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PubMed1993

Synergies and strategies underlying normal and vestibulary deficient control of balance: implication for neuroprosthetic control.

Future developments of neuroprosthetic control will probably permit locomotion and posture to be maintained without the aid of crutches and will therefore require some form of balance control. Three fundamental questions will arise. First, the question of the location of imbalance-sensing transducers must be assessed. Secondly, the synergy, which is the relative amplitude and timing of muscle activity, and/or the strategy of joint torques required to re-establish a stable posture for different types of balance disturbances must be addressed. Thirdly, the control laws that map either trunk muscle activity or imbalance-sensing transducer outputs into multi-joint postural control of standing by paraplegic individuals must be generated. The most appropriate means of gathering the relevant information applicable to neuroprosthetic control systems is through the detailed analysis of normal and non-normal human models. In order to gain such detailed insights into normal balance control and its dependence on head angular and linear accelerations, the synergy and strategy of balance corrections in normal subjects or patients with vestibular deficits were investigated for two types of support surface perturbation, a dorsiflexion rotation (ROT) and a rearward translation (TRANS). These experimentally induced perturbations to upright stance were adjusted to cause equal amplitudes of ankle dorsiflexion, thus providing additional information about the role of lower leg proprioception on balance control. Synergies defined on the basis of peak cross-correlations of each recorded muscle's EMG to that of the largest muscle response were significantly different for TRANS and ROT. Translation synergies consisted of a sequential coactivation at several levels (soleus and abdominals some 30 msec before hamstrings, and trapezius some 15 msec before paraspinals), whereas the sequential activation of paraspinals and tibialis anterior dominated the balance synergy to ROT. Likewise, response strategies, defined using cross-correlations of joint torques, differed. That for TRANS was organised as a multi-link strategy with neck torques leading those of all other joints by 40 msec or more; hip joint lead ankle torques by 30 msec. That for ROT was organised around hip and ankle torques without a major correlation to neck torques. Vestibulary deficient subjects developed weaker synergies with respect to subjects with normal balance systems under eyes-open conditions and there was no clear synergy with eyes closed. Consequently, hip torques were delayed some 180 msec with respect to ankle torques, and correlations to neck torques were completely out of phase under eyes-closed conditions. Fundamental changes in TRANS synergies and strategies also occurred in vestibulary deficient subjects for eyes-open and eyes-closed conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Ankle↗
PubMed2004

The effect of static torsion on the compressive strength of the spine: an in vitro analysis using a porcine spine model.

STUDY DESIGN: Matched porcine cervical spine motion segments were subjected to two main conditions and compared: axial compression and axial compression combined with varying axial torque. OBJECTIVES: To determine the effect of torsion on the acute compressive strength of the spine. SUMMARY OF BACKGROUND DATA: The spine is often subjected to compression together with axial torque as a component of complex loading, yet there is a lack of documentation on its effect on the compressive strength and injury mechanics. METHODS: Matched cohorts of porcine cervical spine (C5-C6) motion segments were compressed to failure at a rate of 3,000 N/s combined with 0 Nm, 5 Nm, 20 Nm, or 30 Nm of axial torque. Three "failure" points were recorded from the stress/strain association: the first "step" (initial microfracture), the initial slope change (yield point or "slow crush" mechanism), and the ultimate failure point (fracture). Furthermore, resultant injuries were documented using planar radiography and visual inspection following dissection of the motion segments. RESULTS: Axial torque affected the failure characteristics during acute compressive loading. The ultimate strength of the motion segments was significantly reduced with increasing static torques. The compressive load at which initial microfracture occurred, indicated by the first "step" in the load-deformation curve, was increased with 5 Nm, 10 Nm, and 20 Nm of applied torsion in comparison to no torque, but this effect was reduced with 30 Nm of torque. The "slow crush" mechanism of failure was not affected by the addition of axial torque. No radiographic gross injuries to the facet joints were observed. Damage appeared to be confined to the endplate and trabecular network of the vertebral body. CONCLUSIONS: Based on this animal model, shown to have similar biomechanical behavior to humans, axial torque appears to significantly reduce the compressive strength of the spine.

Animals↗
PubMed1985

Discharge properties of primate forearm motor units during isometric muscle activity.

Activity of single motor units (MUs) was recorded in forelimb muscles of rhesus macaques while they generated isometric ramp-and-hold torques about the wrist. Multiunit electromyographic (EMG) activity was recorded from 10-12 identified flexor and extensor muscles of the wrist and digits with implanted EMG wire electrodes. Single MUs from these muscles were recorded with a remotely controlled tripolar microelectrode array. The parent muscle of each MU was determined by compiling MU-triggered averages of multiunit EMGs. The MU firing patterns during the isometric task were determined from response histograms aligned with change in torque. At moderate torque levels, MUs (n = 86) exhibited four types of discharge patterns during the ramp-and-hold trajectory: phasic-tonic (23%), tonic (33%), decrementing (39%), and phasic (5%). Phasic-tonic MUs exhibited a phasic burst of activity during the torque ramp which exceeded the firing rate during the static hold period. Both phasic-tonic and tonic MUs exhibited a constant mean firing rate during the hold period; the discharge of decrementing MUs gradually decreased during the static hold. Phasic MUs fired only during the change in force. The relation between MU firing rate and torque was investigated as the monkeys generated responses of different levels of static torque during the hold period. Mean firing rate during the hold was found to be proportional to static torque up to moderate torque levels, where it reached a maximum. In the linear range, the mean rate-torque slope was 3.4 +/- 1.9 imp/s per 10(5) dyn . cm (n = 9).

Animals↗
PubMed1987

Neural compensation for muscular fatigue: evidence for significant force regulation in man.

We have investigated the role of reflex regulation of muscle force in normal human subjects by comparing changes in the stretch-evoked increments in elbow joint flexor electromyogram (EMG) and elbow joint torque before and after fatigue. Elbow flexor muscle fatigue was induced by repetitive voluntary isometric contractions. To assess the appropriateness of the EMG signal as an index of neural excitation of muscle under fatiguing conditions, we examined the time course of recovery of joint torque and EMG power spectrum following fatigue. Fatigue-related changes in the EMG power spectra recovered within 5-10 min after fatiguing exercise was terminated, yet the muscle weakness induced by the exercise lasted greater than 7 h and was substantial in magnitude. The decoupling of torque and EMG recovery allowed us to compare pre- and postfatigue EMG stretch responses without adjusting for differences in EMG spectral content. Torque and EMG responses to stretch were quantified by time-averaging over 250-ms "isometric" and "steady-state" periods, just before and just after a ramp angular stretch of the elbow joint, respectively. The torque increment elicited by stretch was lower following fatigue in seven of eight experiments. However, the average decrease of 20.13 +/- 14.42% in these seven subjects was somewhat smaller than the corresponding average shift in the slope of the isometric EMG-torque relationship of 85.84 +/- 90.29% (n = 8). Furthermore, the stretch-induced EMG increment was larger following fatigue in all eight sessions (average of 56.14 +/- 28.96%, n = 8), with six of the shifts reaching statistical significance for alpha = 0.05. Because the pattern of torque and EMG responses before and after fatigue suggested the presence of an active force regulator, we used a simple model of the neuromuscular system to estimate a loop gain value for each session. When pre- and postfatigue responses were matched by isometric background torque level, an average loop gain value of 7.9 was computed, whereas for responses matched by average prestretch EMG level, the loop gain estimates averaged 2.1. Although our assessment of force regulation was essentially static and derived from the responses to a single type of perturbation, the change in the incremental torque and EMG stretch responses indicates that meaningful neural compensation for fatigue occurred. Moreover, the loop gain estimates derived from these responses are an order of magnitude larger than those previously reported in animal models, suggesting that force regulation may be important in the control of human muscle contraction.

Adaptation, Physiological↗
PubMed1990

Stiffness regulation by reflex action in the normal human hand.

1. The torque and electromyographic (EMG) responses to stretch of the first dorsal interosseous muscle (externally imposed joint rotation) were recorded in five normal human subjects. The total measured stiffness was decomposed into three individual stiffness components; passive, intrinsic, and reflex. 2. The passive component was measured with the subject relaxed. Compared with the total response at the height of short latency reflex action, the passive component comprised 6-32% of the total stiffness recorded at an initial torque level of 20 N-cm [15-39% maximum voluntary contraction (MVC)]. The passive response also reflected a significant acceleration component during rapid joint rotation due primarily to digit inertia. 3. The intrinsic stiffness component, attributed to the mechanical properties of the active muscle fibers, was estimated by recording the response to joint rotation with the muscle activated in a distributed manner using a single intramuscular electrode. The dynamic stiffness (measured at the end of a ramp displacement) and the static stiffness (measured 1 s after onset of the displacement) both scaled in a straight-line manner with the initial torque level. This relationship held whether the initial torque level was varied by changes in recruitment or temporal summation. 4. The reflex component was calculated by subtracting the passive and the estimated intrinsic component from the total response. The timing of the EMG signal recorded during measurement of the total response and the fact that the estimated intrinsic component matched the total active response over the first 65-100 ms after displacement onset supported the case that this was the true reflex component. The peak of the reflex activity occurred 155-360 ms after displacement onset and, at this peak, accounted for 18-44% of the total stiffness (at an initial torque level of 20 N-cm). 5. Over the low to intermediate torque range employed, we observed that both intrinsic muscle stiffness and total stiffness increased with initial torque. Because total stiffness increased more rapidly than intrinsic stiffness, the difference between them (equal to reflex stiffness) also increased with initial torque. Furthermore, when the total active response trials (passive stiffness removed) were shifted vertically so that the initial torque levels matched, it was seen that reflex action did not reduce the stiffness range to less than the stiffness range encountered for the intrinsic response alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed2006

Quantification of functional weakness and abnormal synergy patterns in the lower limb of individuals with chronic stroke.

BACKGROUND: The presence of abnormal muscle activation patterns is a well documented factor limiting the motor rehabilitation of patients following stroke. These abnormal muscle activation patterns, or synergies, have previously been quantified in the upper limbs. Presented here are the lower limb joint torque patterns measured in a standing position of sixteen chronic hemiparetic stroke subjects and sixteen age matched controls used to examine differences in strength and coordination between the two groups. METHODS: With the trunk stabilized, stroke subjects stood on their unaffected leg while their affected foot was attached to a 6-degree of freedom load cell (JR3, Woodland CA) which recorded forces and torques. The subjects were asked to generate a maximum torque about a given joint (hip abduction/adduction; hip, knee, and ankle flexion/extension) and provided feedback of the torque they generated for that primary joint axis. In parallel, EMG data from eight muscle groups were recorded, and secondary torques generated about the adjacent joints were calculated. Differences in mean primary torque, secondary torque, and EMG data were compared using a single factor ANOVA. RESULTS: The stroke group was significantly weaker in six of the eight directions tested. Analysis of the secondary torques showed that the control and stroke subjects used similar strategies to generate maximum torques during seven of the eight joint movements tested. The only time a different strategy was used was during maximal hip abduction exertions where stroke subjects tended to flex instead of extend their hip, which was consistent with the classically defined "flexion synergy." The EMG data of the stroke group was different than the control group in that there was a strong presence of co-contraction of antagonistic muscle groups, especially during ankle flexion and ankle and knee extension. CONCLUSION: The results of this study indicate that in a standing position stroke subjects are significantly weaker in their affected leg when compared to age-matched controls, yet showed little evidence of the classic lower-limb abnormal synergy patterns previously reported. The findings here suggest that the primary contributor to isometric lower limb motor deficits in chronic stroke subjects is weakness.

Journal Article↗
PubMed1989

Isokinetic dynamometry. Applications and limitations.

Isokinetic contraction is the muscular contraction that accompanies constant velocity limb movements around a joint. The velocity of movement is maintained constant by a special dynamometer. The resistance of the dynamometer is equal to the muscular forces applied throughout the range of movement. This method allows the measurement of the muscular forces in dynamic conditions and provides optimal loading of the muscles. However, during movements in the vertical plane, the torque registered by the dynamometer is the resultant torque produced by the muscular and gravitational forces. The error depends on the angular position and the torque potential of the tested muscle group. Several methods have been developed for the correction of gravitational errors in isokinetic data. The torque output also contains artefacts that are associated with the inertial forces during acceleration and deceleration periods before the development of the constant preset angular velocity. For an accurate assessment of muscle function, only constant velocity data should be analysed. The most frequently used isokinetic parameters are the maximum torque and the angular position where it was recorded, the torque output at different angular velocities of movement, the torque ratio of reciprocal muscle groups and the torque output during repeated contractions. The unique features of isokinetic dynamometry are optimal loading of the muscles in dynamic conditions and constant preselected velocity of movement. These features provide safety in the rehabilitation of patients with muscular and ligamentous injuries. Isokinetic dynamometry has also been used for the training of various muscle groups in order to improve the muscular performance in dynamic conditions. The movement velocity of different activities can be simulated during training in order to improve the training effect. Data acquisition and analysis have been improved by using computer systems interfaced to isokinetic dynamometers. Recently developed computer systems provide correction for gravitational and inertial errors, accurate computation of isokinetic parameters and real-time display of the torque output.

Biomechanical Phenomena↗
PubMed1999

Biomechanical response in the ankle to stimulation of lumbosacral nerve roots with spiral cuff multielectrode--preliminary study.

Biomechanical response in the ankle to tetanic stimulation of the lumbosacral root was investigated to assess the potential for lower limb functional neurostimulation. Myotomal response in the leg was measured as the three-dimensional isometric torque in the ankle after extradural tetanic stimulation of the L3-S1 roots exposed surgically for herniated disc removal in five patients. The cuff multielectrode was employed to investigate functional topography of the roots by monopolar, bipolar, and tripolar electrode configurations. Four response patterns in the direction of three-dimensional torque vectors were observed. The L-5 and S-1 roots had the same response pattern, but S-1 roots produced stronger torques. Dorsiflexion torque was not obtained by stimulation of L-5 roots despite coactivation of the tibial anterior and peroneal muscles. Dorsiflexion torques were produced only by stimulating the L-4 roots. More selective bipolar and tripolar stimulations recruited force at higher thresholds and less gain. Additionally, some muscles were not activated by tripolar stimulation of the same root. In one L-4 root, the torque at lower electrical threshold was replaced by inverse torque at higher threshold, providing indirect evidence that different muscles may have motoneuron populations that differ in diameter or location within the root. Although dorsiflexion and plantarflexion torques are functional per se, they are accompanied by foot inversion and leg rotation torques (as well as proximal muscle contractions). Further experimental investigations on direct extradural stimulation of lumbosacral roots, either single or in combination, are recommended to explore the potential of lumbosacral nerve root stimulation for restoration of leg function.

Ankle↗
PubMed1994

The central complex of Drosophila melanogaster is involved in flight control: studies on mutants and mosaics of the gene ellipsoid body open.

Visual flight control is studied in three mutant alleles of the gene ellipsoid body open (ebo) of Drosophila melanogaster. In mutant ebo flies the central complex is disturbed to varying degrees. Defects range from a small opening in the ellipsoid body to the dissociation of the ring into two parts, a cleft in the fan-shaped body and hypoplasia in the protocerebral bridge. Other parts of the brain are not visibly affected. Flight behavior is normal with respect to the amplitude of the optomotor response and to the object response (single rotating stripe). A reduced amplitude in the small random oscillations of the torque trace (yaw torque activity), however, is found in all three alleles. In two of them the frequency of torque spikes is reduced. In the allele ebo678 the dynamics of the optomotor response is altered. Upon reversal of the direction of rotation mutant flies take longer than wild type to shift their yaw torque to the new response level (optomotor reversal time). Finally, these flies also behave abnormally in the flight simulator in which their yaw torque controls the angular velocity of the panorama. Many ebo678 flies fixate a single stripe less persistently than normal flies, some even trying to fly away from it (antifixation). In ebo678 gynandromorphs the four behavioral phenotypes ("yaw torque activity", "torque spike frequency", "on-target fixation" and "optomotor reversal time") are all highly correlated with the phenotype of the ellipsoid body. Yaw torque activity and torque spike frequency in addition are correlated with the phenotype of the thorax suggesting that these behavioral defects are in part caused by mutant influences on the ventral ganglion. The results support the hypothesis that the central complex is involved in the control of flight behavior.

Animals↗
PubMedDate not supplied

An improved method for muscle force assessment in neuromuscular disease.

We describe here the reliability and validity of methods to quantify involuntary muscle torque induced by non-invasive nerve stimulation. A rigid apparatus was used to hold the subject's limb in a predetermined position and confine movement to a specific direction (i.e. ankle dorsiflexion or thumb adduction). An incorporated strain gauge was used to measure isometric torque, and all data were recorded by a data acquisition program. The innervating nerves were stimulated by surface electrodes, using either single stimuli to generate a twitch, or short trains of stimuli to produce tetanic contraction of the individual muscle under study. The average peak tetanic torque generated by the dorsiflexor muscles in healthy control was 20.4 +/- 3.8 Nm and varied by 3.7% with repeated testing. The mean torque generated by the adductor pollicis muscle in controls was 1.5 +/- 0.4 Nm and varied by 4.6% with repeated testing. In patient populations significant changes in activated torque were readily quantified, and the effects of treatment can be easily assessed. Furthermore, several specific parameters of recorded isometric contractions were measured; e.g. time between stimulus and torque onset, peak rate of torque development, time to peak torque, half-relaxation time, and others (none of which are measurable when using voluntary contraction of muscle). Compared to current assessment methods, monitoring muscle torque generated by nerve stimulation improves objectivity, reliability, and quantitative capabilities. The presented method has significant potential both in diagnosing neuromuscular disorders and determining treatment efficacy.

Ankle↗
PubMed2004

Direct measurement of the passive stiffness of rat sperm and implications to the mechanism of the calcium response.

Glass microprobes were used to measure the stiffness of the flagella of Triton X-100-extracted rat sperm models. The sperm models were treated with 50 microM sodium vanadate and 0.1 mM Mg-ATP to evaluate the stiffness of the passive flagellar structure without the influence of the dynein motor proteins. The passive stiffness was determined to be 4.6 (+/- 1.1) x 10(-19) N x m(2). Rat sperm models exposed to greater than 10(-5) M calcium ions exhibit a strong bend in the basal 40 microm of the flagellum, resulting in a fishhook-like appearance. The torque required to bend a passive rat sperm flagellum into the fishhook-like configuration was determined. The result was compared to the previously published measurement of the torque required to straighten the flagella of rat sperm in the Ca(2+)-induced fishhook configuration [Moritz et al., 2001: Cell Motil. Cytoskeleton 49:33-40]. The torque required to induce a fishhook in a passive flagellum was 2.7 (+/- 0.7) x 10(-14) N x m and the torque to straighten an active Ca(2+)-induced fishhook was 2.6 (+/- 1.4) x 10(-14) N x m. These values are identical within the limit of error of the measurement technique. This finding suggests that the fishhook configuration observed in the Ca(2+) response of rat sperm is the result of a Newtonian equilibrium, where active torque produced by dynein is counterbalanced by an equal and opposite passive torque that results from bending the flagellum. Consistent with this mechanism, the Ca(2+)-induced fishhook configuration is progressively relaxed by incremental increases in sodium vanadate concentration. This supports an active role of the dynein motors in producing the torque for the response. When rat sperm respond to Ca(2+), the bend in the flagellum always forms in the direction opposite the curvature of the asymmetric sperm head. Based on this polarity, the bending torque for the Ca(2+) response must result from the action of the dyneins on outer doublets 1 through 4.

Animals↗
PubMed2003

Evidence for strength imbalances as a significant contributor to abnormal synergies in hemiparetic subjects.

Abnormal synergies in the paretic shoulder and elbow of hemiparetic subjects were quantified during maximal voluntary contractions (MVCs) in 27 subjects with a history of stroke and 8 age-matched control subjects. A six-axis load cell allowed simultaneous measurement of the primary torque the subject was attempting to maximize and the secondary torques at other joint actions. For example, during MVC of shoulder flexion, shoulder flexion is the primary torque and the secondary torques are internal/external rotation, abduction/adduction, and elbow flexion/extension. In general, the stroke subjects had increased secondary torques compared to controls, resulting in abnormal joint torque coupling within the set consisting of elbow flexion, internal rotation, adduction, shoulder flexion. Unlike previous studies, abnormal secondary torques in several cases were due to strength imbalances, which occur when the strength deficit for a particular joint action is greater than the strength deficit in the opposite joint action. This hypothesis was supported by electromyographic recordings and by the finding that subjects with larger strength imbalances tended to produce larger secondary torques. Possible mechanisms and consequences for rehabilitative treatments are discussed.

Aged↗
PubMed2004

Displacement of the medial meniscus within the passive motion characteristics of the human knee joint: an RSA study in human cadaver knees.

The objective of this study was to validate an in vitro human cadaver knee-joint model for the evaluation of the meniscal movement during knee-joint flexion. The question was whether our model showed comparable meniscal displacements to those found in earlier meniscal movement studies in vivo. Furthermore, we determined the influence of tibial torque on the meniscal displacement during knee-joint flexion. Three tantalum beads were inserted in the medial meniscus of six human-cadaver joints. The knee joints were placed and loaded in a loading apparatus, and the movements of the beads were determined by means of RSA during knee-joint flexion and extension with and without internal tibial (IT) and external tibial (ET) torque. During flexion without tibial torque, all menisci moved in posterior and lateral direction. The anterior horn showed significantly greater excursions than the posterior horn in both posterior and lateral direction. Internal tibial torque caused an anterior displacement of the pathway on the tibial plateau. External tibial torque caused a posterior displacement of the pathway. External tibial torque restricted the meniscal displacement during the first 30 degrees of knee-joint flexion. The displacements of the meniscus in this experiment were similar to the displacements described in the in vivo MRI studies. Furthermore, the application of tibial torque confirmed the relative immobility of the posterior horn of the meniscus. During external tibial torque, the posterior displacement of the pathway on the tibial plateau during the first 30 degrees of flexion might be restricted by the attached knee-joint capsule or the femoral condyle. This model revealed representative meniscal displacements during simple knee-joint flexion and also during the outer limits of passive knee-joint motion.

Aged↗
PubMed2001

General coordination of shoulder, elbow and wrist dynamics during multijoint arm movements.

Studies of multijoint arm movements have demonstrated that the nervous system anticipates and plans for the mechanical effects that arise from motion of the linked limb segments. The general rules by which the nervous system selects appropriate muscle activities and torques to best deal with these intersegmental effects are largely unknown. In order to reveal possible rules, this study examined the relationship of muscle and interaction torques to joint acceleration at the shoulder, elbow and wrist during point-to-point arm movements to a range of targets in the horizontal plane. Results showed that, in general, dynamics differed between the joints. For most movements, shoulder muscle torque primarily determined net torque and joint acceleration, while interaction torque was minimal. In contrast, elbow and wrist net torque were determined by a combination of muscle and interaction torque that varied systematically with target direction and joint excursion. This "shoulder-centered pattern" occurred whether subjects reached targets using straight or curved finger paths. The prevalence of a shoulder-centered pattern extends findings from a range of arm movement studies including movement of healthy adults, neurological patients, and simulations with altered interaction effects. The shoulder-centered pattern occurred for most but not all movements. The majority of the remaining movements displayed an "elbow-centered pattern," in which muscle torque determined initial acceleration at the elbow and not at the shoulder. This occurred for movements when shoulder excursion was <50% of elbow excursion. Thus, both shoulder- and elbow-centered movements displayed a difference between joints but with reversed dynamics. Overall, these findings suggest that a difference in dynamics between joints is a general feature of horizontal plane arm movements, and this difference is most commonly reflected in a shoulder-centered pattern. This feature fits well with other general shoulder-elbow differences suggested in the literature on arm movements, namely that: (a) agonist muscle activity appears more closely related to certain joint kinematics at the shoulder than at the elbow, (b) adults with neurological damage display less disruption of shoulder motion than elbow motion, and (c) infants display adult-like motion first in the shoulder and last at the wrist.

Adult↗
PubMed2002

Isometric axial rotation of the human trunk from pre-rotated postures.

The purpose of this investigation was to study the torque and electromyogram (EMG) in axial rotation from pre-rotated postures. A group of 50 young adults (27 men and 23 women) volunteered for the study. These prepared subjects carried out axial rotation with pre-rotated postures in the direction of pre-rotation and away from it. Torque and EMG were recorded bilaterally from latissimus dorsi, erector spinae at L(3) and T(10) levels, pectoralis, rectus abdominis, external and internal oblique. In 15 degrees pre-rotated posture the axial rotation in the direction of pre-rotation reduced the torque by between 11% and 17% and away from it increased the torque by 12% to 16%. In 30 degrees pre-rotated posture the decrement in torque in the direction of pre-rotation was 24%-33%, and in the opposite direction the gain was between 21% and 32%. Even with decreased torque with rotation in the pre-rotation direction the EMG increased up to 123%. The EMG magnitude and slopes of EMG in these activities demonstrated significant increases while in the opposite direction slight decreases were observed. The EMG of each muscle was significantly different from all other muscles ( P<0.001). A significant ( P<0.01) but low correlation between EMG and torque was obtained. Significant linear regressions between torque and EMG of different muscles were obtained ( P<0.01; r=up to 0.70).

Adolescent↗
PubMed2005

Effect of joint angle on mechanomyographic amplitude during unfused and fused tetani in the human biceps brachii muscle.

The influence of muscle length-dependent changes in contractile properties on the mechanomyogram (MMG) was investigated during evoked contractions of the biceps brachii muscle. The biceps of nine healthy subjects was stimulated by single twitches, unfused (10 Hz), and fused (30 Hz) frequencies at elbow joint angles of 75, 90, 105, 120, 135, and 150 degrees. During evoked contractions, the longitudinal movement was estimated by the fluctuation of torque signal, and the lateral movement was detected by MMG. Contraction time and half relaxation time were calculated from the single twitches. For repetitive stimulations, followed by eliminating DC component from torque signals, the root mean square values calculated from the torque and MMG signals, which were torque fluctuation and RMS-MMG, respectively. For the 10 Hz stimulation condition, reductions in the torque fluctuation and RMS-MMG were concomitantly observed with increasing elbow angle, and there was a significant correlation between the torque fluctuation and RMS-MMG. On the other hand, for 30 Hz stimulation, there were no significant differences in the torque fluctuation and RMS-MMG over all elbow angles, and no significant correlation between the two parameters. Moreover, the torque fluctuation and RMS-MMG for 10 Hz stimulation were correlated with the contraction time and half relaxation time obtained at each elbow angle, while there were no correlations for the 30 Hz condition. These data suggest that MMG could be a reliable tool to study the development of fusion and the changes in muscle contractile properties during repetitive unfused contractions.

Adult↗
PubMed2000

Trunk muscle strength in eccentric and concentric lateral flexion.

The aim of this study was to investigate the position and velocity dependency of the strength (torque) output of lateral flexor muscles of the trunk. Twelve male volunteers with no history of back pain participated. Movement was constrained to the frontal plane and the velocity was controlled by an isokinetic dynamometer. The eccentric and concentric strength of lateral flexor muscles on the left side was measured in a supine position at velocities of 15, 30, 45 and 60 degrees x s(-1) and static strength at 20, 10, 0, -10 and -20 degrees of lateral trunk flexion. Average peak torque values ranged between 211 and 218 Nm (eccentric) and between 66 and 140 Nm (concentric) over all tested velocities, and the average static torque ranged between 80 and 172 Nm over all tested positions. The shape of the torque position curves was unaffected by speed and peak torque occurred at an average position of 11-15 degrees to the contralateral (right) side in both eccentric and concentric actions. In eccentric actions, torque output was significantly higher than that during concentric and static actions. Increasing the speed of contraction did not affect eccentric torque values, whereas both peak and angle-specific concentric torque decreased with increasing speed. These results are in general accordance with earlier findings from other muscle groups, such as the knee extensors. However, they are partially at variance with results obtained in studies of lateral lifting and lowering, indicating that there are other limiting factors in complex tasks that do not just involve the trunk muscles.

Adult↗
PubMed1983

Gravity and positional homeostasis of the cell.

Normally bilateralization takes place in the presence of the Earth's gravity which produces torque, shear, tension and compression acting upon the naked aggregates of cytoplasm in the zygote which is only stabilized by a weak cytoskeleton. In an initial examination of the effects of these quantities on development, an expression is derived to describe the tendency of torque to rotate the egg and reorganize its constituents. This expression yields the net torque resulting from buoyancy and gravity acting upon a dumbbell shaped cell with heavy and light masses at either end and "floating" in a medium. Using crude values for the variables, torques of 2.5 x l0(-13) to 8.5 x 10(-1) dyne-cm are found to act upon cells ranging from 6.4 micrometers to 31 mm (chicken egg). By way of camparison six microtubules can exert a torque of 5 x 10(-9) dyne-cm. (1) Gravity imparts torque to cells; (2) torque is reduced to zero as gravity approaches zero; and (3) torque is sensitive to cell size and particulate distribution. Cells must expend energy to maintain positional homeostasis against gravity. Although not previously recognized, Skylab 3 results support this hypothesis: tissue cultures used 58% more glucose on Earth than in space. The implications for developmental biology, physiology, genetics, and evolution are considered. At the cellular and tissue level the concept of "gravity receptors" may be unnecessary.

Animals↗