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At least 217 records · Page 12Linked to original sources
PubMed1988

Muscle force and moment arm contributions to torque production in frog hindlimb.

The relative contribution of maximum muscle tetanic tension (Po) and muscle moment arm to maximum knee flexion torque was investigated in the frog hindlimb. Isometric torque was measured in frog semitendinosus muscle-bone complexes throughout the range of 0-160 degrees of flexion. Optimal joint angle (the angle at which isometric torque was maximum) was observed at 140 degrees of flexion. After torque measurements, the muscle was excised and the muscle length-tension relationship measured for determination of Po and optimal muscle length. In addition, the kinematics of the knee joint and therefore, the muscle moment arm was measured as a function of joint angle using principles of rigid body kinematics. Stepwise linear regression indicated that maximum torque was most highly correlated with Po (r = +0.77, P less than 0.01) and accounted for approximately 75% of the measured torque. In addition, there was no significant correlation between maximum torque and maximum muscle moment arm (r = +0.11, P greater than 0.7) suggesting that muscle force, not musculoskeletal anatomy, represents the major determinant of maximum torque production in the frog hindlimb.

Animals↗
PubMed1992

Muscle, joint, and tendon contributions to the torque profile of frog hip joint.

The relative contributions of muscle force, moment arm, and tendon compliance were determined as a function of joint angle in the frog semitendinosus-hip joint system. Muscle, joint, and tendon properties were individually measured and then combined to predict the torque generated at the hip joint as a function of joint angle (i.e., the hip torque profile). Predicted torques were then compared to experimentally measured torques using a stepwise regression model to quantify the relative importance of muscle, joint, and tendon contributions to the hip torque profile. Variation in moment arm accounted for 74% of the variability observed in the hip torque profile, while addition of the muscle's intrinsic sarcomere length-tension property accounted for an additional 19% of the torque profile variability. Tendon compliance, which permitted a small amount of sarcomere shortening, accounted for only about 4% of the torque profile variability. We conclude that in this muscle-joint system, the relative fiber length-to-moment arm ratio is the major determinant of the shape of the isometric joint profile. The fiber length-to-moment arm ratio in other mammalian systems is also discussed.

Animals↗
PubMed1988

Coordination and inhomogeneous activation of human arm muscles during isometric torques.

1. In this study we have recorded the activity of motor units of the important muscles acting across the elbow joint during combinations of voluntary isometric torques in flexion/extension direction and supination/pronation direction at different angles of the elbow joint. 2. Most muscles are not activated homogeneously; instead the population of motor units of muscles can be subdivided into several subpopulations. Inhomogeneous activation of the population of motor units in a muscle is a general finding and is not restricted to some multifunctional muscles. 3. Muscles can be activated even if their mechanical action does not contribute directly to the external torque. For example, m. triceps is activated during supination torques and thus compensates for the flexion component of the m. biceps. On the other hand, motor units in muscles are not necessarily activated if their mechanical action contributes to a prescribed torque. For example, there are motor units in the m. biceps that are activated during flexion torques, but not during supination torques. 4. The relative activation of the muscles depends on the elbow angle. Changing the elbow angle affects the mechanical advantage of different muscles differently. In general, muscles with the larger mechanical advantage receive the larger input. 5. We have calculated the relative contributions of some muscles to isometric torques. These contributions depend on the combination of the torques exerted. 6. Existing theoretical models on muscle coordination do not incorporate subpopulations of motor units and therefore need to be amended.

Arm↗
PubMedDate not supplied

Concentric and eccentric torque comparisons for knee extension and flexion in young adult males and females using the Kinetic Communicator.

The purposes of this investigation were to establish average leg torque values as a proportion of body weight for both concentric and eccentric contractions for leg extension and leg flexion, to determine leg flexion/extension ratios for both concentric and eccentric contractions, and to compare those values in males and females from ages 15 to 34 years. The Kinetic Communicator (Kin-Com, Chattecx Corp., Chattanooga, TN), a relatively new computerized strength testing device, was used so that both concentric and eccentric torques could be measured. Pilot study results indicated that Kin-Com results were reliable, r greater than 0.88. Average torque, across the full range of motion, and peak torque expressed in newton meters were divided by body weight in kilograms to produce torque values adjusted by body weight. No differences across age or sex were observed for flexion/extension ratios, but the males' weight-adjusted torque values were significantly (P less than 0.01) greater than the females'. Younger (ages 15 to 24 years) male and female subjects produced significantly (P less than 0.01) greater torque for concentric contractions than older subjects (25 to 34 years). In rehabilitation programs using the Kin-Com, the weight-adjusted torque values and flexion/extension ratios will be useful in determining patients' strength recovery from knee or leg injury and/or surgery.

Adolescent↗
PubMed1993

Knee extension and flexion torque as a function of thigh asymmetry.

Although tape measurement of thigh girth is a common component of a clinical knee examination, the implications of thigh girth asymmetry are not well understood. The purpose of this study was to examine the relationship between thigh girth asymmetry and torque asymmetry for extension and flexion of the knee. Thirty subjects with thigh girth asymmetry of at least 2 cm, measured at a site 15 cm proximal to the superior pole of the patella, were studied. Subjects were measured for girth at 10 sites along each thigh. Knee flexion and extension torque production were also tested on a Cybex II isokinetic dynamometer. Girth asymmetry was determined by the difference in measurements between the subjects' smaller and larger thighs. Percent girth asymmetries varied by site, with the greatest average girth asymmetry (asymmetry = 5.94%) at 16 cm proximal to the superior patellar pole. Percent peak torque asymmetries were computed from the differences between subjects' stronger vs. weaker thighs. Correlations and regressions of both extension and flexion torque asymmetries upon girth asymmetry sites showed higher associations and less error for more proximal measurements. Fair to moderate correlation coefficients (r = .37-.42, p < .05) were statistically significant for extension torque asymmetry compared with girth asymmetry at sites 12, 14, 16, and 20 cm proximal to the patella and for flexion torque asymmetry only at the 14-cm site. Although girth and torque asymmetries were found to be somewhat related, percent girth asymmetry provided only a limited prediction of percent peak torque asymmetry.

Adolescent↗
PubMed1995

A comparison of torque production during dynamic strength testing of shoulder abduction in the coronal plane and the plane of the scapula.

Quantitative measurement of the shoulder abductors is important in a comprehensive assessment of shoulder muscle performance. Testing in traditionally accepted positions may be compromising to the glenohumeral static and dynamic stabilizers; therefore, there is a need to investigate testing in other planes of motion. The purpose of this study was to compare torque produced during isokinetic testing of shoulder abduction in the coronal plane and the scapular plane. Twenty female subjects with no previous shoulder pathology were tested at 90 degrees/sec and 210 degrees/sec in the coronal and scapular planes using the Cybex II isokinetic dynamometer. Both peak torque and mean peak torque of three trials were recorded. A t test for related samples (p < .05) revealed no significant difference in the peak and mean peak torque produced at each speed. Using a two-way analysis of variance with repeated measures, no significant difference was found in the peak torque produced between the two planes. However, torque production at 90 degrees/sec in both test positions was significantly higher than torque production at 210 degrees/sec (F1,19 = 159.610, p < .001). Although anatomical, functional, and clinical reasons have been proposed for performing exercise and testing procedures of the shoulder abductors in the scapular plane, the results of this study indicate that in healthy young women, there is no difference in torque production between the two planes.

Adult↗
PubMed1991

Isometric and isokinetic torque curves at the knee joint.

Isometric and isokinetic torques of bilateral quadriceps and hamstrings were measured with Isokinetic Rehabilitation and Testing System (Model No. Cybex 340) on 40 normal untrained subjects, 20 males and 20 females, ranging between the ages of 23 and 35 years. The mean peak isometric and isokinetic torque values of both muscle groups showed no significant differences between dominant (right) and nondominant (left) limbs in both sexes; however there were significant differences between the male and the female. As the angular velocity increased, the peak torque significantly decreased, and the point of peak torque output occurred significantly later in the range of motion for quadriceps and hamstrings (p less than 0.01). There were no significant changes in the hamstrings to quadriceps (H/Q) ratios as the angular velocity increased. However, there were significant differences of mean H/Q ratio between male and female (p less than 0.01). Height had significant positive correlation with peak isometric and isokinetic torques for both quadriceps and hamstrings (p less than 0.01). Weight was found to correlate significantly with peak isometric and isokinetic torques (p less than 0.01). The mean isometric torques were significantly higher than the mean isokinetic torques for any joint angles in both sexes (p less than .01).

Adult↗
PubMed1992

Alterations in the in vivo torque-velocity relationship after Achilles tendon rupture. Further evidence of speed-specific impairment.

The torque-velocity relationship of the ankle plantar flexors was determined in 31 patients recovering from Achilles tendon rupture. Isokinetic torque measurements were made at speeds of 0 to 240 degrees.s-1 at 24 degrees.s-1 intervals. Measurements of instantaneous torque were made at joint angles corresponding to neutral and 10 degrees plantar flexion. In 17 patients treated surgically, there was little difference between the injured and the uninjured leg. In contrast, patients who were treated by casting exhibited major differences between the injured and uninjured legs. This difference became amplified when torque values at 10 degrees plantar flexion were compared. Additionally, the differences between the injured and uninjured legs were not uniform. The differences in torque were greatest at slow test speeds and least at fast test speeds. Comparisons of the injured surgical and injured nonsurgical legs demonstrated that the surgical group had significantly greater torque. This difference was also speed specific. These findings demonstrate that both groups exhibited speed-specific impairment with the loss of muscle strength being greatest at slow speeds. Also, the degree of impairment was dependent on the ankle position at which torque was measured. Surgical treatment provides better functional results as observed by the torque-velocity relationship.

Achilles Tendon↗
PubMedDate not supplied

Elbow torques and EMG patterns of flexor muscles during different isometric tasks.

This paper examines the torque responses and EMG activity levels in four muscles acting at the elbow joint during different combinations of one- and two- degree of freedom isometric torque production (single and dual tasks, respectively). Flexor and supinator/pronator torques and surface EMG signals from m. biceps brachii, m. brachialis, m. brachioradialis and m. triceps brachii were measured in 16 male subjects while they performed maximal effort isometric contractions of pure flexion, pure supination, pure pronation, combined flexion and supination and combined flexion and pronation. In the single tasks, the torque responses were consistent with task requirements, but the dual task results were surprising in that flexor torque levels were reduced as compared to pure flexion, while supinator/pronator torque levels were as high or higher than in pure supination or pronation. Muscle activity levels varied with task, and could not always explain the differences observed in torque responses. These data are discussed within the framework of subpopulations of task-specific motor units within each muscle. The implications of such task-specific muscle units are related to musculoskeletal modelling and previous EMG - torque relationships found at the elbow.

Analysis of Variance↗
PubMed1989

Isometric and isokinetic knee extension and flexion torque in men and women aged 20-70.

An investigation was made of the influence of age and sex on peak muscle torque in knee extension and flexion during maximal isokinetic and isometric contraction. The study was performed on both legs of 139 clinically healthy men and 141 clinically healthy women aged 20, 30, 40, 50, 60 or 70 years. Maximum knee extension and flexion muscle torque (Newtonmetre, Nm) was measured isokinetically at various angles of velocity (12, 90 and 150 degrees/s) and isometrically under standardized conditions (Cybex II). No significant differences were found between the right and the left leg in the whole material. Muscle torque was higher in men than in women in all age groups (p less than 0.001). Both isokinetic and isometric torque decreased with age in both sexes. Isokinetic torque decreased significantly (p less than 0.05) between 20 and 30 years of age in men and between 40 and 50 years of age in women (at all velocities studied; p less than 0.05). A significant decrease (p less than 0.05) was found between the ages of 60 and 70 years in both sexes. Maximum isometric torque showed a significant decrease (p less than 0.05) between 60 and 70 years in men and women. There were no significant differences in isokinetic or isometric torque between moderately active and inactive men or women. Significant correlations were found between muscle torque and body weight, height and body surface area.

Adult↗
PubMed1995

Biomechanical analysis of bone mineral density, insertion technique, screw torque, and holding strength of anterior cervical plate screws.

The bone mineral density (BMD) of 99 cadaveric cervical vertebral bodies (C3-7) was determined using dual x-ray absorptiometry. The vertebral bodies were randomly assigned to receive either a unicortical (51 bodies) or bicortical (48 bodies) Caspar cervical plating screw. The initial insertion torque was measured using a digital electronic torque wrench, and the force required to withdraw the screw from the vertebral body was determined. The mean BMD for the total group of 99 was 0.787 +/- 0.154 g/cm2, the mean insertion torque was 0.367 +/- 0.243 newton-meters, and the mean pullout force was 210.4 +/- 158.1 newtons. A significant correlation was noted between BMD and torque (p < 0.0001, r = 0.42), BMD and pullout force (p < 0.0001, r = 0.54), and torque and pullout force (p < 0.0001, r = 0.88). Although the BMD of the unicortical and biocortical groups was equivalent (p = 0.92), the insertion torque and pullout force differed significantly (p = 0.02 and p = 0.008, respectively) for the unicortical and bicortical groups. A holding index for each screw and insertion technique was defined as the product of the BMD and insertion torque. The calculated holding index and resultant pullout force were significantly correlated for both techniques of screw insertion (r = 0.92), and a significant difference in holding index was observed with unicortical versus bicortical screw placement (p = 0.04). The determination of BMD and measurement of insertion torque to create a unique holding index provides an assessment of bone-screw interaction and holding strength of the screw, both of which impact on the resultant stability of cervical instrumentation. As the number of cervical plating systems increases, the determination of a holding index for various screws and insertion techniques may assist in the comparison of cervical instrumentation.

Absorptiometry, Photon↗
PubMed2004

Relationship between plantar-flexor torque generation and the magnitude of the movement-related potentials.

This study investigates whether rate of torque development (RTD) and/or torque amplitude are reflected in the movement-related potentials (MRPs) preceding and accompanying isometric activation of plantar flexor muscles. Subjects were asked to perform six different tasks involving the left ankle joint. The tasks consisted of voluntary isometric plantar flexions at three different RTDs (two fixed rates and a 'ballistic' task) ending at two different torque amplitudes. The main observations from the analysis of the MRPs were: 1) the readiness potentials (RP) demonstrated a statistically significant discrimination between low and high torque amplitudes; 2) the RP, the motor potentials (MP) and the movement-monitoring potentials (MMP) could be statistically differentiated among the different RTDs; and 3) in general the MRPs demonstrated an ipsilateral tendency in relation to the involved limb. The results indicate that RP is a suitable parameter for differentiation between levels of isometric plantar flexion torque and MP and MMP are sensitive to a differentiation between RTDs. The correlation between MRPs and motor tasks involving different rates of torque development and levels of torque suggests that MRPs may comprise a potential solution for programming of intended movements to be executed by systems based on neural rehabilitation technology.

Adult↗
PubMed1999

Directional effects of changes in muscle torques on initial path during simulated reaching movements.

Adults are able to reach for an object for the first time with appropriate direction, speed, and accuracy. The rules by which the nervous system is able to set muscle activities to accomplish these outcomes are still debated and, indeed, the sensitivity of kinematics to variations in muscle torques is unknown for complex arm movements. As a result, this study used computer simulations to characterize the effects of change in muscle torque on initial hand path. The same change was applied to movements towards 12 directions in the horizontal plane, and changes were systematically manipulated such that: (1) torque amplitude was changed at one joint, (2) timing of torque was changed at one joint, and (3) amplitude and/or timing was changed at two joints. Results showed that simultaneous changes in torque amplitude at shoulder and elbow joints affected initial speed uniformly across direction. These results add to conclusions from previous experimental and modeling work that the simplest rule to produce a desired change in speed for any direction is to scale torque amplitude at both joints. In contrast, all simulations showed nonuniform effects on initial path direction. For some regions of the workspace, initial path direction was little affected by either a +/-30% change in amplitude or a +/-100-ms change in timing, whereas for other regions the same changes produced large effects on initial path direction. These findings suggest that the range of possible torque solutions to achieve a particular initial path direction varies within the workspace and, consequently, the requirements for an accurate initial path will vary within the workspace.

Biomechanical Phenomena↗
PubMed2002

Effect of immobilization and retraining on torque-velocity relationship of human knee flexor and extensor muscles.

The effect of 2 weeks immobilization of the uninjured right knee and 10 weeks of retraining on muscle torque-velocity characteristics was investigated in nine young subjects. Left and right knee extension and flexion maximal voluntary isometric torque (Tmax) and dynamic torque at 60 degrees s(-1) (T60) and 180 degrees x s(-1) (T180) were measured before (PRE) and after immobilization (POST) and after 3 (R3) and 10 (R10) weeks of dynamic retraining. The torque-velocity relationship was quantified by expressing T60 and T180 relative to Tmax (NT60 and NT180, respectively). For the right extensor muscles, percutaneous biopsy samples were obtained from the vastus lateralis muscle and fibre type distribution was measured. POST extension and flexion torque (mean of Tmax, T60 and T180) decreased by 27% and 11%, respectively. During the course of the experiment, the changes in NT60 and NT180 were similar. POST extensor muscle NTV (mean of NT60 and NT180) was decreased significantly (12%, P<0.05), but no significant change was found for flexor muscle NTV (+ 3%). At R3 Tmax, dynamic torque and NTV were restored to normal. Unlike isometric torque, NTV did not change from R3 to R10. No changes in fibre type distribution were found. The adaptation of muscle length is suggested as the mechanism to explain the change in NTV.

Adenosine Triphosphate↗
PubMed2000

The use of magnetic resonance images to investigate the influence of recruitment on the relationship between torque and cross-sectional area in human muscle.

The purpose of the present study was to investigate the effect of recruitment on the relationship between peak torque and physiological cross-sectional area (PCSA) in human muscle. A group of 11 healthy men participated in this study. Isokinetic knee extension torques at seven (0, 30, 60, 120, 180, 240, and 300 degrees x s(-1)) velocities were determined. Magnetic resonance imaging (MRI) was performed to calculate PCSA of right quadriceps femoris (QF) muscle. Exercise-induced contrast shifts in spin-spin relaxation time (T2)-weighted MRI were taken at rest and immediately after repetitive knee-extension exercise and T2 of QF were calculated. The MRI pixels with T2 values more than 1 SD greater than the means at rest were considered to represent QF muscle that had contracted. The area of activated PCSA within the total in QF was expressed as percentage activated PCSA and used as an index of muscle recruitment. The PCSA correlated with peak torque at 0 degree x s(-1) (r = 0.615, P<0.05); in contrast, activated PCSA correlated with peak torque at 120 degrees x s(-1) (r = 0.603, P<0.05) and 180 degrees x s(-1) (r = 0.606, P<0.05). Additionally, there was a significant difference in correlation coefficients between the activated PCSA-peak torque relationship and the PCSA-torque relationship (P<0.05). These results suggested that muscle recruitment affects the PCSA-torque relationship.

Adult↗
PubMed2001

Time of day effects on isometric and isokinetic torque developed during elbow flexion in humans.

The aim of this study was, firstly, to confirm or refute the existence of circadian rhythms during several velocities of concentric action of the elbow flexor muscles and, secondly, to compare the characteristics of these circadian rhythms with those obtained during isometric actions. Eight volunteer subjects participated in this study. The circadian rhythms were obtained from six test sessions (TS) carried out at different times of day over 6 days with only one TS a day. During each TS, oral temperature and the torque of the muscle action were measured. The subjects made, on an isokinetic ergometer, two maximal isokinetic concentric elbow flexions at five angular velocities (60, 120, 180, 240 and 300 degrees.s-1) and at an angle of 60 degrees. Torque-angular velocity relationships, which characterised the functioning of the muscle during concentric and isometric actions, were established for the different times of day. The values of the torque recorded at each of the angular velocities presented a clear circadian rhythm. After normalisation of the torque values, no significant differences were observed among the computed characteristics of the circadian rhythms obtained at different angular velocities. Since the circadian rhythms during isometric and concentric torque were the same, the characteristics of the circadian rhythms of the musculo-skeletal system can be studied using either type of muscle action. The results indicated that torque and temperature varied concomitantly during the day. Thus, the recording of body temperature allows one to estimate the times of occurrence of maximal and minimal values in the circadian rhythm of muscle torque.

Adult↗
PubMed2000

Improved extraction torque of hydroxyapatite-coated pedicle screws.

Loosening of the screws is a problem in instrumentation with pedicle screws. Coating with hydroxyapatite improves the holding characteristics for metal implants, but the possible effects on the anchorage of pedicle screws have not been described. In this study, seven patients were operated on with spinal instrumentation using four stainless steel pedicle screws. Hydroxyapatite-coated screws were used in either the upper or the lower of the instrumented levels. The insertion torque was measured. In four cases the screws were removed after 10-22 months and the extraction torque was measured. The mean insertion torque was found to be significantly greater in the hydroxyapatite-coated screws (107 Ncm) than in the standard screws (76 Ncm). In three cases, the extraction torque for the hydroxyapatite-coated screws exceeded the range for the torque wrench (600 Ncm), while the conventional screws were loose (< 5 Ncm). In one case, the extraction torque was 475 and 550 Ncm for the coated screws, and 5 and 25 Ncm for the conventional screws. The difference in extraction torque was significant. Hydroxyapatite coating was shown to have improved the purchase of pedicle screws very effectively. By using fully coated screws, as in the present study, extraction was extremely difficult compared to extraction of conventional stainless steel screws, which were regularly loose. By reducing the area of the screws that is coated, it may be possible to achieve an enhanced purchase while extraction will be easier when compared to fully coated screws.

Adolescent↗
PubMed2006

Relationship between locking-bolt torque and load pre-tension in the Ilizarov frame.

The wire-bolt interface in an Ilizarov frame has been mechanically tested. The optimal torque to be applied to the frame locking-bolts during physiological loading has been defined. The set-up configuration was as is used clinically except a copper tube was used to simulate bone. The force-displacement curves of the Ilizarov wires are not altered by locking-bolt torque. The force in the bone model at which pre-tension is lost increases as the locking-bolts are tightened to 14 Nm torque, but decreases if torque exceeds 14 Nm. Thus, 14 Nm is the optimal locking-bolt torque in frame. The relationship between pre-tension versus load for different locking-bolt torques arises because at low and high clamping torques poor wire holding and plastic deformation respectively occur. Wire damage was seen under light and electron microscopy. Clinically, over or under-tightening locking-bolts will cause loss of pre-tension, reduction in frame stiffness and excessive movement at the fracture site, which may be associated with delayed union.

Biomechanical Phenomena↗