19,523 research outputs found

    Parameter interdependence and success of skeletal muscle modelling

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    In muscle and movement modelling it is almost invariably assumed that force actually exerted is determined by several independent factors. This review considers the fact that length force characteristics are not a relatively fixed property of muscle but should be considered the product of a substantial number of interacting factors. Level of activation and recruitment are influential factors in relation to aspects of muscle architecture. For the level of activation effects of its short term history (potentiation, fatigue in sustained contractions) have to be taken into account and are reviewed on the basis of recent experimental results as well as available literature. History is also an important determinant for the effect of length changes. This concept is introduced on the basis of recent experimental evidence as well as available literature. Regarding effects of muscle architecture, the concepts of primary and secondary distribution of fibre mean sarcomere length are introduced as well as effects of muscle geometry for mono- and bi-articular muscles on those distributions. Implications for motor control are discussed and the need for intramuscular coordination indicated

    Locomotor system simulations and muscle modeling of the stick insect (Carausius morosus)

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    It is a matter of fact that even so called "primitive species" (like insects) readily outperform any human locomotive invention with respect to agility, adaptability and reliability - to name the least. The work at hand deals with two aspects that contribute to the pre-eminence of biological, terrestrial locomotor systems, namely motion control and muscle properties. In the first part of this work, a new, biologically well-founded approach for the control of articulated legs is presented. This controller, based on the detailed physiological knowledge of the stick insect's (Carausius morosus) leg control, redundantizes complex forward or backward kinematic calculations by dexterous employment of sensory feedback and muscle properties. This section shows that the collection of segmental coordination rules (which have been studied in the stick insect for several decades) is indeed able to generate periodic, robust middle leg stepping movements in a physical simulation of the animal. Furthermore, the controller is capable of handling stepping in the front and hind leg; although for hind leg stepping minor modifications were necessary. The second part of this work is about muscle modeling and it is divided into three chapters. Lynchpin of any motion is the muscle, and nowadays it is well-accepted that muscle properties are complex and highly variable. Hence, no trivial relationship between motor neuron activity and motion can be expected and typically, computer modeling is required to link the two. This part therefore first describes how a model of the stick insect's extensor tibiae muscle can be developed for individual muscles. The approach presented offers a way to measure and model all properties for the generation of a classical Hill-type model, in a single animal. Therefore it was necessary to reduce the number of measurements, stimulations and the overall time span of the experiment to a degree this muscle could take without severe loss in vitality. After this approach has been described, the next section deals with a possible application of individual muscle modeling. The variation of muscle model parameters is investigated for 10 different individuals. The question of parameter independence is addressed, and in fact it could be shown that there is co-variation between two different pairs of parameters. One correlation was found between two parameters modeling passive static force curve, the other between one parameter of the force-length and one of the force-activation curve. Both correlations suggest that the model can be reduced further. In the final section, isometric and isotonic simulations were performed with different model configurations. It is investigated how far averaging parameters of different animals would influence model performance. This is studied by comparing the error produced by four different model configurations, differing in their share of averaged parameters. Compared to a model entirely composed of averaged parameters, performance of the muscle specific model improves by approximately 40%

    Are mice good models for human neuromuscular disease? Comparing muscle excursions in walking between mice and humans

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    The mouse is one of the most widely used animal models to study neuromuscular diseases and test new therapeutic strategies. However, findings from successful pre-clinical studies using mouse models frequently fail to translate to humans due to various factors. Differences in muscle function between the two species could be crucial but often have been overlooked. The purpose of this study was to evaluate and compare muscle excursions in walking between mice and humans

    Musculoskeletal modelling of an ostrich (Struthio camelus) pelvic limb: influence of limb orientation on muscular capacity during locomotion

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    We developed a three-dimensional, biomechanical computer model of the 36 major pelvic limb muscle groups in an ostrich (Struthio camelus) to investigate muscle function in this, the largest of extant birds and model organism for many studies of locomotor mechanics, body size, anatomy and evolution. Combined with experimental data, we use this model to test two main hypotheses. We first query whether ostriches use limb orientations (joint angles) that optimize the moment-generating capacities of their muscles during walking or running. Next, we test whether ostriches use limb orientations at mid-stance that keep their extensor muscles near maximal, and flexor muscles near minimal, moment arms. Our two hypotheses relate to the control priorities that a large bipedal animal might evolve under biomechanical constraints to achieve more effective static weight support. We find that ostriches do not use limb orientations to optimize the moment-generating capacities or moment arms of their muscles. We infer that dynamic properties of muscles or tendons might be better candidates for locomotor optimization. Regardless, general principles explaining why species choose particular joint orientations during locomotion are lacking, raising the question of whether such general principles exist or if clades evolve different patterns (e.g., weighting of muscle force–length or force–velocity properties in selecting postures). This leaves theoretical studies of muscle moment arms estimated for extinct animals at an impasse until studies of extant taxa answer these questions. Finally, we compare our model’s results against those of two prior studies of ostrich limb muscle moment arms, finding general agreement for many muscles. Some flexor and extensor muscles exhibit self-stabilization patterns (posture-dependent switches between flexor/extensor action) that ostriches may use to coordinate their locomotion. However, some conspicuous areas of disagreement in our results illustrate some cautionary principles. Importantly, tendon-travel empirical measurements of muscle moment arms must be carefully designed to preserve 3D muscle geometry lest their accuracy suffer relative to that of anatomically realistic models. The dearth of accurate experimental measurements of 3D moment arms of muscles in birds leaves uncertainty regarding the relative accuracy of different modelling or experimental datasets such as in ostriches. Our model, however, provides a comprehensive set of 3D estimates of muscle actions in ostriches for the first time, emphasizing that avian limb mechanics are highly three-dimensional and complex, and how no muscles act purely in the sagittal plane. A comparative synthesis of experiments and models such as ours could provide powerful synthesis into how anatomy, mechanics and control interact during locomotion and how these interactions evolve. Such a framework could remove obstacles impeding the analysis of muscle function in extinct taxa

    A STUDY ON DYNAMIC SYSTEMS RESPONSE OF THE PERFORMANCE CHARACTERISTICS OF SOME MAJOR BIOPHYSICAL SYSTEMS

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    Dynamic responses of biophysical systems - performance characteristic

    Spacelab 3 Mission Science Review

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    Papers and abstracts of the presentations made at the symposium are given as the scientific report for the Spacelab 3 mission. Spacelab 3, the second flight of the National Aeronautics and Space Administration's (NASA) orbital laboratory, signified a new era of research in space. The primary objective of the mission was to conduct applications, science, and technology experiments requiring the low-gravity environment of Earth orbit and stable vehicle attitude over an extended period (e.g., 6 days) with emphasis on materials processing. The mission was launched on April 29, 1985, aboard the Space Shuttle Challenger which landed a week later on May 6. The multidisciplinary payload included 15 investigations in five scientific fields: material science, fluid dynamics, life sciences, astrophysics, and atmospheric science

    In Situ Muscle Power Differs Without Varying In Vitro Mechanical Properties in Two Insect Leg Muscles Innervated by the Same Motor Neuron

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    The mechanical behavior of muscle during locomotion is often predicted by its anatomy, kinematics, activation pattern and contractile properties. The neuromuscular design of the cockroach leg provides a model system to examine these assumptions, because a single motor neuron innervates two extensor muscles operating at a single joint. Comparisons of the in situ measurements under in vivo running conditions of muscle 178 to a previously examined muscle (179) demonstrate that the same inputs (e.g. neural signal and kinematics) can result in different mechanical outputs. The same neural signal and kinematics, as determined during running, can result in different mechanical functions, even when the two anatomically similar muscles possess the same contraction kinetics, force-velocity properties and tetanic force-length properties. Although active shortening greatly depressed force under in vivo-like strain and stimulation conditions, force depression was similarly proportional to strain, similarly inversely proportional to stimulation level, and similarly independent of initial length and shortening velocity between the two muscles. Lastly, passive pre-stretch enhanced force similarly between the two muscles. The forces generated by the two muscles when stimulated with their in vivo pattern at lengths equal to or shorter than rest length differed, however. Overall, differences between the two muscles in their submaximal force-length relationships can account for up to 75% of the difference between the two muscles in peak force generated at short lengths observed during oscillatory contractions. Despite the fact that these muscles act at the same joint, are stimulated by the same motor neuron with an identical pattern, and possess many of the same in vitro mechanical properties, the mechanical outputs of two leg extensor muscles can be vastly different

    Genetics of muscle growth in chickens and mice

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    The role of muscle tendon unit elasticity in real life activities.

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    The interaction of a muscle and associated tendon during dynamic activities such as locomotion is critical for both force production and economical movement. It is generally assumed that, under sub-maximal conditions, muscle activation patterns are optimised to achieve maximum efficiency of work. Here, I explore the interaction between the contractile component (CC) and the elastic tendinous tissue to understand the relationship between a muscle's power output and efficiency. In this thesis, I examine the interaction of the CE and the elastic tendinous tissue and its effect on power output and efficiency of muscle using both experimental and modelling techniques. In the first chapter, a model of muscle energetics is developed and validated against dynamic muscle contractions of different muscle types. I then used this model to explore how optimal muscle power and efficiency varies with different activation conditions, clastic properties and length change trajectories. The third and forth chapter presents experiments which explore ultrasound measurement techniques for determining the length changes and mechanical properties of the human gastrocnemius medial is (GM) muscle fibres and Achilles tendon (AT) respectively. I then used similar techniques to explore musclc-tcndon unit (MTU) interaction during gait under different gait conditions. Specifically, I explore how GM power output and efficiency vary with different speeds and inclination and explore how variation in tendinous compliance might influence muscle efficiency. The results suggest that muscles remain highly efficient due to compliant tendons allowing muscle fibres to act at highly powerful and efficient velocities. However variation in power output and particularly muscle function affects the efficiency of muscle. Finally, I determined that the optimal value of tendon stiffness for maximum GM efficiency during walking and running is close to that determined experimentally

    General dynamics of the physical-chemical systems in mammals

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    Biodynamic regulator chain models for physical chemical systems in mammal
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