcanhar para o meio do pé e quando o individuo se propulsiona (localizado nos metatarsos). Na corrida a trajetória é muito menor, devido ao apoio e impulso do sujeito localizado principalmente nos metatarsos. Menos avaliada é a análise da velocidade do centro de pressão (VCoP), que relata a rapidez da transição dos pontos do centro de pressão ao longo do movimento, permitindo observar quanto tempo o sujeito apoia o seu peso numa determinada região do pé. Para o ciclo de marcha comum, costuma apresentar um padrão distinto caracterizado pela presença de 3 picos: estes distinguem a transação rápida do vetor na parte posterior e anterior do pé. A presente tese continua e complementa trabalho previamente realizado no Instituto Superior Técnico, com principal objectivo a análise da deformação da pele do tornozelo [1] e correlação de variáveis biomecânicas na marcha normal [2], destacando-se por uma análise da deformação da perna inteira e por uma sincronização exata com as restantes variáveis biomecânicas. É apresentada uma análise detalhada dos ciclos de marcha e corrida de 9 indivíduos saudáveis (2 masculinos, 7 femininos), com idades entre 20-28 anos, demonstrando uma sincronização completa da progressão temporal da deformação da pele da perna, força de reação do solo (GRF), centro de pressão (CoP), velocidade do centro de pressão (VCoP) e evolução angular das articulações principais (joelho e tornozelo). O equipamento de recolha de dados consistiu em duas câmaras de alta velocidade sincronizadas com uma plataforma de força, ambas adquirindo dados durante 3 segundos a uma frequência de 500 imagens (dados) por segundo. De modo a permitir a análise da deformação da pele da perna através de correlação de imagem tridimensional (3D-DIC), foi necessário cumprir os requerimentos necessários de criação e aplicação de um padrão aleatório, anisotrópico e de elevado contraste (i.e. pontos pretos em fundo branco): para tal foram utilizadas tintas acrílicas, atóxicas, para pintar a perna (cor branca), desde a base do pé até a meio da coxa, cobrindo toda a área lateral, anterior e posterior de forma a poder analisar a deformação nas mesmas vistas. Para aplicar o padrão, foi escolhido o método de estampagem, sendo desenhados e impressos em 3D dois carimbos para “marcar” a perna com cor preta: um maior para rapidamente cobrir a área extensa da perna, um mais pequeno para carimbar as zonas de relevo mais acentuado (i.e. joelho e tornozelo). Para a calibração do software de análise foi necessária a criação de uma grelha de calibração (fornecida pelo programa) adequada á experiência: de forma a capturar a evolução de todo o movimento, o campo de visão foi severamente alargado comparativamente a estudos anteriores, focados no estudo do complexo tornozelo-pé – para ocupar este espaço foi necessária a impressão da grelha em formato A1 (594 x 841 mm). A análise de deformação da pele da perna foi realizada usando a ferramenta VIC-3D da Correlated Solutions para obter a deformação Lagrangiana, extraindo 3 variáveis para análise: e1, deformação máxima principal, e2, deformação mínima principal e von Mises, escalar. Os dados de força e momento registados foram obtidos pelo software da placa de forças AMTI e interpretados através de código MATLAB – GRF corresponde diretamente aos valores da componente vertical da força registada, Fz; CoP e VCoP foram obtidos através da aplicação de equações que utilizam os valores de momento e força para extrair o valor destas grandezas. Para a evolução angular das articulações, a sua variação foi medida através da ferramenta Kinovea, ancorando 6 pontos-chave (3 por ângulo medido) nas imagens analisadas e calculando a sua progressão. Para a análise de marcha são apresentadas três vistas: lateral, posterior e anterior. Além do andar e correr, o comportamento de equilíbrio do corpo também foi analisado com o objectivo de identificar um padrão comum na restauração do balanço após os sujeitos serem puxados na direção oposta a meio da fase de apoio. Com a sincronização de todos os dados, é oferecida uma descrição completa da fase de apoio durante a marcha, fornecendo uma base de dados rica e detalhada das suas características desde o início até ao fim do movimento, validada por resultados presentes na literatura. É possível observar os picos de intensidade de GRF conjuntamente com o pico gerado pelo impacto do calcanhar na totalidade dos testes do ciclo de marcha. Uma comparação das mesmas variáveis entre mais 3 sujeitos permite verificar a existência da repetição do mesmo padrão e notar ligeiras diferenças, como a ausência de pico de impacto de calcanhar em alguns sujeitos e um máximo global em diferentes etapas do ciclo (presente no 1º ou 2º pico). A evolução da trajetória do centro de pressão e da velocidade de centro de pressão também se encontram de acordo com o esperado entre os vários sujeitos. A sincronização destas 3 variáveis permite ao utilizador facilmente observar a sua relação e evolução simultânea ao longo da execução do movimento. Nos resultados dos testes de corrida, à semelhança dos testes do andar, os resultados foram os esperados de acordo com o estudo efetuado, com um pico singular de força registado e uma trajetória de centro de pressão bastante reduzida. Nos testes de análise de equilíbrio após perturbação na direção oposta do movimento, foi identificado um padrão na resposta dos sujeitos, no andar e corrida, caracterizado pela ação da perna em balanço como agente principal de restabelecimento de equilíbrio. Uma observação aprofundada do evento do impacto do calcanhar permite identificar um período onde o ângulo entre a perna e o pé se mantêm constante, sugerindo uma rotação de corpo rígido, constituído pelo complexo perna-pé, com o bloquear da articulação do tornozelo. Assim, foi possível introduzir uma nova etapa na descrição do ciclo de marcha, ausente na literatura comum, com a identificação do movimento rígido do complexo-tornozelo-pé após contacto com o chão, que decorre entre o impacto do calcanhar e o apoio total do pé no chão.Knowledge of skin strain, alongside the kinetics and kinematics of the human body are essential for the planning and development of medical devices in close and frequent contact with the human skin and rehabilitation methods, providing further insight into each subject’s unique gait characteristics. The present thesis continues and complements previous work performed at Instituto Superior Técnico aimed at skin strain field analysis of the ankle [1] and correlation of multiple biomechanical quantities in normal gait [2]. The following work features a detailed analysis of walking and running gait of 9 healthy subjects (2 male, 7 female), with ages ranging between 20-28 years old, featuring full synchronization of the temporal progression of leg skin strain, ground reaction force (GRF), centre of pressure (CoP), velocity of centre of pressure (VCoP) and principal joint (knee and ankle) angular evolution. Experimental setup consisted of two high framerate cameras synchronized with a force platform, both acquiring data for 3 seconds at 500 frames (data points) per second. Strain analysis was performed through three-dimensional digital image correlation (3D-DIC) using Correlated Solutions’ VIC-3D tool to obtain the Lagrangian strain; GRF, CoP and VCoP data were obtained from the AMTI force plate software, and interpreted using MATLAB code. For the joint angular evolution, their variation was measured with Kinovea. For walking gait, 3 views are presented: lateral, posterior and anterior. Besides normal walking and running gait, the body’s balance behaviour was also analysed with the purpose of identification of a common pattern in balance restoring after the subjects were pulled midstance in the opposite direction. With the synchronization of all data, a complete description of the stance phase during gait is offered, supplying a rich and detailed database of its characteristics from beginning to end. A close up view on the heel strike transient event also introduces a novel stage in stance gait description, with the identification of a rigid body rotation of the ankle-foot complex after heelstrike

Mixed experimental and numerical approach for characterizing the biomechanical response of the human leg under elastic compression.

8 p.International audienceElastic compression is the process of applying an elastic garment around the leg, supposedly for enhancing the venous flow. However, the response of internal tissues to the external pressure is still partially unknown. In order to improve the scientific knowledge about this topic, a slice of a human leg wearing an elastic garment is modeled by the finite-element method. The elastic properties of the tissues inside the leg are identified thanks to a dedicated approach based on image processing. After calibrating the model with magnetic resonance imaging scans of a volunteer, the pressure transmitted through the internal tissues of the leg is computed. Discrepancies of more than 35% are found from one location to another, showing that the same compression garment cannot be applied for treating deficiencies of the deep venous system or deficiencies of the large superficial veins. Moreover, it is shown that the internal morphology of the human leg plays an important role. Accordingly, the approach presented in this paper may provide useful information for adapting compression garments to the specificity of each patient

Influence of muscle-tendon unit structure, function, and menstrual cycle phase in dancers’ physical performance

Flexibility and jump are crucial capabilities for dancers but reaching good performance in both is a challenge. Given that muscle-tendon stiffness (SMTU) might affect both these capabilities and that muscle structure and concentration of female hormones across the menstrual cycle may affect SMTU, this thesis aimed to determine the factors that might affect SMTU and, therefore, physical performance in female dancers, especially through the menstrual cycle. A piece of equipment to measure and train flexibility in highly flexible participants was developed and validated. Then, fifteen young adult dance students under oral contraception, eleven dance students without contraception and twenty non-dancers without contraception completed several laboratory-based tests. Participants underwent semitendinosus and rectus femoris ultrasound imaging, flexibility and vertical jump tests including electromyography, kinematics, and pain mixed-method assessment. Participants also provided serum/saliva samples on test days, including ovulatory, follicular and luteal phases. An intervention involving stretching the most flexible limb allowed evaluation of limb asymmetries and impact on function. Results showed no statistical structural and functional differences between dancers and non-dancers. Asymmetries in flexibility, but SMTU, between limbs, were found for all groups. Those asymmetries appear to not influence jump performance. Four-series of passive constant torque stretch was not sufficient to cause or increase any asymmetry or to affect SMTU. Stretching did not change jump height, muscle activation and kinematics of vertical jumps. Dancers presented irregular menstrual cycle with the change in hormone across the phases being associated with changes in key outcome variables. Thus, oestrogen and relaxin appear to be positively correlated to muscle laxity while progesterone is positively correlated to SMTU. This thesis’ results will provide data for the development of training strategies to improve performance and potentially decrease injuries in dancers. Additionally, contributing to research on hormonal factors in female performance and, therefore, women’s health

Analysis of the backpack loading efects on the human gait

Gait is a simple activity of daily life and one of the main abilities of the human being. Often during leisure, labour and sports activities, loads are carried over (e.g. backpack) during gait. These circumstantial loads can generate instability and increase biomechanicalstress over the human tissues and systems, especially on the locomotor, balance and postural regulation systems. According to Wearing (2006), subjects that carry a transitory or intermittent load will be able to find relatively efficient solutions to compensate its effects.info:eu-repo/semantics/publishedVersio

Impact of static stretch and muscular contractions on force production within the human triceps surae muscle-tendon complex

Pre-performance routines commonly include stretching and intense muscular contractions in an attempt to optimise muscular performance and reduce injury risk. However, the isolated and combined effects of stretching and muscle contractions on neuromuscular performance are not well described. The aims of this research were to examine the effects of acute static stretch and intense muscular contractions on force production of the human plantarflexors and to examine possible mechanical and neuromuscular mechanisms underpinning any changes. Techniques including isokinetic dynamometry, electromyography (EMG), sonography and motion analysis were used in three studies on recreationally active human volunteers (n=20). In the first study, three 60-s passive stretches was found to significantly reduce concentric plantarflexor joint moment (5.0%; P\u3c0.05), which was correlated (r = 0.81; P\u3c0.01) with a reduction in EMG amplitude (9.2%; P\u3c0.05). No reduction in Achilles tendon stiffness or gastrocnemius medialis (GM) muscle operating length was found, and all measures recovered by 30 min. This indicates that post-stretch force losses are transient and are largely associated with reduced neuromuscular activity (EMG amplitude) rather than changes in the muscles’ operating lengths. Nonetheless, strong muscular contractions, commonly performed during preperformance routines and incorporated into research designs, may influence the effects of stretch. In the second study it was found that six 8-s maximal isometric contractions reduced Achilles tendon stiffness (10.9%; P\u3c0.01) and passive joint moment (4.9%; P\u3c0.01) and also significantly reduced concentric moment (11.5%; P\u3c0.01), which was again correlated (r = 0.90; P\u3c0.01) with a reduction in EMG amplitude (21.0%; P\u3c0.01). Importantly, a subsequent bout of static stretch, which was identical to that used in study 1, did not result in a further change in any measure (P \u3e 0.05). Whilst concentric moment and EMG recovered 30 min later, the decreases in Achilles tendon stiffness and passive moment remained. Thus, the normal stretch-induced reductions in force production were removed when isometric contractions were performed prior to stretch, but this was because concentric strength and neuromuscular activity were already affected; the reduction in concentric moment without a decrease in isometric moment indicates a contraction mode-specific response. The final study revealed that the use of concentric contractions (6×8-s) also resulted in similar reductions in Achilles tendon stiffness (11.7%; P\u3c0.01) and concentric joint moment (6.6%; P\u3c0.01) as the isometric contractions, and these were correlated (r = 0.94; P\u3c0.01) with a reduction in EMG amplitude (10.2%; P\u3c0.01). However, a further reduction in concentric moment was detected following an identical bout of static stretch (5.8%; P\u3c0.01) with no further change in EMG. Importantly, EMG recovered 30 min later while concentric moment remained depressed (9.2%; P\u3c0.01), indicating a musclebased mechanism for these force losses. No reduction in GM muscle operating length was found, removing this as a mechanism underpinning the losses in force. The findings from the present series of studies have important implications for research study design as the warm-up imposed on subjects prior to stretch seems to strongly influence the impact of stretch. Furthermore, the results also have important practical implications in the formulation of preperformance routines where maximal force production in the plantarflexors is an important goal

Splint: the efficacy of orthotic management in rest to prevent equinus in children with cerebral palsy, a randomised controlled trial

<p>Abstract</p> <p>Background</p> <p>Range of motion deficits of the lower extremity occur in about the half of the children with spastic cerebral palsy (CP). Over time, these impairments can cause joint deformities and deviations in the children's gait pattern, leading to limitations in moblity. Preventing a loss of range of motion is important in order to reduce secondary activity limitations and joint deformities. Sustained muscle stretch, imposed by orthotic management in rest, might be an effective method of preventing a decrease in range of motion. However, no controlled study has been performed.</p> <p>Methods</p> <p>A single blind randomised controlled trial will be performed in 66 children with spastic CP, divided over three groups with each 22 participants. Two groups will be treated for 1 year with orthoses to prevent a decrease in range of motion in the ankle (either with static or dynamic knee-ankle-foot-orthoses) and a third group will be included as a control group and will receive usual care (physical therapy, manual stretching). Measurements will be performed at baseline and at 3, 6, 9 and 12 months after treatment allocation. The primary outcome measure will be ankle dorsiflexion at full knee extension, measured with a custom designed hand held dynamometer. Secondary outcome measures will be i) ankle and knee flexion during gait and ii) gross motor function. Furthermore, to gain more insight in the working mechanism of the orthotic management in rest, morphological parameters like achilles tendon length, muscle belly length, muscle fascicle length, muscle physiological cross sectional area length and fascicle pennation angle will be measured in a subgroup of 18 participants using a 3D imaging technique.</p> <p>Discussion</p> <p>This randomised controlled trial will provide more insight into the efficacy of orthotic management in rest and the working mechanisms behind this treatment. The results of this study could lead to improved treatments.</p> <p>Trial Registration Number</p> <p>Nederlands Trial Register <a href="http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=2091">NTR2091</a></p

Effect Of Counter-Movement Frequency On Performance in a Single Joint Maximal Jumping Task

Optimal performance in a maximal jumping task occurs when a countermovement is utilized prior to the concentric phase of the movement. Performance augmentation results from the near isometric behavior of the fascicles and storage of elastic energy in tendon structures. Furthermore, it has been suggested that stretch shortening cycle (SSC) tasks should be performed at resonant frequency for optimal performance and mechanical efficiency in both cyclical and maximal SSC tasks. We aimed to determine if performing a counter-movement at resonant frequency results in optimal SSC performance. In addition, we aimed to examine muscle-tendon length changes during maximal hops to examine if higher contribution of tendon length to total MTU length effects performance in a maximal height hop. Higher contribution of tendon length to total MTU length change should optimize elastic storage and augment performance in a maximal SSC task