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PubMed2004

Excitability changes in human forearm corticospinal projections and spinal reflex pathways during rhythmic voluntary movement of the opposite limb.

Rhythmic movements brought about by the contraction of muscles on one side of the body give rise to phase-locked changes in the excitability of the homologous motor pathways of the opposite limb. Such crossed facilitation should favour patterns of bimanual coordination in which homologous muscles are engaged simultaneously, and disrupt those in which the muscles are activated in an alternating fashion. In order to examine these issues, we obtained responses to transcranial magnetic stimulation (TMS), to stimulation of the cervicomedullary junction (cervicomedullary-evoked potentials, CMEPs), to peripheral nerve stimulation (H-reflexes and f-waves), and elicited stretch reflexes in the relaxed right flexor carpi radialis (FCR) muscle during rhythmic (2 Hz) flexion and extension movements of the opposite (left) wrist. The potentials evoked by TMS in right FCR were potentiated during the phases of movement in which the left FCR was most strongly engaged. In contrast, CMEPs were unaffected by the movements of the opposite limb. These results suggest that there was systematic variation of the excitability of the motor cortex ipsilateral to the moving limb. H-reflexes and stretch reflexes recorded in right FCR were modulated in phase with the activation of left FCR. As the f-waves did not vary in corresponding fashion, it appears that the phasic modulation of the H-reflex was mediated by presynaptic inhibition of Ia afferents. The observation that both H-reflexes and f-waves were depressed markedly during movements of the opposite indicates that there may also have been postsynaptic inhibition or disfacilitation of the largest motor units. Our findings indicate that the patterned modulation of excitability in motor pathways that occurs during rhythmic movements of the opposite limb is mediated primarily by interhemispheric interactions between cortical motor areas.

Adult↗

PubMed1977

The effect of lesions of the sensorimotor cortex and the capsular pathways on servo responses from the human long thumb flexor.

Lesions of the sensorimotor cortex, or of the capsular pathways beneath it, caused (with one exception out of 14 cases) diminution "r loss of the servo responses in the thumb, which are based on the long-latency stretch reflex. When not absent the long-latency stretch reflex tended to be late in onset. When absent it was often replaced by a large early reflex response at spinal latency. In general the results are consistent with the transcortical theory of the long-latency stretch reflex for the thumb, but, in detail, they indicate that the theory will require elaboration.

Adult↗

PubMed1999

Voluntary and reflex control of human back muscles during induced pain.

1. Back pain is known to change motor patterns of the trunk. The purpose of this study was to examine the motor output of the erector spinae (ES) muscles during pain in the lumbar region. First, their voluntary activation was assessed during flexion and re-extension of the trunk. Second, effects of cutaneous and muscle pain on the ES stretch reflex were measured, since increased stretch reflex gain has been suggested to underlie increased muscle tone in painful muscles. 2. The trunk movement and electromyographical (EMG) signals from the right and left ES during pain were compared with values before pain. Controlled muscle pain was induced by infusion of 5 % saline into the right lumbar ES. Cutaneous pain was elicited by mechanical or electrical stimulation of the dorsal lumbar skin. The stretch reflex was evoked by rapidly indenting the right lumbar ES with a servo-motor prodder. 3. The results from the voluntary task show that muscle pain decreased the modulation depth of ES EMG activity. This pattern was associated with a decreased range and velocity of motion of the painful body segment, which would normally serve to avoid further injury. Interestingly, when subjects overcame this guarding tendency and made exactly the same movements during pain as before pain, the EMG modulation depth was still reduced. The results seem to reconcile the controversy of previous studies, in which both hyper- and hypoactivity of back muscles in pain have been reported. 4. In the tapped muscle, the EMG response consisted of two peaks (latency 19.3 +/- 2.1 and 44.6 +/- 2.5 ms, respectively) followed by a trough. On the contralateral side the first response was a trough (26.2 +/- 3.2 ms) while the second (46.4 +/- 4.3 ms) was a peak, similar to the second peak on the tapped side. Cutaneous pain had no effect on the short-latency response but significantly increased the second response on the tapped side. Surprisingly, deep muscle pain had no effect on the stretch reflex. A short-latency reciprocal inhibition exists between the right and left human ES. 5. It is concluded that deep back pain does not influence the stretch reflexes in the back muscles but modulates the voluntary activation of these muscles.

Adult↗

PubMed2004

Decreased stiffness at the ankle joint in patients with long-term Type 1 diabetes.

AIMS: To evaluate contractile and reflex properties of the soleus muscle together with ankle joint stiffness in long-term Type 1 patients. METHODS: Stretch reflex and muscle function of the soleus muscle was tested in 15 Type 1 diabetes mellitus patients and 15 controls. M-wave amplitude and maximal twitch torque was elicited by supramaximal stimulation of the tibial nerve. The stretch reflex was elicited by a 4 degree rotation of the ankle. RESULTS: Rise time and fall time of the maximal twitch torque were increased compared with controls. The amplitude of the short latency stretch reflex was significantly reduced in patients at contraction levels of 5-30 Nm. At a contraction level of 5 Nm the median stretch reflex threshold was 10 degrees/s in patients and 6 degrees/s in controls (P = 0.03). Stiffness was decreased in diabetic patients, especially at lower contraction levels. There was no significant correlation between the clinical neuropathy score and stiffness. In contrast, high neuropathy score was correlated with low amplitude of the reflex amplitude (rho = -0.51, P = 0.05). CONCLUSIONS: We demonstrate altered contractile properties, a decrease in stretch reflex of the soleus muscle, and a reduced stiffness at the ankle joint in patients with long-term Type 1 diabetes. These changes may cause delayed muscle contraction and impaired reflex modulation which could contribute to gait disturbances and increased number of falls in diabetic patients.

Adult↗

PubMed1984

Crossed and uncrossed central effects of muscle spindle afferents from the lateral pterygoid muscle of the guinea pig.

Physiological evidence is presented for the presence of stretch reflexes in the lateral pterygoid (Pt) muscle of the guinea pig. The central reflex effects of excitation of Pt stretch reflex afferents were also investigated. Passive lateral jaw displacement, which resulted in stretch of the Pt muscle on the side of jaw movement and stretch of the zygomatico-mandibularis (Z) muscle on the side contralateral to the movement, evoked increased EMG activity in these muscles. Stimulation of the trigeminal mesencephalic nucleus (mes V) evoked monosynaptic reflexes in both the Pt and Z nerves. Tonic stretch of the Pt muscle facilitated the monosynaptic reflex in the Pt nerve evoked by stimulation of mes V. Tonic vibration of the Pt muscle facilitated the mes V evoked monosynaptic reflex in the nerves to the ipsilateral Pt and contralateral Z muscles. Conversely, tonic vibration of the Z muscle facilitated the monosynaptic reflex evolved by mes V stimulation in the contralateral Pt and ipsilateral Z nerve. The results support the view that muscle spindles exist in the Pt and Z muscles and that there is a monosynaptic stretch reflex for both the Pt and Z muscles with cell bodies located in the mes V nucleus. It was also shown that the ipsilateral Pt muscle and the contralateral Z muscle act as synergists in the production of lateral jaw movements and that the organization of the stretch reflexes originating from the Pt and Z muscles support their synergistic action.

Animals↗

PubMed1997

Impaired modulation of tonic muscle activities and H-reflexes in the soleus muscle during standing in patients with Parkinson's disease.

The presence of postural disturbance in patients with Parkinson's disease (PD) was assessed by the displacement of the centre of foot pressure (CFP) and by changes in the amplitude of the soleus H-reflex when patients maintained an upright standing posture, followed by a forward-leaning posture. Thirteen patients and 13 age-matched normal controls (N) were studied. PD patients showed the following differences when compared to normal subjects: (1) the range of displacement of the CFP associated with forward leaning was significantly smaller (P<0.01); (2) the ratio of the increase in the soleus EMG activity to the CFP displacement (deltaEMG/deltaCFP) was larger (P<0.01), and the value of the deltaEMG/deltaCFP increased significantly in relation to the scale of clinical severity (P<0.01); and (3) the ratio of the increase in the amplitude of the soleus H-reflex to the soleus muscle EMG activity (deltaH-reflex/deltaEMG) was significantly lower in PD patients (P<0.05). The value of the deltaH-reflex/deltaEMG decreased significantly with the scale of clinical severity among the patients (P<0.05). These results suggest that the modulation of both the tonic stretch reflex and the phasic stretch reflex in the soleus muscle during standing are impaired in PD patients, and these impairments may partly cause their disability in the maintenance of a standing posture. Abnormalities in Ib inhibition and presynaptic inhibition are considered to be possible mechanisms in the disturbed modulation of the tonic stretch reflex and the phasic stretch reflex in PD patients during standing.

Adult↗

PubMed1985

Long-latency spinal reflexes in humans.

Stretching human muscles with a mechanical device gave rise to multiple peaks in the rectified and averaged electromyogram. In the first dorsal interosseous the latency of the first peak (M1) was 32.4 +/- 2.4 ms (SD) and the latency of the second peak (M2) was 55.1 +/- 11.3 ms, in both cases measured from the time of the stimulus to the take-off point of the peak. Often a third peak (M3) was seen, having a considerably longer latency. The origin of peak M1 was considered to be in the stretch reflex arc because of its latency and its invariable association with muscle movement. Peak M2 was due to stimulation of afferent terminals in the skin and/or subcutaneous tissues by the mechanical device producing the muscle stretch. The conduction velocity of the pathway involved in the generation of the M1 component is the same as that for M2. This implies that central processing in the spinal cord delays the M2 response. The M2 mechanism does not involve a transcortical (long-loop) pathway because in foot muscles the M1-M2 delay remains the same as is found for hand muscles, although M1 latency is prolonged (to 39.4 +/- 6.2 ms for extensor digitorum longus). This indicates that there is not time for M2 impulses to traverse a pathway any longer than that passing to and from the spinal cord.

Afferent Pathways↗

PubMed1992

Preservation of the masseter reflex in Friedreich's ataxia.

In Friedreich's ataxia, the muscle stretch reflexes are absent or hypoactive in the upper and lower extremities because of pathologic involvement of the dorsal root ganglion cells. Paradoxically, the masseter reflex remains unaffected and may even be hyperactive in some cases. The masseter reflex is hypothesized as unique among stretch reflexes in that its afferent nerve cell body (the mesencephalic nucleus) is located intra-axially within the brainstem rather than in the craniospinal ganglia, where the afferent nerve cell bodies subserving the other stretch reflexes are located. This study supported this hypothesis by demonstrating that the masseter reflex is (1) usually absent in patients who are areflexic as a result of primary disorders of peripheral nerve axons or myelin, and (2) preserved in other disorders that primarily involve the dorsal root ganglion cells.

Blinking↗

PubMed2002

A method to evaluate reflex excitability of the human ankle plantarflexors despite changes in maximal activation capacities.

Stretch reflexes were evoked in the submaximally activated ankle extensors during sinusoidal length perturbations. A mean stretch reflex (SR) amplitude ((-)SRA), i.e., SR area/SR duration was quantified for the soleus muscle and for the gastrocnemii muscles. (-)SRA was also expressed in relative values ((-)SRA(rel)), i.e., SRA was related to the corresponding background electromyogram (EMG). Sinusoidal length perturbations were applied in two ways: (1) at a fixed frequency (16 Hz) and at different levels of voluntary contraction [10% to 70% maximal voluntary contraction (MVC)] and (2) at a constant activation level (50% MVC) and at frequencies ranging from 6 to 16 Hz. Then, new parameters are proposed to characterize muscle reflex excitability. The first parameter, SR(index), consisting in the slope of the (-)SRA-EMG relationship, was considered to be more representative of central influences on the reflex pathway. Secondly, the frequency distribution of the stretch reflex was analyzed and the area under the (-)SRA(rel)-frequency curve gave the second parameter (FD-(-)SRA(rel)). This parameter should account for both central and peripheral mechanisms on the reflex pathway. These parameters were found to be higher for the highly excitable soleus than for the less excitable gastrocnemii muscles. SR(index) and FD-(-)SRA(rel) can be proposed as a tool to analyze changes in reflex excitability, which can accompany a process of neuromuscular plasticity. In order to validate the procedure, the proposed parameters were quantified in a case study before and after a period of plyometric training.

Adult↗

PubMed1973

Quantitative study of the effect of L-dopa and phenoxybenzamine on the rigidity of Parkinson's disease.

The static and dynamic components of the tonic stretch reflex and shortening reactions have been studied in biceps brachii, triceps, hamstrings, and quadriceps muscles of 19 patients with Parkinson's disease before and during L-dopa therapy. Clinical improvement during L-dopa administration correlated with a reduction in the dynamic component of the tonic stretch reflex in biceps, triceps, and quadriceps but not the hamstrings muscle, and with the static component of the tonic stretch reflex in biceps and triceps but not quadriceps and hamstrings muscles. The only shortening reaction consistently reduced during the L-dopa treatment period was the dynamic shortening reaction of the triceps muscle. The responses of the stretch reflexes to changes in muscle length were not altered by L-dopa therapy. In severely disabled patients the hamstrings and quadriceps stretch reflexes were maximal in a position of partial flexion of the knee joint and this response to muscle length was not altered in these patients despite a dramatic lessening of rigidity in some patients. Shortening reactions commonly remained in some patients after the stretch reflex of the antagonistic muscle was abolished by L-dopa therapy. The administration of phenoxybenzamine to patients being treated with L-dopa reduced the different components of rigidity more than L-dopa alone, and the responses were consistent with phenoxybenzamine suppressing predominantly the descending noradrenergic pathway.

Aged↗

PubMed1999

Conditioned patellar tendon-tap reflexes in patients with ACL reconstruction.

The patellar tendon-tap stretch reflexes were examined in six neurologically healthy young subjects (mean age = 27.1 yrs) who had developed persistent quadriceps strength deficit due to ACL reconstruction. Each subject was tested on two separate days. A specially designed apparatus was used to examine the unilateral and conditioned patellar tendon-tap reflex response utilizing three different conditioning intervals: 25 ms, 75 ms, 150 ms, and a unilateral reflex (control). Peak isometric force and contraction time were measured by using a strain gauge. Also, peak-to-peak EMG was measured by using bipolar surface electrodes which were placed over the middle of the rectus femoris. All data were collected with a microcomputer (sample rate = 1 kHz). Due to the small sample, the Kruskal-Wallis nonparametric analysis of variance was performed. All subjects demonstrated quadriceps strength deficits in the ACL leg when compared with the contralateral leg. This analysis determined that for both the ACL leg and the Non ACL leg the size of stretch reflex was facilitated at the long-latency conditioning intervals (75 and 150 ms), whereas it was inhibited at the short-latency conditioning interval (25ms). However, the ANOVA model failed to reveal any differences in the conditioned stretch reflex between the ACL leg and the Non ACL leg. Also, no differences were observed at the unilateral condition. Taken together, these results indicate that ACL reconstruction results in significant strength deficits, but does not alter unilateral or conditioned reflex profiles.

Adult↗

PubMed1990

Lack of fusimotor modulation in a motor adaptation task in man.

Single-unit activity was recorded from the radial nerve of human subjects along with surface electromyogram, joint angle, velocity, and torque at a metacarpophalangeal joint. Nine afferents from muscle spindles in the extensor digitorum muscles were studied in a motor adaptation task which involved modulations of the long-latency stretch reflex. While subjects slowly moved one finger, a perturbation which rapidly stretched the parent muscle was applied. The subjects' task was to return their finger as fast as possible. In a series of identical control experiments, electromyographic activity and performance alone were recorded, but not spindle afferents. Subjects improved their performance by a varying degree when the test was repeated. Optimal performance was usually associated with increased electromyographic activity at a latency of about 60 ms, which was interpreted as a long-latency stretch reflex. The response of the individual spindle afferents to perturbation was uniform in repeated tests regardless of the size of the reflex, e.g. whether it was large or lacking altogether. It was concluded that modulations of the size of the long-latency stretch reflex in the present motor adaptation task were accounted for by mechanisms other than adjustments of the fusimotor activity, because spindle response to an invariant perturbation remained invariant when the size of the reflex varied substantially.

Adult↗

PubMed1990

Effects of prolonged muscle stretch on reflex and voluntary muscle activations in children with spastic cerebral palsy.

We studied the short term effects of a single session of prolonged muscle stretch (PMS) on reflex and voluntary muscle activations in 22 children with spastic cerebral palsy (CP) assigned to an experimental (n = 12) and a control group (n = 10). Children of the experimental group underwent PMS of the triceps surae (TS) by standing with the feet dorsiflexed on a tilt-table for 30 min, whereas children of the control group were kept at rest. The effects were determined by measuring the associated changes in torque and in electromyographic (EMG) activity of the TS and tibialis anterior (TA) muscles during both passive ankle movements and maximal static voluntary contractions. The results indicate that PMS led to reduced spasticity in ankle muscles as demonstrated by the significant reductions (p less than 0.05) of the neuromuscular responses (torque and EMG) to passive movement. These inhibitory effects lasted up to 35 min after cessation of PMS. In addition, the capacity to voluntarily activate the plantar flexors was significantly (p less than 0.05) increased post-PMS, but the capacity to activate the dorsiflexors was apparently not affected. These findings suggest that repeated sessions of PMS may have beneficial effects in the management of spasticity in children with CP.

Cerebral Palsy↗

PubMed1995

Mechanical and electromyographic analysis of reciprocal inhibition at the human ankle joint.

1. The purpose of the present study is to investigate how reciprocal inhibition influences the mechanical and electromyographic (EMG) properties of the ankle plantar flexors in humans during a voluntary contraction. 2. At different levels of maintained plantar flexion contractions ranging from 0 to 20 Nm, the size of the soleus EMG stretch reflex and the ankle joint stiffness (ration between the torque increment and the amplitude of the stretch) were measured in response to an imposed dorsiflexion. At matched plantar flexion contraction levels, stretch responses were compared before and after reversible block of the common peroneal nerve (CPN). Stretch responses were also measured during an attempted voluntary fictive dorsiflexion after CPN block. 3. In the preactivated soleus muscles, the phasic EMG response to stretch consisted of two peaks labeled M1 and M2. After CPN block, the M1 short-latency stretch reflex on average increased by 25 +/- 5.7%, mean +/- SD (P < 0.001), and the M2 stretch reflex increased on average by 29 +/- 13.0% (P = 0.002). 4. The total stiffness of the ankle joint during a stretch is the sum of the nonreflex and the reflex mediated stiffness. The total stiffness after CPN block increased on average by 13 +/- 2.7% (P = 0.002) and the estimated reflex stiffness by 33 +/- 6.5% (P < 0.001). 5. When the subjects were asked to make a strong dorsiflexion after CPN block, the soleus stretch reflex was depressed to the extent that the reflex mediated mechanical effect around the ankle joint was abolished.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2001

Soleus H-reflex gain in humans walking and running under simulated reduced gravity.

The Hoffmann (H-) reflex is an electrical analogue of the monosynaptic stretch reflex, elicited by bypassing the muscle spindle and directly stimulating the afferent nerve. Studying H-reflex modulation provides insight into how the nervous system centrally modulates stretch reflex responses.A common measure of H-reflex gain is the slope of the relationship between H-reflex amplitude and EMG amplitude. To examine soleus H-reflex gain across a range of EMG levels during human locomotion, we used simulated reduced gravity to reduce muscle activity. We hypothesised that H-reflex gain would be independent of gravity level.We recorded EMG from eight subjects walking (1.25 m s-1) and running (3.0 m s-1) at four gravity levels (1.0, 0.75, 0.5 and 0.25 G (Earth gravity)). We normalised the stimulus M-wave and resulting H-reflex to the maximal M-wave amplitude (Mmax) elicited throughout the stride to correct for movement of stimulus and recording electrodes relative to nerve and muscle fibres. Peak soleus EMG amplitude decreased by ~30% for walking and for running over the fourfold change in gravity. As hypothesised, slopes of linear regressions fitted to H-reflex versus EMG data were independent of gravity for walking and running (ANOVA, P > 0.8). The slopes were also independent of gait (P > 0.6), contrary to previous studies. Walking had a greater y-intercept (19.9% Mmax) than running (-2.5% Mmax; P < 0.001). At all levels of EMG, walking H-reflex amplitudes were higher than running H-reflex amplitudes by a constant amount. We conclude that the nervous system adjusts H-reflex threshold but not H-reflex gain between walking and running. These findings provide insight into potential neural mechanisms responsible for spinal modulation of the stretch reflex during human locomotion.

Adult↗

PubMed2003

On the reflex coactivation of ankle flexor and extensor muscles induced by a sudden drop of support surface during walking in humans.

Recent studies have revealed that the stretch reflex responses of both ankle flexor and extensor muscles are coaugmented in the early stance phase of human walking, suggesting that these coaugmented reflex responses contribute to secure foot stabilization around the heel strike. To test whether the reflex responses mediated by the stretch reflex pathway are actually induced in both the ankle flexor and extensor muscles when the supportive surface is suddenly destabilized, we investigated the electromyographic (EMG) responses induced after a sudden drop of the supportive surface at the early stance phase of human walking. While subjects walked on a walkway, the specially designed movable supportive surface was unexpectedly dropped 10 mm during the early stance phase. The results showed that short-latency reflex EMG responses after the impact of the drop (<50 ms) were consistently observed in both the ankle flexor and extensor muscles in the perturbed leg. Of particular interest was that a distinct response appeared in the tibialis anterior muscle, although this muscle showed little background EMG activity during the stance phase. These results indicated that the reflex activities in the ankle muscles certainly acted when the supportive surface was unexpectedly destabilized just after the heel strike during walking. These reflex responses were most probably mediated by the facilitated stretch reflex pathways of the ankle muscles at the early stance phase and were suggested to be relevant to secure stabilization around the ankle joint during human walking.

Adaptation, Physiological↗

PubMed1973

Electromyographic study of the rigidospasticity of athetosis.

The static and dynamic components of the tonic stretch reflex and shortening reactions have been studied in 10 patients with athetosis. EMG activity could be recorded only from the biceps muscle when the patient was at rest. The dynamic stretch reflex increased with the velocity of stretching in all muscles examined except the biceps. The biceps stretch reflex was found to be inhibited by increasing muscle length, whereas the stretch reflexes of triceps, hamstrings, and quadriceps muscles were facilitated by increasing muscle length. Reinforcement increased resting activity in the biceps and the dynamic shortening reaction of the triceps muscle. Both these effects were suppressed by the action of phenoxybenzamine. Although phenoxybenzamine was shown to reduce muscle tone in a double-blind controlled trial, no corresponding improvement was detected in involuntary movements or the patients' performance in a tracking test. The differences between the pattern of hypertonus in athetosis, Parkinson's disease, spasticity, and activated normal subjects are presented in discussion.

Adult↗

PubMed2000

Reliability of physical examination of the upper extremity among keyboard operators.

BACKGROUND: Physical examination is a traditional outcome measure in epidemiological research. Its value as a reliable measure depends, in part, on the prevalence of positive findings. The purpose of this paper is to determine the empirical reliability of physical examination and anthropometry in a field study of upper extremity disorders among keyboard operators. METHODS: Two experienced examiners independently performed common provocative tests and procedures in physical examinations of the neck and upper extremity among 160 keyboard operators. Two additional examiners conducted anthropometric surveys among 137 workers. Inter-examiner reliability was assessed with observed agreement, kappa statistics, and intra-class correlations (ICC). RESULTS: Observed agreement was between 96% and 100% for neck and upper extremity signs, muscle stretch reflexes, and muscle strength, however, with the exception of provocative tests, reliability statistics were unstable. Among the provocative tests, Phalen and Tinel tests had modest agreement after adjusting for chance (kappa range: 0.20-0.43). The carpal compression test had the best reliability (kappa=0.60 and kappa=0.67, left and right side, respectively). The ICCs for anthropometry ranged from 0.36-0.91. CONCLUSIONS: Results from the study showed that statistically, except for the carpal compression test, physical examination contributed minimal reliable information. This was attributed mainly to the low prevalence of positive findings, and generally mild nature of upper extremity disorders in this population. The results are the best estimate of what would be found in a field study with experienced examiners. While it may reduce bias, separating physical examination from medical history may contribute to the poor reliability of findings. With a shift toward reliable measures, resources can be allocated to more effective tools, like questionnaires, in epidemiological research of upper extremity disorders among keyboard operators.

Adult↗