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At least 595 records · Page 33Linked to original sources
PubMed2006

Removal torque and physico-chemical characteristics of dental implants etched with hydrofluoric and nitric acid. An experimental study in Beagle dogs.

OBJECTIVE: To study the composition, surface characteristics and response to removal torque of an implant surface subjected to hydrofluoric acid etching and posterior passivating with hydrofluoric and nitric acid. STUDY DESIGN: Twelve implants were initially selected and their physico-chemical characteristics were evaluated by means of energy-dispersive X-rays (EDS), scanning electron microscopy (SEM) and photoelectron spectroscopy (XPS). In addition, 24 implants - 12 measuring 8 mm and 12 measuring 10 mm in length - were implanted in 6 Beagle dogs. Twelve implants were removed after a recovery period of 6 weeks, followed by removal of the remaining 12 implants after 12 weeks, using a torque calibrator (Gauge Tonichi model BGT150CN-S) with a force registry range of 0-150 Ncm. RESULTS: EDS analysis of the surface chemical composition only revealed the presence of titanium in the etched surfaces. In the same way as with the surfaces of other dental implants, XPS analysis revealed traces of other elements present in the surface, fundamentally carbon. Following dual acid etching, the surface showed the roughness resulting from acid action, with a morphology that proved to be quite homogeneous. The roughness values obtained exceeded 1 mm. The mean removal torque values after 6 weeks were 79.7 Ncm for the 8 mm implants and 115 Ncm for the 10 mm implants. After 12 weeks, these values increased to 101.2 Ncm and 139.7 Ncm, respectively. CONCLUSIONS: Hydrofluoric and nitric acid etching affords optimum surface characteristics comparable to those of other surfaces. The recorded removal torque values raise the possibility of human clinical application for early or immediate loading procedures.

Acid Etching, Dental↗
PubMed1996

An evaluation of torque (moment) on implant/prosthesis with staggered buccal and lingual offset.

The supposition that staggered buccal and lingual implant offset is biomechanically advantageous was examined mathematically. The method of evaluation utilized a standard hypothetical geometric configuration from which implants could be staggered buccally and/or lingually in both arches. Torque (moment) values were calculated at the gold screw, abutment screw, and 3.5 mm apical to the head of the implant. Comparisons were made in percentages of change from the hypothetical standard to the buccal and/or lingual implant offset. In the maxillary arch, buccal offset decreased the torque (moment) while lingual offset increased it. If more lingually offset implants were present in the maxillary restoration, the total torque would be greater than if they were all in a straight line. Staggered buccolingual implant alignment often requires abutment reangulation. The resultant line of force produced by occlusal anatomy usually results in buccal inclination in the maxillary arch and lingual inclination in the mandibular arch. As a result, mandibular implant/prostheses are greatly favored over similar maxillary configurations because the mandibular resultant line of force usually passes lingually, closer to the components and supporting bone and considerably less torque is produced. Therefore, the concept of staggered offset for multiple implant-supported prostheses can be utilized on the mandible but is not recommended for the maxilla where maximum uniform buccal implant orientation is advised.

Algorithms↗
PubMed1986

Electromyographic studies of the lumbar trunk musculature during the development of axial torques.

The myoelectric activity of selected trunk muscles at the L3 level was studied during the development of a controlled isometric axial torque. Muscle activity was recorded with surface electrodes bilaterally over the erector spinae muscles, the rectus abdominus, the obliques externus, and the obliques internus. Subjects applied graded isometric axial torque efforts with the addition of a Valsalva. The largest myoelectric activities were recorded over the obliques externus and internus. The side of the muscle developing the torque did show the greatest myoelectric activity, but considerable antagonistic activity was also present. Neither the rectus abdominus nor the internal oblique muscles showed any difference from side to side. The calculated forces in the rectus abdominus and the erectores spinae were high, suggesting that a considerable amount of the muscle contraction was used to control the posture. A Valsalva did not decrease myoelectric activity, but did increase the torque developed.

Abdominal Muscles↗
PubMed1995

Characterization of wet powder masses with a mixer torque rheometer. 3. Nonlinear effects of shaft speed and sample weight.

We used mixer torque rheometry to examine the effects of shaft speed and sample weight on the rheological behavior of a model wet mass consisting of microcrystalline cellulose and water. Both variables contribute differently to the measured parameters of mean torque and torque range (amplitude). For small weights, the effect of shaft speed is small, but for large weights, shaft speed has a greater effect. For large sample weights, the effect of shaft speed on measured mean torque can be modeled by the Herschel-Buckley model originally developed for concentrated dispersions, enabling yield stresses and viscosities to be calculated. The data generated compare favorably with those measured previously by capillary rheometry.

Cellulose↗
PubMed1985

The contribution of gravitational torques to limb position sense.

An experiment is reported which examined whether gravitational torque acting about a joint is used by the CNS in elbow joint angle matching. Subjects were required to match the joint angles of their two limbs while the external torques acting about each elbow were systematically varied. It was found that when the matching limb was differentially loaded, the error in the produced reference angle corresponded to the directional prediction of a proposed gravitational torque hypothesis. The data suggest that torque sensation is an accessory source of information in limb positioning.

Adult↗
PubMed1993

Amplitude and frequency measures of surface electromyography during dual task elbow torque production.

Studies of motor unit recruitment thresholds have demonstrated the existence of task-specific motor units within the muscles controlling the elbow. Two degree-of-freedom (df) task specificity was investigated at higher levels of elbow torque using the amplitude and frequency characteristics of surface electromyography (EMG). Flexion and supination torque data were collected together with EMG from electrode pairs on the brachioradialis (BRAD), biceps brachii short head, and medial and lateral aspects of biceps brachii long head, while subjects (n = 14) performed the following four combinations of isometric tasks: (1) maximum voluntary contraction (MVC) flexion (F) and (2) MVC supination (S), each with a targeted torque of zero in the second df; (3) MVC flexion with targeted MVC supination (FS); and (4) MVC supination with targeted MVC flexion (SF). Median power frequency (MEDF) and root mean square (RMS) amplitude under steady-state torque conditions were calculated and analyzed using ANCOVA models with planned contrasts (alpha = 0.05). A significant main effect for task was found in RMS, but not in MEDF. Contrasts showed a significant increase in RMS response in the dual MVC tasks (FS and SF) over the single MVC tasks of F and S. The lack of frequency changes with alterations in RMS data indicates that the underlying recruitment/rate coding scheme in use for dual-df tasks may be different than in single-df tasks, and provides possible support for the notion of motor unit task groups. Task-by-site interactions were found for both MEDF and RMS, and illustrated that the three biceps sites differed from BRAD in their responses to the F versus S tasks.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Maximal power and torque-velocity relationship on a cycle ergometer during the acceleration phase of a single all-out exercise.

Seven subjects pedalled on a Monark cycle ergometer as fast as possible for approximately 7 s against four different resistances which corresponded to braking torques (TB) equal to 19, 38, 57 and 76 N.m at the crank level. Exercise periods were separated by 5-min recovery periods. Pedal velocity was recorded every 50 ms by means of a disc with 360 slots fixed on the flywheel, passing in front of a photo-electric cell linked to a microcomputer which processed the data. Every 50 ms, the time necessary to perform half a pedal revolution (t1/2) was computed by adding the 50-ms periods necessary to reach 669 slots (the number of slots corresponding to half a pedal revolution). To measure t1/2 to an accuracy better than 50 ms, this time was computed by a linear interpolation of the time-slot number relationship. Power (P) was averaged during t1/2 by adding the power dissipated against braking torque and the power necessary to accelerate the flywheel. The torque-velocity (T-v) relationship was studied during the acceleration phase of a sprint against a single TB by computing every 50 ms the relationship between v and T (N.m), equal to the sum of TB and the torque necessary to accelerate the flywheel at the same time. The T-v relationships calculated from the acceleration phase of a single all-out exercise were linear and similar to the previously described relationships between peak velocity and braking force.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗
PubMed1994

Relationship between bone mineral density of the proximal femur and lumbar spine and quadriceps and hamstrings torque in healthy Japanese subjects.

The purpose of this study was to examine the correlations between the muscle torque of the leg extensors (quadriceps femoris) and leg flexors (hamstrings) and the bone mineral density (BMD) of the proximal femur and lumbar spine. To investigate the decline in BMD of proximal femur and lumbar spine, we examined the relative importance of muscle torque, age, and body weight in the prediction of BMD in 340 healthy volunteers (109 males, and 231 females). Age and body weight were independent predictors of femoral BMD in men. Body weight and quadriceps torque were independent predictors of femoral BMD in premenopausal women. Body weight and years after menopause were independent predictors of BMD in postmenopausal women. The BMD was greatly affected by menopause, whereas the muscle torque was independent of the menopause, and showed the negative relationship to age. These results suggest that muscle-building exercise may have the potentiality to elevate the BMD in the proximal femur in premenopausal women.

Adult↗
PubMed1994

The relationship between the electromyogram-amplitude and isometric extension torques of neck muscles at different positions of the cervical spine.

A group of 12 healthy men volunteered for the experiment. Electromyograms (EMG) were obtained from semispinalis capitis, splenius capitis, levator scapulae, and trapezius muscles. The flexion angle of the cervical spine was precisely adjusted to 0 degrees, 10 degrees, 20 degrees, and 30 degrees relative to the horizontal, with a constant angle of the atlanto-occipital joint. The subjects made eight short (about 2 s) vertical extension forces (6%, 12%, 18%, 24%, 30%, 36%, 42%, and 48% of maximal voluntary peak contraction force). For each position, the centre of pressure under the head was determined as the basis for the calculation of the external lever arm. The presence of motor endplate regions was ascertained by multiple surface electrodes. The slopes of individual linear regression lines for the root mean square (rms)-values were dependent on the existence of endplates in the area of the electrodes - endplates caused smaller rms values per Newton metres of external torque. Significant intersubject differences between regression equations could not be eliminated by the normalization of EMG-parameters and/or torques. The elimination of gravity, the continuous monitoring of positions, and the consideration of localization of motor endplate regions were essential prerequisites for the acquisition of reliable relationships between EMG of different neck muscles and external torques. Two important conclusions were derived for the prediction of torques from EMG measurements: firstly, individual regression equations which take into account the position of the head and neck should be used; secondly, normalization procedures do not justify the application of average regressions to a group of subjects.

Adult↗
PubMed1995

Knee extension torque and intramuscular pressure of the vastus lateralis muscle during eccentric and concentric activities.

The objectives of this study were to determine whether the occurrence of delayed onset muscle soreness (DOMS) for the vastus lateralis muscle was associated with elevated intramuscular pressure (IMP); and to assess, whether high eccentric forces occurred at an increased muscle length (as determined by joint angle). Therefore, peak knee extension torque, peak IMP of the vastus lateralis muscle, and the joint angle at which peak torque (JAPT) occurred were determined in eight male subjects during repetitive eccentric and concentric activities until fatigue occurred. Peak torque was significantly higher for eccentric compared to concentric activity (P < 0.01) and declined significantly for both activities (P < 0.01) throughout the protocols. When comparing the start (prior to fatigue) to the end (fatigue state), mean torque for eccentric activity declined from 191 to 147 (N.m) and for concentric activity declined from 166 to 104 (N.m). In contrast, peak IMP was not significantly different between the types of activity and did not change significantly with time. At the start and the end, the mean IMP remained constant for eccentric activity at 54 mmHg (7.2 kPa) but for concentric activity was 78 mmHg (10.4 kPa) and 96 mmHg (12.8 kPa), respectively. All the subjects, however, experienced DOMS of the vastus lateralis muscle exclusively for the eccentric activity leg. The JAPT was not different between activity types and did not change significantly with time; however, a significant interaction between activity type and time was observed (P = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Torque-velocity relationships for the knee extensors in women in their 3rd and 7th decades.

Maximal isokinetic knee extensor strength was measured as torque in 17 young (mean age +/- SD, 21 +/- 3 years) and 16 elderly (68 +/- 5 years) women at 30 degrees (0.52 rad) before full extension, at angular velocities from 0 to 5.24 rad s-1, in 7 increments of 0.87 rad s-1. The elderly women were significantly weaker than the young women at all angular velocities. The rate of loss of absolute torque with increasing velocity was similar for both age groups, but when torque was standardised as a percentage of the individual's maximum, the elderly group showed a significantly greater rate of loss than the younger group. Quick-release from an isometric effort did not increase the recorded torques at 4.36 rad s-1 compared with the free-running method in either age group. The age differences are compatible with lower ratio of type II to type I fibre are in the older group.

Adult↗
PubMed1995

An evaluation of knee extensor and knee flexor torques and EMGs in patients with patellofemoral pain syndrome in comparison with matched controls.

The relationship between concentric and eccentric isokinetic torques and EMGs of quadriceps and hamstring muscles in patients with unilateral patellofemoral pain was studied in 27 patients (13 males, 14 females). The patients and a group of controls matched for age, gender, and physical activity were tested on a Kin-Com dynamometer at 60 degrees/s and 180 degrees/s angular velocity. EMGs were recorded for eight of the patients and their matched controls. In addition, the reproducibility of isokinetic measurements made under the same conditions but on different occasions in patients with patellofemoral pain was evaluated. Twenty-one patients (11 males, 10 females) underwent testing of their quadriceps and hamstring muscles two or three times on a Kin-Com dynamometer. This was performed both concentrically and eccentrically in their painful leg while the patients evaluated their knee pain using Borg's pain scale. The data show that the patients had a significantly lower agonist as well as antagonist EMG activity during knee extension measurements in their painful leg compared with the controls. However, there were no differences in either agonist or antagonist EMG activities during knee flexion measurements between the patients and the controls. The quadriceps muscle torque was considerably weaker in the patients' painful leg compared with both their asymptomatic leg and with the controls. Peak torque for knee extension was reached at a mean of 66 degrees of knee flexion for both patients and controls. However, the patients showed a considerably wider range within which they produced their peak torque in their painful leg than in their asymptomatic and also in comparison with the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Range of motion, muscle torque and training habits in runners with and without Achilles tendon problems.

Achilles tendon injuries are common in runners. The aim of the present study was to analyse the training programme, any Achilles tendon problems, muscle tightness and range of motion of the ankle joint, and concentric and eccentric muscle torques of the calf muscles in middle-distance runners with and without Achilles tendon problems. Eighty-three middle-distance runners answered a questionnaire on their sports background, training habits and any injuries. Thirty-four percent had suffered from some type of problem relating to the Achilles tendon. Ten of the athletes who had suffered from Achilles tendon problems and ten who had never had any Achilles tendon trouble were randomly selected. These 20 runners underwent a clinical examination. The range of motion of the ankle joint was recorded objectively by a hydraulic and computerised isokinetic dynamometer by measuring resistance to passive motion. Concentric and eccentric muscle torques of the gastrocnemius-soleus complex were recorded. The runners with Achilles tendon problems had trained for significantly more years and covered significantly longer distances per week than runners without Achilles tendon problems. There were no significant differences in other training methods or in best results over 800 m and 1500 m. Runners with Achilles tendon problems had a significantly lower range of motion of the ankle joint. They also had significantly lower eccentric torques of the gastrocnemius-soleus complex, but no differences in concentric torques were found between the groups.

Achilles Tendon↗
PubMed1997

Effects of aerobic exercise on the torque-velocity relationship in cycling.

The kinetics of the torque-velocity (T-omega) relationship after aerobic exercise was studied to assess the effect of fatigue on the contractile properties of muscle. A group of 13 subjects exercised until fatigued on a cycle ergometer, at an intensity which corresponded to 60% of their maximal aerobic power for 50 min (MAP60%); ten subjects exercised until fatigued at 80% of their maximal aerobic power for 15 min (MAP80%). Of the subjects 7 exercised at both intensities with at least a 1-week interval between sessions. Pedalling rate was set at 60 rpm. The T-omega relationship was determined from the velocity data collected during all-out sprints against a 19 N.m braking torque on the same ergometer, according to a method proposed previously. Maximal theoretical velocity (omega zero) and maximal theoretical torque (Tzero) were estimated by extrapolation of the linear T-omega relationship. Maximal power (Pmax) was calculated from the values of Tzero and omega zero (Pmax = 0.25 omega zero Tzero). The T-omega relationships were determined before, immediately after and 5 and 10 min after the aerobic exercise. The kinetics of omega zero, Tzero and Pmax was assumed to express the effects of fatigue on the muscle contractile properties (maximal shortening velocity, maximal muscle strength and maximal power). Immediately after exercise at MAP60% a 7.8% decrease in Tzero and 8.8% decrease in Pmax was seen while the decrease in omega zero was nonsignificant, which suggested that Pmax decreased in the main because of a loss in maximal muscle strength. In contrast, MAP80% induced a 8.1% decrease in omega zero and 12.8% decrease in Pmax while the decrease in Tzero was nonsignificant, which suggested that the main cause of the decrease in Pmax was probably a slowing of maximal shortening velocity. The short recovery time of the T-omega relationship suggests that the causes of the decrease of torque and velocity are processes which recover rapidly.

Adult↗
PubMed1993

Reliability of Cybex II isokinetic evaluations of torque in post-poliomyelitis syndrome.

The aim of this study was to ascertain the reliability of isokinetic strength measurements in a population of post-poliomyelitis subjects (PPS). Eight subjects (four males and females, mean age of 47.5 +/- 10 and 56.8 +/- 16 years, respectively) were evaluated, on a weekly basis for three weeks at approximately the same time of day. During each test session the knee flexors and extensors (bilaterally, where possible) were evaluated. Subjects became familiar with the equipment prior to recording three maximal contractions at the four test velocities (1.05, 2.09, 3.14, 4.18rads.s-1). A two-minute rest period was allowed between sets of contractions. The variables of peak torque, angle of peak torque, torque at specific joint angles (0.79 and 1.05rads), total contractile work, maximum power, and average power were measured on-line with the Cybex II a system using a commercially available software package. In both muscle groups, all the variables were significantly weaker on the most affected, but testable limb (p < 0.01) in subjects where both limbs could be tested (n = 5). Peak torque and total work of the quadriceps were observed to decrease with increasing velocity of movement. The effects of velocity were less apparent in the hamstrings. Average and maximum power developed by the knee extensors and flexors increased with increasing velocity of movement. Reliability of performance over three test sessions was confirmed by the intraclass correlation coefficient (ICC) values derived from the univariate ANOVAs calculated for each of the above variables (> 0.80).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Reduction of knee torques and leg-related functional abilities in hereditary motor and sensory neuropathy.

Our purpose was to evaluate a test battery for measuring progress and the effect of interventions in patients with hereditary motor and sensory neuropathy (HMSN types I and II). For this purpose differences in upper leg strength and functional abilities between patients and healthy persons were quantified. Twenty patients participated in the study. They were matched with healthy control subjects with respect to gender, age, body weight, and height. Because of the high reproducibility and sensitivity of the method, muscle strength was quantified as isokinetic and isometric knee torques on an isokinetic dynamometer. Isokinetic knee extension and flexion torques were recorded for three movement velocities (120, 60, and 30 degrees/sec). An extension endurance test was performed at 80% of maximum voluntary contraction. Time scored activities (for instance, stair climbing) that are mainly related to leg function were measured to determine functional abilities. The torques were lower (p < 0.009) and endurance was less (p = 0.03) for patients than for controls. Time scores were higher (p < 0.013) in patients. A strength reduction in the knee extensors and flexors and a decrease in functional abilities was found even in mildly affected patients. Torques and time scores were correlated, although correlation coefficients were rather low. Our results indicate that both types of test are useful for monitoring lower limb function in HMSN patients.

Adolescent↗
PubMed1979

Differential effects of reciprocal wrist torques on responses of somatotopically identified neurons of precentral cortex in awake primates.

The present study was undertaken to investigate the functional significance of previous observations that both reciprocal and bidirectional responses are found in the forelimb area of precentral cortex following oppositely directed torques delivered about a single forelimb joint. Extracellular unit recordings were made in the contralateral precentral cortex of awake monkeys. These units were classified, according to their responses to passive somatosensory stimulation and to the effects of local intracortical microstimulation (ICMS), as being functionally coupled to single joints. Both joint- and cutaneous-sensitive neurons were included. The responses of such classified neurons to oppositely directed torques were then studied. All of the joint-sensitive wrist (flexion-extension) units responded reciprocally to the oppositely directed torques. In contrast reciprocally and bidirectionally responsive neurons were found in the cutaneous-sensitive wrist population and in both the joint- and cutaneous-sensitive non-wrist (F-E) populations. These results are discussed in terms of the expected receptor actions of the applied torques, and are consistent with other evidence that a correlation exists between activities of precentral neurons which respond to sensory events at or about a single forelimb joint, and voluntary movement about the same joint.

Animals↗
PubMed1995

Flexion relaxation during lifting: implications for torque production by muscle activity and tissue strain at the lumbo-sacral joint.

During the full flexion phase of the back lift movement the lumbar part of the erector spinae muscle exhibits a reduced activity level (flexion relaxation). This study addresses the question how the required extension torque in the lumbo-sacral joint (L5/S1 joint) is balanced during the period in which apparently the lumbar erector spinae ceases to take its share. Six subjects participated in the experiment in which they performed seven lifting tasks. The load, the range of movement, and the phase in which the load was handled (lifting or lowering) were varied. A dynamic linked segment model was applied to determine the momentary torques acting at the L5/S1 joint, while the EMGs of the lumbar and thoracic part of the erector spinae muscle were measured. Furthermore, the lengths between markers on the lumbar and thoracic part of the trunk were determined to reveal changes in length during the movement. The dynamic EMGs were normalized to trunk angle-dependent maximal levels. The L5/S1 joint torques were analysed and combined with the normalized EMG data and the kinematics of the trunk, which are assumed to indicate the elongation of passive tissues. Although in the normalization procedure the change of the length-force relationship of the erector spinae was taken into account, the dynamic lumbar EMG activity decreased to a low-activity level (the phenomenon of flexion relaxation). This coincided with a 25% increase in lumbar length suggesting that passive tissue strain provided part of the required extension torque. In the tasks where a barbell was handled a significant increase in EMG level of the thoracic part of the erector spinae occurred just before the flexion relaxation at the lumbar level. Apparently, the extensor function of the lumbar part is then taken over by the thoracic part of the erector spinae muscle. This suggests that an intricate coordinating mechanism is operative that apportions the load to be balanced over active--(lumbar and thoracic part of the erector spinae) and passive structures (post vertebral ligaments).

Adult↗