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PubMed1986

Reflex and mechanical contributions to head stabilization in alert cats.

Five alert cats were tested for their responses to rotation in a device that allowed rotation of the head on the trunk about a vertical axis passing through the C1-C2 vertebral joint. Electrodes were implanted to record the horizontal and vertical electrooculogram and electromyographic (EMG) activity of the dorsal neck muscles splenius, biventer cervicus, and complexus. Head rotation and torque acting on the head were recorded in the horizontal plane during rotations in the 0.05-5.0 Hz frequency range. Responses were interpreted with reference to a closed-loop dynamic model of the head-neck system. Whole-body rotation (WBR) with no neck movement elicited a vestibulocollic reflex (VCR). Neck muscle EMG lagged the sinusoidal platform rotation by approximately 120 degrees at low frequencies, which represents a 60 degrees lead relative to a perfectly compensatory 180 degrees lag. This phase lead was related to the cumulative eye position of the accompanying horizontal vestibular nystagmus as reported by Vidal et al. Horizontal head torque exhibited a similar low-frequency behavior. At high frequencies, EMG exhibited a progressively increasing phase lead and gain increase typical of a second-order lead system as described in decerebrate cats. Torque, however, showed much less lead and gain increase, presumably because of the low-pass filter properties of the process coupling muscle excitation to torque. Head torque did exhibit a steep increase in gain with frequency and a phase approaching that of platform acceleration at high frequencies when weights were attached to the head to increase its moment of inertia. The same +40 dB/decade gain slope and phase approaching 0 degree was observed during WBR rotation of the anesthetized cat in which head inertia is the only factor contributing to the torque. This dynamic behavior was predicted by the inertial component of the model. In the alert unweighted cat, the inertial torque was smaller than VCR-generated torque at frequencies below 4 Hz. Rotation of the neck with the head held fixed in space (HFS rotation) elicited a cervicocollic reflex (CCR). Neck EMG response was very similar to that observed during WBR, both in dynamic behavior and overall gain. Torque, however, was consistently greater than that generated by WBR and showed a steady increase of 8 dB/decade as frequency rose. The added torque can be attributed to the viscoelastic properties of neck muscles. Driven rotation of the head on the fixed body elicited torques that could be closely approximated by a vector sum of torques observed during WBR and HFS rotations.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Muscle activation patterns and kinetics of human index finger movements.

1. The present study was conducted to determine whether dynamic interaction torques are significant for control of digit movements and to investigate whether such torques are compensated by specific muscle activation patterns. 2. Angular positions of the metacarpophalangeal (MP) and proximal interphalangeal (PIP) joints of the index finger in the flexion/extension plane were recorded with the use of planar electrogoniometers. Muscle activation patterns were monitored with the use of fine wire and surface electromyography of intrinsic and extrinsic finger muscles. 3. Dynamic interaction torques associated with index finger movements were large in relation to joint torques produced by muscles, especially in faster movements. The significance of dynamic interaction torques was demonstrated in model simulations of two-joint finger motion in response to joint torque inputs. Removal of interaction torques from the model inputs produced movements that differed greatly from digit motions produced by human subjects. 4. Electromyogram (EMG) and torque patterns associated with finger movements of different speeds indicated that muscle activity is necessary not only for producing motion at the joints but also to counteract segmental interaction torques. This was especially evident during movements that required voluntary maintenance of a constant MP joint angle during motion of the distal segment about the PIP joint. Under these conditions, muscle moments acting at the MP acted directly to counteract torques at the MP arising from motion at the PIP. 5. Neural mechanisms underlying control of index finger movement are discussed with reference to the implications of dynamic interaction torques. Potential control strategies include accurate programming of muscle activation patterns, appropriate use of motion-dependent peripheral afferent information, and control of the finger as a viscoelastic system through coactivation of flexor and extensor musculature. It is concluded that additional research incorporating study of motion in three dimensions and the use of mechanical models of the finger and related musculature is required to determine how interaction torques are compensated during finger motion.

Female↗
PubMed2000

Tension regulation during lengthening and shortening actions of the human soleus muscle.

In the present study we investigated tension regulation in the human soleus (SOL) muscle during controlled lengthening and shortening actions. Eleven subjects performed plantar flexor efforts on an ankle torque motor through 30 degrees of ankle displacement (75 degrees -105 degrees internal ankle angle) at lengthening and shortening velocities of 5, 15 and 30 degrees. S(-1). To isolate the SOL from the remainder of the triceps surae, the subject's knee was flexed to 60 degrees during all trials. Voluntary plantar flexor efforts were performed under two test conditions: (1) maximal voluntary activation (MVA) of the SOL, and (2) constant submaximal voluntary activation (SVA) of the SOL. SVA trials were performed with direct visual feedback of the SOL electromyogram (EMG) at a level resulting in a torque output of 30% of isometric maximum. Angle-specific (90 degrees ankle angle) torque and EMG of the SOL, medial gastrocnemius (MG) and tibialis anterior (TA) were recorded. In seven subjects from the initial group, the test protocol was repeated under submaximal percutaneous electrical activation (SEA) of SOL (to 30% isometric maximal effort). Lengthening torques were significantly greater than shortening torques in all test conditions. Lengthening torques in MVA and SVA were independent of velocity and remained at the isometric level, whereas SEA torques were greater than isometric torques and increased at higher lengthening velocities. Shortening torques were lower than the isometric level for all conditions. However, whereas SVA and SEA torques decreased at higher velocities of shortening, MVA torques were independent of velocity. These results indicate velocity- and activation-type-specific tension regulation in the human SOL muscle.

Adult↗
PubMedDate not supplied

An electromyographic study of isokinetic axial rotation in young adults.

BACKGROUND CONTEXT: Trunk rotation is associated with over 60% of all low back injuries. However, there are gaps in the knowledge about trunk rotation. PURPOSE: To study the axial rotation torque and electromyographs (EMGs) of seven trunk muscles bilaterally in static and isokinetic modes with increasing angular velocity to determine qualitative and quantitative muscle response. STUDY DESIGN: An electromyographic study of seven trunk muscles bilaterally was carried out in 50 normal subjects during static and isokinetic axial rotation at varying angular velocity. The qualitative and quantitative force and EMG measures were made and analyzed phenomenologically and statistically. METHODS: Fifty normal young adults (27 men, 23 women) performed an isometric maximal voluntary contraction (MVC) from the neutral upright-seated posture to their right and left. Also, these subjects performed isokinetic axial rotation from neutral seated position to right and left, and from prerotated right and left "end of range posture" toward the neutral at 10, 20 and 40 degrees per second angular velocity. All experimental trials were made on axial rotation tester designed for the study. EMG was recorded from the erector spinae at L3 and T10 vertebral levels, latissimus dorsi, pectoralis major, rectus abdominis and external and internal obliques bilaterally. The torque and EMG in isokinetic condition were normalized against those of isometric condition. Descriptive statistics were calculated. Data were subjected to analysis of variance, and torque was regressed on EMG. RESULTS: The peak isokinetic torques were significantly lower than the isometric torques (p<.01), but the EMGs of the isokinetic conditions were significantly higher than those of isometric trials (p<.01). The isokinetic axial rotation torque decreased by 1 Nm to 1.5 Nm with per degree increase in velocity of rotation, with the values for 10, 20 and 40 degrees per second angular velocities being significantly different (p<.01). There was a significant increase (p<.01) in percent EMG (up to 28%) per unit torque with increasing angular velocity of rotation. The rotation torque from prerotated position to neutral was significantly higher than that of rotation away from the neutral (p<.001). The EMG magnitude increased significantly with increasing velocity (2% to 17% at 10 degrees per second), 21% to 28% at 20 degrees per second, 30% to 36% at 40 degrees per second). Regression analysis revealed poor predictability of torque based on EMG. The latter was suggested because of the role and behavior of the ligaments and joint capsules of the spine. CONCLUSION: The axial rotation is initiated and maintained by the contralateral external obliques, ipsilateral latissimus dorsi and internal oblique. The ipsilateral erector spinae likely play a stabilizer role. The isometric torque is greater than the isokinetic, which decreases with increasing velocity. Even with decreasing torque, EMG progressively increases, indicating a disproportionally higher stress in the spinal connective tissues potentiating injury. The data presented here suggest that, for safety, load and velocity of rotation should be kept low.

Abdomen↗
PubMed1998

Revision pedicle screws. Bigger, longer shims--what is best?

STUDY DESIGN: To evaluate the effect of change in screw dimensions and hole augmentation in pedicle screw revisions, the insertional torque was determined, and results were compared with those in control specimens in an in vitro study using cadaveric thoracolumbar spines. OBJECTIVES: To determine the best method of salvage for failed pedicle screws, by evaluating the insertional torque after placing a larger diameter or longer screw into a stripped hole. Use of a shim and use of larger and longer screws were also investigated. Finally, the effect on insertional torque of simply removing and replacing a pedicle screw in its original hole was investigated. SUMMARY OF BACKGROUND DATA: The effects of using bigger or longer screws and shims to salvage failed pedicles have been studied. The interaction between how much larger, how much longer, and inserting with or without shims, has not been well studied. Optimizing reinsertional torque through the use of bigger screws risks exceeding the pedicle capacity. Using longer screws risks violation of the anterior vertebral body, thereby placing the great vessels and viscera at risk. By knowing the relative contribution of increase in length and diameter, the surgeon can optimize the risk-benefit ratio. METHODS: Eight cadaveric spines from T10 to S1 were harvested. The specimens underwent radiographic screening and bone densitometry. A modified Latin square randomization was designed to evaluate the screw diameters and lengths. Each pedicle was its own control. A 35- x 6.5-mm screw was used as a control. Test screws were placed after pedicle screw hole failure was achieved and documented by stripping. For the test screws, the diameters were increased by 1 mm and 2 mm, the lengths were increased by 5 mm and 10 mm. Shims were added randomly. The peak insertional torque was measured for each control screw and test screw placement. In addition, during each screw placement, the screw was removed and replaced to determine the effect. RESULTS: Insertional torque, after the pedicle screw is removed and replaced in the same hole, was decreased by 34% (P < 0.000005). Increasing the diameter of the salvage screw by 2 mm caused the insertional torque to be increased by 8.4% of the original. Increasing the length of the screw did not improve the salvage screw insertional torque. There was an interaction effect for the 1-mm increase in diameter and the increase in length. At this diameter, increasing the length had a significant effect (P = 0.009) on the salvage torque. Using a shim created no improvement in salvage insertional torque (P = 0.77). There was a poor linear correlation between torque and bone mineral density (r = 0.18) in these osteoporotic specimens. CONCLUSIONS: Removing and replacing a pedicle screw in its original hole substantially decreases its mechanical fixation. For pedicle salvage, increasing the diameter causes the greatest restoration of strength. Shims had no effect in pedicle salvage in osteoporotic specimens.

Absorptiometry, Photon↗
PubMed2007

Adapted preparation technique for screw-type implants: explorative in vitro pilot study in a porcine bone model.

OBJECTIVE: The aim of this study was to quantify the effect of adapted preparation on the insertion torque of self-tapping implants in cancellous bone. In adapted preparation, bone condensation - and thus, insertion torque - is controlled by changing the diameter of the drilling. MATERIAL AND METHODS: After preparation of cancellous porcine vertebral bone with drills of 2.85, 3, 3.15 or 3.35 mm final diameters, Brånemark sytem Mk III implants (3.75 x 11.5 mm) were inserted in 141 sites. During implantation, the insertion torque was recorded. Prior to implant insertion, bone mineralization (bone mineral density (BMD)) was measured with dental quantative computed tomography. The BMD values measured at the implant position were correlated with insertion torque for varying bone condensation. RESULTS: Based on the average torque recorded during implant insertion into the pre-drilled canals with a diameter of 3 mm, torque increased by approximately 17% on reducing the diameter of the drill by 5% (to 2.85 mm). On increasing the diameter of the osteotomy to 3.15 mm (5%) or 3.35 mm (12%), torque values decreased by approximately 21% and 50%, respectively. CONCLUSION: The results demonstrate a correlation between primary stability (average insertion torque) and the diameter of the implant bed on using a screw-shaped implant. Thus, using an individualized bone mineralization-dependent drilling technique, optimized torque values could be achieved in all tested bone qualities with BMDs ranging from 330 to 500 mg/cm(3). The results indicate that using a bone-dependent drilling technique, higher torque values can also be achieved in poor bone using an individualized drilling resulting in higher bone condensation. As immediate function is dependent on primary stability (high insertion torque), this indicates that primary stability can be increased using a modified drilling technique in lesser mineralized bone.

Animals↗
PubMed2006

Contribution of M-waves and H-reflexes to contractions evoked by tetanic nerve stimulation in humans.

Tetanic neuromuscular stimulation evokes contractions by depolarizing motor axons beneath the stimulating electrodes. However, we have shown that extra torque can develop due to the discharge of spinal neurons recruited by the evoked sensory volley. The present experiments investigated whether extra torque in the ankle plantar- and dorsiflexors was associated with enhanced H-reflexes. The tibial and common peroneal nerves were stimulated using 7-s trains (20 Hz for 2 s, 100 Hz for 2 s, 20 Hz for 3 s). Extra torque was defined as significantly more torque during 20-Hz stimulation after the 100-Hz burst (time2) than before it (time1). In 9 of 11 subjects, extra plantarflexion torque developed during stimulation just above motor threshold. In these nine subjects, torque increased from 8 to 13% MVC (time1 to time2), the soleus H-reflex increased from 13 to 19% Mmax and the M-wave of approximately 2% Mmax did not change significantly. To evoke extra dorsiflexion torque, greater stimulation intensities were required. In 6 of 13 subjects, extra torque developed at intensities that evoked an M-wave of 5-20% Mmax at time1. In these six subjects, torque doubled from 2 to 4% MVC (time1 to time2), whereas tibialis anterior (TA) H-reflexes and M-waves did not change significantly (H-reflex from 0.8 to 2% Mmax; M-wave from 12 to 14% Mmax). In 7 of 13 subjects, extra torque developed at higher stimulation intensities (35-65% Mmax). In these seven subjects, torque increased from 13 to 20% MVC, whereas TA H-reflexes and M-waves were not significantly different (H-reflex from 0.7 to 1% Mmax; M-wave from 49 to 54% Mmax). Thus enhanced H-reflexes contributed to extra plantarflexion, however, other factors generated extra dorsiflexion.

Adult↗
PubMed2000

Horizontal-plane arm movements with direction reversals performed by normal individuals and individuals with down syndrome.

We examined the systematic variation in shoulder and elbow torque, as well as movement kinematics, for horizontal-plane arm movements with direction reversals performed by normal individuals and individuals with Down syndrome. Eight neurologically normal individuals and eight individuals with Down syndrome performed horizontal, planar reversal movements to four different target locations. The four locations of the targets were chosen such that there is a systematic increase in elbow interaction torque for each of the four different target locations. This systematic increase in interaction torque has previously been shown to lead to progressively larger movement reversal errors, and trajectories that do not show a sharp reversal of direction, for movements to and from the target in patients who have proprioceptive abnormalities. We computed joint torques at the elbow and shoulder and found a high correlation between elbow and shoulder torque for the neurologically normal subjects. The ratio of joint torques varied systematically with target location. These findings extend previously reported findings of a linear synergy between shoulder and elbow joints for a variety of point-to-point movements. There was also a correlation between elbow and shoulder torque in individuals with Down syndrome, but the magnitude of the correlation was less. The ratio of joint torques changed systematically with target direction in individuals with Down syndrome but was slightly different from the ratio observed for neurologically normal individuals. The difference in the ratio was caused by the generation of proportionately more elbow torque than shoulder torque. The fingertip path of individuals with Down syndrome showed a sharp reversal in moving toward and then away from the target. In this respect, they were similar to neurologically normal individuals but dissimilar to individuals with proprioceptive deficits. Finally, we observed that individuals with Down syndrome spend proportionately more time in the vicinity of the target than normal individuals. Collectively these results show that there is a systematic relationship between joint torques at the elbow and shoulder. This relationship is present for reversal movements and is also present in individuals with Down syndrome.

Adolescent↗
PubMed1994

Recovery from a 1-minute bout of fatiguing exercise: characteristics, reliability, and responsiveness.

BACKGROUND AND PURPOSE: The purposes of this study were (1) to describe the characteristics of recovery of peak torque after a 1-minute bout of isokinetic exercise of the quadriceps femoris muscle, (2) to determine the short-term reliability of the recovery of peak torque, and (3) to determine whether the recovery of peak torque more closely associates with maximal endurance exercise capacity than does the decline in peak torque at the end of the fatigue test. SUBJECTS: Thirty-three nondisabled subjects, ranging in age from 23 to 34 years (X = 27, SD = 3.4), participated in the reliability portion (phase 1) of the study. A different group of 21 nondisabled subjects, ranging in age from 21 to 47 years (X = 27.5, SD = 5.2), participated in the correlational portion (phase 2) of the study. METHODS: The short-term reliability of percentage of decline in peak torque and recovery of peak torque was assessed in phase 1. Each subject performed two quadriceps femoris muscle fatigue tests (test-retest) on an isokinetic dynamometer. In phase 2, each subject performed a single fatigue test and a test of maximal oxygen uptake (VO2max) to examine the relationships between VO2max and percentage of decline in peak torque at the end of the fatigue test and recovery of peak torque. RESULTS: Intraclass correlation coefficient values at every 30-second interval during recovery were acceptable (ICC = .67-.87), indicating recovery of peak torque is a consistent measure of quadriceps femoris muscle performance. A high negative correlation (r = -.84) was found between the percentage of decline at 30 seconds of recovery and VO2max, but a lower negative correlation (r = -.48) was found between the percentage of decline in torque at the end of the fatigue test and VO2max. CONCLUSION AND DISCUSSION: These results suggest recovery of peak torque is a reliable measure of muscle performance and closely associates with maximal aerobic exercise capacity.

Adult↗
PubMed1995

The sense of effort and two models of single-joint motor control.

Two sets of experiments were carried out. In the first set, human subjects were asked to make the same effort with the elbow flexors at different joint angles under isometric conditions. In some experiments, the subjects were standing with the arm in a vertical (parasagittal) plane; in others, they were seated with the arm in a horizontal (transverse) plane. When muscular torque at a given effort level (ordinate) was plotted as a function of elbow joint angle (abscissa), the resulting isoeffort torque-angle profiles tended to be flat or negatively sloping over a range from 45 degrees to 135 degrees, and they were often nonmonotonic. Increases in effort up to near-maximal levels caused the isoeffort torque-angle profiles to shift upward with little alteration in shape. In the second set of experiments, seated subjects with the arm horizontal resisted baseline torques produced by a motor that acted to extend the elbow joint. Unexpected increases and decreases in torque were superimposed on the baseline torque. The subjects either were instructed to intervene and return the elbow to the initial (90 degree) position, or were told, "Do not intervene voluntarily; let the motor move your arm." Effort was reported both under baseline conditions and after the changes in torque. It was found that changes in effort were a function of the changes in torque opposed by the elbow flexors, and were similar whether the subject had repositioned the arm or allowed it to be moved by the motor. In the latter case, the arm came to rest after displacements that were a function of the size and direction of the torque change. For individual subjects, the largest angular displacements ranged from +/- 10 degrees to +/- 20 degrees for changes in torque of +/- 10 N.m. There was no evidence for any angular dependence of the effort judgements at a given torque over this angular range. Depending on whether effort is primarily an efferent perception proportional to voluntary motor activity or also has a significant afferent (involuntary) component, different models of motor control are supported by these data.

Adult↗
PubMed2003

Control strategy for a hand balance.

The goal of this study was to investigate the control strategy employed by gymnasts in maintaining a hand balance. It was hypothesized that a "wrist strategy" was used in which perturbations in the sagittal plane were corrected using variations in wrist flexor torque with synergistic shoulder and hip torques acting to preserve a fixed body configuration. A theoretical model of wrist strategy indicated that control could be effected using wrist torque that was a linear function of mass center displacement and velocity. Four male gymnasts executed hand balances and 2-dimensional inverse dynamics was used to determine net joint torque time histories at the wrist, shoulder, and hip joints in the sagittal plane. Wrist torque was regressed against mass center position and velocity values at progressively earlier times. It was found that all gymnasts used the wrist strategy, with time delays ranging from 160 to 240 ms. The net joint torques at the shoulder and hip joints were regressed against the torques required to maintain a fixed configuration. This fixed configuration strategy accounted for 86% of the variance in the shoulder torque and 86% of the variance in the hip torque although the actual torques exceeded the predicted torques by 7% and 30%, respectively. The estimated time delays are consistent with the use of long latency reflexes, whereas the role of vestibular and visual information in maintaining a hand balance is less certain.

Hand↗
PubMed1998

Action tremor and weakness in Parkinson's disease: a study of the elbow extensors.

We have previously shown that action tremor persists during maximal wrist extension in patients with Parkinson's disease, and that this contributes to weakness at this joint by preventing the fully fused contraction of the forearm extensor muscles. Antiparkinsonian medication reduces the action tremor in torque and electromyographic (EMG) records, thereby improving strength at the wrist. In the present experiments, peak torque and action tremor were recorded during maximal extension of the elbow in nine patients with Parkinson's disease while they were on and off antiparkinsonian medication, and in eight age- and sex-matched healthy subjects. Peak torque and mean rectified EMG levels were reduced by 34% and 36%, respectively, during maximal elbow extension when patients off medication were compared to those in the treated state. Action tremor was visible in torque records and had a frequency of approximately 10 Hz both in parkinsonian patients and in normal controls. Activity of a similar frequency was often detected in EMG records, especially in patients off therapy. The absolute amplitude of action tremor in torque (A[torque]) and EMG (A[EMG]) records from the elbow was unaffected by therapy and was little different from that recorded in healthy controls. The relative action tremor in torque ([A(torque)/peak torque] x 100) and EMG ([A(EMG)/mean rectified EMG] x 100) was reduced by treatment, but this was the result of the increase in peak torque and mean rectified EMG. Thus, in contrast to the results at the wrist, antiparkinsonian medication has little effect on the 10-Hz action tremor at the elbow. Increased strength is produced by a different mechanism which allows recruitment of triceps motor units outside of this synchronizing influence.

Aged↗
PubMed2000

Practice-related changes in lumbar loading during rapid voluntary pulls made while standing.

OBJECTIVE: To determine if five days of practice on a novel dynamic, multi-joint pulling task resulted in lower magnitudes of lumbar loading or a more consistent relationship between pulling force and lumbar loading. DESIGN: A repeated measures design compared how practice influenced the magnitude of lumbar torque and the correlations between lumbar torque and pulling force. BACKGROUND: Previous studies suggest that practice can decrease the magnitude of lumbar loading on simple manual material handling tasks, but it is unknown whether practice reduces lumbar loading for more complex tasks. Neither is it known whether the consistency of lumbar loading increases with practice. METHODS: Ten healthy adults practiced impulse-like horizontal pulls to targets equaling 20%, 40% and 80% of their estimated maximal dynamic pulling force over 5 days. Movements were unrestrained, other than keeping the feet flat on the ground. We used a four-segment, sagittal plane inverse dynamics model to compute lumbar, hip, knee, and ankle torques on days 1 and 5 from ground reaction forces and moments, pulling forces, and kinematics. RESULTS: An analysis of variance showed significant practice-related changes in lumbar torque at the time of peak pulling force (lumbar torque(peakPF)). The lumbar torque(peakPF) decreased for the 20% pulls, did not change for the 40% pulls, and increased for the 80% pulls. Two subjects showed a significant decrease in lumbar torque(peakPF) for all three force levels. Coefficients of determination between pulling force and lumbar torque (r(2)(PF,LT): a measure of the consistency of the relationship between these two variables) were significantly higher on day 5 than day 1. CONCLUSIONS: Practice on a novel pulling task changed the magnitude of lumbar torques and increased their correlation with pulling force, suggesting that subjects learned strategies that improve motor control of lumbar torques. Relevance The study showed that the magnitude and consistency of lumbar loading changed spontaneously as subjects practiced a novel multijoint pulling task. Such changes may decrease the risk of low-back injury.

Adult↗
PubMed2003

An in vitro study of the torsional properties of new and used rotary nickel-titanium files in plastic blocks.

OBJECTIVE: The purpose of this study was to compare torque (in grams per centimeter) and angle of rotation (in degrees) at the time of fracture of new and used nickel-titanium .04 ProFile rotary files. The relationship between the size of the instrument and the torque at fracture was also investigated. STUDY DESIGN: The torque and angle of rotation at fracture of new and used nickel-titanium .04 ProFile rotary files Nos. 15 to 40 were determined according to American National Standards Institute/American Dental Association Specification No. 28. Analysis of variance was used to compare the torque and angle of rotation at fracture of the different sizes of the new instruments and of new and used instruments of the same size (alpha =.05). The relationship between torque at fracture and the size of the instrument was determined by means of regression analysis. RESULTS: The torque at fracture of the new instruments increased significantly with the diameter. The used instruments, Nos. 25 to 40, had significantly lower values of torque at fracture than did the new ones. There were no statistically significant differences between the angle of rotation at fracture of the new and the used instruments (P >.05). A stronger relationship was found between the size of the file and the torque at fracture for the new instruments (P <.0001) than for the used ones (P <.0001). CONCLUSION: The results of the present study suggest that the values of the torque at fracture of new instruments increased significantly with the diameter. The results also suggest that repeated use of ProFile .04 instruments mainly affected the torque at fracture.

Analysis of Variance↗
PubMed1998

Physical performance differences between weight-trained sprinters and weight trainers.

The present study tested and compared well-trained athletes who were performing low-velocity, high-force resistance training and sprint running training (ST) when recruited, with subjects who were performing low-velocity, high-force resistance training but not sprint training (NST) when recruited. Eleven male sprint runners (mean +/- SD; age = 19.0 +/- 1.4 yr: height = 182.0 +/- 4.7 cm: mass = 75.7 +/- 4.7 kg), and eight male weight-trained athletes who were not currently performing sprint training, or any other additional training, (mean + SD; age = 21.5 +/- 1.8 yr: height = 184.5 +/- 3.6 cm: mass = 78.4 +/- 4.6 kg) participated in the study; all subjects had a minimum of two years resistance training experience. Tests included 1. running speed (20 m time after a 50 m acceleration distance and 20 m acceleration time from a stationary start), 2. isokinetic hip flexor/extensor torque (and torque adjusted for body mass), angle of peak torque, time to reach peak torque and torque acceleration energy at low (1.05 rad x s(-1) [60 degrees x s(-1)), moderate (4.74 rad x s(-1) [270 degrees x s(-1)) and high (8.42 rad x s(-1) [480 degrees x s(-1)) speeds and 3. maximum squat lift. ST subjects produced more isokinetic hip extensor torque when adjusted for body mass at 4.74 rad x s(-1) (270 degrees x s(-1); p<0.05) and reached their peak torque faster (p<0.05). ST subjects also produced more hip flexor torque at 8.42 rad x s(-1) (480 degrees x s(-1); p<0.05), and torque per body mass at 4.74 rad x s(-1) (270 degrees x s(-1)) and 8.42 rad x s(-1) (480 degrees x s(-1); p<0.05) and reached peak flexor torque faster than NST subjects (4.74 rad x s(-1) [270 degrees x s(-1)], p<0.05; 8.42 rad x s(-1) [480 degrees x s(-1), p<0.01). Further, ST subjects performed better in tests of running acceleration over 20 m (p<0.02) and achieved a higher maximum running velocity after a 50 m acceleration distance (p<0.001). No significant differences were found in isokinetic strength at low (1.05 rad x s(-1) [60 degrees x s(-1)) velocities or in maximal squat lift strength. The results of the present study suggest that athletes who perform low-velocity, high force training concurrently with high-velocity training are superior in tests of isokinetic strength at high velocities when compared to athletes who only perform low-velocity, high force training. This may be due to training or genetic factors.

Adult↗
PubMed2001

Mandibular distraction force: laboratory data and clinical correlation.

PURPOSE: In vitro data were collected to measure torque-force values of an internal distraction device. The measurements were correlated with in vivo torque readings in an attempt to better understand the force required to distract the osteogenic bone callus of the human mandible during distraction osteogenesis. METHODS AND MATERIALS: Five internal craniofacial distraction devices were mounted on an apparatus to test load limits and torque measurements. The apparatus aligned the devices so that weight provided a force opposite and parallel to the vector of distraction. Weights were added in 5-lb increments, and the devices were activated 0.5 mm for each torque reading. Torque readings were obtained from a calibrated torque wrench. Measurements were plotted on a graph and correlated with clinical torque readings obtained from 8 patients undergoing mandibular lengthening. RESULTS: The average torque for distracting the human mandible 0.5 mm twice a day was 4.2 +/- 1.6 Newton-centimeters (N-cm). The average slope of the in vitro data shows that 4.2 N-cm of torque is equivalent to a force of 35.6 N. The average force of device failure was 235.8 N. CONCLUSION: Torque-force diagrams offer an effective means for calibrating safety margins and load capabilities for internal distraction devices. Quantification of axial forces encountered in mandibular lengthening will help contribute to the overall understanding and biomechanics of mandibular distraction osteogenesis.

Adolescent↗
PubMed2002

Enhancement of pedicle screw fixation through washers.

This study examined the effect of washer usage on initial pedicle screw fixation and on the salvage of replaced pedicle screws, and the effect of minor adjustments of pedicle screws on insertional torque. Titanium, nontapered pedicle screws (6.5-mm in diameter and 35-mm in length) from one manufacturer and custom-made 5-mm washers were used in the fixation of porcine lumbar spines. Insertional torque was measured with an electronic torque screwdriver and failure strength was determined by straight pullout of the screws using an MTS machine. Initial insertional torque values were significantly greater in pedicle screws placed with washers compared with screws placed without washers. When the screw placed without a washer was salvaged with the addition of a washer, a significant increase in insertional torque resulted. Pullout testing failed to show a significant difference between the screws that were placed with washers and the screws that were placed without washers. In the second part of the experiment, there was a significant decrease in insertional torque after backing out the screw as little as 90 degrees. This current study showed that (1) washers significantly increase the insertional torque of pedicle screws; (2) screws placed without a washer can be salvaged and replaced with a washer, which results in significantly increased insertional torque; and (3) backing out a pedicle screw 90 degrees significantly decreases its insertional torque. Washers can be used with pedicle screws to enhance the initial stability of the screw constructs, and to maximize insertional torque when screws need to be replaced, revised, or adjusted (backed out).

Animals↗
PubMed2003

Torsional properties of new and used rotary K3 NiTi files.

The purpose of this study was to compare torque (gcm) and angle of rotation (degrees) at fracture of new and used NiTi K3 .04 rotary instruments. The relation between size of instrument and torque at fracture was also investigated. The torque and angle of rotation at fracture of new and used NiTi K3 .04 rotary instruments sizes 15 to 40 were determined according to ANSI/ADA Specification No. 28. Analysis of variance was used to compare the torque and angle of rotation at fracture among the different sizes of the new instruments and between new and used instruments of the same size (alpha = 0.05). The relationship between torque at fracture and size of instrument was determined with a regression analysis. Torque at fracture of the new instruments increased significantly with the diameter (p < 0.05). The used instruments, sizes 25 to 40, had significantly lower torque at fracture values compared to the new ones (p < 0.05). The used instruments, sizes 20 and 35 had significantly lower angle of rotation at fracture compared to the new ones (p < 0.05). A stronger relationship was found between the size of the file and the torque at fracture for the new instruments (p < 0.0001) compared to the used ones (p < 0.0001). The results of the present study suggested that the torque at fracture values of new instruments increased significantly with the diameter. The results also suggested that repeated use of .04 K3 instruments affected mainly the torque at fracture.

Analysis of Variance↗