Absorption Of Mechanical Energy Research Articles

Skeletal muscle contraction in protecting joints and bones by absorbing mechanical impacts

We have previously hypothesized that the dissipation of mechanical energy of external impact is a fundamental function of skeletal muscle in addition to its primary function to convert chemical energy into mechanical energy. In this paper, a mathematical justification of this hypothesis is presented. First, a simple mechanical model, in which the muscle is considered as a simple Hookean spring, is considered. This analysis serves as an introduction to the consideration of a biomechanical model taking into account the molecular mechanism of muscle contraction, kinetics of myosin bridges, sarcomere dynamics, and tension of muscle fibers. It is shown that a muscle behaves like a nonlinear and adaptive spring tempering the force of impact and increasing the duration of the collision. The temporal profiles of muscle reaction to the impact as functions of the levels of muscle contraction, durations of the impact front, and the time constants of myosin bridges closing, are obtained. The absorption of mechanical shock energy is achieved due to the increased viscoelasticity of the contracting skeletal muscle. Controlling the contraction level allows for the optimization of the stiffness and viscosity of the muscle necessary for the protection of the joints and bones.

Muscle as a molecular machine for protecting joints and bones by absorbing mechanical impacts

We hypothesize that dissipation of mechanical energy of external impact to absorb mechanical shock is a fundamental function of skeletal muscle in addition to its primary function to convert chemical energy into mechanical energy. In physical systems, the common mechanism for absorbing mechanical shock is achieved with the use of both elastic and viscous elements and we hypothesize that the viscosity of the skeletal muscle is a variable parameter which can be voluntarily controlled by changing the tension of the contracting muscle. We further hypothesize that an ability of muscle to absorb shock has been an important factor in biological evolution, allowing the life to move from the ocean to land, from hydrodynamic to aerodynamic environment with dramatically different loading conditions for musculoskeletal system. The ability of muscle to redistribute the energy of mechanical shock in time and space and unload skeletal joints is of key importance in physical activities. We developed a mathematical model explaining the absorption of mechanical shock energy due to the increased viscosity of contracting skeletal muscles. The developed model, based on the classical theory of sliding filaments, demonstrates that the increased muscle viscosity is a result of the time delay (or phase shift) between the mechanical impact and the attachment/detachment of myosin heads to binding sites on the actin filaments. The increase in the contracted muscle’s viscosity is time dependent. Since the forward and backward rate constants for binding the myosin heads to the actin filaments are on the order of 100s−1, the viscosity of the contracted muscle starts to significantly increase with an impact time greater than 0.01s. The impact time is one of the key parameters in generating destructive stress in the colliding objects. In order to successfully dampen a short high power impact, muscles must first slow it down to engage the molecular mechanism of muscle viscosity. Muscle carries out two functions, acting first as a nonlinear spring to slow down impact and second as a viscous damper to absorb the impact. Exploring the ability of muscle to absorb mechanical shock may shed light to many problems of medical biomechanics and sports medicine. Currently there are no clinical devices for real-time quantitative assessment of viscoelastic properties of contracting muscles in vivo. Such assessment may be important for diagnosis and monitoring of treatment of various muscle disorders such as muscle dystrophy, motor neuron diseases, inflammatory and metabolic myopathies and many more.

The energetic benefits of tendon springs in running: is the reduction of muscle work important?

The distal muscle-tendon units of cursorial species are commonly composed of short muscle fibres and long, compliant tendons. It is assumed that the ability of these tendons to store and return mechanical energy over the course of a stride, thus avoiding the cyclic absorption and regeneration of mechanical energy by active muscle, offers some metabolic energy savings during running. However, this assumption has not been tested directly. We used muscle ergometry and myothermic measurements to determine the cost of force production in muscles acting isometrically, as they could if mechanical energy was stored and returned by tendon, and undergoing active stretch-shorten cycles, as they would if mechanical energy was absorbed and regenerated by muscle. We found no detectable difference in the cost of force production in isometric cycles compared with stretch-shorten cycles. This result suggests that replacing muscle stretch-shorten work with tendon elastic energy storage and recovery does not reduce the cost of force production. This calls into question the assumption that reduction of muscle work drove the evolution of long distal tendons. We propose that the energetic benefits of tendons are derived primarily from their effect on muscle and limb architecture rather than their ability to reduce the cyclic work of muscle.

Does ankle joint power reflect type of muscle action of soleus and gastrocnemius during walking in cats and humans?

The main objective of this paper is to highlight the difficulties of identifying shortening and lengthening contractions based on analysis of power produced by resultant joint moments. For that purpose, we present net ankle joint powers and muscle fascicle/muscle–tendon unit (MTU) velocities for medial gastrocnemius (MG) and soleus (SO) muscles during walking in species of different size (humans and cats). For the cat, patterns of ankle joint power and MTU velocity of MG and SO during stance were similar: negative power (ankle moment×angular velocity<0), indicating absorption of mechanical energy, was associated with MTU lengthening, and positive power (generation of mechanical energy) was found during MTU shortening. This was also found for the general fascicle velocity pattern in SO. In contrast, substantial differences between ankle joint power and fascicle velocity patterns were observed for MG muscle. In humans, like cats, the patterns of ankle joint power and MTU velocity of SO and MG were similar. Unlike the cat, there were substantial differences between patterns of fascicle velocity and ankle joint power during stance in both muscles. These results indicate that during walking, only a small fraction of mechanical work of the ankle moment is either generated or absorbed by the muscle fascicles, thus confirming the contribution of in-series elastic structures and/or energy transfer via two-joint muscles. We conclude that ankle joint negative power does not necessarily indicate eccentric action of muscle fibers and that positive power cannot be exclusively attributed to muscle concentric action, especially in humans.

Generation, absorption, and transfer of mechanical energy during walking in children

The purpose of this study was to characterize the manner in which net joint moments and non-muscular forces generate, absorb, and transfer mechanical energy during walking in able-bodied children. Standard gait data from seven healthy subjects between 6 and 17 years of age were combined with a dynamic model of the whole body to perform a power analysis based on induced acceleration techniques. These data were used to determine how each moment and force generates energy to, absorbs energy from, and transfers energy among the major body segments. The joint moments were found to induce transfers of mechanical energy between body segments that generally exceeded the magnitudes of energy generation and absorption. The amount of energy transferred by gravitational and velocity-dependent forces was considerably less than for the joint moments. The hip and ankle joint moments had relatively simple power patterns that tended to oppose each other, particularly over the stance phase. The knee joint moment had a more complex power pattern that appeared distinct from the hip and ankle moments. The general patterns of mechanical energy flow were similar to previous reports in adults. The approach described in this paper should provide a useful complement to standard clinical gait analysis procedures.

Evaluation on Integrated Molding of Functionally-Graded Epoxy Foams

This paper describes novel integrated molding for fabrication of functionally-graded (FG) syntactic epoxy foams to control distribution of the mechanical properties for highly impact energy absorption. In order to control mechanical properties, the density distributions in the FG epoxy foams were graded by floating phenomenon of the light-weight micro-balloons in the matrix epoxy resin during the curing process. By the turning procedure of the mold before grading the micro-balloons, the FG epoxy foams having the gradual and continuous distributions of density in wide range could be produced. The static compression tests of the fabricated FG epoxy foams suggested that the foams had high absorption of mechanical energy since the foams collapsed progressively due to the grading of the density distribution.

Correlation effects during liquid infiltration into hydrophobic nanoporous media

Correlation effects arising during liquid infiltration into hydrophobic porous medium are considered. On the basis of these effects a mechanism of energy absorption at filling porous medium by nonwetting liquid is suggested. In accordance with this mechanism, the absorption of mechanical energy is a result expenditure of energy for the formation of menisci in the pores on the shell of the infinite cluster and expenditure of energy for the formation of liquid-porous medium interface in the pores belonging to the infinite cluster of filled pores. It was found that in dependences on the porosity and, consequently, in dependences on the number of filled pores neighbors, the thermal effect of filling can be either positive or negative and the cycle of infiltration-defiltration can be closed with full outflow of liquid. It can occur under certain relation between percolation properties of porous medium and the energy characteristics of the liquid-porous medium interface and the liquid-gas interface. It is shown that a consecutive account of these correlation effects and percolation properties of the pores space during infiltration allow to describe all experimental data under discussion.

Amplitude Stress in Ni-Mn-Ga Polymer Composites Bonded with PZT Sensors and Actuators

A new experimental set up to measure acoustic attenuation in ferromagnetic shape memory alloy and composites was designed and built. Acoustic attenuation in polyurethane (PU) polymer composites with Ni-Mn-Ga particulate fillers have been reported which exhibits greater vibration absorption than polymer/magnetostrictive composites due to the rearrangement of twin variants in Ni-Mn-Ga particles. Amplitude stress wave has been analysed for three different test samples. Above the low frequency, the acoustic attenuation is gradually decreased from PU to Ni-Mn-Ga/PU. The Ni-Mn-Ga/PU polymer composite is shown to be ideal for applications that require absorption of mechanical energy.

Concepts for Energy-Interactive Textiles

AbstractThis review examines textile fibers and fabrics in the context of their interaction with various forms of energy, such as electromagnetic (photolytic), electrical, magnetic, thermal, chemical, and mechanical. This interaction can involve conversion, storage, or management of energy. Examples are described suggesting some new material configurations that could be incorporated into textiles to create special energy-interactive textile (EITX) structures. Areas discussed are the management of electron flow (electrical resistivity) and the absorption of mechanical energy in textile fibers and fabrics. Surface resistance studies on carbon nanotubes and conductive carbon-black-filled films of poly(methyl methacrylate) (PMMA) and paraffin wax show that the electrical conductivity of these materials depends upon the matrix material type and the amount of charge-carrying particles in the matrix. PMMA films filled with carbon nanotubes are found to be more electrically conductive than matrices filled with conductive carbon black. Mechanical-energy interactions of flocked textile surfaces show that in compression, they exhibit unique, gradual load-deflection behavior. This effect should be useful in applications requiring impact-energy absorption. Finally, the functional steps in an integrated energy-interactive textile system are discussed.

The influence of shock-type vibrations on the absorption of mechanical energy in the hand and arm

In recent years there has been a discussion as to whether shock-type vibration from hand tools has stronger effects on the hand-arm system in comparison with non-impulsive vibration. The purpose of the investigation is to compare the influence of these two types of vibration on the absorption of mechanical energy in the human hand and on the grip and feed forces applied by the subjects. The energy absorption has been measured by use of a specially designed laboratory handle. The grip and feed forces applied by the subject to the handle were measured simultaneously. In the study two different frequency weighted acceleration levels were used. The outcome showed that the vibration exposure levels made a significant contribution to the vibration absorption as well as to the strength of the grip and feed forces. Moreover, it was found that the hand forces decrease while the absorption of energy increases during the experiment. Furthermore, the influence of shock-type exposure gave a significantly higher hand forces and absorption of energy compared with the non-impulsive exposure. It was, therefore, concluded that the vibration response characteristics of the hand and arm differ, depending upon whether the exposure is of shock or non-impulsive type. Relevance to industry The paper discusses the dynamic response of the hand and arm during exposure to shock and non-impulsive vibration. Whenever possible, a tool that requires low grip and feed forces should be used as well as tools that not generate shock-type excitation. This can be helpful in choosing the proper tool for the job.

Calorimetric analysis of powder compression: II. The relationship between energy terms measured with a compression calorimeter and tableting behavior

A compression calorimeter was used to study the powder compression behavior of materials exhibiting a wide range of material properties and compactibilities. The calorimetric approach was based on the determination of the heat of compression, the work of compression and the calculation of the internal energy change for the compression phase of the tableting cycle (Lammens, Ph.D Thesis, University of Leiden, Leiden, 1980, pp. 158–259; Coffin-Beach and Hollenbeck, Int. J. Pharm., 17 (1983) 313–324; Wurster et al., Int. J. Pharm., 116 (1995) 179–189). The materials studied were Avicel PH-101, anhydrous lactose, Starch 1500, phenacetin, and polyethylene. Negative compression-induced internal energy changes were observed for all of the materials studied. These results indicated that the compression process lowered the energy states of the powders even though absorption of mechanical energy by the powders is thought to occur during the compression process. Negative ΔE values were also at odds with the measured surface area increases. For Avicel PH-101, anhydrous lactose and Starch 1500, these results did support the previous proposal that a negative internal energy change is indicative of extensive interparticulate bonding (Coffin-Beach and Hollenbeck, Int. J. Pharm., 17 (1983) 313–324). However, in the case of polyethylene and phenacetin, where significant destruction of bonds formed during compression occurred during decompression, the compression energy terms did not reflect the consequences of the complete tableting cycle. For materials with poor compactibility, the compression energy terms were unrelated to the degree of permanent interparticulate bonding. Preliminary attempts were made to address the energetics of decompression so as to make the calculated internal energy change reflective of only the irreversible processes occurring during compression.

The Effect of Mechanical Excitation on Ionic Conductivity and Related Properties of Polymer Electrolytes

A recent work1 reported a theoretical basis for enhancement of ionic conductivity in polymer electrolytes under the influence of external mechanical excitation. This paper presents an experimental evidence for the conductivity enhancement. The conductivity of a Li/polymer/Li half cell was increased by a factor of three as the frequency of external mechanical excitation was varied from 0 to 10 kHz. The mechanism of conductivity enhancement has been explained on the basis of absorption of mechanical energy by polymer chains that in turn assist the transport of conducting ions. The enhanced conductivity may subsequently affect the performance of electrochemical devices. Discharge rates of some primary polymer batteries as a function of mechanical excitation were measured, and the results suggest that they are excitation dependent.

Mechanical energy absorption in human hand-arm exposed to sinusoidal vibration.

A possible basis for risk assessment of human exposure to vibration when using hand-held tools may be to determine the amount of mechanical energy that is absorbed by the hand-arm system. The aim of this investigation was to study the absorption of mechanical energy in the human hand-arm system during exposure to sinusoidal vibration within the frequency range of 20 to 1500 Hz. A handle, specially designed for this type of experiments, was used during the measurements. The influence of various experimental conditions, such as three different hand-arm postures, grip force (25-75 N) and vibration levels (27-53 mm/srms), were studied on eight subjects. The outcome clearly shows that the energy absorption properties of the human hand-arm system are more or less dependent on all of the experimental conditions studied, but mainly to the frequency of the vibration stimuli. Furthermore, the results indicate a non-linear relationship between the energy absorbed and all other variables studies.

Absorption of Mechanical Energy in the Skin of the Human Hand While Exposed to Vibrations

When using a vibratory hand-held tool, all mechanical energy entering the hand and arm has to be transmitted through, or absorbed by, the glabrous skin in contact with the handle. Early signs of an incipient vibration injury are often neurological and/or vascular disturbances located in the skin of the palm, such as a reduction in tactile sensibility or episodes of finger blanching. The aim of this investigation was to study the absorption of mechanical energy in the glabrous skin of the human hand while exposed to vibations from five different types of hand-held tools (die grinder, chipping hammer, wrench, nibbler, angle grinder). The influence of various experimental factors such as static load (1–3 N/cm2), five test points, type of tools were studied on five subjects. The frequency weighted value of the acceleration level, according to the guidelines given in the International Standard ISO 5349, was however held constant througout the study, ca 3.1 m/s2rms. The results show that the static load and the type of tool have a great influence on the quantity of energy absorbed. The highest and lowest quantity of energy absorbed was found for the die and angle grinder, respectively. Futhermore, it was found that, the higher the static load the higher the absorption of vibration energy. In contrast, small and insignificant differences were found between different testpoints and between subjects.

Effects of Velocity Shear in Advective Mixed-Layer Models

Abstract A general multidimensional model of the upper mixed layer of oceans and lakes is presented. The density profile is approximated as uniform over the depth of the layer. Such an assumption is not made for the distribution of the horizontal velocity component, as there is no observational evidence for it. In fact, many observations indicate that important velocity shears exist in regions where advection can be expected to play an important role in the dynamics of the mixed layer (such as lakes, near upwelling and frontal areas, and in equatorial oceanic regions). It is shown that vertical shear in the horizontal velocity field combined with a horizontal density gradient can result in the production or absorption of mechanical energy. Production results if the velocity shear tends to destabilize the density profile, consumption if the tendency is stabilizing so that work against gravity must be done to mix the stabler density profile to uniformity. In the mechanical energy equation, this effect of th...

Joint torque and energy patterns in normal gait.

Experiments were conducted on normal level gait to determine the synergistic patterns present in the forces causing joint moments and those associated with the generation, absorption and transfer of mechanical energy. The following generalizations can be made about the patterns: (i) During swing phase three forces (gravitational, muscle and knee joint acceleration) are responsible for shank rotation, and are shown to act together during both acceleration and deceleration.--(ii) The patterns of generation, absorption and transfer of mechanical energy at the joints are detailed. These patterns demonstrate inter-segment transfers of energy through the joint centres, and through the muscles, as well as the more recognized generation and absorption by the muscles themselves.--As a result of the complexity shown in these patterns it is cautioned that fundamental relationships that may have been derived from controlled biomechanical experiments (such as horizontal flexion and extension of the forearm) are not likely to apply to more normal movements such as gait.

Dilatometric studies of polymers undergoing high and low rate tensile deformation

AbstractSpecific volume change and stress‐strain data were obtained simultaneously during tensile deformation on several plastics known to be resistant to impact loading. Tensile deformation rates of 20 percent/minute and 106 percent/minute and temperatures of −190° to 55°C were employed. A common sequence of deformation modes was observed in all materials studied (rubber modified acrylics and styrene, ABS materials, polycarbonate, impact grade polypropylenes, and high density polyethylene). In all cases the major mode of deformation to failure at low rates and/or higher temperatures is volume conserving and primarily a shear flow process. At higher rates of deformation or lower temperatures, a transition occurs and the specific volume of the material increases in direct proportionality to the tensile strain above the apparent yield point. Volume increases of 17 to 50% were observed and these were equal to 85 percent or more of the observed tensile strain at failure. These observations indicate that microcavitation may be the major process available for the absorption of mechanical energy at impact rates in plastic materials.