Neural Control and Biomechanics of the Octopus Arm Muscular Hydrostat

openOctopus vulgaris is a cephalopod mollusk with outstanding motor capabilities, built upon the action of eight soft and exceptionally flexible appendages. In the absence of any rigid skeletal-like support, the octopus arm works as a “muscular hydrostat” and movement is generated from the antagonistic action of two main muscle groups (longitudinal, L, and transverse, T, muscles) under an isovolumetric constrain. This peculiar anatomical organization evolved along with novel morphological arrangements, biomechanical properties, and motor control strategies aimed at reducing the computational burden of controlling unconstrained appendages endowed with virtually infinite degrees of freedom of motion. Hence, the octopus offers the unique opportunity to study a motor system, different from those of skeletal animals, and capable of controlling complex and precise motor tasks of eight arms with theoretically infinite degrees of freedom. Here, we investigated the octopus arm motor system employing a bottom-up approach. We began by identifying the motor neuron population and characterizing their organization in the arm nervous system. We next performed an extensive biomechanical characterization of the arm muscles focusing on the morphofunctional properties that are likely to facilitate the dynamic deformations occurring during arm movement. We show that motor neurons cluster in specific regions of the arm ganglia following a topographical organization. In addition, T muscles exhibit biomechanical properties resembling those of vertebrate slow muscles whereas L muscles are closer to those of vertebrate fast muscles. This difference is enhanced by the hydrostatic pressure inherently present in the arm, which causes the two muscles to operate under different conditions. Interestingly, these features underlie the different use of arm muscles during specific tasks Thus, the octopus evolved several arm-embedded adaptations to reduce the motor control complexity and increase the energetic efficiency of arm motion. This study find relevance also in the blooming field of soft-robotics. Indeed, an increasing number of researchers are currently aiming to design and construct bio-inspired soft-robotic manipulators, more flexible and versatile than their “hard” counterparts and more suited to perform gentle tasks and to interact with biological tissues. In this context, the octopus emerged as a pivotal source of inspiration for motor control principles underlying motion in soft-bodied limbs.openXXXIV CICLO - NEUROSCIENZE - Neuroscienze e neurotecnologieDI CLEMENTE, Alessi

Muscular activity and its relationship to biomechanics and human performance

The purpose of this manuscript is to address the issue of muscular activity, human motion, fitness, and exercise. Human activity is reviewed from the historical perspective as well as from the basics of muscular contraction, nervous system controls, mechanics, and biomechanical considerations. In addition, attention has been given to some of the principles involved in developing muscular adaptations through strength development. Brief descriptions and findings from a few studies are included. These experiments were conducted in order to investigate muscular adaptation to various exercise regimens. Different theories of strength development were studied and correlated to daily human movements. All measurement tools used represent state of the art exercise equipment and movement analysis. The information presented here is only a small attempt to understand the effects of exercise and conditioning on Earth with the objective of leading to greater knowledge concerning human responses during spaceflight. What makes life from nonliving objects is movement which is generated and controlled by biochemical substances. In mammals. the controlled activators are skeletal muscles and this muscular action is an integral process composed of mechanical, chemical, and neurological processes resulting in voluntary and involuntary motions. The scope of this discussion is limited to voluntary motion

Ultrasonography for the prediction of musculoskeletal function

Ultrasound (US) imaging is a well-recognised technique for studying in vivo characteristics of a range of biological tissues due to its portability, low cost and ease of use; with recent technological advances that increased the range of choices regarding acquisition and analysis of ultrasound data available for studying dynamic behaviour of different tissues. This thesis focuses on the development and validation of methods to exploit the capabilities of ultrasound technology to investigate dynamic properties of skeletal muscles in vivo exclusively using ultrasound data. The overarching aim was to evaluate the influence of US data properties and the potential of inference algorithms for prediction of net ankle joint torques. A fully synchronised experimental setup was designed and implemented enabling collection of US, Electromyography (EMG) and dynamometer data from the Gastrocnemius medialis muscle and ankle joint of healthy adult volunteers. Participants performed three increasing complexity muscle movement tasks: passive joint rotations, isometric and isotonic contractions. Two frame rates (32 and 1000 fps) and two data precisions (8 and 16-bits) were obtained enabling analysis of the impact of US data temporal resolution and precision on joint torque predictions. Predictions of net joint torque were calculated using five data inference algorithms ranging from simple regression through to Artificial Neural Networks. Results indicated that accurate predictions of net joint torque can be obtained from the analysis of ultrasound data of one muscle. Significantly improved predictions were observed using the faster frame rate during active tasks, with 16-bit data precision and ANN further improving results in isotonic movements. The speed of muscle activation and complexity of fluctuations of the resulting net joint torques were key factors underpinning the prediction errors recorded. The properties of collected US data in combination with the movement tasks to be assessed should therefore be a key consideration in the development of experimental protocols for in vivo assessment of skeletal muscles

Workshop on Countering Space Adaptation with Exercise: Current Issues

The proceedings represent an update to the problems associated with living and working in space and the possible impact exercise would have on helping reduce risk. The meeting provided a forum for discussions and debates on contemporary issues in exercise science and medicine as they relate to manned space flight with outside investigators. This meeting also afforded an opportunity to introduce the current status of the Exercise Countermeasures Project (ECP) science investigations and inflight hardware and software development. In addition, techniques for physiological monitoring and the development of various microgravity countermeasures were discussed

The Rheology of Striated Muscles

Striated muscles are actuators of animal bodies. They are responsible for several biomechanical functions critical to survival and these include powering the cardiovascular system and modulating the mechanical interactions the body has with its surroundings. Nearly two centuries of active research on muscle phenomena has led to detailed insights into its microscopic composition, but accurate predictive models of muscle at larger scales remain elusive. This thesis reports on efforts to accurately capture the mechanical properties of striated muscles based on current knowledge of actomyosin dynamics. Specifically, this thesis derives the rheology of striated muscles from the dynamics. Muscle rheology is a characterization of the forces that it develops in resistance to externally imposed changes to its length, i.e. its mechanical behavior as a material. For example, the rheology of elastic solids is stiffness and that of viscous fluids is a damping coefficient. Detailed analyses of actomyosin dynamics suggest that the smallest functional units of striated muscles, half-sarcomeres, are viscoelastic and can function as either a solid-like struct or a fluid-like damper depending on time-durations of interest and neural inputs. Such adaptability may underlie the vastly different biomechanical functions that striated muscles provide to animal bodies. Furthermore, muscles are active structures because their properties require metabolic energy and depend on neural inputs. Striated muscles can therefore exhibit rheologies and functions that elastic springs and viscous fluids cannot. The analysis presented in this thesis may extend beyond muscles and biomedical applications. It may help to engineer muscle-like actuators based on principles of tunable properties and to understand the physics of other materials that can similarly transition between being solid-like and fluid-like

Computational Intelligence in Electromyography Analysis

Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG may be used clinically for the diagnosis of neuromuscular problems and for assessing biomechanical and motor control deficits and other functional disorders. Furthermore, it can be used as a control signal for interfacing with orthotic and/or prosthetic devices or other rehabilitation assists. This book presents an updated overview of signal processing applications and recent developments in EMG from a number of diverse aspects and various applications in clinical and experimental research. It will provide readers with a detailed introduction to EMG signal processing techniques and applications, while presenting several new results and explanation of existing algorithms. This book is organized into 18 chapters, covering the current theoretical and practical approaches of EMG research

Characterisation of the biomechanical, passive, and active properties of femur-tibia joint leg muscles in the stick insect Carausius morosus

The understanding of locomotive behaviour of an animal necessitates the knowledge not only about its neural activity but also about the transformation of this activity patterns into muscle activity. The stick insect is a well studied system with respect to its motor output which is shaped by the interplay between sensory signals, the central neural networks for each leg joint and the coordination between the legs. The muscles of the FT (femur-tibia) joint are described in their morphologies and their motoneuronal innervation patterns, however little is known about how motoneuronal stimulation affects their force development and shortening behaviour. One of the two muscles moving the joint is the extensor tibiae, which is particularly suitable for such an investigation as it features only three motoneurons that can be activated simultaneously, which comes close to a physiologically occuring activation pattern. Its antagonist, the flexor tibiae, has a more complex innervation and a biomechanical investigation is only reasonable at full motoneuronal recruitment. Muscle force and length changes were measured using a dual-mode lever system that was connected to the cut muscle tendon. Both tibial muscles of all legs were studied in terms of their geometry: extensor tibiae muscle length changes with the cosine of the FT joint angle, while flexor tibiae length changes with the negative cosine, except for extreme angles (close to 30° and 180°). For all three legs, effective flexor tibiae moment arm length (0.564 mm) is twice that of the extensor tibiae (0.282 mm). Flexor tibiae fibres are 1.5 times longer (2.11 mm) than extensor tibiae fibres (1.41 mm). Active isometric force measurements demonstrated that extensor tibiae single twitch force is notably smaller than its maximal tetanical force at 200 Hz (2-6 mN compared to 100-190 mN) and takes a long time to decrease completely (> 140 ms). Increasing either frequency or duration of the stimulation extends maximal force production and prolongs the relaxation time of the extensor tibiae. The muscle reveals `latch´ properties in response to a short-term increase in activation. Its working range is on the ascending limb of the force-length relationship (see Gordon et al. (1966b)) with a shift in maximum force development towards longer fibre lengths at lower activation. The passive static force increases exponentially with increasing stretch. Maximum forces of 5 mN for the extensor, and 15 mN for the flexor tibiae occur within the muscles´ working ranges. The combined passive torques of both muscles determine the rest position of the joint without any muscle activity. Dynamically generated forces of both muscles can become as large as 50-70 mN when stretch ramps mimick a fast middle leg swing phase. FT joint torques alone (with ablated muscles) do not depend on FT joint angle, but on deflection amplitude and velocity. Isotonic force experiments using physiological activation patterns demonstrate that the extensor tibiae acts like a low-pass filter by contracting smoothly to fast instantaneous stimulation frequency changes. Hill hyperbolas at 200 Hz vary a great deal with respect to maximal force (P0) but much less in terms of contraction velocity (V0) for both tibial muscles. Maximally stimulated flexor tibiae muscles are on average 2.7 times stronger than extensor tibiae muscles (415 mN and 151 mN), but contract only 1.4 times faster (6.05 mm/s and 4.39 mm/s). The dependence of extensor tibiae V0 and P0 on stimulation frequency can be described with an exponential saturation curve. V0 increases linearly with length within the muscle´s working range. Loaded release experiments characterise extensor and flexor tibiae series elastic components as quadratic springs. The mean spring constant of the flexor tibiae is 1.6 times larger than of the extensor tibiae at maximal stimulation. Extensor tibiae stretch and relaxation ramps show that muscle relaxation time constant slowly changes with muscle length, and thus muscle dynamics have a long-lasting dependence on muscle length history. High-speed video recordings show that changes in tibial movement dynamics match extensor tibiae relaxation changes at increasing stimulation duration

RESEARCH TOWARDS THE DESIGN OF A NOVEL SMART FLUID DAMPER USING A MCKIBBEN ACTUATOR

Vibration reducing performance of many mechanical systems, decreasing the quality of manufactured products, producing noise, generating fatigue in mechanical components, and producing an uncomfortable environment for human bodies. Vibration control is categorized as: active, passive, or semi-active, based on the power consumption of the control system and feedback or feed forward based on whether sensing is used to control vibration. Semi-active vibration control is the most attractive method; one method of semi-active vibration control could be designed by using smart fluid. Smart fluids are able to modify their effective viscosity in response to an external stimulus such as a magnetic field. This unique characteristic can be utilised to build semi-active dampers for a wide variety of vibration control systems. Previous work has studied the application of smart fluids in semi-active dampers, where the kinetic energy of a vibrating structure can be dissipated in a controllable fashion. A McKibben actuator is a device that consists of a rubber tube surrounded by braided fibre material. It has different advantages over a piston/cylinder actuator such as: a high power to weight ratio, low weight and less cost. Recently McKibben actuator has appeared in some semi-active vibration control devise. This report investigates the possibility of designing a Magnetorheological MR damper that seeks to reduce the friction in the device by integrating it with a McKibben actuator. In this thesis the concept of both smart fluid and McKibben actuator have been reviewed in depth, and methods of modelling and previous applications of devices made using these materials are also presented. The experimental part of the research includes: designing and modelling a McKibben actuator (using water) under static loads, and validating the model experimentally. The research ends by presenting conclusions and future work