2,561 research outputs found
Inertial Load Compensation by a Model Spinal Circuit During Single Joint Movement
Office of Naval Research (N00014-92-J-1309); CONACYT (Mexico) (63462
Computationally efficient modeling of proprioceptive signals in the upper limb for prostheses: a simulation study.
Accurate models of proprioceptive neural patterns could one day play an important role in the creation of an intuitive proprioceptive neural prosthesis for amputees. This paper looks at combining efficient implementations of biomechanical and proprioceptor models in order to generate signals that mimic human muscular proprioceptive patterns for future experimental work in prosthesis feedback. A neuro-musculoskeletal model of the upper limb with 7 degrees of freedom and 17 muscles is presented and generates real time estimates of muscle spindle and Golgi Tendon Organ neural firing patterns. Unlike previous neuro-musculoskeletal models, muscle activation and excitation levels are unknowns in this application and an inverse dynamics tool (static optimisation) is integrated to estimate these variables. A proprioceptive prosthesis will need to be portable and this is incompatible with the computationally demanding nature of standard biomechanical and proprioceptor modelling. This paper uses and proposes a number of approximations and optimisations to make real time operation on portable hardware feasible. Finally technical obstacles to mimicking natural feedback for an intuitive proprioceptive prosthesis, as well as issues and limitations with existing models, are identified and discussed
Artificial Human Balance Control by Calf Muscle Activation Modelling
The natural neuromuscular model has greatly inspired the development of control mechanisms in addressing the uncertainty challenges in robotic systems. Although the underpinning neural reaction of posture control remains unknown, recent studies suggest that muscle activation driven by the nervous system plays a key role in human postural responses to environmental disturbance. Given that the human calf is mainly formed by two muscles, this paper presents an integrated calf control model with the two comprising components representing the activations of the two calf muscles. The contributions of each component towards the artificial control of the calf are determined by their weights, which are carefully designed to simulate the natural biological calf. The proposed calf modelling has also been applied to robotic ankle exoskeleton control. The proposed work was validated and evaluated by both biological and engineering simulation approaches, and the experimental results revealed that the proposed model successfully performed over 92% of the muscle activation naturally made by human participants, and the actions led by the simulated ankle exoskeleton wearers were overall consistent with that by the natural biological response
The Distributed Lambda Model (DLM): A 3-D, Finite-Element Muscle Model Based on Feldman's Lambda Model; Assessment of Orofacial Gestures
International audiencePurpose: The authors aimed to design a distributed Lambda model (DLM), which is well-adapted to implement three-dimensional (3-D) Finite Element descriptions of muscles. Method: A muscle element model was designed. Its stress-strain relationships included the active force-length characteristics of the Lambda model along the muscle fibers, together with the passive properties of muscle tissues in the 3-D space. The muscle element was first assessed using simple geometrical representations of muscles in form of rectangular bars. Then, it was included in a 3-D face model, and its impact on lip protrusion was compared with the impact of a Hill-type muscle model. Results: The force-length characteristic associated with the muscle elements matched well with the invariant characteristics of the Lambda model. The impact of the passive properties was assessed. Isometric force variation and isotonic displacements were modeled. The comparison with a Hill-type model revealed strong similarities in terms of global stress and strain. Conclusion: The DLM accounted for the characteristics of the Lambda model. Biomechanically no clear differences were found between the DLM and a Hill-type model. Accurate evaluations of the Lambda model, based on the comparison between data and simulations, are now possible with 3-D biomechanical descriptions of the speech articulators because to the DLM
On Neuromechanical Approaches for the Study of Biological Grasp and Manipulation
Biological and robotic grasp and manipulation are undeniably similar at the
level of mechanical task performance. However, their underlying fundamental
biological vs. engineering mechanisms are, by definition, dramatically
different and can even be antithetical. Even our approach to each is
diametrically opposite: inductive science for the study of biological systems
vs. engineering synthesis for the design and construction of robotic systems.
The past 20 years have seen several conceptual advances in both fields and the
quest to unify them. Chief among them is the reluctant recognition that their
underlying fundamental mechanisms may actually share limited common ground,
while exhibiting many fundamental differences. This recognition is particularly
liberating because it allows us to resolve and move beyond multiple paradoxes
and contradictions that arose from the initial reasonable assumption of a large
common ground. Here, we begin by introducing the perspective of neuromechanics,
which emphasizes that real-world behavior emerges from the intimate
interactions among the physical structure of the system, the mechanical
requirements of a task, the feasible neural control actions to produce it, and
the ability of the neuromuscular system to adapt through interactions with the
environment. This allows us to articulate a succinct overview of a few salient
conceptual paradoxes and contradictions regarding under-determined vs.
over-determined mechanics, under- vs. over-actuated control, prescribed vs.
emergent function, learning vs. implementation vs. adaptation, prescriptive vs.
descriptive synergies, and optimal vs. habitual performance. We conclude by
presenting open questions and suggesting directions for future research. We
hope this frank assessment of the state-of-the-art will encourage and guide
these communities to continue to interact and make progress in these important
areas
Vibration as an exercise modality: how it may work, and what its potential might be
Whilst exposure to vibration is traditionally
regarded as perilous, recent research has focussed on
potential benefits. Here, the physical principles of forced
oscillations are discussed in relation to vibration as an
exercise modality. Acute physiological responses to isolated
tendon and muscle vibration and to whole body
vibration exercise are reviewed, as well as the training
effects upon the musculature, bone mineral density and
posture. Possible applications in sports and medicine are
discussed. Evidence suggests that acute vibration exercise
seems to elicit a specific warm-up effect, and that vibration
training seems to improve muscle power, although the
potential benefits over traditional forms of resistive exercise
are still unclear. Vibration training also seems to
improve balance in sub-populations prone to fall, such as
frail elderly people. Moreover, literature suggests that
vibration is beneficial to reduce chronic lower back pain
and other types of pain. Other future indications are
perceivable
A computational model of spasticity based on a decoupling of the alpha and gamma efferents
It is generally accepted that spasticity results from changes in the excitability of the stretch reflex. This change lowers the threshold of the motoneurons of the spinal cord where the integration of a signal from velocity/position sensors is processed and then fed back to the contracting muscle (alphaextrafusal and gamma-intrafusal fibers). The stretch reflex depends on the initial length of the muscle, the stretch velocity and voluntary activity. The exact sequence of the triggering events remains unknown, is poorly understood and as a result is controversial. The clinical classification scales are mainly subjective and by definition, inaccurate.
This computational model of spasticity is based on the concept of the existence of a normal neuromuscular control coupling function, which ordinarily encloses the extrafusal and intrafusal fibers, and explains the spasticity as a result of the uncoupling of this normal mechanism. The model involves mechanical parameters and basic neuromuscular control theory
Neuromuscular Response Characteristics in Men and Women After Knee Perturbation in a Single-Leg, Weight-Bearing Stance.
Objective: We examined whether muscle response times and activation patterns in the lower extremity differed between men and women in response to a rotational knee perturbation while standing in a single-leg, weight-bearing stance.
Design and Setting: We used a lower extremity perturbation device to produce a sudden, forward, and either internal or external rotation moment of the trunk and femur relative to the weight-bearing tibia. Subjects completed 10 trials of both internal and external rotation perturbation; the first 5 acceptable trials were averaged and used for data analysis. Two separate, repeated-measures analyses of variance were used to compare myoelectric response times and activation patterns between men and women for both internal and external rotation perturbation.
Subjects: Thirty-two female (19 lacrosse, 13 soccer) and 32 male (lacrosse) healthy intercollegiate athletes participated in the study. Measurements: We used surface electromyography to record long latency reflex times of the medial and lateral quadriceps, hamstring, and gastrocnemius muscles.
Results: Women responded faster than men, primarily due to a shorter latency in quadriceps activation. However, men and women exhibited no difference in muscle-recruitment order.
Conclusions: Although men and women demonstrated similar muscle-recruitment patterns to an imposed lower extremity perturbation, women tended to activate their quadriceps earlier than men. Whether this earlier quadriceps activation diminishes the ability of the hamstrings to adequately stabilize the knee joint or subjects the anterior cruciate ligament to greater risk of injury is still unknown and requires further study. Furthermore, although surface electromyography and measurement of myoelectric response times are useful in evaluating the timing, activation order, and coactivity patterns of the knee musculature, future studies should evaluate sex differences across the complete response continuum, including measures of intrinsic muscle stiffness, electromechanical delay, and time to force production
Incremental embodied chaotic exploration of self-organized motor behaviors with proprioceptor adaptation
This paper presents a general and fully dynamic embodied artificial neural system, which incrementally explores and learns motor behaviors through an integrated combination of chaotic search and reflex learning. The former uses adaptive bifurcation to exploit the intrinsic chaotic dynamics arising from neuro-body-environment interactions, while the latter is based around proprioceptor adaptation. The overall iterative search process formed from this combination is shown to have a close relationship to evolutionary methods. The architecture developed here allows realtime goal-directed exploration and learning of the possible motor patterns (e.g., for locomotion) of embodied systems of arbitrary morphology. Examples of its successful application to a simple biomechanical model, a simulated swimming robot, and a simulated quadruped robot are given. The tractability of the biomechanical systems allows detailed analysis of the overall dynamics of the search process. This analysis sheds light on the strong parallels with evolutionary search
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