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PubMed2004

[Incisor torque control with fixed appliance].

OBJECTIVE: To evaluate the properties of orthodontic rectangular arch wires in torsion. METHODS: To measure and analyze the torsional moments and angles of 0.46 mm x 0.63 mm rectangular orthodontic arch wires in single 0.022 inch bracket of the maxillary central incisor with a torsion measurement apparatus. RESULTS: (1) The torsional stiffness of stainless steel arch wires, Chinese nitinol arch wires, 7.0 mm vertical loop arch wires, 3.0 mm and 6.0 mm horizontal loop arch wires is 4.909, 1.325, 4.137, 3.448 and 3.024 Nmm per degree, respectively. (2) The arch wires will be twisted 19.143, 36.832, 19.851, 21.812 and 22.418 degrees; respectively to obtain optimal force. (3) Vertical and horizontal loop decreased the torsional stiffness of the rectangular stainless steel arch wire. CONCLUSION: The straight rectangular stainless steel arch wire is not well suitable for the torque control of the incisor. Loop design in arch wire is capable of decreasing torsional stiffness. The horizontal loop is more effective than vertical loop.

Humans↗
PubMed2006

Bilateral isokinetic peak torque of quadriceps and hamstring muscles in professional soccer players with dominance on one or both two sides.

AIM: Dominance of one leg may cause asymmetry between the contralateral muscle groups and develop predisposition for injury to the leg with the weaker muscle strength. The purpose of this study was to examine the strength balance in the extensor and flexor muscle groups, as well as the hamstring to quadriceps (H/Q) ratios of both legs in professional soccer players with dominance on one or both legs. METHODS: Forty-two professional soccer players of the first Greek division participated in this study. Participants were divided into 3 groups according to their leg use during training sessions and matches. Fifteen players comprised the first group with dominance to the right leg, 12 players formed the second group with dominance to the left leg, and 15 players consisted the third group with dominance to both the right and left legs. Maximum voluntary concentric torque of the hamstring and quadriceps muscles of both legs was assessed using a Norm isokinetic dynamometer at angular velocities of 12 degrees, 60 degrees, 180 degrees and 300 degrees/s. RESULTS: No significant differences in the strength balance found between the groups. The isokinetic variables comparing the right and left body side in each group, with dominance on one or both legs, did not differ. No differences were recorded in the H/Q between the right and left legs for any of the subject groups. CONCLUSIONS: There is no evidence of muscle imbalances in extensor and flexor muscle groups and H/Q ratios between the right and left legs in professional soccer players with dominance on one or both legs. The training sessions and matches appear to have imposed strength balance for the right and left body sides of professional soccer players.

Adult↗
PubMed1996

Torque and histomorphometric evaluation of c.p. titanium screws blasted with 25- and 75-microns-sized particles of Al2O3.

A comparison was made between screw-shaped c.p. titanium implants blasted with either 25- or 75-microns particles of Al2O3. The implant surfaces were investigated with respect to topography and composition before implantation in rabbit bone. Grit blasting with 25- or 75-microns particles produced two different surface roughnesses, but no significant difference in the surface composition for the two surfaces. After 12 weeks insertion time in the rabbit tibia and femur, a higher removal torque and more bone-to-metal contact was found for the implants blasted with 75-microns particles compared with the 25-microns-blasted ones.

Aluminum Oxide↗
PubMed1976

Torque feedback radiometer for ultrasonic power measurements.

A radiometer for use in ultrasonic power measurements in the 10-200 milliwatt regime has been built and tested. The device is based on the torque feedback principle applied to a friction-free taut-band meter movement. Measurements using the instrument have been made on two commercial ultrasound instruments.

Radiometry↗
PubMed2003

Three dimensional ultrasound analysis of fascicle orientation in human tibialis anterior muscle enables analysis of macroscopic torque at the cellular level.

The purpose of this study was to test the hypothesis that the internal structure of the bipennate human tibialis anterior muscle is sufficiently homogenous throughout the muscle that the cellular stresses could be interpreted correctly from measurable anatomic properties and torque in the limb. This result is needed for facile comparison of extrinsic mechanical data and intrinsic energetic fluxes. Three-dimensional imaging of the fascicles of the human tibialis anterior muscle was made by capturing a series of ultrasound images while registering their location in space. Subsequent tracing of hundreds of structures in the ultrasound images with the use of custom software identified muscle boundaries, tendon surfaces, and fascicles as anatomic elements in 3-D space. The tendon was reconstructed as a mesh through the tracings identified as a component of the tendon. The angle of insertion of each identified fascicle at the tendon was calculated against the nearest normal in the mesh of the tendon. In three subjects the average angle of insertion of the fascicles onto the internal tendon was 11 degrees (coefficient of variation 40%). The angle decreased along the length of the muscle from approximately 15 degrees near the belly of the muscle to 6 degrees near the ankle in fascicles superior and inferior to the central tendon. The angle increased by several degrees during a voluntary contraction. Despite the differences in angles of insertion that can be measured, these distinctions have little significance for the distribution of forces along cellular axes within the muscle: the angles, their distribution within the muscle and change with contraction are small. For this bipennate muscle the cosine of the angle of insertion of the cellular bundles is always close to unity. Thus measurements of whole muscle mechanical data are simply related to mechanical stress of its cells.

Biomechanical Phenomena↗
PubMed1995

Estimation of dynamic joint torques and trajectory formation from surface electromyography signals using a neural network model.

In this study, human arm movement was reconstructed from electromyography (EMG) signals using a forward dynamics model acquired by an artificial neural network within a modular architecture. Dynamic joint torques at the elbow and shoulder were estimated for movements in the horizontal plane from the surface EMG signals of 10 flexor and extensor muscles. Using only the initial conditions of the arm and the EMG time course as input, the network reliably reconstructed a variety of movement trajectories. The results demonstrate that posture maintenance and multijoint movements, entailing complex via-point specification and co-contraction of muscles, can be accurately computed from multiple surface EMG signals. In addition to the model's empirical uses, such as calculation of arm stiffness during motion, it allows evaluation of hypothesized computational mechanisms of the central nervous system such as virtual trajectory control and optimal trajectory planning.

Arm↗
PubMed1980

An evaluation of nonlinearities in the motor output response to applied torque perturbations in man.

Nonlinearities present in the motor output response of biceps and triceps muscles in normal human subjects to applied torque perturbations were evaluated quantitatively. When the applied perturbations were relatively continuous, consisting of a pseudo-random train of pulses, the identified nonlinearities were small, never exceeding 20% of the amplitude of the linear component of the response and usually being much less.

Electromyography↗
PubMed1987

Relationships between individual isometric muscle forces, EMG activity and joint torque in monkeys.

The aim of the present work was to determine the EMG activity and the moment of force developed by the main elbow flexor muscles, and to establish on this basis the degree of their participation in isometric contractions performed at various positions of the elbow. This was achieved by recording the following biomechanical parameters: EMG and tensile stress (or force) from biceps brachii (BB) and brachioradialis (BR); EMG from brachialis; external resultant force (FE). There was: a linear or quadratic relationship between the integrated EMG from each muscle and FE; a linear relationship between the force produced by BB or BR and FE. The slope of these relationships depended on the elbow angle, except for that between BB force and FE. It is proposed that iEMG changes compensate for those of the force lever arm. It has been calculated that the contribution of BR to external torque decreased from the extension to flexion while that of BB increased from 70 degrees to 90 degrees and then decreased. How far these data can be extrapolated to man is a matter of discussion based on iEMG and anthropometrical data.

Animals↗
PubMed1986

Prediction of peak torque and contraction work at different isokinetic angular velocities of plantarflexion.

Contraction work (CW) and peak torque (PT) of maximum isokinetic plantar flexions were measured in clinically healthy subjects randomly chosen from the official census list of Umeå, Sweden, in three groups: 40-44, 50-54 and 60-64 years of age, with similar proportions of men and women. Maximum isokinetic plantar-flexions were performed at angular velocities of 30, 60, 120 and 180 degrees X s-1. Body-weight, height and crural circumference were measured. Subjects rated their levels of leisure and occupational activities. To establish formulae to predict CW and PT, stepwise regression procedures were applied. The predictive powers (r2) of the formulae which incorporated age, sex and crural circumference, were higher for PT (30 degrees X s-1: 0.82, 60 degrees X s-1: 0.79, 120 degrees X s-1: 0.75, 180 degrees X s-1: 0.56) than for CW (30 degrees s-1: 0.63, 60 degrees s-1: 0.63, 120 degrees s-1: 0.60, 180 degrees s-1: 0.52). Thus the part of the variance explained decreased with increasing angular velocity, but more than 50% was still explained at 180 degrees s-1. The results indicate that the mechanical output of the plantar flexors is predictable.

Adolescent↗
PubMed1977

Measurement of edgewise torque force in vitro.

The construction of a model for the measurement of palatal root torque is described. It was demonstrated that: 1. Halfway between the apex of a tooth and the arch wire the force was double that which was delivered at the apex. 2. The lateral incisors were subjected to appreciably more force than the central incisors. 3. The smaller the number of teeth acted upon, the greater the force they received.

Humans↗
PubMed1991

Speed variation and resultant joint torques during sit-to-stand.

The purpose of this study was to test the hypothesis that a progressively faster speed of ascent requires significantly greater peak resultant joint torque (RJT) at major load-bearing joints of the lower limb during the sit-to-stand (STS) transfer. Eight healthy adults performed the STS at slow, natural, and fast speeds. A motion analysis system and two force platforms were employed to record kinetic data, and equations of motion were applied to compute the RJT for the ankle, knee, and hip. The results of the study supported the hypothesis that when the speed of ascent increased progressively, the peak hip flexion, knee extension, and ankle dorsiflexion RJTs increased disproportionately. However, the peak hip extension and ankle plantar flexion RJTs remained relatively constant across the range of the speeds. Implications for clinical practice pertaining to the timing and magnitude of RJT, as well as for interventions that emphasize the adaptive characteristics of movements, are suggested.

Adult↗
PubMed1975

Effects of dentate cooling on precentral unit activity following torque pulse injections into elbow movements.

(1) The effects were studied of brief, reversible cooling of the dentate nucleus of two Cebus monkeys on the activity of 69 precentral neurons that were related to self-paced elbow flexions or extensions. Sixty-two neurons were studied when movements were randomly perturbed by transient load changes. (2) During unperturbed movements dentate cooling altered precentral activity and movement parameters in the same direction. Extension movements and extension-related precentral neurons developed oscillations and rhythmical activity at about 4 Hz with increased peak values of acceleration and discharge intensity. Flexion peak accelerations and dynamic properties of flexion-related precentral neurons decreased. (3) Dentate cooling had no major effects on the "early" precentral responses to torque pulses and on the initial rapid movement adjustment. (4) Dentate cooling decreased intensity of "late" precentral responses and slowed their frequency together with associated movement oscillations from 5-6 Hz to 3-4 Hz. EMG bursts of biceps and triceps were prolonged accordingly. (5) It is concluded that the tightly coupled interaction between precentral motor cortex and the evolving movement was independent of dentate function in the early stage of the cortical load compensation. The dentate nucleus was involved, however, in adjusting intensity and frequency of subsequent late precentral responses and of movement oscillations.

Adaptation, Physiological↗
PubMed1992

A cephalometric study of Class II, division 1 treatment using differential torque mechanics.

A pilot study was designed in which 19 growing patients with Class II, Division 1 malocclusions who were undergoing differential torque treatment were cephalometrically evaluated. No extraoral force or Class II elastics were used. Findings indicate that the 2 x 4 appliance can be useful in the treatment of selected Class II, Division 1 malocclusions in growing children.

Cephalometry↗
PubMed2004

The interfacial torque on a partially submerged sphere.

For a heavy spherical particle floating at the surface of a liquid, we show that the resultant torque exerted on the particle about its center by the interfacial forces is always zero, regardless of the position and shape of the contact line, provided only that the interfacial tension and the contact angle are constant. Interfacial tension therefore cannot rotate a spherical particle about its center.

Journal Article↗
PubMed2006

A method to capture six-degrees-of-freedom mechanical measurements of isometric shoulder and elbow torques during event-related fMRI.

Functional magnetic resonance imaging (fMRI) experiments investigating cortical activity while controlling task performance are difficult to conduct due to the high magnetic field environment and a lack of compatible measurement tools. We describe a method to measure the generation of isometric shoulder and elbow torques with a six-degrees-of-freedom (DOF) load cell during an event-related fMRI study. Feasibility of this method is demonstrated by finding cortical activity on the motor cortices in a participant during an event-related study of shoulder abduction and elbow flexion. The described methodology permits researchers to control and measure intersubject and intrasubject motor task performance during event-related brain imaging.

Adult↗
PubMed1988

Torque and rotation rate of the bacterial flagellar motor.

This paper describes an analysis of microscopic models for the coupling between ion flow and rotation of bacterial flagella. In model I it is assumed that intersecting half-channels exist on the rotor and the stator and that the driving ion is constrained to move together with the intersection site. Model II is based on the assumption that ion flow drives a cycle of conformational transitions in a channel-like stator subunit that are coupled to the motion of the rotor. Analysis of both mechanisms yields closed expressions relating the torque M generated by the flagellar motor to the rotation rate v. Model I (and also, under certain assumptions, model II) accounts for the experimentally observed linear relationship between M and v. The theoretical equations lead to predictions on the relationship between rotation rate and driving force which can be tested experimentally.

Bacterial Physiological Phenomena↗
PubMed1993

Torque and switching in the bacterial flagellar motor. An electrostatic model.

A model is presented for the rotary motor that drives bacterial flagella, using the electrochemical gradient of protons across the cytoplasmic membrane. The model unifies several concepts present in previous models. Torque is generated by proton-conducting particles around the perimeter of the rotor at the base of the flagellum. Protons in channels formed by these particles interact electrostatically with tilted lines of charges on the rotor, providing "loose coupling" between proton flux and rotation of the flagellum. Computer simulations of the model correctly predict the experimentally observed dynamic properties of the motor. Unlike previous models, the motor presented here may rotate either way for a given direction of the protonmotive force. The direction of rotation only depends on the level of occupancy of the proton channels. This suggests a novel and simple mechanism for the switching between clockwise and counterclockwise rotation that is the basis of bacterial chemotaxis.

Bacterial Physiological Phenomena↗
PubMed1996

Preparation of bead-tailed actin filaments: estimation of the torque produced by the sliding force in an in vitro motility assay.

By coating covalently the surface of a polystyrene bead (diameter = 1 micron) with gelsolin, we have succeeded in attaching the bead selectively at the barbed end of an actin filament and forming a 1:1 bead-actin filament complex. On a layer of heavy meromyosin on a nitrocellulose-coated coverglass, this bead-actin filament complex slid smoothly, trailing the bead at its end. Therefore we called this preparation "bead-tailed" actin filaments. The sliding velocity was indistinguishable from that of nonbeaded filaments. With use of this system, we tried to detect the axial rotation (rotation around the filament axis) in a sliding actin filament. Although a single bead at the tail end did not serve as the marker for the axial rotation, we occasionally found another bead bound to the tail bead. In this case, the orientation of the bead-aggregate could be followed continuously with a video monitor while the filament was sliding over heavy meromyosin. We observed that actin filaments slid over distances of many tens of micrometers without showing a complete turn of the bead-aggregates. On the basis of the calculation of rotational friction drag on the bead-aggregate, we estimate that the rotational component of the sliding force and the torque produced on a sliding actin filament (length < or = 10 microns) did not accumulate > 1 pN and 5 pN.nm, respectively. In the present system of randomly oriented heavy meromyosin lying on a nitrocellulose film without an external load.

Actins↗