PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Reflex, Stretch”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources
PubMed1992

Task-dependent changes in the response of human wrist joints to mechanical disturbance.

1. Subjects sat with their right hands in a mould which was attached to the shaft of a servo-controlled motor. 2. There were two different tasks. In one, the subject attempted to maintain a constant wrist flexing force, while the motor imposed flexion-extension movements. In the other, the subject attempted to maintain a constant wrist position while the motor exerted variable flexion-extension forces. 3. The 'maintain force' task was punctuated by randomly timed ramp extension movements to test the stretch reflex activity. The 'maintain position' task was punctuated by force changes which were the same as those recorded during the ramp extensions mentioned above. In this way it was possible to test stretch reflexes with the same disturbance during the 'maintain force' and 'maintain position' tasks. 4. When, after some practice, subjects had become good at maintaining the constant force, later components of the stretch reflex (after 40 ms) were found to be smaller than when they were maintaining a constant position. 5. Attempts to maintain a constant position often involved co-activation of the wrist extensor muscles. This could be prevented by local anaesthesia of the radial nerve. The long-latency stretch reflex of the flexors was still task dependent after this had been done. 6. The roles of co-activation and of task-dependent reflex responses are discussed.

Adult↗
PubMed1999

Measurement of the effect of a bolus dose of intrathecal baclofen by a repetitive movement test.

We assessed the repetitive movement (RM) test for measuring the effect of a trial bolus dose of intrathecal baclofen on spasticity. The RM test measures passive range of motion (ROM) by electrogoniometry and stretch reflex activity (SRA) of the flexors and extensors of the knee and ankle by surface electromyography. The SRA has a dynamic component (dynamic stretch reflex, DSR) and a tonic component (tonic stretch reflex, TSR). Four hypotheses were formulated: (a) RM results show a negative relationship between SRA and ROM; (b) values on the RM test are correlated with clinical scores of tonus and spasticity; (c) RM results show a reduction in SRA after administration of the clinically optimal dose of baclofen; and (d) RM results show a dose-dependent effect of intrathecal baclofen on SRA. Twenty-four patients were selected because they had impairments and disabilities caused by intractable spasticity. A bolus of baclofen was administered with incremental doses (25-150 micrograms) until an optimal effect or no effect was obtained. The main outcome measures were RM test and clinical assessments of the Ashworth and spasm score. The results were (a) For the ankle a negative correlation was found between ROM and TSR of the flexor and extensors; for the knee a significant negative correlation was found only with the DSR of the biceps femoris. (b) A positive correlation was found between the Ashworth score and TSR of the extensors and between the spasm score and DSR and TSR of the gastrocnemius muscle. (c) Significant differences were found between baseline measurements and the optimal dose of baclofen for all measures. (d) A significant dose-dependent effect of intrathecal baclofen on the level of SRA was observed. The RM test is thus a useful clinical tool for objectively measuring the effect of intrathecal baclofen administration on spasticity in patients with an upper motor neuron syndrome.

Adolescent↗
PubMed1975

Reflex patters initiated by the secondary sensory fiber endings of muscle spindles: a proposal.

Muscle spindles have two kinds of sensory fibers, each with stretch-sensitive endings on the nuclear bag muscle fibers and the nuclear chain muscle fibers within the spindle. The stretch reflex responses initiated by the primary sensory fibers have been well defines. There are other stretch reflexes of poorly defined origin and distribution. Clinical studies on spastic patients indicate that these stretch reflexes show regional responses or regional synergies. Stretch of flexor muscles of proximal joints of an extremity causes slowly recruiting, prolonged, reflex flexion in that extremity, in the contralateral extremity and also in the ipsilateral extremity, producing the crossed extension-flexion reflex and long spinal reflex. Likewise, stretch of extensor muscles of the proximal joints initiates a similar extension reflex in the same distribution. Stretch of the distal flexors of an extremity reflexly spreads flexion through that extremity. Stretch of the distal extensors of an extremity spreads extension throughout that extremity. These reflexes can be abolished by intramuscular neurolysis with phenol. They have long internuncial pathways and involve both alpha and gamma motoneurons. The demonstration that these reflex patterns are initiated by stretch of the muscle and show characteristics similar to those shown in physiological studies by the secondary sensory spindle reflexes suggests that they are initiated by stretch of the endings of the secondary sensory fibers of muscle spindles.

Humans↗
PubMed1982

Self-regulation of spasm and spasticity in cerebral palsy.

Four young adult cerebral palsied subjects with a mixture of spasticity and athetosis attended an experimental reflex training program for three one-hour sessions each week over an 18 month period. During each session on-line measures of contraction level and tonic stretch reflex sensitivity from the biceps brachii muscle were shown to the subject on meter displays. Subjects were asked to attempt to control the displays. They were given goals such as: (1) reduce both contraction level and reflex sensitivity displays to zero and (2) increase the contraction level display to 10% of maximum while keeping the reflex sensitivity display at a minimum. Achievement of goals was automatically sensed and used to activate a cassette tape of the subject's favourite music. Contraction level and reflex sensitivity scores were averaged over one-minute intervals to provide a record of long term progress. Elbow-angle and IEMG data were recorded on FM tape for off-line analysis. All four subjects learned to suppress involuntary muscle activity and resting tonic stretch reflex responses. They also learned to produce a two or three-fold variation in action tonic stretch reflex sensitivity while sustaining 10% maximum voluntary contraction. In other words, subjects learned to self-regulate spasm and spasticity at the elbow and to regulate tonic stretch reflex sensitivity independently of contraction level. A visual tracking task requiring voluntary movement about the elbow was employed to assess improvement in functional control of elbow movement. One athetotic subject improved tracking accuracy as a consequence of reducing the amount of involuntary arm movement while the other three subjects showed negligible improvement in functional control.

Biofeedback, Psychology↗
PubMed1989

The history of reflex hammers.

Following the simultaneous description of muscle stretch reflexes by Heinrich Erb and Carl Westphal in 1875, neurologists used direct finger taps or chest percussion hammers to elicit these phenomena. Because of inadequacies of chest percussion hammers for eliciting muscle stretch reflexes, a variety of hammers were developed specifically for this purpose. In 1888, J. Madison Taylor, working for S. Weir Mitchell at the Philadelphia Orthopedic Hospital, designed the first such "reflex hammer." Taylor's hammer had a triangular rubber head and a short, flattened metal handle. Krauss (1894), Berliner (1910), Troemner (1910), Babinski (1912), and Wintle (1925) also designed popular reflex hammers. Many of these hammers and several others are still in use.

Equipment and Supplies↗
PubMed2004

Mechanical measurements of the effects of intrathecal baclofen dosage adjustments in cerebral palsy: a pilot study.

OBJECTIVE: The purpose of this pilot study was to determine the feasibility of using mechanical measures of stretch reflexes to monitor spasticity after intrathecal baclofen dosage changes. DESIGN: Mechanical measures were made in studying six participants with cerebral palsy who were undergoing treatment for spasticity using intrathecal baclofen therapy. Mechanical measurements of stretch reflexes were made before and after pump implant in four of the six participants and after dosage changes in all participants, for a period of up to 2 yrs. The measurements comprised electromyograms and resistive torque responses to movement of the ankle, imposed with an isokinetic dynamometer. For each test session, random movements were applied to the ankle at each of four to seven speeds, repeated three or five times. RESULTS: Stretch reflex excitability decreased in three of four participants after initiation of intrathecal baclofen therapy and decreased with increasing dosages in three of the six participants. Broken catheters coincided with heightened mechanical measures in two cases. CONCLUSION: Mechanical measures of stretch reflexes change after intrathecal baclofen dosage adjustments, reflecting the clinical course of intrathecal baclofen therapy.

Adolescent↗
PubMed1991

Wrist muscle activation patterns and stiffness associated with stable and unstable mechanical loads.

The objectives of this study were to examine the effects of load mechanical characteristics and agonist-antagonist muscle cocontraction, on the stretch reflex response of wrist flexor muscles, and to measure the associated wrist stiffness. Subjects were required to maintain a constant wrist angle while operating against flexor loads with different stability characteristics (constant, elastic or unstable). We measured the stretch reflex responses and joint stiffness by applying step displacements of 3 degrees and 10 degrees. Subjects used very little cocontraction of wrist flexor and extensor muscles when the load was constant or elastic, but increased cocontraction dramatically when the load was unstable, in order to increase the wrist stiffness. Although the magnitude of stretch reflex responses also increased with cocontraction, this simply reflected the level of tonic flexor muscle activity. We found no evidence to suggest that phasic stretch reflexes contributed significantly to the joint stiffness in this task. Clear differences in flexor muscle synergy were observed in the presence and absence of cocontraction, particularly when comparing the FCR and FCU muscles.

Adult↗
PubMed1986

Once more on the equilibrium-point hypothesis (lambda model) for motor control.

The equilibrium control hypothesis (lambda model) is considered with special reference to the following concepts: (a) the length-force invariant characteristic (IC) of the muscle together with central and reflex systems subserving its activity; (b) the tonic stretch reflex threshold (lambda) as an independent measure of central commands descending to alpha and gamma motoneurons; (c) the equilibrium point, defined in terms of lambda, IC and static load characteristics, which is associated with the notion that posture and movement are controlled by a single mechanism; and (d) the muscle activation area (a reformulation of the "size principle")--the area of kinematic and command variables in which a rank-ordered recruitment of motor units takes place. The model is used for the interpretation of various motor phenomena, particularly electromyographic patterns. The stretch reflex in the lambda model has no mechanism to follow-up a certain muscle length prescribed by central commands. Rather, its task is to bring the system to an equilibrium, load-dependent position. Another currently popular version defines the equilibrium point concept in terms of alpha motoneuron activity alone (the alpha model). Although the model imitates (as does the lambda model) spring-like properties of motor performance, it nevertheless is inconsistent with a substantial data base on intact motor control. An analysis of alpha models, including their treatment of motor performance in deafferented animals, reveals that they suffer from grave shortcomings. It is concluded that parameterization of the stretch reflex is a basis for intact motor control. Muscle deafferentation impairs this graceful mechanism though it does not remove the possibility of movement.

Journal Article↗
PubMed1991

The mechanism of spastic muscle hypertonus. Variation in reflex gain over the time course of spasticity.

The electromyographic (EMG) response of the initially passive biceps brachii muscle to imposed extension applied at the elbow was studied in 19 hemiparetic and 12 normal subjects. In relaxed normal subjects, the biceps muscle was found to respond only at displacement velocities above 175 deg/s, with a single early burst of activity in the biceps EMG. In contrast, the hemiparetic subjects, in addition to the early EMG activity, also showed considerable late activity, which persisted even with stretch velocities as low as 35 deg/s. This late activity is a stretch reflex, present in fully plegic arms. It was seen in all spastic subjects in whom the tone of the biceps had been clinically assessed to be raised, but was never observed in subjects with normal muscle tone. The mean level of this EMG response was highly correlated with displacement velocity and its duration to the duration of the applied displacement. It is suggested that this reflex EMG activity is the major factor in the genesis of spastic hypertonus in the arm and that it arises not from a reduction in the threshold of the stretch reflexes of the muscle, but from a pathological increase in stretch reflex gain. It is further shown that this activity is at a high level between the first and third months after the onset of spasticity and that the reflex gain is significantly reduced when spasticity is established for a year or more. It is concluded that, while changes in passive mechanical properties may play a role when spasticity has been established for more than a year, the major cause of spastic muscle hypertonus is a pathological increase in stretch reflex activity.

Adult↗
PubMed2001

Adaptive changes in locomotor control after partial denervation of triceps surae muscles in the cat.

This report concerns a test of the hypothesis that gain in the stretch reflex pathway of cat medial gastrocnemius (MG) muscle during locomotion increases after denervation of its synergists, lateral gastrocnemius (LG), soleus (SOL) and plantaris (PL) muscles. In four cats, MG, tibialis anterior (TA) and vastus lateralis (VL) muscles were implanted with electromyogram (EMG) electrodes. The cats walked on a row of elevated pegs, some of which were spring-loaded and could be triggered to pop up at the moment of foot touchdown, rapidly dorsiflexing the foot. Pre-stretch EMG activity in MG as well as short-, medium- and long-latency responses to the dorsiflexions were compared before and after unilateral denervation of synergists. Short- and medium-latency responses of MG to perturbations increased in proportion to the increase in pre-stretch EMG in the days and weeks after partial denervation. This argues against an adaptive increase in stretch reflex gain independent of centrally generated extensor drive. Local anaesthesia of the skin of the paw did not significantly change the sizes of the stretch responses of MG before or after partial denervation. We conclude that pre-stretch EMG activity as well as stretch reflexes in MG muscle increased substantially after denervation of synergistic muscles. The data were consistent with an adaptive increase in central locomotor drive, causing more motoneuronal activity, which in turn resulted in an increase in the size of stretch reflexes.

Adaptation, Physiological↗
PubMed1991

Changes in the response to magnetic and electrical stimulation of the motor cortex following muscle stretch in man.

1. The effect of muscle stretch on the EMG response from the stretched muscle to transcranial magnetic stimulation of the motor cortex was studied in eight subjects. Muscle stretch was produced by increasing the torque of a motor acting through a lever which was held at constant position by a flexion force of the index and middle fingers. EMG responses were recorded from fine-wire electrodes inserted into flexor digitorum profundus muscle in the forearm. They consisted of a spinal latency component and a long-latency component which could in some subjects be separated into an early and a late phase. 2. In four subjects, four intervals between the stretch and the cortical stimulus were explored using three intensities of cortical stimulation. At all three intensities, when the magnetic cortical stimulus was timed to produce an EMG response in the period of the later part of the long-latency stretch reflex the response was larger than when it was timed to produce a response in the period of the short-latency spinal reflex or when superimposed on the tonic muscle activity used to resist the standing torque of the motor. 3. When the intensity of magnetic cortical stimulation was reduced so that it was just below threshold to produce an EMG response in the short-latency reflex period or on the background tonic EMG activity, it still was capable of producing a response when superimposed on the long-latency stretch reflex. 4. In four subjects the time course of this effect was studied in more detail using only one intensity of magnetic cortical stimulus set to be just above threshold to produce a response in tonically active muscles. The time course of the facilitatory effect was similar to the time course of the later part of the long-latency stretch reflex. From these data it was not possible to determine whether the early part of the long-latency stretch reflex also was accompanied by the facilitatory effect since this component was present in only one of the four subjects. 5. The facilitatory effect persisted after the ulnar and median nerves were totally blocked at the wrist by injections of local anaesthetic. This suggests that inputs from muscle receptors of the stretched muscle contribute to the effect.4=

Adult↗
PubMed1992

Tonic vibration reflexes and background force level.

On Earth, the functional stretch reflex is an important component in the maintenance of posture and muscle tone. In parabolic flight experiments, we evaluated whether the functional stretch reflex, as reflected in the tonic vibration reflex, adjusts appropriately for changes in background gravitoinertial force level. Virtually immediate alterations of appropriate sign occurred.

Forearm↗
PubMed1983

Modulation of reflex activity of motor units in response to stretch of a human finger muscle.

Changes in stretch reflex responses were examined in two types of motor task, force control and position control, by applying a small quick stretch to the middle finger extensor digitorum communis (EDC) muscle at an unpredicted time and observing activities of single motor units. Subjects were asked to maintain a constant extending isometric force at the metacarpophalangeal (MP) joint for force control, and to maintain a constant middle finger position against an applied force for position control. No significant differences in the tonic activities of EDC motor units were seen between the two types of motor task when the same force was exerted about the MP joint. Tonic activities of the EDC muscle and its antagonists were thus similar for both types of motor task. Ten of the eighteen motor units investigated showed obvious reflex responses (increase in firing rate) with latencies of 30-60 msec after the stretch. This reflex response was greater for position control than for force control, given the same operating conditions of tonic force, finger position, and activities of motor units. Enhancement of the stretch reflex for position control was also observed in surface electromyograms of the same muscle.

Adult↗
PubMed1990

A review of myotatic reflexes and the development of motor control and gait in infants and children: a special communication.

Although the mechanism of the phasic myotatic (or "stretch") reflex is well-known, the role of this reflex in adult gait remains speculative. The acquisition and development of locomotor skills with respect to the development of the myotatic reflex require further study in both healthy and neurologically impaired children. In this article, the well-documented properties of the healthy adult's myotatic reflex are compared with recent findings of the myotatic reflex in healthy infants and children and contrasted with reflex properties in patients with cerebral palsy. These data allow us to begin to characterize the emerging features of the stretch reflex in normal and pathological early development. From these data, we can begin to speculate about the relationship between changes in stretch reflexes and the acquisition of skillful movement and gait in early childhood.

Adult↗
PubMed2000

Stretch-shortening cycle: a powerful model to study normal and fatigued muscle.

Stretch-shortening cycle (SSC) in human skeletal muscle gives unique possibilities to study normal and fatigued muscle function. The in vivo force measurement systems, buckle transducer technique and optic fiber technique, have revealed that, as compared to a pure concentric action, a non-fatiguing SSC exercise demonstrates considerable performance enhancement with increased force at a given shortening velocity. Characteristic to this phenomenon is very low EMG-activity in the concentric phase of the cycle, but a very pronounced contribution of the short-latency stretch-reflex component. This reflex contributes significantly to force generation during the transition (stretch-shortening) phase in SSC action such as hopping and running. The amplitude of the stretch reflex component - and the subsequent force enhancement - may vary according to the increased stretch-load but also to the level of fatigue. While moderate SSC fatigue may result in slight potentiation, the exhaustive SSC fatigue can dramatically reduce the same reflex contribution. SSC fatigue is a useful model to study the processes of reversible muscle damage and how they interact with muscle mechanics, joint and muscle stiffness. All these parameters and their reduction during SSC fatigue changes stiffness regulation through direct influences on muscle spindle (disfacilitation), and by activating III and IV afferent nerve endings (proprioseptic inhibition). The resulting reduced stretch reflex sensitivity and muscle stiffness deteriorate the force potentiation mechanisms. Recovery of these processes is long lasting and follows the bimodal trend of recovery. Direct mechanical disturbances in the sarcomere structural proteins, such as titin, may also occur as a result of an exhaustive SSC exercise bout.

Humans↗
PubMed2005

Flexor reflex responses triggered by imposed knee extension in chronic human spinal cord injury.

Hypersensitivity of the flexor reflex pathways to input from force-sensitive muscle afferents may contribute to the prevalence and severity of muscle spasms in patients with spinal cord injury (SCI). In this study, we triggered flexor reflexes with constant velocity knee movements in 15 subjects with SCI. Ramp and hold knee extension perturbations were imposed on one leg while the hip and ankle were held in an isometric position using an instrumented leg brace. Knee, ankle and hip torque responses and electromyograms from six muscles of the leg were recorded following controlled knee extension at four different velocities. Tests were conducted with the hip in both flexed and extended positions. During the movement into knee extension, a velocity-dependent stretch reflex, represented by a progressively increasing knee flexion torque, was observed. In addition, another type of reflex that resembled a flexor reflex (flexion of the hip and ankle) was also triggered by the imposed knee extension. The magnitude of the ankle dorsiflexion torque responses was significantly correlated to the stretch reflex torque at the knee in 9 of the 15 subjects. We concluded that stretch reflexes initiate a muscle contraction that then can contribute to a flexor reflex response, possibly through muscle group III/IV afferent pathways. These results suggest that spasticity in SCI consists of a myriad of complex reflex responses that extend beyond stretch reflexes.

Adult↗
PubMed1995

Reduced servo-control of fatigued human finger extensor and flexor muscles.

1. In healthy human subjects holding the index finger semi-extended at the metacarpophalangeal joint against a moderate load, electromyographic (EMG) activity was recorded from the finger extensor and flexor muscles during different stages of muscle fatigue. The aim was to study the effect of muscle fatigue on the level of background EMG activity and on the reflex responses to torque pulses causing sudden extensor unloadings. Paired comparisons were made between the averaged EMG and finger deflection responses under two conditions: (1) at a stage of fatigue (following a sustained co-contraction) when great effort was required to maintain the finger position, and (2) under non-fatigue conditions while the subject tried to produce similar background EMG levels to those in the corresponding fatigue trials. 2. Both the unloading reflex in the extensor and the concurrent stretch reflex in the flexor were significantly less pronounced and had a longer latency in the fatigue trials. Consequently, the finger deflections had a larger amplitude and were arrested later in the fatigue trials. 3. It is concluded that--with avoidance of 'automatic gain compensation', i.e. reflex modifications attributable to differences in background EMG levels--the servo-like action of the unloading and stretch reflexes is reduced in fatigued finger extensor and flexor muscles.

Adult↗