Quick-release Experiments Research Articles

Muscle-like contraction control of tendon-sheath artificial muscle

The development of artificial muscles has focused on a high energy–weight ratio and soft structures, however, little work has been done towards muscle-like contraction behaviors. This unfortunately leads to a lack of comfort and safety, which is especially important for robotic applications like orthotics and exoskeletons. In this paper, we propose a contraction control method for a tendon-sheath artificial muscle to contract and relax like biological muscles. In view of the nonlinear transmission characteristics of the tendon-sheath artificial muscle, a transmission model is established and its accuracy is verified through experiments. A muscle-like contraction control method is then proposed based on the transmission model and the Hill-type muscle model. Through this method, the contraction force of the tendon-sheath artificial muscle can be adjusted according to the output displacement and velocity of the tendon-sheath mechanism estimated by the transmission model. Isometric contraction and quick-release experiments are then conducted. The experimental results demonstrate that this control method allows the tendon-sheath artificial muscle to contract with specific muscle-like force–length and force–velocity properties.

Parameter estimation and experimental design for Hill-type muscles: Impulses from optimization-based modeling

The benefits of optimization-based modeling for parameter estimation of Hill-type muscle models are demonstrated. Therefore, we examined the model and data of Günther et al. (2007), who analyzed isometric, concentric, and quick-release contractions of a piglet calf muscle. We found that the isometric experiments are suitable for derivative-based parameter estimation while the others did not provide any additional value. During the estimation process, certain parameters had to be fixed. We give possible reasons and provide impulses for modelers. Subsequently, unnecessarily complex or deprecated model parts were exchanged and the new model was fitted to the data. In order to be able to provide a reliable estimation of the whole parameter set, we propose two isometric and two quick-release experiments, which are real-life feasible and together allow an identification of all parameters based on a local sensitivity analysis. These experiments can be used as qualitative guidelines for practitioners to reduce the experimental effort when estimating parameters for macroscopic muscle models.

Muscle Strength and Neuromuscular Control in Low-Back Pain: Elite Athletes Versus General Population.

The purpose of the study was to investigate the athletic-based specificity of muscle strength and neuromuscular control of spine stability in chronic non-specific low-back pain (LBP). Thirty elite athletes and 29 age-matched non-athletes with (15 athletes and 15 non-athletes) and without LBP (15 athletes and 14 non-athletes) participated in the study. Muscle strength was measured during maximal isometric trunk flexion and trunk extension contractions. The neuromuscular control of spine stability was analyzed by determining trunk stiffness, trunk damping, and onset times of the lumbar and thoracic erector spinae muscles after sudden perturbations (quick release experiments) as well as maximum Lyapunov exponents (local dynamic stability) using non-linear time series analysis of repetitive lifting movements. LBP was assessed using the visual analog scale. We found lower maximal trunk extension moments (p = 0.03), higher trunk damping (p = 0.018) and shorter onset times (p = 0.03) of the investigated trunk muscles in LBP patients in both athletes and non-athletes. Trunk stiffness and the local dynamic stability did not show any differences (p = 0.136 and p = 0.375, respectively) between LBP patients and healthy controls in both groups. It can be concluded that, despite the high-level of training in athletes, both athletes and non-athletes with LBP showed the same deconditioning of the lumbar extensor muscles and developed similar strategies to ensure spine stability after sudden perturbations to protect the spine from pain and damage. The findings highlight that specific training interventions for the trunk muscles are not only crucial for individuals of the general population, but also for well-trained athletes.

Nature as an engineer: one simple concept of a bio-inspired functional artificial muscle

The biological muscle is a powerful, flexible and versatile actuator. Its intrinsic characteristics determine the way how movements are generated and controlled. Robotic and prosthetic applications expect to profit from relying on bio-inspired actuators which exhibit natural (muscle-like) characteristics. As of today, when constructing a technical actuator, it is not possible to copy the exact molecular structure of a biological muscle. Alternatively, the question may be put how its characteristics can be realized with known mechanical components. Recently, a mechanical construct for an artificial muscle was proposed, which exhibits hyperbolic force–velocity characteristics. In this paper, we promote the constructing concept which is made by substantiating the mechanical design of biological muscle by a simple model, proving the feasibility of its real-world implementation, and checking their output both for mutual consistency and agreement with biological measurements. In particular, the relations of force, enthalpy rate and mechanical efficiency versus contraction velocity of both the construct’s technical implementation and its numerical model were determined in quick-release experiments. All model predictions for these relations and the hardware results are now in good agreement with the biological literature. We conclude that the construct represents a mechanical concept of natural actuation, which is suitable for laying down some useful suggestions when designing bio-inspired actuators.

Can Quick Release Experiments Reveal the Muscle Structure? A Bionic Approach

The goal of this study was to understand the macroscopic mechanical structure and function of biological muscle with respect to its dynamic role in the contraction. A recently published muscle model, deriving the hyperbolic force-velocity relation from first-order mechanical principles, predicts different force-velocity operating points for different load situations. With a new approach, this model could be simplified and thus, transferred into a numerical simulation and a hardware experiment. Two types of quick release experiments were performed in simulation and with the hardware setup, which represent two extreme cases of the contraction dynamics: against a constant force (isotonic) and against an inertial mass. Both experiments revealed hyperbolic or hyperbolic-like force-velocity relations. Interestingly, the analytical model not only predicts these extreme cases, but also additionally all contraction states in between. It was possible to validate these predictions with the numerical model and the hardware experiment. These results prove that the origin of the hyperbolic force-velocity relation can be mechanically explained on a macroscopic level by the dynamical interaction of three mechanical elements. The implications for the interpretation of biological muscle experiments and the realization of muscle-like bionic actuators are discussed.

Proof of Concept: Model Based Bionic Muscle with Hyperbolic Force-Velocity Relation

Recently, the hyperbolic Hill-type force-velocity relation was derived from basic physical components. It was shown that a contractile element CE consisting of a mechanical energy source active element AE, a parallel damper element PDE, and a serial element SE exhibits operating points with hyperbolic force-velocity dependency. In this paper, a technical proof of this concept was presented. AE and PDE were implemented as electric motors, SE as a mechanical spring. The force-velocity relation of this artificial CE was determined in quick release experiments. The CE exhibited hyperbolic force-velocity dependency. This proof of concept can be seen as a well-founded starting point for the development of Hill-type artificial muscles.

Proof of Concept: Model Based Bionic Muscle with Hyperbolic Force-Velocity Relation

Recently, the hyperbolic Hill-type force-velocity relation was derived from basic physical components. It was shown that a contractile element CE consisting of a mechanical energy source (active element AE), a parallel damper element (PDE), and a serial element (SE) exhibits operating points with hyperbolic force-velocity dependency. In this paper, a technical proof of this concept was presented. AE and PDE were implemented as electric motors, SE as a mechanical spring. The force-velocity relation of this artificial CE was determined in quick release experiments. The CE exhibited hyperbolic force-velocity dependency. This proof of concept can be seen as a well-founded starting point for the development of Hill-type artificial muscles.

Experiments and mechanochemical modeling of smooth muscle contraction: Significance of filament overlap

The main function of smooth muscle is to maintain/regulate the size of different hollow organs through contraction and relaxation. The magnitude of the active force during contraction is dependent on the number of attached cross-bridges, which can be linked to the overlap between the thin and thick filaments. The relevance of filament overlap and the active cross-bridges in smooth muscle is investigated through a mechanical model founded on Hill's three-element model. The mechanical model describes a sarcomere-equivalent contractile unit supported by structural observations with a distinct filament overlap and a realistic framework for the filament sliding behavior based on force–velocity experiments. The mechanical model is coupled to the four-state latch-model by Hai and Murphy to capture the electromechanical activation from intracellular calcium concentration to load-bearing cross-bridges. The model is fitted to isometric experiments performed on the pig carotid media and on isotonic quick-release experiments found in the literature. The proposed coupled mechanochemical model with the description of the filament overlap, which has a significant influence on the results, is able to predict isometric experimental data performed at different muscle lengths. The relevance of the filament overlap and the load-bearing cross-bridges is investigated through the model by simulating additional scenarios that has been documented in the literature.

Nonlinear Model-Based System Identification of Lead–Rubber Bearings

A nonlinear model-based system identification method is proposed, formulated, implemented, and applied to a three-span continuous base-isolated bridge. Transverse and rotational rigid-body motions of the bridge superstructure are formulated into two degrees-of-freedom dynamic governing equations. To model hysteretic behavior of lead–rubber bearings, the Menegotto–Pinto model is used. The proposed system identification procedures consist of two phases to address ill-conditioning issues. The uncertainty of parameters is considered, which results in probability distributions instead of single values for identified parameters. The proposed system identification is adopted in the comparison of experimental data sets. Hypothesis testing is used to determine the closeness of identification results. The proposed method is applied to quick-release field experiments on the bridge to investigate aging and temperature dependent effects in lead–rubber bearings.

ISOFIT: a model-based method to measure muscle–tendon properties simultaneously

Estimation of muscle parameters specifying force-length and force-velocity behavior requires in general a large number of sophisticated experiments often including a combination of isometric, isokinetic, isotonic, and quick-release experiments. This study validates a simpler method (ISOFIT) to determine muscle properties by fitting a Hill-type muscle model to a set of isovelocity data. Muscle properties resulting from the ISOFIT method agreed well with muscle properties determined separately in in vitro measurements using frog semitendinosus muscles. The force-length curve was described well by the results of the model. The force-velocity curve resulting from the model coincided with the experimentally determined curve above approximately 20% of maximum isometric force (correlation coefficient R>0.99). At lower forces and thus higher velocities the predicted curve underestimated velocity. The stiffness of the series elastic component determined with direct experiments was approximately 10% lower than that determined by the ISOFIT method. Use of the ISOFIT method can decrease experimental time up to 80% and reduce potential changes in muscle parameters due to fatigue.

NOT ALL OSCILLATIONS ARE RUBBISH: FORWARD SIMULATION OF QUICK-RELEASE EXPERIMENTS

Quick-release experiments often produce noticeable oscillations on the measured force and length data in the first few milliseconds after the force release. We measured oscillations in experiments with several species (Rattus norvegicus, Galea musteloides, Rana pipiens) and different experimental setups. These oscillations are generally ignored as artifacts.This study investigates the cause of the oscillations. A biomechanical model of the experimental setup was developed consisting of a geometric model describing the setup and a Hill-type muscle-tendon model including the force-length-velocity relation and a linear spring in series. Muscle properties of each muscle were determined by the ISOFIT method. Model calculations and forward simulations of quick-release experiments based on experimentally determined muscle properties reveal that the observed oscillations are not artifacts (instrument and control), but the result of interactions of muscle-tendon properties with the inertia of muscles, bones and lever system.

Muscle contraction as a Markov process. I: Energetics of the process.

Force generation during muscle contraction can be understood in terms of cyclical length changes in segments of actin thin filaments moving through the three-dimensional lattice of myosin thick filaments. Recent anomalies discovered in connection with analysis of myosin step sizes in in vitro motility assays and with skinned fibres can be rationalized by assuming that ATP hydrolysis on actin accompanies these length changes. The paradoxically rapid regeneration of tension in quick release experiments, as well as classical energetic relationships, such as Hill's force-velocity curve, the Fenn effect, and the unexplained enthalpy of shortening, can be given mutually self-consistent explanations with this model. When muscle is viewed as a Markov process, the vectorial process of chemomechanical transduction can be understood in terms of lattice dependent transitions, wherein the phosphate release steps of the myosin and actin ATPases depend only on occurrence of allosteric changes in neighbouring molecules. Tropomyosin has a central role in coordinating the steady progression of these cooperative transitions along actin filaments and in gearing up the system in response to higher imposed loads.

Muscle contraction as a Markov process I: energetics of the process

Force generation during muscle contraction can be understood in terms of cyclical length changes in segments of actin thin filaments moving through the three-dimensional lattice of myosin thick filaments. Recent anomalies discovered in connection with analysis of myosin step sizes in in vitro motility assays and with skinned fibres can be rationalized by assuming that ATP hydrolysis on actin accompanies these length changes. The paradoxically rapid regeneration of tension in quick release experiments, as well as classical energetic relationships, such as Hill's force–velocity curve, the Fenn effect, and the unexplained enthalpy of shortening, can be given mutually self-consistent explanations with this model. When muscle is viewed as a Markov process, the vectorial process of chemomechanical transduction can be understood in terms of lattice dependent transitions, wherein the phosphate release steps of the myosin and actin ATPases depend only on occurrence of allosteric changes in neighbouring molecules. Tropomyosin has a central role in coordinating the steady progression of these cooperative transitions along actin filaments and in gearing up the system in response to higher imposed loads.

Estimation of cross-bridge stiffness from maximum thermodynamic efficiency.

In muscle, work is performed by myosin cross-bridges during interactions with actin filaments. The amount of work performed during each interaction can be related to the mechanical properties of the cross-bridge; work is the integral of the force produced with respect to the distance that the cross-bridge moves the actin filament, and force is determined by the stiffness of the attached cross-bridge. In this paper, cross-bridge stiffness in frog sartorius muscle was estimated from thermodynamic efficiency (work/free energy change) using a two-state cross-bridge model, assuming constant stiffness over the working range and tight-coupling between cross-bridge cycles and ATP use. This model accurately predicts mechanical efficiency (work/enthalpy output). A critical review of the literature indicates that a realistic value for maximum thermodynamic efficiency of frog sartorius is 0.45 under conditions commonly used in experiments on isolated muscle. Cross-bridge stiffness was estimated for a range of power stroke amplitudes. For realistic amplitudes (10-15 nm), estimated cross-bridge stiffness was between 1 and 2.2 pN nm-1. These values are similar to those estimated from quick-release experiments, taking into account compliance arising from structures other than cross-bridges, but are substantially higher than those from isolated protein studies. The effects on stiffness estimates of relaxing the tight-coupling requirement and of incorporating more force-producing cross-bridge states are also considered.

A mechanical device for studying mechanical properties of human muscles in vivo

A mechanical device, primarily devoted to biomechanical studies of human calf muscles during microgravity experiments is presented. It allows investigation of both contractile and visco-elastic properties of musculo-articular systems using, respectively, isokinetic movements, quick-release tests and sinusoidal perturbations. This device is a specifically designed ergometer associated to an experimental protocol designed for pre- and post-flight tests. The protocol was evaluated on 22 healthy subjects and typical results are briefly presented. Preliminary results are discussed in terms of agreement with currently available data and a detailed evaluation of test-retest measurements is provided for quick-release experiments. Complementary investigations are suggested and potential fields of research are indicated.

The effect of actin filament compliance on the interpretation of the elastic properties of skeletal muscle fibres.

Recently, X-ray diffraction studies provided direct evidence for an appreciable length change in the actin filament upon activation. This finding has profound implications on the interpretation of the elastic properties of skeletal muscle fibre. In this study we determined the compliance of the actin filament during activation, using the data obtained previously from quick stretch and release experiments on skeletal muscle fibres of the frog. The effects of filament compliance are demonstrated clearly in the elastic properties of partially activated fibres. The low-frequency elasticity increases linearly with tension, reflecting an increase in the number of force-producing cross-bridges. At higher frequencies, this linearity is lost. In this study we describe the data consistently in terms of a cross-bridge stiffness increasing linearly with tension and a constant Young's modulus for the actin filament of 44 MN m-2. This corresponds to a compliance of 23 pm microns-1 per kN m-2 tension developed. Using this value for the actin filament Young's modulus, its contribution to the elastic properties of skeletal muscle fibre of the frog is considered in rigor and relaxation. The filament compliance hardly affects the overall elasticity of the muscle fibre in relaxation. In contrast, it contributes to a large extent to the overall elasticity in rigor. Taking account of the filament compliance, we find that the Young's modulus in rigor exhibits an increase from 14 MN m-2 at frequencies below 500 Hz to 55 MN m-2 above 40 kHz.

Experimental observations of the aerodynamic characteristics of urban trees

The paper presents some of the experimental result that have been obtained during an extensive investigation of the behaviour of urban trees in high winds. In particular, results are presented of tests to determine tree mechanical and aerodynamic parameters. The mechanical properties that were measured (stiffness, natural frequency, and damping) were obtained from tree winching ans quick release experiments. It was fouind that, for the small number of specimens tested, the stiffness of each specimen did not vary greatly through the year, but the magnitudes of natural frequencies and damping ratios were dependent upon whether or not the tree was in leaf. For a tree in leaf the natural frequency was lower and the damping higher than when not in leaf. Measurements of tree deflection in the wind (for a semi-mature plane tree) enabled further estimates of natural frequency and damping ratio to be made, and also enabled drag coefficient values to be measured. It was shown that these coefficients are substantially greater when the tree is leaf, than when it is not in leaf. These experiments did not lend support to the hypothesis that tree drag is proportional to velocity, rather than (velocity) 2, as has been previously suggested.

Studies of the diffuse x-ray scattering from contracting frog skeletal muscles

Using x-rays from synchrotron radiation, we studied diffuse scattering, sometimes together with the myosin layer lines. With an area detector, sartorius muscles and a time resolution of 150 ms, earlier results from semitendinosus muscles contracting isometrically at 6 degrees C (Lowy, J., and F. R. Poulsen. 1987. J. Mol. Biol. 194:595-600) were confirmed and extended. Evidence from intensity changes both in the diffuse scattering and in the myosin layer lines showed that the majority of the heads become disordered at peak tetanic tension. With a linear detector and a time resolution of 5 ms, it was found that during tension rise the intensity increase of the diffuse scattering (which amounted maximally to 12% recorded near the meridian) runs approximately 20 ms ahead of the mechanical change, comparing half-completion times. This suggests that an appreciable number of heads change orientation before peak tension is reached. In quick release experiments the diffuse scattering intensity showed very little change. Recorded near the meridian during rapid shortening, however, it decreased progressively with a half-time of approximately 40 ms. This change amounted to approximately 35% of that observed during the initial tension rise. We interpret this to indicate that during rapid shortening a certain number of heads assume an orientation characteristic of the relaxed state. Viewed in the context of the behavior of the first myosin layer line and the (1, 1) equatorial reflection in similar experiments (Huxley, H. E., M. Kress, A. R. Faruqi, and R. M. Simmons. 1988. Molecular Mechanism of Muscle Contraction), the present results provide further support for the view that the diffuse scattering is mostly due to disordered myosin heads; whilst ordered heads produce the myosin layer lines (Poulsen, F. R., and J. Lowy.1983. Nature lLond.l. 303:146-152).

Force-velocity relation and rate of ATP hydrolysis in osmotically compressed skinned smooth muscle of the guinea pig.

Chemically skinned guinea pig taenia coli fibre bundles showed a concentration-dependent decrease in width when incubated in media containing Dextran T500 (0-0.2 g ml-1). The maximal reduction in width, observed at 0.2 g ml-1 dextran, was 32%. The effect was reversible upon removal of dextran. Isometric force was slightly increased (about 10%) at the lowest dextran concentration (0.025 g ml-1) but decreased at higher concentrations (40% decrease at 0.2 g/ml-1). The energetic tension cost (ATP turnover/force) was decreased by about 40% after dextran addition. Force development and relaxation were markedly slower in 0.1 g ml-1 and absent in 0.2 g ml-1 dextran. In isotonic quick-release experiments 0.025 g ml-1 dextran did not influence maximal shortening velocity (Vmax) and relative stiffness, whereas 0.1 g ml-1 markedly increased stiffness and decreased Vmax to about 27%. Vanadate induced relaxation in the activated muscle (pCa 4.5) both in the absence and presence (0.1 g ml-1) of dextran and increased the rate of relaxation (pCa 9) at 0.1 g ml-1 dextran. The isometric rate of crossbridge turnover, as reflected by the energetic tension cost and the rate of relaxation, was decreased at all degrees of osmotic compression. Crossbridge turnover rate during shortening (Vmax) was unaffected at an osmotic compression of 12% (width) but was decreased at higher compression (32%).

Mechanical behavior of vascular smooth muscle in cylindrical segments of arteries in vitro.

Vascular smooth muscle mechanics have been studied in vitro in cylindrical segments of dog carotid artery, human internal mammary artery, and human saphenous vein. Such cylindrical preparations maintain normal vessel geometry and also permit correlation of mechanical phenomena with transmural pressure. These studies show that the vascular muscle in cylindrical arteries develops a maximum active stress of 1.1 X 10(5) N/m2 for the whole wall, or 2.2-3.7 X 10(5) N/m2 for the volume of the wall occupied by vascular muscle. These values are similar to those reported for strip studies of vascular muscle and various preparations of skeletal muscle, but are two to five times that reported for cardiac papillary muscle preparations. In cylindrical preparations of arteries, maximum isometric active stress occurs at 150 mm Hg, whereas that in veins occurs at less than 15 mm Hg. Quick release experiments of cylindrical segments of vessels avoid the compliance of inactive tissue trapped beneath ligatures in strip studies. Quick release experiments in cylindrical segments of dog carotid artery reveal that at maximum isometric stress, the series elastic component (SEC) is extended 8-11%. Experiments employing temperature variations and degradative enzymes show that the SEC is located largely in elastin, with a lesser portion located in the contractile apparatus. At short- and long-muscle lengths, the active muscle develops decreased active stress and that developed at long lengths persists at all muscle lengths, even after shortening. This has been termed "attenuation" and appears to contribute to the static length-stress and pressure-diameter hysteresis exhibited by vessels. Excitation of vascular muscle in vessel segments held at constant pressure discloses that isobaric contraction decreases artery diameter a maximum of approximately 25%. This occurs at a dimension corresponding to approximately 100 mm Hg in the relaxed vessel. Isometrically and isobarically contracted vessels tend to fall along the same pressure-diameter coordinates, indicating equivalence of both modes of contraction. Distention of contracted vessels indicates that active vascular muscle markedly resists distention up to 150-250 mm Hg; at higher pressures the contracted vessel exhibits decreased stiffness as the contracted muscle yields. The vascular muscle, therefore, has a biphasic effect on circumferential elastic modulus relative to that of the relaxed vessel.(ABSTRACT TRUNCATED AT 400 WORDS)