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Results for “Reflex, Stretch”

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At least 271 records · Page 15Linked to original sources
PubMed1996

Impaired stretch reflex and joint torque modulation during spastic gait in multiple sclerosis patients.

The modulation of the short latency stretch reflex of the soleus muscle during walking was investigated in seven spastic multiple sclerosis (MS) patients and nine healthy control subjects. Ankle joint stretches were applied by a system which can rotate that ankle joint in any phase of the step cycle during treadmill walking. The torque related to the muscle fibres contracting prior to the stretch and the passive tissues around the ankle joint were measured as the "non-reflex torque". At the same time the short latency stretch reflex-mediated EMG response was measured. The findings show that the stretch reflex modulation was impaired in spastic patients during walking. The stretch reflex modulation was quantified by a modulation index of an average 50% (range -5 to 100%) in the patients and 93% (78-100%) in the control subjects (P < 0.05). The passive stiffness of the ankle joint was at the same time increased in the patients (P < 0.05). It is proposed that the impaired modulation of the stretch reflex along with increased ankle joint stiffness contribute to the impaired walking ability in spastic MS patients.

Adult↗
PubMed2003

Effect of muscle relaxants on experimental jaw-muscle pain and jaw-stretch reflexes: a double-blind and placebo-controlled trial.

A randomised, double-blind, placebo-controlled three-way cross-over study was performed to investigate the effect of two muscle relaxants (tolperisone hydrochloride and pridinol mesilate) on experimental jaw-muscle pain and jaw-stretch reflexes. Fifteen healthy men participated in three randomised sessions separated by at least 1 week. In each session 300 mg tolperisone, 8 mg pridinol mesilate or placebo was administered orally as a single dose. One hour after drug administration 0.3 ml hypertonic saline (5.8%) was injected into the right masseter to produce muscle pain. Subjects continuously rated their perceived pain intensity on an electronic 10-cm visual analogue scale (VAS). The pressure pain threshold (PPT) was measured and short-latency reflex responses were evoked in the pre-contracted (15% maximal voluntary contraction) masseter and temporalis muscles by a standardised stretch device (1 mm displacement, 10 ms ramp time) before (baseline), 1 h after medication (post-drug), during ongoing experimental muscle pain (pain-post-drug), and 15 min after pain had vanished (post-pain). Analysis of variance demonstrated significantly lower VAS peak pain scores (5.9 +/- 0.4 cm) after administration of tolperisone hydrochloride compared with pridinol mesilate (6.8 +/- 0.4 cm) and placebo (6.6 +/- 0.4 cm) (P=0.020). Administration of pridinol mesilate was associated with a significant decrease in PPTs compared with tolperisone hydrochloride and placebo (P=0.002) after medication, but not after experimental jaw-muscle pain. The normalised peak-to-peak amplitude of the stretch reflexes were not significantly influenced by the test medication (P=0.762), but were in all sessions significantly facilitated during ongoing experimental jaw-muscle pain (P=0.034). In conclusion, tolperisone hydrochloride provides a small, albeit significant reduction in the perceived intensity of experimental jaw-muscle pain whereas the present dose had no effect on the short-latency jaw-stretch reflex.

Adult↗
PubMed1978

Stretch reflex of the biceps and brachioradialis muscles in patients with upper motor neuron syndrome.

The position of elbow flexion commonly observed in patients with upper motor neuron lesions is attributed by many clinicians to hyperactive stretch reflexes. The purpose of this study was to examine the passive stretch reflexes of the biceps and brachioradialis muscles in order to assess their possible relative contributions to the flexion posture. Twenty-one patients with upper motor neuron lesions were tested, using an automated system to produce controlled passive movement strech reflexes. Ratios derived from the electromyographic activity elicited during passive movement were used for quantitative comparisons. The stretch reflex response of the brachioradialis muscle was larger and earlier than the biceps response. A surprising finding was reciprocal activity in these two synergists following phasic stretch.

Adult↗
PubMed1988

Nonlinear identification of stretch reflex dynamics.

The objective of this study was to use nonlinear identification techniques to study the dynamics of stretch reflexes in the human calf muscles (gastrocnemius-soleus). Stochastic perturbations of ankle position were applied while subjects maintained a constant, tonic contraction of gastrocnemius-soleus. Linear models of the relation between ankle velocity and the electromyographic (EMG) activity under these conditions typically accounted for less than 40% of the observed EMG variance. Nonlinear system identification techniques were then applied. The first- and second-order Wiener kernels were computed as the initial stage of this analysis. These did not provide an adequate description of system behavior; subsequent simulation studies showed that the major problem with the Wiener analysis was that the input spectrum was not adequately white. Nevertheless, the shape of the second-order Wiener kernel suggested that a Hammerstein structure consisting of a static nonlinearity followed by a dynamic linear system would be appropriate. Consequently, we used an iterative procedure for Hammerstein system identification to determine the form of the static nonlinearity and the associated linear dynamics. The resulting nonlinear model provided a much better description of the system's behavior than did the linear models (variance accounted for greater than 60%). Furthermore, they confirmed our previous empirical findings; the static nonlinearity closely resembled a half-wave rectifier while the dynamics were typified by a pure delay and a velocity filter. The application of nonlinear identification techniques thus produced a much improved, physically meaningful model of stretch reflex behavior.

Electromyography↗
PubMed2006

[Electromyographic study of stretch reflexes in the normal and prosthetic hip].

PURPOSE OF THE STUDY: Several studies have been devoted to the effect of proprioception on joint function. Modifications in feedback control from the cord have been observed in unstable joints due to capsule and ligament laxity. A few studies have examined the effect of knee and hip arthroplasty on proprioception, but none have established whether stretch reflexes affect function of a prosthetic joint. The purpose of the present study was to demonstrate the electromyographic characteristics of stretch reflexes of the normal hip joint and to compare them with those observed in the prosthetic hip. MATERIAL AND METHODS: Two groups of patients were studied. The first included eleven subjects free of neurological disorders whose studied limb was healthy. The second group included ten subjects with a total hip prosthesis who had undergone extensive capsulectomy during the arthroplasty. Voluntary muscle contraction was noted in each subject. In addition, electromyographic recordings were made to note response of the ipsilateral and contralateral quadriceps crural and tensor of the fascia lata during changes in joint position. Recordings were made with the subject in the supine position, the limb suspended, hip flexed at 45 degrees and knee extended. Three series of ten recordings were made in random order to measure the latency of muscle response to free fall of the limb, accelerated fall of the relaxed limb, and accelerated fall associated with calibrated contraction of the quadriceps. Mean latency of muscle response was calculated for each trial. RESULTS: In the conditions of this study, there was no statistically significant difference (p = 0.05) in the reflex time course between natural and prosthetic hips. DISCUSSION: Changes due to joint replacement and capsulectomy do not appear to affect the stretch reflexes of the hip joint.

Aged↗
PubMed1971

Stretch reflexes in the upper limb of spastic man.

The reflex response to stretch has been studied in the upper limb of 20 spastic patients. The amplitude of reflex EMG was found to be closely related to the velocity of stretch. Reflex EMG in biceps and triceps muscles was augmented by increasing the length of the muscle, although minimal inhibition of reflex EMG in biceps was obtained in two patients by extreme stretch. The clasp-knife sensation in the upper limb cannot be related to autogenic inhibition but may be explained by the characteristics of a velocity-dependent reflex in which limb movement is braked by the mechanical effect of increasing muscle tension. It is suggested that this be called the pseudo-clasp-knife reaction to distinguish it from the clasp-knife phenomenon of the quadriceps muscle, since the underlying neurophysiological mechanism is quite different.

Cerebrovascular Disorders↗
PubMed1987

Absence of stretch reflex gain enhancement in voluntarily activated spastic muscle.

Static and dynamic stiffnesses of voluntarily activated elbow muscles were compared in spastic and contralateral arms of 15 subjects with spastic hemiparesis. Stiffnesses were estimated from the positional deflections induced by applying load perturbations to each forearm. In 11/15 subjects (73%), stiffness were comparable on the two sides. In the remaining 4/15 subjects (27%), stiffness were consistently greater on the spastic side, however, EMG recordings from these spastic muscles were of much smaller amplitude than those of the contralateral muscles, indicating that this increase was probably caused by changes in the mechanical properties of elbow muscles, rather than by stretch reflex enhancement. We conclude that for voluntarily activated muscles of spastic hemiparetic subjects, reflex stiffness (and presumably stretch reflex gain), of spastic and contralateral limbs is not significantly different. These findings impose important constraints upon theories attempting to explain spastic hypertonia, and they also provide guidelines for clinical quantification of spasticity.

Adult↗
PubMed2007

A stretch reflex in extraocular muscles of species purportedly lacking muscle spindles.

It is generally assumed that proprioceptive feedback plays a crucial role in limb posture and movement. However, the role of afferent signals from extraocular muscles (EOM) in the control of eye movement has been a matter of continuous debate. These muscles have atypical sensory receptors in several species and it has been proposed that they are not supported by stretch reflexes. We recorded electromyographic activity of EOM during passive rotations of the eye in sedated rats and squirrel monkeys and observed typical stretch reflexes in these muscles. Results suggest that there is a similarity in the reflexive control of limb and eye movement, despite substantial differences in their biomechanics and sensory receptors. Like in some limb skeletal muscles, the stretch reflex in EOM in the investigated species might be mediated by other length-sensitive receptors, rather than muscle spindles.

Animals↗
PubMed1991

Intact inhibition of the stretch reflex during general tetanus.

Tetanus toxin at lethal doses (2-10 x 10(3) mouse minimal lethal doses per kg body weight, mMLD/kg) was injected i.v. into 10 cats under pentobarbital anaesthesia. After the appearance of the first sign of generalized tetanus the animal was anaesthetized by a mixture of urethane and chloralose. Experiments were performed several hr thereafter when the toxin action was anticipated to be optimal. The stretch reflexes were elicited manually, by the contraction of the antagonistic muscles or by a stretch device. In toxin treated animals the spontaneous electromyographic activity was inhibited by strong stretching of the tested muscle or by that of the antagonistic muscle. The stretch reflex of the extensor muscle elicited by a contraction of the flexor muscle was inhibited by electrical stimulation of the flexor afferent fibres. The stretch reflex elicited by a stretch device as well as the electrically elicited monosynaptic reflex were inhibited by conditioning stimulation of the antagonistic nerve. The inhibition curves were almost the same as those of healthy animals. It is concluded that the spinal inhibitions, such as antagonistic group Ia, autogenic group Ib, groups II and III and the presynaptic inhibitions, were kept intact in severe general tetanus.

Anesthesia↗
PubMed1991

Stretch reflex inhibition using electrical stimulation in normal subjects and subjects with spasticity.

The effect of electrically stimulating the tibialis anterior muscle on the stretch reflex of the soleus muscle in normal subjects and subjects with spasticity is investigated. Stimulation of the tibialis anterior just prior to the onset of a mechanical disturbance, which causes a stretch in the soleus, inhibits the stretch reflex of the soleus in normal subjects and may inhibit clonus in subjects with spasticity.

Biomechanical Phenomena↗
PubMed1989

Modulation of stretch reflex by anticipation of the stimulus through visual information.

A stretch stimulus was applied to the right elbow flexor by the free gravitational fall of a weight. The subject was instructed to flex the elbow joint to lift the weight quickly (resist task) or to extend the elbow joint to overtake the falling weight (assist task) as the voluntary reaction to the stretch stimulus. In the resist task, when the subject could predict the time of stretch stimulus onset by watching through the mirror the behavior of the experimenter going to give the stretch stimulus, the integrated EMG (I-EMG) of M2 (50-80 ms after the stimulus onset) and M 3 (80-100 ms) components of stretch reflex were significantly enhanced compared with when the experimenter's movements were invisible to the subject, while no differences were observed in the background discharge before the stretch stimulus onset (BGA) and the short latency reflex (M 1). In the assist task, the M 2 and M 3 were depressed when the visual information about the stimulus presentation was available, while the BGA and M 1 were unchanged. From these results, it is suggested that (1) the preparatory set should be classified into two categories, i.e., task-related "topographical set" and timing-related "chronographic set", and (2) visual information about the process of stimulus presentation can modulate the reflex activity of stretched muscle allowing the required task to be executed efficiently by accurately anticipating the stretch stimulus onset.

Adolescent↗