The role of the tonic stretch reflex during standing in man.
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Adult↗
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[Experiences with a modification method of the stretch-reflex in electromyography].
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Electromyography↗
Effects of local and remote muscle pain on human jaw reflexes evoked by fast stretches at different clenching levels.
Muscle pain imposes significant changes on natural motor tasks, but the consequences for stretch reflexes are still disputed. The present study examined the jaw reflexes to fast (10 ms) stretches of the mandible in an experimental model with local pain in the masseter muscle and remote pain in the tibialis anterior muscle. The stretch reflexes were elicited in healthy volunteers (n=13) before, during, and after periods with constant levels of experimental pain and while the subjects clenched at 0%, 15%, 30%, and 45% of the maximal voluntary contraction (MVC) levels. Surface electromyography (EMG) was used to record the reflex responses. Pain in the masseter muscle (mean +/- SEM, 3.8+/-0.4 on a 10-cm visual analogue scale), but not in the tibialis anterior muscle (3.4+/-0.3; paired t-test, P=0.318) was associated with significant changes in both prestimulus EMG activity (ANOVA, P=0.002) and in peak-to-peak amplitudes of the stretch reflex (ANOVA, P=0.022). However, when the changes in prestimulus EMG activity were taken into consideration a significant increase in the stretch reflex persisted in the painful muscle at 15% and 30% MVC. Local circuits at the trigeminal level involving the fusimotor system are proposed to mediate a significant part of this modulatory effect.
Adult↗
Segmental neurophysiological mechanisms in scoliosis.
Segmental spinal reflexes (stretch reflexes) were studied in patients with scoliosis. The proprioceptive responses to the phasic stretch of the paraspinal muscles were asymmetric in all patients, and were increased on the convex side. The asymmetry was more pronounced when the patients were standing. The observed asymmetry of the reflex responses was taken to indicate asymmetry in the tone and postural activity of the superficial layer of the paraspinal muscles. A reciprocal relationship was found in the segmental reflex organisation between the superficial and deep layers of the paraspinal muscles. The increase in reflex response of the superficial muscles on the convex side can be due to diminished reciprocal inhibition from weak, deep muscles. Thus a segmental neurogenic disorder involving predominantly the deep paraspinal muscles of the convexity of the curve may be the primary lesion responsible for the development of scoliosis.
Adolescent↗
Starting position and stretching velocity effects on the reflex threshold angle of stretch reflex in the soleus muscle of normal and spastic subjects.
BACKGROUND AND PURPOSE: Although both starting position and stretching velocity play an important role in reflex response, their interaction with stretch reflexes has not been thoroughly investigated. This study examined the interaction effect of starting position and stretching velocity on the reflex threshold angle (RTA) of the stretch reflex in the soleus muscle of normal and spastic subjects. METHODS: The spastic group included 11 ankles from 7 subjects with a history of upper motor neuron lesions. Their ages ranged from 22 to 40 years. Another 10 healthy subjects served as the control group. RTAs of the stretch reflex in the soleus muscle were measured for a matrix of starting positions and stretching velocities. The matrix design enabled the use of a 2-way analysis model to investigate the effect of starting position and stretching velocity on the RTA. RESULTS: No interaction effect was found in either the phasic stretch reflex (PSR) or the tonic stretch reflex (TSR) in the spastic group, or in the PSR in the normal group. The RTA of the PSR in both spastic and normal groups was significantly affected by starting position but not by stretching velocity. In contrast, the RTA of the TSR in the spastic group was affected by both starting position and stretching velocity. Stretching velocity and starting position played independent roles in determining the RTA of both the PSR and the TSR of the spastic group and in the PSR of the normal group. CONCLUSIONS: The lack of interaction between length-sensitive and velocity-sensitive muscle spindles in both normal and spastic subjects supports the hypothesis that they independently modulate the stretch reflex. Results for the RTA of the TSR demonstrated that spasticity results in disinhibition of motoneuron excitability with different thresholds.
Adult↗
The immediate effects of tension of counterforce forearm brace on neuromuscular performance of wrist extensor muscles in subjects with lateral humeral epicondylosis.
STUDY DESIGN: Within-subject repeated-measures study. OBJECTIVES: To examine the immediate effects of counterforce forearm brace on isokinetic strenght stretch reflex, passive stretching pain threshold of the wrist extensors, and proprioception of the wrist in subjects with lateral humeral epicondylosis for different strap tensions of a forearm brace. BACKGROUND: Counterforce forearm bracing has been used for treating lateral humeral epicondylosis, but the effect of brace tension has not been well reported. METHODS AND MEASURES: Fifteen subjects diagnosed with lateral humeral epicondylosis on their dominant arm were tested under 4 randomized conditions: (1) no brace, (2) brace with minimal tension, (3) brace with 25-N tension, and (4) brace with 50-N tension. The tests included isokinetic wrist extensors strength, passive stretching force in wrist flexion to elicit pain in the wrist extensors, wrist proprioception, and stretch reflex latency of the extensor carpi ulnari. A repeated-measures MANOVA was used to analyze the data and significant results were further analyzed with post hoc linear contrasts (alpha = .05). RESULTS: Among the 4 conditions, significant differences were found in wrist proprioception P = .032) and pain threshold to passive stretching of the wrist extensors (P = .05), but were not found in wrist extension isokinetic strength and stretch reflex latency of the extensor carpi ulnaris. CONCLUSION: A forearm counterforce brace, as applied in this study, affects wrist joint proprioception and increases the pain threshold to passive stretching of the wrist extensors in subjects with lateral humeral epicondylosis, but it has no effect on wrist extensor strength and stretch reflex latency of the extensor carpi ulnaris.
Adult↗
Motor control in patients with incomplete spinal cord injuries and various voluntary movement capabilities.
BACKGROUND: In this study, we attempted to verify the hypothesis that further improvements in volitional movement of patients with a spinal cord injury would diminish and ultimately suppress the segmental responses, while enhancing the supraspinal inhibitory influence. METHODS: Eleven patients with an incomplete spinal cord injury and partial preservation of motor function (ASIS grades C and D) were recruited. Their lower limbs were evaluated using polyelectromyography (PEMG) during voluntary movements, reinforcement maneuvers, tonic vibratory reflex, passive stretch reflex, irradiation of the passive stretch reflex (PSRirrad), and plantar reflex suppression. RESULTS: The reinforcement maneuver response, tonic vibratory response, passive stretch reflex, and PSRirrad were most active in limbs with partially preserved volitional movement, but for which patients were still incapable of lifting their heel off the examination table. In contrast, plantar reflex suppression was strongest in limbs with partially preserved volitional movement, for which patients were capable of lifting the heel off the examination table. CONCLUSIONS: Supraspinal inhibitory effects were most active in those limbs which were capable of lifting the heel off the examination table, compared to limbs with partially preserved volitional activity but without visible movement or which were incapable of lifting the heel off the examination table. The capability for volitional activity paralleled the supraspinal inhibitory effects.
Adult↗
The strength of the reflex response to sinusoidal stretch of monkey jaw closing muscles during voluntary contraction.
1. Rhesus monkeys were trained to exert steady biting forces of 3--60 N for 1--2 sec. This behaviour was well maintained while sinusoidal or step opening and closing movements were imposed on the jaw. 2. The amplitude of the force modulation during sinusoidal stretching was divided by the amplitude of movement to obtain the magnitude of stiffness. This estimate was made at frequencies from 2 to 50 Hz at amplitudes of 100 and 500 micrometer (half the peak-to-peak movement at the incisors). 3. Peak magnitudes of stiffness were seen with frequencies of 8--15 Hz when the amplitude of movement was small; there was a great deal of variation between individual animals. This variation was most striking with mean forces of 25--35 N. The stiffness was greatest in animals that showed considerable spontaneous tremor, and the highest levels of stiffness were often recorded with frequencies near which tremor amplitude was large. A marked phase lag in the force response was often seen during small amplitude stretching at 8--30 Hz. 4. Estimates of stiffness for larger amplitude (500 micrometer) stretching showed less variation; the magnitude of stiffness showed maximum values below 10 Hz and a minimum at 15--30 Hz. Force always showed a phase lead on position although this lead became small in the frequency range where with smaller movement there had been phase lags. The magnitude of stiffness increased with increasing mean force. 5. Bilateral electrolytic lesions were made in the brain stems of three animals; they reduced by over 95% the expected number of cells in the mesencephalic nucleus of the fifth cranial nerve on either side. These lesions interrupted the afferent pathway for the stretch reflex and so abolished excitatory electromyogram (e.m.g.) responses to step stretches of the jaw closing muscles. 6. Such reflex responses as persisted after the lesions were small and inhibitory. E.m.g. silences followed both step stretch and release; the response to release was a 'load compensation' that could not be attributed to spindle afferents. 7. After the lesions the responses to movements of 100 micrometer showed neither negative values for the phase nor marked peaks in the stiffness magnitude at low frequencies; these features therefore take origin in the action of the stretch reflex. The stiffness that was measured after the lesions may be attributed to the non-reflex components resisting stretch, particularly to the properties of the contracting muscles. Thus, the phase of the force response was markedly advanced at all frequencies and the stiffness seen for 100 micrometer was similar to that for 500 micrometer. Stiffness increased with increasing mean force, as before surgery. 8. Vector subtraction of the stiffness seen at each frequency after interrupting the stretch reflex from that seen before doing so gave a quantitative estimate of the strength of the stretch reflex. The reflex activity calculated in this way showed attenuation and progressive phase lag as the frequency increased above 10 Hz...
Afferent Pathways↗
Central suppression of regenerated proprioceptive afferents.
Long after a cut peripheral nerve reinnervates muscle and restores force production in adult cats, the muscle does not respond reflexively to stretch. Motivated by the likelihood that stretch areflexia is related to problems with sensing and controlling limb position after peripheral neuropathies, we sought to determine the underlying mechanism. Electrophysiological and morphological measurements were made in anesthetized rats having one of the nerves to the triceps surae muscles either untreated or cut and immediately rejoined surgically many months earlier. First, it was established that reinnervated muscles failed to generate stretch reflexes, extending observations of areflexia to a second species. Next, multiple elements in the sensorimotor circuit of the stretch reflex were examined in both the PNS and CNS. Encoding of muscle stretch by regenerated proprioceptive afferents was remarkably similar to normal, although we observed some expected abnormalities, e.g., increased length threshold. However, the robust stretch-evoked sensory response that arrived concurrently at the CNS in multiple proprioceptive afferents produced synaptic responses that were either smaller than normal or undetectable. Muscle stretch failed to evoke detectable synaptic responses in 13 of 22 motoneurons, although electrical stimulation generated monosynaptic excitatory postsynaptic potentials that were indistinguishable from normal. The ineffectiveness of muscle stretch was not attributable therefore to dysfunction at synapses made between regenerated Ia afferents and motoneurons. Among multiple candidate mechanisms, we suggest that centrally controlled neural circuits may actively suppress the sensory information encoded by regenerated proprioceptive afferents to prevent recovery of the stretch reflex.
Afferent Pathways↗
Locomotion in patients with spinal cord injuries.
Following central motor lesions, two forms of reorganization can be observed that lead to improved mobility: (1) the development of increased muscle tone and (2) the activation of spinal locomotor centers induced by specific treadmill training. Tension development is different from normal during spastic gait and appears to be independent of exaggerated monosynaptic stretch reflexes. Exaggerated stretch reflexes are associated with an absence or reduction of functionally essential polysynaptic reflexes. Based on observations of the locomotor capacity of the spinal cat, recent studies have indicated that spinal locomotor centers can be activated and trained in patients with complete or incomplete paraplegia when the body is partially unloaded. The level of electromyographic activity in the gastrocnemius muscle, however, is considerably lower in patients with central motor lesions than in persons without neurological impairments. During the course of a daily locomotor training program, the amplitude of gastrocnemius muscle electromyographic activity increases during the stance phase and inappropriate tibialis anterior muscle activity decreases. Such training programs can improve the ability of patients with incomplete paraplegia to walk on stationary surfaces. This article reviews the pathophysiology and functional importance of increased muscle tone and the effects of treadmill training on the locomotor pattern underlying new attempts to improve the mobility of patients with paraplegia.
Animals↗
Spinal cord lesion: effects of and perspectives for treatment.
Following central motor lesions, two forms of adaptation can be observed which lead to improved mobility: (1) the development of spastic muscle tone, and (2) the activation of spinal locomotor centers induced by specific treadmill training. Tension development during spastic gait is different from that during normal gait and appears to be independent of exaggerated monosynaptic stretch reflexes. Exaggerated stretch reflexes are associated with an absence or reduction of functionally essential polysynaptic reflexes. When supraspinal control of spinal reflexes is impaired, the inhibition of monosynaptic reflexes is missing in addition to a reduced facilitation of polysynaptic reflexes. Therefore, overall leg muscle activity becomes reduced and less well modulated in patients with spasticity. Electrophysiological and histological studies have shown that a transformation of motor units takes place following central motor lesions with the consequence that regulation of muscle tone is achieved at a lower level of neuronal organization which in turn enables the patient to walk. Based on observations of the locomotor capacity of the spinal cat, recent studies have indicated that spinal locomotor centers can be activated and trained in patients with complete or incomplete paraplegia when the body is partially unloaded. However, the level of electromyographic activity in the gastrocnemius (the main antigravity muscle during gait) is considerably lower in the patients compared to healthy subjects. During the course of a daily locomotor training program, the amplitude of gastrocnemius, electromyographic activity increases significantly during the stance phase, while inappropriate tibialis anterior activation decreases. Patients with incomplete paraplegia benefit from such training programs such that their walking ability on a stationary surface improves. The pathophysiology and functional significance of spastic muscle tone and the effects of treadmill training on the locomotor pattern underlying new attempts to improve the mobility of patients with paraplegia are reviewed.
Humans↗
Reflex responses of fusimotoneurons to sinusoidal muscle stretching.
Reflex response of fusimotoneurons to sinusoidal muscle stretching were investigated in decerebrated cats. Nerve impulses of single fusimotoneurons were recorded from thin filaments dissected from otherwise intact nerves to triceps surae muscles. Amplitude of the sinusoidal stretching of these muscles was 3 mm peak-to-peak and the frequencies 0.1-10 Hz. Electric muscle activity was also recorded in some experiments. Fusimotor responses were similar to those of the skeletomotoneurons in that both were advanced in phase with respect to muscle length changes, while their amplitude increased with increase in stretching frequency. Modulation at the frequency corresponding to the second harmonic of the input signal was predominant in fusimotor responses. It is supposed to appear mainly due to the convergence to fusimotoneurons of afferent impulses from different muscle receptors arriving after different delays. Its functional role is discussed.
Animals↗
Muscle, reflex and central components in the control of the ankle joint in healthy and spastic man.
In understanding the control of the ankle joint during different motor tasks, we have to investigate at least three components, namely the influence of i) the passive and intrinsic properties of the intact and active muscle system around the joint (termed the non-reflex component), ii) the mechanical importance of the stretch reflex in the stretched and unloaded muscles, and iii) the supraspinal control of the stretch reflex. This thesis is dealing with the importance of the three components in healthy and spastic persons during sitting, standing, and walking. The results are based on stretch reflex and H-reflex measurements from the ankle extensor muscles. During stretch reflex experiments the foot was mounted to a platform (portable during walking) from which the ankle joint torque and the position were measured. To elicit a stretch reflex, the ankle joint was rotated by a strong motor connected to the platform. The mechanical importance of the stretch reflex was investigated by measuring the changes in joint torque. Electrically, the stretch reflex was recorded as the compound muscle action potential through bipolar surface EMG electrodes placed over the soleus muscle. During H-reflex experiments, the tibial nerve was stimulated at the popliteal fossa and the H-reflex recorded over the soleus muscle as during stretch reflex experiments. To investigate how the contractile properties of a muscle in humans depend on the history of activation, we investigated the intrinsic stiffness of the ankle extensors in healthy subjects. At matched background contraction in sitting subjects, a prolonged contraction increased the intrinsic muscle stiffness by 49%. Muscle yielding has been considered especially important for understanding the reflex compensation. We found a general lack of muscle yield and a mechanically important non-reflex stiffness of the ankle extensors showing that non-reflex stiffness is a prominent factor in normal movements of the ankle joint. In both healthy and spastic persons, we found a mechanically strong stretch reflex in the isometric, contracted muscles during sitting. This posed the question; how is the reflex regulated during more functional motor tasks. This was dealt with by studying the H-reflex during isometric ramp contractions and during walking in healthy and spastic persons. In the healthy subjects the H-reflex was modulated in consistency with a task dependent control. In the spastic patients the H-reflex lacked a task dependent modulation. In consistency with earlier findings it was suggested that the decreased modulation could have been caused by decreased control of the pre-synaptic inhibition of the Ia terminals or a change in recruitment gain. To test if the stretch reflex behaved as the H-reflex, the short latency stretch reflex was investigated during walking. Here we found that the stretch reflex was strongly modulated during a step in healthy subjects as seen for the H-reflex, but when comparing the stretch reflex at matched excitation levels (same background EMGs) during standing and walking, no task-specific reflex modulation was found except the one relating to the excitation level. Therefore, the results emphasise that at least during walking and standing it is not always possible to draw conclusions about the stretch reflex based on observations of the H-reflex. When investigating the modulation of the short latency stretch reflex during walking in spastic patients, we found that the stretch reflex modulation was impaired in spastic patients at least to the extent demonstrated earlier for the H-reflex. The passive stiffness of the ankle joint was at the same time increased in the patients. At matched ankle extensor contraction levels, stretch responses were compared before and after reversible block of the common peroneal nerve and during an attempted, voluntary, fictive dorsiflexion after common peroneal nerve block. (ABSTRACT TRUNCATED)
Afferent Pathways↗
Contribution of lung stretch depressor reflex to nonlinear fall in cardiac output during PEEP.
The hypothesis that lung stretch reflexes elicit negative cardiovascular effects during positive end-expiratory pressure (PEEP) application in a ramp procedure up to 15 cmH2O was tested in piglets under steady-state anesthesia and muscle relaxation. The effects of lung stretch on hemodynamics were studied by comparing the differences in responses during PEEP application with two different tidal volumes. In both ventilatory conditions cardiac output and aortic pressure decreased nonlinearly in three phases with the rise of PEEP: a gradual decrease in phase I, a sharp decrease in phase II, and again a more gradual decrease in phase III. Heart rate decreased significantly in phase II. In the series with the larger tidal volume, implying more lung stretch during insufflation, phase II was between a PEEP of 2.6 and 9 cmH2O. In the series with the smaller tidal volume, phase II occurred between 5.7 and 10.5 cmH2O. To assess the contribution of lung stretch reflexes to the decrease in cardiac output we also related cardiac output to the changes in central venous pressure. Again a nonlinear response was observed, indicating that an additional effect besides the rise in mean central venous pressure was involved in the decrease in cardiac output. During ventilation with the smaller tidal volume, phase II of the decrease in cardiac output was also shifted to higher values of mean central venous pressure, which only could be ascribed to the differences in lung stretch at insufflation. It appeared that under circumstances of artificial ventilation the onset of the reflex is determined by a characteristic threshold of lung stretch.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Effect of counterforce forearm bracing on wrist extensor muscles performance.
OBJECTIVES: We examined (1) the effect of a counterforce forearm brace on isokinetic strength, stretch reflex, passive stretching, and proprioception of the forearm muscles in healthy subjects and (2) the effect of different strap tensions of the brace on the above variables. DESIGN: The dominant hand of 15 healthy subjects were tested under four randomized conditions: (1) no brace, (2) brace with minimal tension, (3) brace with 2.5 kg force tension, and (4) brace with 5 kg force tension. The tests included isokinetic wrist extensors strength, passive stretching to the wrist extensors until onset of pain, joint proprioception, and reflex latency of forearm extensor muscles. A repeated measures multivariate analysis of variance test was used to analyze the data, and significant results were further analyzed with post hoc linear contrasts with alpha at 0.0083. RESULTS: There was no difference in isokinetic strength, proprioception, and stretch reflex latency among the four conditions. For passive stretching, there was a significant difference (P = 0.001) in that using a brace produced a higher pain threshold than without a brace. CONCLUSION: A forearm counterforce brace has no effect on strength, proprioception, and stretch reflex latency, but it increases the pain threshold.
Adult↗
The reflex response to sinusoidal stretching of soleus in the decerebrate cat.
1. Soleus muscle in the decerebrate cat was stretched sinusoidally through various distances, at various frequencies while tension and e.m.g. activity were recorded.2. Two patterns of stretch reflex activity were seen. In one, slow stretching led to a large increase in tension, whereas in the other tension increased little during slow stretching, but rose steeply during a more rapid stretch. Intermediate states were also seen.3. Both these reflex patterns were abolished when the fusimotor fibres were blocked with Xylocaine.4. At low frequencies of stretching the e.m.g. activity was greatest at peak muscle length; at higher frequencies the greatest activity was found during lengthening. This angular advance of e.m.g. activity on length was greatest at 3.3-5 c/s. At the higher frequencies the e.m.g. activity was less in advance of muscle length.5. Angular advance of e.m.g. activity was greatest in the preparations that were also the most sensitive to slow stretching.6. Muscle contraction follows an electrical stimulus with a small delay. The delay between the end of stimulation and the end of muscle relaxation is longer, and may exceed 200 msec in cat soleus.7. The timing of the reflex tension during sinusoidal stretching depended on how far the angular advance of the e.m.g. combined with the damping properties of muscle offset the time delays in the reflex pathway.8. Changes in muscle tension generally preceded changes in muscle length. When, however, stretch amplitudes of 1 mm (peak to peak) were used, a phase delay of tension was sometimes seen. This only occurred in preparations that also showed little sensitivity to slow stretching.9. Phase delay of tension was usually found with frequencies of approximately 6-8 c/s, and this corresponds to the clonus frequency for soleus.10. The mechanisms of the two types of reflex behaviour, and the damping properties of the system are discussed.
Animals↗
Modulation of stretch-evoked reflexes in single motor units in human masseter muscle by experimental pain.
The interaction between muscle pain and motor function of the jaw has been examined in recent years, but the nature of the modulation of the short-latency stretch reflex by pain is not fully understood. In this study, the reflex responses to stretch were measured in single low-threshold motor units that were kept discharging at a constant frequency, before, during and after the induction of experimental pain in one masseter muscle by controlled infusion of hypertonic saline. The probability of evoking a reflex response in individual motor units in the painful muscle at near-monosynaptic latency was reduced by a mean of about 20%. However, the overall reflex response in the surface electromyogram of both the ipsi- and contralateral masseter muscles was greater during pain. This was apparently a secondary response to the pain-induced increase in pre-stimulus activity in the motoneurone pools of both muscles, because increased motoneurone excitability may facilitate stretch reflexes. It is concluded that the most likely explanation for the reduced reflex response of low-threshold masseter motor units during experimental pain is a tonic reduction in the fusimotor drive to the masseter spindles.
Adult↗
Quantitated flexor response in acute spinal cord injury patients.
Flexor reflexes were compared with phasic stretch reflexes in 12 acute spinal cord injury patients with upper motor neuron lesions. Initial flexor reflex activity appeared later than initial stretch reflex activity in the majority of cases whereas maximal flexor reflexes developed at about the same time as maximal stretch reflexes. A quantitative method for evaluating flexor and stretch reflex activity at bedside is presented.
Ankle Joint↗