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At least 379 records · Page 21Linked to original sources
PubMed1995

The development of goal-directed reaching in infants: hand trajectory formation and joint torque control.

Nine young infants were followed longitudinally from 4 to 15 months of age. We recorded early spontaneous movements and reaching movements to a stationary target. Time-position data of the hand (endpoint), shoulder, and elbow were collected using an optoelectronic measurement system (ELITE). We analyzed the endpoint kinematics and the intersegmental dynamics of the shoulder and elbow joint to investigate how changes in proximal torque control determined the development of hand trajectory formation. Two developmental phases of hand trajectory formation were identified: a first phase of rapid improvements between 16 and 24 weeks of age, the time of reaching onset for all infants. During that time period the number of movement units per reach and movement time decreased dramatically. In a second phase (28-64 weeks), a period of "fine-tuning" of the sensorimotor system, we saw slower, more gradual changes in the endpoint kinematics. The analysis of the underlying intersegmental joint torques revealed the following results: first, the range of muscular and motion-dependent torques (relative to body weight) did not change significantly with age. That is, early reaching was not confined by limitations in producing task-adequate levels of muscular torque. Second, improvements in the endpoint kinematics were not accomplished by minimizing amplitude of muscle and reactive torques. Third, the relative timing of muscular and motion-dependent torque peaks showed a systematic development toward an adult timing profile with increasing age. In conclusion, the development toward invariant characteristics of the hand trajectory is mirrored by concurrent changes in the control of joint forces. The acquisition of stable patterns of intersegmental coordination is not achieved by simply regulating force amplitude, but more so by modulating the correct timing of joint force production and by the system's use of reactive forces. Our findings support the view that development of reaching is a process of unsupervised learning with no external or innate teacher prescribing the desired kinematics or kinetics of the movement.

Adult↗
PubMed1988

Eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man.

The primary purpose of this investigation was to study the eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man using a recently developed combined isometric, concentric and eccentric controlled velocity dynamometer (the SPARK System). A secondary purpose was to compare the method error associated with maximal voluntary concentric and eccentric torque output over a range of testing velocities. 21 males (21-32 years) performed on two separate days maximal voluntary isometric, concentric and eccentric contractions of the quadriceps femoris at 4 isokinetic lever arm velocities of 0 degree.s-1 (isometric), 30 degrees.s-1, 120 degrees.s-1 and 270 degrees.s-1. Eccentric peak torque and angle-specific torques (measured every 10 degrees from 30 degrees to 70 degrees) did not significantly change from 0 degrees.s-1 to 270 degrees.s-1 (p greater than 0.005) with the exception of angle-specific 40 degrees torque, which significantly increased; p less than 0.05). The mean method error was significantly higher for the eccentric tests (10.6% +/- 1.6%) than for the concentric tests (8.1% +/- 1.7%) (p less than 0.05). The mean method error decreased slightly with increasing concentric velocity (p greater than 0.05), and increased slightly with increasing eccentric velocity (p greater than 0.05). A tension restricting neural mechanism, if active during maximal eccentric contractions, could possibly account for the large difference seen between the present eccentric torque-velocity results and the classic results obtained from isolated animal muscle.

Adult↗
PubMed1995

Effect of prior isometric muscle action on concentric torque output during plantar flexion.

The influence of different levels of prior isometric muscle action on the concentric torque output during plantar flexion was examined at two angular velocities (60 degrees.s-1 and 120 degrees.s-1) in ten healthy female subjects. The levels of the prior muscle actions were 25%, 50%, 75% and 100% of the maximal voluntary isometric contraction (MVIC). A KINetic-COMmunicator II dynamometer was used to measure torque output during plantar flexion within a range of motion of 78 degrees-120 degrees of the ankle joint. Simultaneous recordings of electromyograms (low-pass filtered and rectified) were obtained from the gastrocnemius medialis muscle and the soleus muscle. Torque-angle curves were made for the plantar flexions using different prior muscle actions. Up to 75% of MVIC, the torque output in the first part of the range of motion increased with the level of the prior isometric muscle action; at higher levels of MVIC the torque did not appear to increase any further. Later in the range of motion, after 24 degrees in the plantar flexion at a velocity of 60 degrees.s-1 and 31 degrees at 120 degrees.s-1, the prior muscle actions had no further influence. No increase was found in the electromyograms, with one exception, during the concentric movements when preceded by higher levels of MVIC. It would seem therefore that the increase in torque output early in the range of motion cannot be explained on the basis of differences in electrical muscle activation in this study.

Adult↗
PubMed1986

Effect of body posture and common hand tools on peak torque exertion capabilities.

An experimental investigation was conducted to investigate the effects of body posture and of different types of common non-powered hand tools on maximum volitional torque exertion capabilities of males and females. Thirty-six males and 14 females applied peak torque in 21 different body postures while using nine different hand tools. The data analysis indicated that, for both males and females, the magnitude of volitional torque is strongly influenced by the type of tool used and the posture assumed. Between the two, however, the effect of hand tool is more profound. The correlation between the tool type and volitional torque was of the order of 0.71. No other variable was as strongly correlated with volitional torque. Maximum volitional torque profiles, as a function of posture and tool type, are provided for males and females.

Journal Article↗
PubMed1992

A noninvasive technique for in vivo measurement of joint torques of biarticular muscles.

The objective of this work was to develop a noninvasive method to measure the joint torques produced by biarticular muscles at two joints simultaneously. During intramuscular stimulation of the cat medial gastrocnemius (MG) muscle, torques at the ankle and knee joints were calculated from forces measured in two dimensions at the end point of the cat paw under isometric conditions. The method was verified by the known anatomical properties of cat MG muscle and the tibialis anterior (TA) muscle. The MG muscle was shown to produce a significant flexion torque at the knee, besides an extension torque at the ankle. This was in agreement with its anatomical arrangement. The TA muscle produced primarily an ankle flexion torque. The small knee torque, due to measurement errors, yielded an estimate of measurement accuracy of 3.0 +/- 2.1% (n = 52). The coupling ratio of the MG muscle, defined as T(ankle)/T(knee), varied significantly with both knee and ankle angles. The profile of MG mechanical coupling agreed qualitatively with changes in limb configuration. The method can be used to measure recruitment properties of electrically stimulated biarticular muscles, and may potentially be used to study the biomechanics of biarticular coupling.

Animals↗
PubMed1996

Peak torque, average power, and hamstrings/quadriceps ratios in nondisabled adults and adults with mental retardation.

OBJECTIVE: To compare isokinetic hamstring and quadriceps peak torque (Nm), average power (watts), and corresponding hamstring/quadriceps (HQ) ratios (as percentages) of adult men with Down syndrome(DS), with mental retardation without Down syndrome (NDS), and nondisabled sedentary controls (SC). DESIGN: Repeated measures analysis of variance. SETTING: Subjects were tested at a university exercise science laboratory. SUBJECTS: Volunteer sample of 35 subjects: SC(n=13), DS(n=9), and NDS (n=13). INTERVENTION: Subjects performed isokinetic strength tests at 60 degrees /sec and 90 degrees/sec using gravity effected torque procedures. Subjects with DS and NDS performed the test on two separate days with best results selected for statistical comparisons. Sedentary controls performed the test once. MAIN OUTCOME MEASURES: Isokinetic hamstring and quadriceps peak torque and average power, and corresponding HQ ratios on a Cybex 340 isokinetic dynamometer. RESULTS: In all isokinetic parameters measured, sedentary controls demonstrated significantly higher scores than subjects with DS and NDS. There was no significant difference between subjects with DS and NDS, although mean peak torque and average power scores were greater in subjects with NDS. Finally, there were no significant differences in peak torque and average power HQ ratios across groups (p> .01), although group mean peak torque HQ ratios were greatest for sedentary controls (range=61% to 63%) and approximated accepted HQ ratio norms, and lowest for subjects with DS(range=40% to 46%). CONCLUSIONS: Individuals with mental retardation are in need of progressive resistance exercise programs to improve hamstring and quadriceps strength and normalize HQ strength and power ratios.

Adult↗
PubMed1996

Effects of infection control procedures on the accuracy of a new mechanical torque wrench system for implant restorations.

Loosening of screw components for implant restorations has been attributed to insufficient tightening. The degree of tightening may be increased and more closely controlled by use of calibrated mechanical torque wrenches. The DynaTorq wrench system has been introduced to the market and consists of three individual wrenches with torque values of 10, 20, and 30 newton-centimeters (Ncm). This study evaluated the accuracy of the DynaTorq wrench system before and after steam autoclave and Chemiclave sterilization treatment. Before sterilization treatments, the wrenches demonstrated high accuracy and precision. Autoclaving resulted in increases in torque values for the 10 Ncm torque wrench compared with baseline measurements. Except for the effect of autoclaving on the 10 Ncm torque wrench, sterilization procedures did not adversely affect the accuracy of the DynaTorq torque wrench system.

Bone Screws↗
PubMed1997

A three-dimensional multivariate model of passive human joint torques and articular boundaries.

OBJECTIVE: The development of a novel three-dimensional mathematical model of passive human joint torques that is of practical use, takes into account the complex non-linear interactions that exist between the moments generated by the various passive structures spanning the joint in question, and is applicable to all types of articular joints. DESIGN: Mathematical model validated by practical implementation. BACKGROUND: Previous models of passive human joint torques were predominantly one-dimensional and did not take into account the interactions of the various structural components. METHODS: Mathematical modelling is used in conjunction with repeated passive torque experiments on the right elbow joint of a healthy 29-year-old male. On the basis of the experimentally observed torque-angle data, the full set of articular model parameters characterizing the two-dimensional passive elastic torque function of the subject's right elbow joint could be determined. RESULTS: In addition to the passive elastic torque functions, the two-dimensional contour of the elbow joint's articular boundaries was also obtained. CONCLUSIONS: The present model is especially useful for assessing certain pathological conditions in any body joint investigated, and in addition is best suited for the inclusion in large-scale dynamic simulation models of the human neuromusculoskeletal system.

Journal Article↗
PubMed1993

Torque and pullout analysis of six currently available self-tapping and "emergency" screws.

Insertional torque (IT), stripping torque (ST), and uniaxial pullout tests were performed to evaluate the effectiveness of six screw systems (Wurzburg, Techmedica, Synthes, Timesh, Steinhouser, Luhr) in thin porcine rib. The Timesh 2.2-mm self-tapping screw produced the largest insertional and stripping torque of all systems tested as well as the largest difference between the insertional and stripping torque. The Timesh emergency screw also had the largest insertional and stripping torque as well as the largest difference between the insertional and stripping torque. In pullout tests, the Timesh screw was found to be the most retentive. The overall data indicated that the ideal self-tapping screw should have the largest difference possible between drill size and external diameter, a channel, and at least three self-tapping threads for maximum retention.

Animals↗
PubMed1993

Moments with the edgewise appliance: incisor torque control.

Traditional edgewise orthodontic mechanics are significantly limited in their ability to provide incisor torque control because of the limitations of bracket-to-bracket mechanics and the poorly defined reciprocal actions inherently produced. Attempts to address this issue clinically have been largely empirical. The science of mechanics dictates that all incisor torque control mechanisms must act through one of two basic principles: the moment of a couple or the moment of a force. The torquing arch is a modification of the traditional edgewise system and employs the moment of a couple to achieve incisor torque control and precise definition of reciprocal effects. The torquing arch force system includes a large moment to rotate incisors in a crown facial/root lingual direction, and concurrent equilibrium forces to extrude incisors and intrude molars. Alternatively, the base arch uses the moment of a force to also rotate incisors in a crown facial/root lingual direction. The base arch, however, includes a large moment to rotate molars in a crown distal/root mesial direction, and concurrent equilibrium forces to intrude incisors and extrude molars. Depending on how they are employed, torquing arches and base arches may also rotate molars in a faciolingual direction, enhance or diminish posterior anchorage, and increase or conserve arch perimeter. Contemporary quality orthodontic care requires an awareness and control of all of the forces created by orthodontic appliances.

Biomechanical Phenomena↗
PubMed1998

Brain torque and sex differences in schizophrenia.

The opposing asymmetry of the frontoparietal brain regions has been referred to as 'torque' and may be used as an index of speed of neurodevelopment. It has been recently suggested that torque is minimized in male schizophrenia, reflecting anomalous neurodevelopment. This study examined volumetric and linear torque in a group of 20 schizophrenia patients and 20 healthy individuals; all were right-handed and under the age of 46 years. None of the main or interaction effects on torque were statistically significant, although the sex difference in torque among schizophrenia patients (male larger than female) was more than seven times that in healthy subjects. Torque was significantly associated with years of education and age of illness onset (schizophrenia). These findings support the hypothesis that slowed neurodevelopment may be associated with male schizophrenia and may contribute to earlier age of onset and fewer years of education.

Adult↗
PubMed1981

Relationship between muscle length, muscle activity, and torque of the hamstring muscles.

The relationship between muscle length, integrated electromyographic activity, and torque of the biceps femoris muscle was investigated while the line of action of the muscle at the knee was held constant. Muscle length was changed by varying the hip joint angle. Sixteen subjects produced 1) maximal isometric contractions, 2) contractions with constant submaximal torque, and 3) contractions with constant submaximal muscle activity at four different hip positions (0, 45, 90, and 135 degrees of flexion). Simultaneous readings of hip angle, muscle torque, and raw and integrated electromyographic activity revealed that changes in muscle length influence production of integrated muscle activity and development of torque differently. During maximal isometric contraction, an increase in integrated electromyographic activity and a decrease in torque occurred as the muscle was shortened; the opposite occurred when the muscle was at lengthened positions. A greater difference in this relationship was noted when the respective electromyographic activity and torque were held constant. Some clinical questions were raised.

Adult↗
PubMed1985

Effect of quadriceps femoris muscle stretch on knee extension torque.

Peak and angle specific knee extension torques produced after a quadriceps femoris muscle stretch and after a 15-second rest were compared to determine the effect of stretch on knee extension torque. Twenty healthy subjects performed eight maximum voluntary knee extensions at 90 degrees/sec under each condition. Although peak torque and torques at 15, 30, 45, and 60 degrees from full extension were measured, knee extension torque was only significantly greater (p less than .02) at 60 degrees of knee flexion after quadriceps femoris muscle stretch. The absolute difference, which was only a mean 4.9 N X m (3.6 ft-lb), was not substantial. When quadriceps femoris muscle stretch is a consequence of passive knee flexion at 90 degrees/sec, knee extension torque is apparently facilitated only during the initial part of the knee extension movement. Therefore, in healthy patients, a muscle stretch, such as used in this study, is probably of little therapeutic value.

Adult↗
PubMed1996

Force and torque vary between laryngoscopists and laryngoscope blades.

Several studies have examined the effects of patient characteristics on force of laryngoscopy, but little attention has been paid to the importance of technique and equipment. This study investigated whether force, torque, head extension, and view varied significantly between laryngoscopists and compared force and torque using Macintosh 3 and Miller 2 blades. The study population consisted of ASA grade I and II patients requiring general anesthesia and endotracheal intubation for elective surgery. Force, torque, head extension, and laryngeal view were highly reproducible when laryngoscopy was repeated by the same individual, Force and torque showed great variation between laryngoscopies performed by different anesthetists, For example, peak force varied over a range of 56 newtons among patients, but could also vary as much as 30 newtons between different anesthetists repeating laryngoscopy in the same patient. Force and head extension were 30% less with Miller laryngoscope compared to the Macintosh. Thus, laryngoscopic force and torque depend on technique and equipment. Further studies of force and torque may lead to improved techniques. The force-measuring laryngoscope could be a useful tool in teaching laryngoscopy.

Adult↗
PubMed1986

Mechanical response of a lumbar motion segment in axial torque alone and combined with compression.

In the current study, a nonlinear three-dimensional finite element program has been used to analyze the response of a lumbar L2-3 motion segment subjected to axial torque alone and combined with compression. The analysis accounts both for material and geometric nonlinearities and treats the facet articulation as a general moving-contact problem. The disc nucleus has been considered as an incompressible inviscid fluid and the annulus as a composite of collagenous fibers embedded in a matrix of ground substance. The spinal ligaments have been modeled as a collection of nonlinear axial elements. Effects of loss of intradiscal pressure and removal of the facets on the joint response have been analyzed as well. Torsion is primarily resisted by the articular facets that are in contact and the disc annulus. The ligaments play an insignificant role in this respect. For the intact segment, with an increase in torque, the axis of rotation shifts posteriorly in the disc so that under maximum torque it is located posterior to the disc itself. Loss of disc pressure increases this posterior shift whereas removal of the facets decreases it. Torque, by itself, cannot cause the failure of disc fibers, but can enhance the vulnerability of those fibers located at the posterolateral and posterior locations when the torque acts in combination with other types of loading, such as flexion. The most vulnerable element of the segment in torque is the posterior bony structure.

Biomechanical Phenomena↗
PubMed2000

Ordering dynamics of heisenberg spins with torque: crossover, spin waves, and defects

We study the effect of a torque induced by the local molecular field on the phase ordering dynamics of the Heisenberg model when the total magnetization is conserved. The torque drives the zero-temperature ordering dynamics to a new fixed point, characterized by exponents z=2 and lambda approximately 5. This "torque-driven" fixed point is approached at times such that t>>g(2), where g is the strength of the torque. All physical quantities, like the domain size L(t) and the equal and unequal time correlation functions, obey a crossover scaling form over the entire range of g. An attempt to understand this crossover behavior from the approximate Gaussian closure scheme fails completely, implying that the dynamics at late times cannot be understood from the dynamics of defects alone. We provide convincing arguments that the spin configurations can be decomposed in terms of defects and spin waves which interact with each other even at late times. In the absence of the torque term, the spin waves decay faster, but even so we find that the Gaussian closure scheme is inconsistent. In the latter case the inconsistency may be remedied by including corrections to a simple Gaussian distribution. For completeness we include a discussion of the ordering dynamics at T(c), where the torque is shown to be relevant, with exponents z=4-varepsilon/2 and lambda=d (where varepsilon=6-d). We show to all orders in perturbation theory that lambda=d as a consequence of the conservation law.

Journal Article↗
PubMed2006

A torque estimator for a traveling wave ultrasonic motor--application to an active claw.

Depending on its electrical-to-mechanical energy conversion process, the torque on a traveling wave ultrasonic motor (TWUM)'s shaft is not directly proportional to a measurable electrical variable, such as current or voltage. But it is derived from a complicated process at the stator/rotor interface. The load torque is thus quite unknown, and this can be a disadvantage in applications in which a torque limitation is required or a torque measurement is needed. The aim of this article is to come up with a straightforward torque estimator on a TWUM. For that purpose, the motor is modeled; this modeling leads to different estimator strategies. More specifically, we chose a strategy for which a speed sensor is useless, relying only on the stator's resonant behavior. The parameters of the motor needed for the estimator are measured afterward, and some nonlinearities are identified and taken into account. Several experimental trials then are carried out to check the performance of the estimator. A claw actuated by a TWUM is presented because this is a typical application in which the knowledge of the torque helps guarantee the safety of the device.

Journal Article↗
PubMed1993

The axial torque of the lumbar back muscles: torsion strength of the back muscles.

The maximal, axial torque generated by the lumbar back muscles was determined by modelling the action of the 49 fascicles of longissimus thoracis, iliocostalis lumborum and the lumbar multifidus on radiographs of the lumbar spine of nine young male subjects in upright standing and in full lumbar flexion. No single fascicle exerted more than 2 Nm of axial torque in the upright posture, and the collective torque of all muscles acting a segment did not exceed 5 Nm. All torques were considerably less in full flexion. The lumbar back muscles exert very little torque on the lumbar spine, and contribute only about 5% of the total torque involved in trunk rotation. None of the lumbar back muscles can be considered a rotator. The oblique abdominal muscles are the principal rotators of the trunk. Preventative and rehabilitation programmes concerned with torsion injuries should focus on the abdominal muscles rather than the back muscles for stability in axial rotation.

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