Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Torque”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources
PubMed2003

Influence of torque control motors and the operator's proficiency on ProTaper failures.

OBJECTIVE: The purpose of this study was to evaluate the influence of 2 electric torque control motors and operator experience with a specific nickel-titanium rotary instrumentation technique on the incidence of deformation and separation of instruments. STUDY DESIGN: ProTaper (PT) nickel-titanium rotary instruments were used at 300 rpm. In the first part of the study, electric high torque control (group 1) and low torque control (group 2) motors were compared. In the second part of the study, 3 operators with varying experience (groups 3, 4, and 5) were also compared. Twenty sets of PT instruments and 100 canals of extracted human molars were used in each group. Each set of PT instruments was used in up to 5 canals and sterilized before each case. For irrigation, 2.5% NaOCl was used. The number of deformed and separated instruments among the groups (within each part of the study) was statistically analyzed for significance with pair-wise comparisons by using the Fisher exact test (alpha =.05). RESULTS: In part 1, instrument deformation and separation did not occur in groups 1 and 2. In part 2, 25 and 12 instruments were deformed and separated, respectively, with the least experienced operator. Instrument deformation and separation did not occur with the most experienced operator. The Fisher exact test revealed a significant difference between groups 3 and 4 with respect to instrument deformation (P =.0296). In addition, the Fisher exact test revealed that the incidence of instrument deformation was statistically different between groups 3 and 5 (P <.0001) and groups 4 and 5 (P =.0018). The incidence of instrument separation was significantly higher in group 5 than in groups 3 and 4 (P =.001). CONCLUSIONS: Preclinical training in the use of the PT technique at 300 rpm is crucial to prevent instrument separation and reduce the incidence of instrument deformation. The use of an electric high torque control motor is safe with the experienced operator.

Clinical Competence↗
PubMed2001

Differential effects of exhaustive cycle ergometry on concentric and eccentric torque production.

The purpose of this study was to investigate the potential differences in peak isokinetic concentric end eccentric torque following low- and high-intensity cycle exercise fatigue protocols. Ten healthy, recreationally-active men were tested in a balanced, randomized testing sequence for peak eccentric and concentric isokinetic torque (60 degrees/sec) immediately before and after three experimental conditions each separated by 48 hours: 1) a bout of high intensity cycling consisting of a maximal 90-second sprint; 2) a bout of low-intensity cycling at 60 rpm equated for total work with the high-intensity protocol: and 3) no exercise (control bout). Blood was drawn from an antecubital vein and plasma lactate concentrations were determined immediately before and after each experimental bout. Post-exercise plasma lactate concentrations were 15.1 +/- 2.5 and 4.7 +/- 1.9 mmol l(-1), respectively, following the high- and low-intensity protocols. The high intensity exercise bout resulted in the only post-exercise decrease in concentric and eccentric isokinetic peak torque. The percent decline in maximal force production was significantly (P< 0.05) greater for concentric muscle actions compared to eccentric (29 vs 15%, respectively). In conclusion, a 90-second maximal cycling sprint results in a significant decline in maximal torque of both concentric and eccentric muscle actions with the greatest magnitude observed during concentric muscle actions.

Adult↗
PubMed2003

Three-dimensional relationship between the critical contact angle and the torque angle.

The purpose of this study was to analyze the relationship between the critical contact angle and the torque angle in an orthodontic bracket and archwire assembly in 3 dimensions. Three-dimensional mathematical models were created with geometric bracket-archwire parameters that included 2 slot sizes, 3 bracket widths, and 3 to 4 wire sizes. From this, 3-dimensional mathematical equations (3DMEs) for the critical contact angle and the maximum torque that result in critical contact angles of 0 were derived and calculated. To evaluate the effects of archwire-bracket parameters on critical contact angles, analysis of variance (ANOVA) was performed at the significance level of P < or = .05. For all bracket-archwire combinations, the critical contact angle decreased as bracket width, torque angle, and wire size increased. Therefore, all bracket-archwire parameters except slot height had an effect on the critical contact angle. Results of the critical contact angle produced from our 3DMEs were the same as those produced by 3D computer-aided design (SolidWorks Corp, Concord, Mass), thus confirming the validity of our derived equations. In addition, the effect of a beveled edge was investigated in some archwires. Furthermore, torsional play angles were calculated and found to be similar to those in previous reports. The results of this study provide theoretic and experimental bases for clinical orthodontic practice and indicate that torque angles should be included in the evaluation of the critical contact angle.

Analysis of Variance↗
PubMed2006

On structural transitions, thermodynamic equilibrium, and the phase diagram of DNA and RNA duplexes under torque and tension.

A precise understanding of the flexibility of double stranded nucleic acids and the nature of their deformed conformations induced by external forces is important for a wide range of biological processes including transcriptional regulation, supercoil and catenane removal, and site-specific recombination. We present, at atomic resolution, a simulation of the dynamics involved in the transitions from B-DNA and A-RNA to Pauling (P) forms and to denatured states driven by application of external torque and tension. We then calculate the free energy profile along a B- to P-transition coordinate and from it, compute a reversible pathway, i.e., an isotherm of tension and torque pairs required to maintain P-DNA in equilibrium. The reversible isotherm maps correctly onto a phase diagram derived from single molecule experiments, and yields values of elongation, twist, and twist-stretch coupling in agreement with measured values. We also show that configurational entropy compensates significantly for the large electrostatic energy increase due to closer-packed P backbones. A similar set of simulations applied to RNA are used to predict a novel structure, P-RNA, with its associated free energy, equilibrium tension, torque and structural parameters, and to assign the location, on the phase-diagram, of a putative force-torque-dependent RNA "triple point."

DNA↗
PubMed2004

The measurement and lateral comparison of the peak torque caused by the fast abduction exercise of stretched upper extremities in normal and trained adults.

The maximal torque effect of the middle portion of action of the deltoid muscle while raising an out-stretched upper limb was measured from left and right sides of normal untrained young adults and of the same age elite athletes. Seventeen strongly right-handed untrained males and females and 10 elite tennis players were tested. All participants were required to raise (abduct) one arm (right and then left, or vice versa) as fast as possible with maximal amplitude while standing on an electronic platform scale which measured to 0.001 kg. An assumed force at the centre of mass of the entire upper limb was considered. The force consisted of two components, namely static weight force of the upper limb and a dynamic force component created by upward acceleration of the limb. Using regression equations and scaling methods the static weight of the upper limb was derived and combined with the dynamic component to produce the total force, applied to the centre of mass of the limb. The total force multiplied by the distance from the centre of mass to point of rotation of the limb equated to the torque produced by deltoid muscle. Using video system analyses the angle of abduction was measured for each individual exercise. The additional anthropometrical tests identified proportionality and body mass indices for each participant. There was no significant difference in dynamic force and torque between left and right limb from the three groups. Sportsmen demonstrated greater lateral abduction when performing the exercise from the dominant side of the body. Sportsmen also demonstrated greater range of abduction, bigger dynamic force and torque on both sides in comparison to untrained adults. Remarkably, the absolute and relative length of arms of athletes were shorter in comparison to untrained males, but the radius of gyration from the stretched upper limb (from its centre of gravity to the shoulder joint) were greater. This phenomenon may be due to distal shifting of the gravity center of the entire upper limb in elite athletes, perhaps, because greater investment of the distal portion of the limb with skeletal muscle tissue.

Adult↗
PubMed2006

The relationship between shoulder torques and the perception of muscular effort in loaded reaches.

The objective of this study was to define the quantitative relationship between external dynamic shoulder torques and calibrated perceived muscular effort levels for load delivery tasks, for application in job analyses. Subjects performed a series of loaded reaches and, following each exertion, rated their perceived shoulder muscular effort. Motion and task physical requirements data were processed with a biomechanical upper extremity model to calculate external dynamic shoulder torques. Calculated torque values were then statistically compared to reported calibrated perceived muscular effort scores. Individual subject torque profiles were significantly positively correlated with perceived effort scores (r2 = 0.45-0.77), with good population agreement (r2 = 0.50). The accuracy of the general regression model improved (r2 = 0.72) with inclusion of factors specific to task geometry and individual subjects. This suggests two major conclusions: 1) that the perception of muscular shoulder effort integrates several factors and this interplay should be considered when evaluating tasks for their impact on the shoulder region; 2) the torque/perception relationship may be usefully leveraged in job design and analysis.

Biomechanical Phenomena↗
PubMed2000

Reliability of torque measurements during passive isokinetic knee movements in healthy subjects.

In the literature, few data are available about the reliability of torque measured during passive isokinetic knee movements. This study investigated the consistency of torque measurements during passive knee movements at 60, 180 and 300 degrees/second in 30 healthy subjects. Intraclass correlation values ranged between 0.78 and 0.92 when the results of two consecutive tests were compared. When retests were performed after repositioning the subjects, intraclass correlation values ranged between 0.43 and 0.87. These findings indicate the necessity for meticulous standardization of the test situation. Series of 10 consecutive movements, specifically repetitions of knee flexion at 180 and 300 degrees/second, indicated that torque measurements during the first two movements were less stable than those following. A concurrent change in electromyographic activity in the rectus femoris muscle suggested that these torque variations resulted from habituation of the stretch reflex.

Biomechanical Phenomena↗
PubMed2001

Lower extremity isometric joint torque in children with juvenile chronic arthritis.

OBJECTIVE: To determine the intratester reliability of joint torque testing with a hand-held dynamometer (HHD) during contractions of four major lower extremity muscles in children with juvenile chronic arthritis (JCA) and to compare results for children with JCA to results for children without disability. METHODS: Eleven children with JCA and 14 children with normal musculoskeletal function were tested with a HHD using isometric muscle contractions of the right quadriceps, hamstrings, tibialis anterior and triceps surae. RESULTS: Intratester reliability values exceeded the 0.92 level, regardless of the number of trials, for all motions tested. Statistically lower joint torque values were found in a subgroup of children with JCA for contractions of the tibialis anterior (p=0.003) and triceps surae (p=0.05) muscles. CONCLUSIONS: HHD offers a reliable means of testing the joint torque generated with contraction of these lower extremity muscles in children with JCA. Findings in children with JCA compared to children without disability agree with previous reports concerning quadriceps muscle function, but also point to concerns for muscles associated with generating ankle joint torque.

Adolescent↗
PubMed2002

Changes in upper limb joint torque patterns and EMG signals with fatigue following a stroke.

PURPOSE: Little is known concerning changes in neuromuscular fatigue following a stroke. The purpose of this study was to evaluate the effect of a stroke on fatigue-related changes in upper limb torque patterns and electromyographic signals. METHOD: The paretic and non-paretic upper limb of 10 adults (51-79 years) who had a stroke (time since stroke: 3-75 months) were compared. Subjects had to perform a fatigue task consisting of a sustained maximal isometric contraction in elbow flexion until torque decreased to below 50% of initial. The main variables of interest assessed before, during and after fatigue were: (1) the torque in elbow flexion, as well as associated forces/torques at the shoulder and forearm; (2) the level of voluntary activation; (3) the amplitude (RMS); and (4) frequency content (median frequency) of electromyographic signals. RESULTS: Compared to the non-paretic side, the paretic side showed a lower level of voluntary activation and higher relative torque levels at the forearm and shoulder which could both be exaggerated with fatigue, and a lesser fatigue-related decrease in median frequency. CONCLUSIONS: Thus, greater fatigue-related changes in features of the central command (ability to maximally activate a muscle and ability to isolate effort to a muscle group) were observed for the paretic compared with the non-paretic side. This could be a confounding factor when assessing changes in peripheral measures of fatigue following a stroke using voluntary contractions.

Aged↗
PubMed2006

Joint torque and mechanical energy flow in the support legs of skilled race walkers.

This study analyzed the joint torque and the mechanical energy flow in the support legs of skilled male race walkers. Twelve race walkers were videotaped using a high-speed camera at a frame rate of 250 Hz set perpendicular to the sagittal plane of motion; their ground reaction forces were measured with two force platforms. A two-dimensional, 14-segment, linked model was used to calculate the kinetics of the support leg joints. In the initial part of the support phase, the mechanical energy flowed into the thigh and shank by the torque of the large hip extensors and knee flexors. In the middle part, the mechanical energy generated by the torque of the large plantar flexors flowed to the foot and from the foot to the shank by the ankle joint force. The mechanical energy flow by the forward joint force of the support hip was significantly related to the walking speed in the final part of the support phase. Our findings suggest that race walkers in the final part of the support phase should exert the torque of the knee extensors and hip flexors to transfer the mechanical energy more effectively to the support thigh and shank.

Adolescent↗
PubMedDate not supplied

Maximal acceptable torques of highly repetitive screw driving, ulnar deviation, and handgrip tasks for 7-hour workdays.

This study represents a continuation of a series of psychophysical studies on repetitive motions of the wrist and hand conducted at the Liberty Mutual Research Center for Safety and Health. The purpose of the study was to quantify maximum acceptable torques of six motions performed on separate days but within the context of the same experiment. The six motions were screw-driving clockwise with a 31-mm handle, a 40-mm handle, and a 39-mm yoke handle; screw-driving counterclockwise with a 31-mm handle; ulnar deviation with a power grip (similar to knife cutting), and a handgrip task (similar to a pliers task). A psychophysical methodology was used in which the subject adjusted the resistance on the handle, and the experimenter manipulated or controlled all other variables. Ten subjects performed the six tasks at repetition rates of 15, 20, and 25 motions per minute. Subjects performed the tasks for 7 hours per day, 5 days per week, for 4 weeks. The subjects were instructed to work as if they were on an incentive basis, getting paid for the amount of work they performed. Symptoms were recorded by the subjects during the last 5 min of each hour. The results revealed that mean maximum acceptable torques ranged from 0.33 to 0.65 Nm for screw driving, 1.08 to 1.13 Nm for ulnar deviation, and 4.80 to 4.85 Nm for the handgrip task. These values represent 14 to 24% (median of 17%) of maximum isometric torque depending on the frequency and motion. A table of maximum acceptable torques and forces of the six motions is presented for application in the field.

Adult↗
PubMed2002

Movement-provoked muscle torque and EMG activity in longstanding motor complete spinal cord injured individuals.

Muscle resistance was evaluated by measurement of movement-provoked torque performed during simultaneous thigh muscle EMG recordings in individuals with a motor complete spinal cord injury (SCI). Fifteen men with a motor complete (ASIA grade A or B) cervical injury participated in the study. The activity started at an average of 0.11 seconds after the start of the provoking movement as evidenced by EMG recordings. However, no activity at all was found before the end of the movement provocation for 0.3 seconds in >60% of the test situations, whereas muscle torque was recorded in all cases. Significantly higher resistive muscle torque (p = 0.049) was provoked during extension movement compared with that of flexion. On the contrary, the maximum muscle activity was significantly higher (p = 0.009) during flexion movement compared with that during extension, with no differences between muscle groups. The resistive muscle torque seems to measure the passive viscoelastic component rather then the active spastic component of the movement-provoked muscle resistance in our group of motor complete SCI individuals.

Adult↗
PubMed2004

Torque properties of a rat oesophagus for physiological and diabetic conditions.

In this paper the torque of an oesophagus is studied for physiological and diabetic conditions. Since the function of the oesophagus is mainly mechanical, this work is focused on providing quantitative measurement of the passive biomechanical properties of the oesophagus torque. The oesophagus was treated as a membrane when calculating the stress and strain. The torque versus twist-angle relation was approximated to be linear at a specified pressure and longitudinal stretch ratio. Thus, the shear modulus can be computed by the torque, twist angle and polar moment of inertia in this state. The shear modulus varies greatly with the changing inflation pressure and longitudinal stretch ratio. When the longitudinal stretch ratio or transmural pressure is constant, the shear modulus is increased after 28 days of diabetes.

Animals↗
PubMed1997

Are patellofemoral pain and quadriceps femoris muscle torque associated with locomotor function?

BACKGROUND AND PURPOSE: The purpose of this investigation was to determine the influence of pain and muscle weakness on gait variables in subjects with patellofemoral pain (PFP). SUBJECTS: Nineteen female subjects with a diagnosis of PFP and 19 female subjects without PFP participated in the study. METHODS: Subjects underwent gait analysis (stride characteristics and joint motion) during level walking, ascending and descending stairs, and ascending and descending ramps, in addition to isometric torque testing of the knee extensors of the involved limb. Pain and functional status also were assessed. RESULTS: Compared with the comparison group, the primary gait compensation in the PFP group was a reduced walking speed, which was a function of both a reduced stride length and cadence. Knee extensor torque was the only predictor of gait function, with increased torque correlating with improved stride characteristics. In addition, PFP was not associated with locomotor function. CONCLUSION AND DISCUSSION: These findings suggest that functional ability in persons with PFP is associated with increased quadriceps femoris muscle torque. Future research is needed to determine whether function improves with quadriceps femoris muscle strengthening.

Adolescent↗
PubMed2001

Effects of eccentric exercise on trunk extensor torque and lumbar paraspinal EMG.

PURPOSE: Little is known about the effects of eccentric contractions on the function of the lumbar paraspinal muscles. The purpose of this study was to determine the effects of a single bout of eccentric contractions using the trunk extensor muscles on torque and lumbar paraspinal electromyographic (EMG) parameters. METHODS: Twenty healthy men between the ages of 18 and 49 yr participated in the study. Subjects performed a single bout of 50 maximal voluntary concentric (N = 10) or eccentric (N = 10) trunk extension movements while surface EMG signals were recorded from the multifidus and iliocostalis lumborum muscles. A series of isometric contractions were performed both before the exercise protocol and at five additional time points over the following 7 d. RESULTS: During the exercise protocol, peak torque decreased 30% and 24% in the eccentric and concentric groups, respectively, whereas no change occurred in EMG root-mean-square (RMS). There were no group differences in peak torque generation at any of the postexercise protocol time points. Compared with the preexercise protocol values, multifidus EMG was elevated 27% immediately post and 15 min post in the eccentric group. Similarly, compared with the concentric group, multifidus EMG in the eccentric group was increased 34%, 40%, and 25% immediately post, 15 min post, and 1 d after the exercise protocol, respectively. CONCLUSION: Eccentric contractions using the trunk extensor muscles result in higher levels of multifidus EMG activity to produce a given level of torque. This reduction in neuromuscular efficiency persisted for one day with recovery to baseline levels by the third day. Contrary to studies using other muscle groups, no sustained alteration in muscle function was observed.

Adolescent↗
PubMed2003

The effects of external torque on polyethylene tibial insert damage patterns.

The forces and torques that occur during walking gait, particularly during toe-off, promote articulation in the posteromedial quadrant of tibial inserts. Retrieved components of failed knee arthroplasties show ultrahigh molecular weight polyethylene damage patterns in this region. Component-designed constraint, compromised polymer, and surgical factors account for these observations. The current authors compare the contact stresses that developed on four implant designs during toe-off for optimally aligned and externally torqued components using the finite element method. Under 16 N-m of torque, the four designs studied varied regarding their centers of rotation and magnitude of external rotation, which are related directly to their specific articulating surface geometry. Designs with conforming condylar geometry had greater rotational constraint and therefore, less external rotation. These conforming designs offer the benefits of lower stresses and tend to limit contact near the edge of the plateau. However, because of their increased rotational constraint, torque is transmitted more readily to the implant-bone interface, increasing the potential for implant loosening. The data presented serve as an indicator of the potential for polyethylene tibial component surface damage and define the role that implant geometry plays in resisting external rotation.

Finite Element Analysis↗
PubMed2004

Biomechanical evaluation of relationship of screw pullout strength, insertional torque, and bone mineral density in the cervical spine.

BACKGROUND: Understanding of implant failure mechanisms is important in the successful utilization of anterior cervical plates. Many variables influence screw purchase, including the quality of the bone. The purpose of this study was to assess the relationship of screw pullout and screw insertional torque across a wide range of bone mineral densities (BMDs). METHODS: A total of 54 cervical vertebrae in 12 cervical spines were evaluated for BMD using dual-energy x-ray absorptiometry scanning. Actual and perceived peak torques of 3.5-mm anterior cervical screws were determined at each level followed by screw pullout strength testing. RESULTS: A high correlation was observed between screw pullout strength and BMD. However, there was a low correlation of peak insertional torque to pullout strength. CONCLUSION: These findings suggest the quality of the bone is more instrumental in the success or failure of anterior cervical screws than is the insertional torque with which the screws are placed.

Biomechanical Phenomena↗
PubMed2006

An in vitro analysis of implant screw torque loss with external hex and internal connection implant systems.

PURPOSE: The purpose of this study was to examine, in a controlled environment, effects of connection design upon screw stability. Implant fixtures have 2 types of connections to the abutment: internal connection and external hex. Four implant systems were tested: Bio-Lok (external hex; Bio-Lok International, Inc., Deerfield Beach, FL); Zimmer (internal connection; Zimmer Dental, Carlsbad, CA); Nobel Biocare (external hex; Nobel Biocare USA, Inc., Yorba Linda, CA); and Astra Tech (internal connection; Astra Tech Inc., Waltham, MA). MATERIALS AND METHODS: Ten samples of each system, including base, implant, abutment, and molar crown, were loaded to 200 N for 1 x 10(6) cycles. Screws were tightened to manufacturers' recommendations,and torque audits done at 2.5 x 10(5), 5 x 10(5), 7.5 x 10(5), and 1 x 10(6) cycles. RESULTS: The Bio-Lok samples lost an average of 10% of the original torque values, the Astra Tech group lost almost all of the torque and loosened, while the Zimmer and Nobel Biocare samples lost an average of 50% of the torque but did not loosen (P <or= 0.05). CONCLUSIONS: It may be concluded from this study that although internal connections are clinically favored, this study did not show any advantage relative to screw loosening. However, screw design may be a significant factor in loosening of the joint.

Crowns↗