Lever Arm Length Research Articles

Mathematical modelling and simulation of a jet pipe electrohydraulic flow control servo valve

In this paper, the mathematical model of a jet pipe electrohydraulic flow control servo valve with a built-in mechanical feedback is developed. The actuator dynamics is also included. The solid and finite element (FE) models of the critical and precision components, feedback spring assembly and flexure tube of jet pipe assembly, were carried out first and simulated with appropriate boundary and loading conditions in a commercially available FE code, IDEAS, version 7.0, to ascertain the stiffnesses. To validate the obtained finite element results, experiments were carried out with a specially designed and fabricated test set-up. Moderately good agreement was observed between finite element and experimental values. The required simulation parameters for a jet pipe servo valve-actuator system, such as the moment of inertia, mass of the spool, mass of the piston, stiffness of the critical and precision components, and lever arm length, were obtained from the solid and finite element models. The developed model was simulated in commercially available software, MATLAB 6.5, Release 13. The step response of the valve was analysed. The simulation clearly showed the dynamics of the jet pipe, spool, and actuator displacement in achieving the equilibrium position when the applied torque and restoring torques balance, known as the steady state.

Damage Tolerance of Carbon Fabric/Epoxy Composite for Korean Tilting Train Carbody

Interlaminar fracture behavior of carbon fabric/epoxy composite, which is one of the candidate composites for the Korean tilting train carbody, was investigated. Specimens were made of a CF3227 plain fabric with an epoxy resin. An initial starter crack was formed by inserting a 12.5 thick Teflon film at the one end of the specimen. Interlaminar fracture toughness was evaluated using the mixed mode flexural fixture, which provides a wide range of mixed mode deformation by varying the length of lever arm. According to the results, the crack growth was progressive and stable under mode I dominantly mixed mode ratio and was relatively rapid and unstable under mode II dominantly mixed mode ratio. The mixed mode interlaminar fracture behavior can be predicted by a mixed mode fracture criterion depending on the point at which the crack growth was associated.

Radiographic geometric measures of the hip joint and abductor muscle function in patients after total hip replacement

The aim of this study was to evaluate the correlation between radiographic geometric measurements (abductor lever arm and abductor muscle length) and abductor muscle function in osteoarthritic hip joint patients after surgery. Thirteen patients (11 males and 2 females, aged 55 to 74 years old) were evaluated at least 6 months after unilateral total hip replacement due to primary coxarthrosis. The length of the abductor muscles and their lever arm were measured on standardized antero-posterior hip radiographs taken in supine position; the product of these two values, namely the dysfunction index (DI), was considered an estimate for the hip abductor torque. The abductor muscle function was evaluated through the measurement of the range (degrees) and duration (seconds) of maximal active hip abduction (with patients in lateral decubitus) and through the time sustaining the Trendelenburg test position (single leg stance). Considering the percentage of variation, related to the contralateral hip joint (used as control), a significant positive correlation was found between both, abductor lever length and DI, and the time of maximal hip abduction (r = 0.61 and r = 0.63, P < 0.05). Moreover, a positive trend (P = 0.08) was found between DI and the time spent in Trendelenburg position (r = 0.54). The presented data provide evidence that lever arm and DI of hip abductor muscles are correlated with muscular capacity to resist fatigue. These results emphasize the importance of thorough surgical planning before total hip replacement with emphasis to the geometric hip parameters, which seem to determine the clinical outcome.

Influence of Lever Arm and Stabilization on Measures of Hip Abduction and Adduction Torque Obtained by Hand-Held Dynamometry

Krause DA, Schlagel SJ, Stember BM, Zoetewey JE, Hollman JH. Influence of lever arm and stabilization on measures of hip abduction and adduction torque obtained by hand-held dynamometry. Objective To examine the reliability of clinical techniques for testing hip abductor and adductor muscle performance. Design Repeated measures. Setting Academic laboratory. Participants A sample of 21 healthy subjects (12 men, 9 women) between 22 and 31 years of age. Interventions Not applicable. Main Outcome Measures Reliability of repeated measures was estimated by calculating intraclass correlation coefficients. Torque production capability was calculated by multiplying force output obtained with a hand-held dynamometer by the length of the resistance lever arm. Results The reliability of abduction testing was greatest in the long-lever condition. Adduction test reliability was greatest in the long-lever condition with bench stabilization. The maximal hip abduction torque tested in the long-lever position was significantly greater ( t 20=9.21, P<.001) than that in the short-lever position. The maximal hip adduction torque occurred using a long lever for resistance application and a bench to stabilize the nontest leg (F 1,20=15.64, P=.001). Conclusions Muscle performance testing of hip abductors and adductors with a hand-held dynamometer can be performed with good to excellent intratester and intertester reliability. Hip abduction testing is best performed with a long lever. Hip adduction is best performed with a long lever and a bench to stabilize the nontest extremity.

Steady-state analysis of a precision hydraulic flow control servovalve using the finite element method

In the present paper, an attempt has been made to simulate the steady-state operation of the jet pipe Electro-Hydraulic ServoValve (EHSV) using the Finite Element Method (FEM). The jet pipe servovalve has two stages and consists of two main assemblies: first-stage torque motor assembly and second-stage valve assembly. Between the first and second stage there is a mechanical feedback to stabilize the valve operation. Each assembly has various delicate and precise components. The finite element analysis has been carried out on jet pipe and feedback spring assembly. The analysis shows that the stiffness of flexure tube and feedback spring assembly plays the major role in achieving steady-state valve operation. The stiffness of these components is obtained through the FEM and these results are validated with experiment. The commercial ABAQUS finite element code has been used for the simulation. The mathematical model of the jet pipe EHSV has been developed and simulated using MATLAB to study the spool dynamics with the main emphasis on the steady-state valve operation. The required simulation parameters, like moment of inertia, stiffness of the components and lever arm length. are obtained from the FEM.

Scaling of the marsupial middle ear and its functional significance

AbstractThe marsupial middle ear performs an anatomical impedance matching for acoustic energy travelling in air to reach the cochlea. The size of the middle ear sets constraints for the frequencies transmitted. For generalized placental mammals, it has been shown that the limit for high‐frequency hearing can be predicted on the basis of middle ear ossicle mass, provided that the ears fulfil requirements of isometry. We studied the interspecific size variation of the middle ear in 23 marsupial species, with the following measurable parameters: skull mass, condylobasal length, ossicular masses for malleus, incus and stapes, tympanic membrane area, oval window area, and lever arm lengths for malleus and incus. Our results show that the middle ear size grows with negative allometry in relation to body size and that the internal proportions of the marsupial middle ear are largely isometric. This resembles the situation in placental mammals and allows us to use their isometric middle ear model to predict the high‐frequency hearing limit for marsupials. We found that the isometry model predicts the high‐frequency hearing limit for different marsupials well, indicating that marsupials can be used as auditory models for general therian mammalian hearing. At very high frequencies, other factors, such as the inner ear, seem to constrain mammalian hearing.

BIOMECHANICS OF THE INTACT AND REPLACED HUMAN ANKLE JOINT

The main objective of the study was to develop advanced biomechanical models of the intact human ankle complex. It was also aimed at designing a total ankle replacement which would better reproduce the physiological function of the joint. Passive flexion was analyzed in a number of lower-leg preparations with stereophotogrammetry and radiostereometry. The articular surfaces and fibres within the calcaneofibular and tibiocalcaneal ligaments were observed to prescribe the changing positions of bones, ligaments and instantaneous axis of rotation. Joint motion included rolling as well as sliding. Computer-based models elucidated this kinematics at the intact joint, and how changing positions of the centre of rotation and muscle lines of action affect lever arm length at different flexion angles. The mechanical response of the joint to anterior drawer and talar tilt tests was explained in terms of fibre recruitment. The experimental evidence and the geometrical models gave the basis for the design of a novel ankle replacement. A three-component, convex-tibia prosthesis was developed with articular surface shapes that are compatible with the geometry of the ligaments. The proposed prosthesis based on ligament/shape compatibility is showing encouraging results in initial implantation.

The stroke size of myosins: a reevaluation

In this article results are reviewed from different experimental approaches to determine the size of the power stroke generated by myosin molecules during their ATPase cycle. While data from fiber studies and protein crystallography predict a stroke size of about 10 nm for skeletal muscle myosins, single molecule studies imply a stroke size for these myosins of only about 5 nm. Single molecule studies also showed the stroke size to be proportional to the length of the light chain binding domain, acting like a lever arm. At the same lever arm length, however, the stroke size of smooth muscle myosin II is found about twice as large and a stroke size of about 14 nm was reported for class-I myosins. It was proposed that such different stroke sizes for molecules with same lever arm length result from different extend of converter domain rotation. Only for class-I myosins, however, an about 30 degrees larger rotation of the converter was found so far by protein crystallography. This, however, is far too small to account for the almost 3-fold larger stroke size reported from single molecule studies. In this contribution we discuss some factors that might account for the apparent discrepancies between single molecule studies on the one hand and protein crystallography as well as some fiber studies on the other hand. In addition, we present some modeling to illustrate that the power stroke very likely is underestimated to a large extent in current single molecule approaches. We further show that differences in the stroke size for various classes of myosins reported from single molecule studies might be related to small differences in the probability to execute the power stroke kinetics. We demonstrate that such small changes in power stroke kinetics can seriously affect the extent to which the 'true' power stroke is underestimated by present single molecule approaches.

Effects of anatomic conformation on three-dimensional motion of the caudal lumbar and lumbosacral portions of the vertebral column of dogs

To determine the association between the 3-dimensional (3-D) motion pattern of the caudal lumbar and lumbosacral portions of the canine vertebral column and the morphology of vertebrae, facet joints, and intervertebral disks. Vertebral columns of 9 German Shepherd Dogs and 16 dogs of other breeds with similar body weights and body conditions. Different morphometric parameters of the vertebral column were assessed by computed tomography (CT) and magnetic resonance imaging. Anatomic conformation and the 3-D motion pattern were compared, and correlation coefficients were calculated. Total range of motion for flexion and extension was mainly associated with the facet joint angle, the facet joint angle difference between levels of the vertebral column in the transverse plane on CT images, disk height, and lever arm length. Motion is a complex process that is influenced by the entire 3-D conformation of the lumbar portion of the vertebral column. In vivo dynamic measurements of the 3-D motion pattern of the lumbar and lumbosacral portions of the vertebral column will be necessary to further assess biomechanics that could lead to disk degeneration in dogs.

Ontogeny of muscle mechanical advantage in capuchin monkeys (Cebus albifrons and Cebus apella)

AbstractTerrestrial locomotion requires that animals maintain postural stability against the flexing force of gravity. To counteract volume/area relationships that limit muscle force and may compromise stability, larger animals increase the effective mechanical advantage of their extensor musculature by walking on more extended limbs and showing allometric increases in extensor muscle lever arm lengths. Assuming these size‐related principles are uniform, similar adaptations should characterize ontogenetic increases in size. Previous research on non‐primate mammals has shown, however, that extensor muscle mechanical advantage is greater early in ontogeny and decreases with negative allometry during growth. This study extended this work by investigating patterns of relative elbow lever arm growth in two capuchin monkeys, Cebus albifrons and Cebus apella. Unlike previously studied mammals, growing capuchin monkeys face unique anatomical constraints, including relatively long limb bones and positively allometric limb growth. These constraints could augment the flexing torque of gravity at the limb joints and require compensatory increases in extensor muscle mechanical advantage as size increases through growth. Forearm length and the length of elbow extensor and flexor muscle lever arms were measured in longitudinal radiographic series of growing capuchin monkeys. In contrast to other mammals, all lengths scaled to body mass with positive allometry. Anatomical mechanical advantage (lever arm length/forelimb length) scaled with negative allometry, however, matching the non‐primate mammalian trend. Greater muscle mechanical advantage during early locomotion may help young mammals overcome relatively weak extensor muscles and other growth‐related limits on locomotor performance. Additional data on ontogenetic changes in gait dynamics and musculoskeletal growth are required to validate this hypothesis.

Lever-arm and mini-implant system for anterior torque control during retraction in lingual orthodontic treatment.

Anterior torque control during retraction is difficult to achieve with lingual orthodontic treatment. This article describes the use of a lever-arm and mini-implant system as absolute anchorage for controlled retraction of the anterior teeth during lingual orthodontic treatment and evaluates 2 protrusion cases treated with this system. Various clinical situations are discussed and analyzed from a biomechanical standpoint. Mini-implants are needed to control the point of force application in the posterior area and produce en masse retraction with no anchorage loss. When the length of the lever-arm is adjusted to the position of the mini-implant, the desired line of action of the retraction force with respect to the center of resistance of the anterior segment is selected. Controlled retraction of the anterior teeth was achieved with no loss of anchorage. The mini-implant, in conjunction with the lever-arm, is useful not only for absolute anchorage but also for anterior torque control during retraction in lingual orthodontic treatment.

Restoration of femoral offset in total hip arthroplasty

To explore the factors effecting restoring femoral offset and the relation between femoral offset and hip abductor strength during total hip arthroplasty (THA). Ninety-nine THA for 81 patients were performed from March 1998 to January 2002. And follow-up was finished. There were 53 women and 28 men and the average age was 57 years (29 to 80). The right hip had been replaced in 28 cases, the left in 35 cases and the bilateral in 18 cases. The mean duration of clinical and roentgenographic follow-up was 36.8 months (range, 19 approximately 66 months). A posterolateral approach was used in all THA. The femoral offset and the abductor lever arm were measured from each radiograph. The measurement of the hip abduction strength was made for some THA by the Cybex machine. Statistical data analysis was performed by SPSS10.0 software. Femoral offset correlated positively with the length of the abductor lever arm (r = 0.613; P < 0.001). Simple regression analysis showed that femoral offset was significantly and positively related to the length of femoral neck and neck-shaft angle (r = 0.451, P = 0.001; r = 0.567, P < 0.001). There was a highly significant and positive correlation between femoral offset (and consequently abductor lever arm) and hip abductor strength (r = 0.500, P = 0.009; r = 0.477, P = 0.014). It is very important to template both sides of hip preoperatively for restoring femoral offset in THA. Femoral component with more anatomical neck-shaft angle will be used with the increase in the femoral neck length.

A type V myosin (Myo2p) and a Rab-like G-protein (Ypt11p) are required for retention of newly inherited mitochondria in yeast cells during cell division.

Two actin-dependent force generators contribute to mitochondrial inheritance: Arp2/3 complex and the myosin V Myo2p (together with its Rab-like binding partner Ypt11p). We found that deletion of YPT11, reduction of the length of the Myo2p lever arm (myo2-Delta6IQ), or deletion of MYO4 (the other yeast myosin V), had no effect on mitochondrial morphology, colocalization of mitochondria with actin cables, or the velocity of bud-directed mitochondrial movement. In contrast, retention of mitochondria in the bud was compromised in YPT11 and MYO2 mutants. Retention of mitochondria in the bud tip of wild-type cells results in a 60% decrease in mitochondrial movement in buds compared with mother cells. In ypt11Delta mutants, however, the level of mitochondrial motility in buds was similar to that observed in mother cells. Moreover, the myo2-66 mutant, which carries a temperature-sensitive mutation in the Myo2p motor domain, exhibited a 55% decrease in accumulation of mitochondria in the bud tip, and an increase in accumulation of mitochondria at the retention site in the mother cell after shift to restrictive temperatures. Finally, destabilization of actin cables and the resulting delocalization of Myo2p from the bud tip had no significant effect on the accumulation of mitochondria in the bud tip.

Triathlon Wet Suit and Technical Parameters at the Start and End of a 1500-m Swim

The aim of this study was to determine the effect of wearing a triathlon wet suit on the technical parameters of the front crawl stroke. Eight highly trained male triathletes were filmed with underwater camcorders during two 1500-m swim tests: one with a wet suit (WS) and the other with a standard suit (SS). Two conditions were considered: Condition I (CI) and Condition XV (CXV), representing the 1st and the 15th 100-m, respectively. Views were synchronized and digitized using kinematic analysis software (Schleihauf, 1994) to obtain 3-D coordinates of the anatomical landmarks of the body. Results showed that the wet suit and duration of the exercise significantly influenced stroke parameters. The swim with WS was characterized by greater stroke length and a progressive increase in stroke frequency, resulting from a more extended elbow position during the stroke and from a decrease in the absolute and relative times of the propulsive phase. These changes indicated more efficient upper limb action. The duration of exercise modified the swim with WS and SS. The loss of velocity observed in CXV was related to a decrease in stroke length, or more precisely a reduction in lever arm length during the aquatic phase, insufficiently offset by a slight increase in stroke frequency. These two motor responses, a less extended elbow position and a stroke frequency increase, emerged as an easier motor solution for coping with the effect of fatigue. This solution could be regarded as an adaptation to the duration of the exercise.

Different degrees of lever arm rotation control myosin step size.

Myosins are actin-based motors that are generally believed to move by amplifying small structural changes in the core motor domain via a lever arm rotation of the light chain binding domain. However, the lack of a quantitative agreement between observed step sizes and the length of the proposed lever arms from different myosins challenges this view. We analyzed the step size of rat myosin 1d (Myo1d) and surprisingly found that this myosin takes unexpectedly large steps in comparison to other myosins. Engineering the length of the light chain binding domain of rat Myo1d resulted in a linear increase of step size in relation to the putative lever arm length, indicative of a lever arm rotation of the light chain binding domain. The extrapolated pivoting point resided in the same region of the rat Myo1d head domain as in conventional myosins. Therefore, rat Myo1d achieves its larger working stroke by a large calculated ∼90° rotation of the light chain binding domain. These results demonstrate that differences in myosin step sizes are not only controlled by lever arm length, but also by substantial differences in the degree of lever arm rotation.

The mechanics of back-extensor torque production about the lumbar spine

The purpose of this study was to develop and evaluate a biomechanical model of lumbar back extension over a wide range of positions for the lumbar spine, incorporating the latest information on muscle geometry and intra-abdominal pressure (IAP). Analysis of the Visible Human data was utilised in order to obtain anatomical information unavailable from the literature and magnetic resonance imaging was used to generate subject-specific anatomical descriptions. The model was evaluated by comparisons with measured maximal voluntary static back-extension torques. Predicted maximal specific muscle tensions agreed well with in vitro measurements from the literature. When modelling the maximal static back-extension torque production, it was possible to come fairly close to simultaneous equilibrium about all the lumbar discs simply by a uniform muscle activation of all back-extensor muscles (the caudal part showed, however, less agreement). This indicates that equilibrium in the lumbar spine is mainly regulated by passive mechanical properties, e.g. muscle length changes due to postural changes, rather than due to complex muscle coordination, as earlier proposed. The model showed that IAP (measured during torque exertions) contributes about 10% of the total maximal voluntary back-extensor torque and that it can unload the spine from compression. The spinal unloading effect from the IAP was greatest with the spine held in a flexed position. This is in opposition to the effects of changed muscle lever arm lengths, which for a given load would give the largest spinal unloading in the extended position. These findings have implications for the evaluation of optimal lifting techniques.

当科における大腿骨外反骨切り術の治療成績

The purpose of the present study is to report the mid-term results of modified Sugioka transtrochanteric valgus ostetomy (TVO) for the treatment of secondary osteoarthritis. The lateral displacement of the greater trochanter was simultaneously performed. Fourteen TVOs were performed in 14 patients with unilateral osteoarthritis of the hip from 1993. We assessed 8 hips in 8 patients in this study. The mean age of the patients at the time of surgery was 46.4 years (41 to 55 years). The average follow-up was 3.9 years (2.4-7.2years). The patients were evaluated for radiographic changes of the joint space, roof osteophyte, weight bearing surface of acetabulum, AHI, abductor lever arm, capital drop, bone cyst in the acetabulum or femoral head as well as clinical results using JOA score. The mean JOA score improved from 57.4 to 76.3. The widening of joint space, lengthening of weight bearing surface of acetabulum were seen in seven hips. The length of the abductor lever arm after surgery was not proportional to the JOA score at the latest follow-up. In one patient, total hip arthroplasty was required after 2.2 years. This procedure is considered useful for the treatment of osteoarthritis in dysplastic hips.

Role of the lever arm in the processive stepping of myosin V.

Myosin V is a two-headed molecular motor that binds six light chains per heavy chain, which creates unusually long lever arms. This motor moves processively along its actin track in discrete 36-nm steps. Our model is that one head of the two-headed myosin V tightly binds to actin and swings its long lever arm through a large angle, providing a stroke. We created single-headed constructs with different-size lever arms and show that stroke size is proportional to lever arm length. In a two-headed molecule, the stroke provides the directional bias, after which the unbound head diffuses to find its binding site, 36 nm forward. Our two-headed construct with all six light chains per head reconstitutes the 36-nm processive step seen in tissue-purified myosin V. Two-headed myosin V molecules with only four light chains per head are still processive, but their step size is reduced to 24 nm. A further reduction in the length of the lever arms to one light chain per head results in a motor that is unable to walk processively. This motor produces single small approximately 6-nm strokes, and ATPase and pyrene actin quench measurements show that only one of the heads of this dimer rapidly binds to actin for a given binding event. These data show that for myosin V with its normal proximal tail domain, both heads and a long lever arm are required for large, processive steps.

A model for lever-arm length calculation of the flexor and extensor muscles at the ankle.

A sagittal-plane mathematical model of joint mobility, including the mechanical effect of the extensor retinacula, was used to predict the lever arm lengths of the main flexor and extensor muscles of the human ankle over the range of movement. In plantarflexion, the centre of rotation lies posteriorly and distally, maximising the lever arm of the tibialis anterior. The action of the gastrocnemius and soleus is maximised in dorsiflexion. Traditional calculation of ankle joint moment based on a fixed centre of rotation is acceptable only in exercises such as level walking with a limited range of motion about the neutral position. The present model with a moving centre is particularly advised in exercises which take the joint nearer to the extremes of sagittal motion.

Dynamic simulation of the natural and replaced human ankle joint.

Disappointing results for total ankle replacement have been explained by poor knowledge of the mechanics of the intact and replaced joints. Dynamic simulation tools have the capacity to simulate dynamic conditions that occur in human joints. The Working Model 2D tool was used to simulate the mechanics of the intact and replaced ankle joints, based on previously validated mathematical models. Elementary objects were used to model ligaments, articular surfaces, retinacula and muscle-tendon units. The performance of several pairs of prosthetic articular surfaces was also analysed. According to the results of these simulations, rolling as well as sliding motion occurs in the natural ankle, governed by a ligamentous linkage. Elongation of the tibiocalcaneal and calcaneofibular ligaments was found to be 1.5% and 4.8%, respectively. A 13% change in lever arm length occurred for both the tibialis anterior and gastrocnemius muscles during ankle flexion. Unlike the currently available three-component designs, the newly proposed convex-tibial ligament-compatible prosthesis was found to be able to restore the original mobility and physiological function of the ligaments. This prosthesis combines freedom from restraint with congruity of the components throughout the range of flexion.