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PubMed1984

Long latency reflex force of human finger muscles in response to imposed sinusoidal movements.

Reflex stiffness of the flexing human index finger was studied using sinusoidal movements at 3-16 Hz. The Nyquist stiffness diagram indicates the presence of a 'presonance' at around 4 Hz, its 'C' shape after correction for the mechanical properties of the relaxed finger is consistent with the involvement of a stretch reflex in its generation. This contention was supported by the presence of negative friction around 4 Hz and the disappearance of the modulation of the stiffness curve after afferent ischaemic block. Correction for the mechanical properties of active muscle, measured after afferent block, permitted the isolation of the reflex component of stiffness. The circular form of the Nyquist diagram indicates a relatively flat frequency response for the reflex over the range tested, and its radius gives a measure of reflex gain. The low value of the frequency at which the frictional force is minimal, suggests the involvement of a reflex of longer than spinal latency. This is discussed in relation to mechanisms of tremor genesis and the interaction of spinal and long latency reflexes in distal hand muscles.

Biomechanical Phenomena↗
PubMed1995

Modulation of somatocardiac sympathetic reflexes mediated by opioid receptors at the spinal and brainstem level.

Modulation of somatosympathetic reflexes at the spinal cord and the brainstem was studied by administering opioid receptor agonists into the intrathecal space of the lumbar spinal cord and into the subarachnoid space of the cisterna magna in rats anesthetized with alpha-chloralose and urethane. Somatocardiac sympathetic A- and C-reflexes were elicited by electrical stimulation of myelinated (A) and unmyelinated (C) afferent fibers of the tibial nerve, respectively. Intrathecal administration of the mu-opioid receptor agonist DAMGO selectively depressed the C-reflex in a dose-dependent manner (minimum effective dose 10 ng), whereas the intrathecal injection of the delta-opioid receptor agonist DPDPE and the kappa-opioid receptor agonist U-50,488H only at doses of 10 micrograms and 100 micrograms, respectively, led to a significant depression of the C-reflex. Injection of DAMGO into the cisterna magna enhanced both A- and C-reflexes in a dose-dependent manner (minimum effective dose 1 ng). The administration of neither DPDPE nor U-50,488H into the cisterna magna affected A- or C-reflexes. It is concluded that the activation of mu-opioid receptors is mainly or exclusively responsible for suppressing somatosympathetic C-reflexes at the spinal cord and for enhancing them at the brainstem.

Adrenergic Fibers↗
PubMed1987

Reflex inhibition of efferent renal sympathetic nerve activity by 5-hydroxytryptamine and nicotine is elicited by different epicardial receptors.

Intrapericardial administration of 5-hydroxytryptamine (5-HT) induced reflex effects consisting in an inhibition of renal sympathetic nerve activity (RSNA), bradycardia and a fall in blood pressure. Nicotine caused the same reflex effects as 5-HT. The reflex effects of both 5-HT and nicotine were abolished by vagotomy. MDL 72222, an antagonist at 5-HT M-receptors, abolished or attenuated the decreases in RSNA, heart rate and blood pressure induced by 5-HT, leaving the reflex effects of nicotine unchanged. In the absence of MDL 72222 the reflex bradycardia partially concealed a positive chronotropic response to 5-HT. After blockade of the bradycardia response by MDL 72222, 5-HT elicited a significant tachycardia, which was not altered by propranolol and phentolamine, but was prevented by phenoxybenzamine. 5-HT probably reaches the sinoatrial node and activates 5-HT receptors that mediate directly the increase in heart rate. The nicotine receptor antagonist hexamethonium selectively abolished or attenuated the reflex effects of nicotine without interfering with those of 5-HT. We conclude that 5-HT and nicotine elicit similar reflex effects in epicardial vagal nerve endings by stimulation of M-receptors or nicotine receptors, respectively.

Animals↗
PubMed1995

Modulation of the human nociceptive reflex by cyclic movements.

During static conditions the nociceptive reflex is known to vary as a function of, for example, the stimulus position, stimulus intensity, and muscle contraction. The aim of the present human study was to investigate whether the reflex and the corresponding perception of pain are modulated by cyclic movements of the limb involved. Reflexes, evoked by nociceptive electric stimulation of the sural nerve, were recorded from the biceps femoris and the rectus femoris muscles in eight volunteers. Four different experiments were performed to compare the nociceptive reflex and pain score elicited during active isometric/dynamic flexion/extension of the knee joint. The amplitudes of the reflexes were largest for the dynamic conditions. The reflexes, evoked during dynamic extension and isometric contraction of the rectus femoris muscle, had the shortest latencies but the recordings from the biceps femoris muscle were larger than from the rectus femoris muscle. Knee joint angle recordings showed that the largest angle variations occurred for the dynamic conditions and were only marginally disturbed for the isometric conditions. A given stimulus intensity evoked the highest pain intensity during isometric contractions. This indicates that there would seem to be no causal relationship between the size of the nociceptive reflex and the pain intensity.

Adult↗
PubMed1990

Different spinal effects of opioid agonists on spinal and spino-bulbo-spinal reflexes in rats.

The effects of morphine-HCl (MOR), methionine-enkephalin (ME) and dynorphin (DYN) on spinal and spino-bulbo-spinal (SBS) reflexes were studied. Although spinal intrathecal administration of MOR (15 micrograms) did not produce any apparent effect on these reflexes, systemically administered MOR (3 mg/kg i.v.) reduced the electrical toe stimulation-induced SBS reflex. Furthermore, MOR (3 mg/kg i.v.) increased the polysynaptic reflex induced by electrical stimulation of low-threshold dorsal root afferents in intact (non-spinal) rats, but not in spinal rats. Intrathecally administered DYN (0.5 and 5 micrograms) reduced both the electrical toe stimulation-induced spinal and SBS reflexes, while ME (15 micrograms) only reduced the SBS reflex. These results indicate the physiological multiplicity of spinal opioid receptors. MOR may affect supraspinal nuclei but not the spinal pathway which possesses MOR-sensitive opioid receptors, whereas ME and DYN affect spinal opioid peptide receptors and modulate the reflex activities in which they participate.

Animals↗
PubMedDate not supplied

The interaction of the Bainbridge and Bezold-Jarisch reflexes in the conscious dog.

Experiments were undertaken to determine the efferent path of the Bainbridge reflex and to investigate the interaction of the Bainbridge reflex with the Bezold-Jarisch reflex in conscious, chronically instrumented dogs. The Bainbridge reflex was elicited by distending the left atrium by inflating a chronically implanted balloon catheter. The Bezold-Jarisch reflex was elicited using chemical stimulation of left ventricular receptors with infusions of veratridine (0.1-0.8 micrograms/kg/min) into the left circumflex coronary artery. Heart-rate responses to left atrial balloon inflation were compared before and after either beta-1 antagonism with metoprolol or cholinergic antagonism with atropine, and before and during left ventricular receptor stimulation with intracoronary veratridine. Left atrial balloon inflation alone caused a significant increase in heart rate (70.1 +/- 5 bpm), left atrial pressure (14 +/- 3 mmHg) and mean arterial blood pressure (10 +/- mmHg). Heart-rate responses to left atrial distension were inhibited, but not abolished by either cholinergic or beta-1 antagonism. Left atrial distension after both cholinergic and beta-1 antagonism abolished the heart-rate response to balloon inflation. These results indicate that the efferent component of the Bainbridge reflex has both a vagal and a sympathetic component in conscious dogs. Left atrial distension during simultaneous left ventricular receptor stimulation resulted in a significantly decreased tachycardia than did left atrial distension alone (26 +/- 3 bpm compared to 68 +/- 8 bpm in the control experiments). In addition, the slope of the heart rate vs left atrial pressure relationship was significantly inhibited by left ventricular receptor stimulation (1.8 +/- 0.2 bpm/mmHg compared to 5.7 +/- 0.3 bpm/mm Hg in the control experiments). There were no significant differences in either the left atrial pressure or arterial blood pressure changes between the two groups. These data suggest an interaction between these two reflexes that may be occurring in the central nervous system.

Animals↗
PubMedDate not supplied

Patterns of reflex action, their autonomic components, and their behavioral significance.

This is a discussion of the evidence that autonomic system reflexes are invariably triggered by stimuli that evoke both simple and complex somatic reflexes. Stimuli not only initiate reverberatory activity but sequences of reinforcements from higher centers. Reflexes come in chains, one reaction triggering another. Reflex actions are patterned, and these patterns are appropriate to the behavioral requirement indicated by stimuli. Reciprocal action produces a powerful braking or stimulatory action. Coactivation or synergic action of autonomic "antagonists" also occurs and can effect a greater cardiac output in certain vascular reflexes that can sympathetic action alone. Coactivation of vagus and sympathetic fibers occurring in reflex action or resulting from stimulation of specific areas in the hypothalamus has a physiologic importance to attainment of maximal cardiac function. Finally, two additional suggestions are made: (1) that the rhythmic reflex feedback discharge of the vagus from the baroreceptors aids in maintaining the regularity of cardiac rhythm as by interaction of oscillators and (2) that the autonomic system, due to its early and often conditioned response, can be determinative as well as modulatory and supportive of behavior.

Animals↗
PubMedDate not supplied

Higher reflexes.

The term reflex is used in a broad sense. Reflexes having a drive component are denoted as higher. Four types of higher reflexes are distinguished: avoidance, escape approach and consummatory. Each of these reflexes has a different drive component. The result of the reflex is a removal of the corresponding drive. For this purpose three different strategies are used. Complex higher reflexes are usually programmed and occur frequently in a chain form. A given function of an organism is performed by a system of reflexes controlled by one or more drives.

Animals↗
PubMed1997

Phasic and tonic stretch reflexes in muscles with few muscle spindles: human jaw-opener muscles.

We investigated phasic and tonic stretch reflexes in human jaw-opener muscles, which have few, if any, muscle spindles. Jaw-unloading reflexes were recorded for both opener and closer muscles. Surface electromyographic (EMG) activity was obtained from left and right digastric and superficial masseter muscles, and jaw orientation and torques were recorded. Unloading of jaw-opener muscles elicited a short-latency decrease in EMG activity (averaging 20 ms) followed by a short-duration silent period in these muscles and sometimes a short burst of activity in their antagonists. Similar behavior in response to unloading was observed for spindle-rich jaw-closer muscles, although the latency of the silent period was statistically shorter than that observed for jaw-opener muscles (averaging 13 ms). Control studies suggest that the jaw-opener reflex was not due to inputs from either cutaneous or periodontal mechanoreceptors. In the unloading response of the jaw openers, the tonic level of EMG activity observed after transition to the new jaw orientation was monotonically related to the residual torque and orientation. This is consistent with the idea that the tonic stretch reflex might mediate the change in muscle activation. In addition, the values of the static net joint torque and jaw orientation after the dynamic phase of unloading were related by a monotonic function resembling the invariant characteristic recorded in human limb joints. The torque-angle characteristics associated with different initial jaw orientations were similar in shape but spatially shifted, consistent with the idea that voluntary changes in jaw orientation might be associated with a change in a single parameter, which might be identified as the threshold of the tonic stretch reflex. It is suggested that functionally significant phasic and tonic stretch reflexes might not be mediated exclusively by muscle spindle afferents. Thus, the hypothesis that central modifications in the threshold of the tonic stretch reflex underlie the control of movement may be applied to the jaw system.

Electromyography↗
PubMed1999

Comparison of the effects of venlafaxine, paroxetine and desipramine on the pupillary light reflex in man.

RATIONALE: The time-course of the pupillary light reflex response is determined by the successive activation of the parasympathetic and sympathetic innervations of the iris, the latency and the amplitude reflecting parasympathetic and the recovery time mainly sympathetic activity. OBJECTIVE: To compare the effects of single doses of three antidepressants (venlafaxine: serotonin/noradrenaline reuptake inhibitor, paroxetine: selective serotonin reuptake inhibitor, and desipramine: tricyclic antidepressant) on resting pupil diameter and the pupillary light reflex response. METHODS: Fifteen healthy male volunteers participated in five weekly sessions, each of which was associated with one treatment (venlafaxine 75 mg or 150 mg, paroxetine 20 mg, desipramine 100 mg, or placebo) according to a double-blind, double-dummy, balanced, cross-over design. An infrared binocular television pupillometer was used for the recording of the resting pupil diameter and the pupillary light reflex in darkness, in previously dark-adapted eyes. Resting pupil diameter in darkness was recorded before and after treatment. The pupillary light reflex was elicited after treatment, with six light flashes (green, 565 nm peak wavelength) of 200 ms duration and of incremental illuminance (measured in the plane of the cornea): 3.0 x 10(-3) 8.5 x 10(-3) 2.5 x 10(-2), 7.0 x 10(-2), 0.18, 0.43 mW cm(-2). The parameters studied were: latency, amplitude and 75% recovery time. RESULTS: Analyses of variance followed by post hoc tests (least significant difference test or Dunnett's test; P < 0.05) revealed that both doses of venlafaxine produced a significant increase in resting pupil diameter, decrease in amplitude and shortening of the 75% recovery time of the light reflex response; venlafaxine 150 mg prolonged the latency, while the other treatments had no significant effects. CONCLUSIONS: The increase in resting pupil diameter could be indicative of parasympathetic inhibition and/or sympathetic activation. The shortening of the recovery time of the light reflex response is consistent with sympathetic potentiation resulting from noradrenaline uptake blockade in the iris. The prolongation of the latency and decrease of the amplitude of the light reflex response are indicative of a parasympatholytic effect of venlafaxine. However, as venlafaxine has negligible affinity for muscarinic cholinoceptors, this effect cannot be attributed to the blockade of cholinoceptors in the iris. A possible explanation for this finding is that it reflects a central rather than a peripheral effect of the drug: the blockade of noradrenaline uptake in the brain could lead to the potentiation of the noradrenergic inhibition of central parasympathetic (Edinger-Westphal) neurones. These results demonstrate the ability of therapeutically relevant single doses of venlafaxine to potentiate noradrenergic responses in man, consistent with the blockade of noradrenaline uptake.

Adrenergic Uptake Inhibitors↗
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↗
PubMed2003

Long-loop reflex from arm afferents to remote muscles in normal man.

The present study was designed to examine the effects of median nerve stimulation on motoneurones of remote muscles in healthy subjects using H-reflex, averaged EMG and PSTH methods. Stimulation of the median nerve induced facilitation of soleus H-reflex from about 50 ms and it reached a peak at about 100 ms of conditioning-test interval. Afferents that induced the facilitation consisted of at least two types of fibres, the high-threshold cutaneous fibres and the low-threshold fibres. When the effects were examined by the averaged surface EMG and PSTH, no facilitation but rather inhibition or inhibition-facilitation was induced in all tested muscles except for the upper limb muscles on the stimulated side. The inhibition latency was shortest in masseter muscle and longest in leg muscles, while values for the contralateral upper limb muscles were in the middle, indicating that the onset of inhibition was delayed from rostral to caudal muscles. Inputs from the median nerve converged to inhibitory interneurones, which mediate the masseter inhibitory reflex. Our findings suggested that inputs from the median nerve initially ascend to the brain, at least to the brainstem, and then descend to the spinal cord. Therefore, inhibition induced by median nerve stimulation was not considered as an interlimb reflex mediated by a propriospinal pathway, but long-loop reflex, at least via the pons. The discrepancy between the results of reflex and motor units suggests that facilitation of soleus H-reflex following median nerve stimulation was mainly due to reduced presynaptic inhibition.

Adult↗
PubMed2003

On the soleus H-reflex modulation pattern during walking.

In a recent paper it was claimed that in the majority (9/15) of subjects studied the soleus H-reflex increases progressively during the swing phase of walking. This pattern was at odds with our numerous observations made since 1986, as was the very large proportion of subjects reported to exhibit this pattern. We therefore reinvestigated the issue in an extensive series of experiments and detailed subsequent analysis on 21 subjects. In most subjects (13/21) the soleus H-reflex was completely inhibited during most or all of the swing phase (group A). In 8/21 subjects (group B) there was a small H-reflex mean 16% (SD=10.6%) of the value in quiet standing present during most or all of swing, but there was no systematic modulation pattern; the reflex amplitude fluctuated in a seemingly random manner. The difference between the two somewhat arbitrary groups could not be explained on the basis of greater electromyographic activity in the tibialis anterior (TA) during the swing phase or at the time of heel contact. However, by normalizing the mean level of TA activity to the peak level, the ratio was significantly greater for the group A subjects. This highlights the importance of reciprocal inhibition in accounting for the suppression of the soleus H-reflex in swing. In the discussion we emphasize that the presence of a small H-reflex during swing in the group B subjects is unlikely to have any functional role. What is of functional importance is the strong inhibition of the H-reflex during swing which reflects the ensemble of neural mechanisms at play to prevent the unwanted activation of the powerful ankle extensor muscles.

Adult↗
PubMed2004

Plasticity of lumbosacral monosynaptic reflexes after a ventral root transection injury in the adult cat.

Injuries to spinal ventral roots may induce plastic changes in adjacent segmental reflex pathways. Earlier studies in the cat have demonstrated that a partial loss of target motoneurons, following a ventral root avulsion injury, induces a compensatory enhancement of monosynaptic reflexes in adjacent segments. Here, we studied electrophysiologically the effects of a primarily non-lethal motoneuron injury of lumbosacral ventral roots on monosynaptic reflexes in adjacent intact motoneurons in the adult cat. A unilateral L7 or a combined L7 and S1 ventral root transection was first performed. We next recorded bilaterally monosynaptic reflexes from the L6 and S1 ventral roots while stimulating the bilateral L6, L7 and S1 dorsal roots at 6 and 12 weeks postoperatively. We demonstrated a prominent strengthening of monosynaptic reflexes in the immediately adjacent spinal cord segments. The reflexes had almost doubled in size at 6 and 12 weeks postoperatively. Possible mechanisms and factors contributing to the reflex enhancement are discussed.

Animals↗
PubMed2004

Modulation of cutaneous reflexes in human upper limb muscles during arm cycling is independent of activity in the contralateral arm.

The amplitudes and signs of cutaneous reflexes are modulated during rhythmic movements of the arms and legs (during walking and arm or leg cycling for instance). This reflex modulation is frequently independent of the background muscle activity and may involve central pattern generator (CPG) circuits. The purpose of the present study was to investigate the nature and degree of coupling between the upper limbs during arm cycling, with regard to the regulation of cutaneous reflexes. Responses to electrical stimulations of the right, superficial radial nerve (five 1 ms pulses, 300 Hz) were recorded bilaterally in six arm muscles of eight participants during arm cycling involving only the limb ipsilateral to the stimulation, only the limb contralateral to the stimulation, and bilateral movement when the limbs were both in-phase and 180 degrees out of phase. The pattern of cutaneous reflex modulation throughout the arm cycle was independent of the functional state of the limb contralateral to the recording site, irrespective of whether recordings were made ipsilateral or contralateral to the stimulation. Furthermore, cutaneous reflexes were significantly (p<0.05) modulated with arm position in only 8% of cases in which the limb containing the responding muscle was either stationary or being moved passively by the experimenter. The results show that there is relatively weak coupling between the arms with regard to the regulation of cutaneous reflexes during rhythmic, cyclical arm movements. This suggests a loose connection between the CPGs for each arm that regulate muscle activity and reflex amplitude during rhythmic movement.

Adult↗
PubMed2006

Rhythmic arm cycling produces a non-specific signal that suppresses Soleus H-reflex amplitude in stationary legs.

Rhythmic arm cycling significantly suppresses Hoffmann (H-) reflex amplitude in Soleus muscles of stationary legs. The specific parameters of arm cycling contributing to this suppression, however, are unknown. Between the arms or legs, movement results in suppression of the H-reflex that is specifically related to the phase of movement and the locus of limb movement. We speculated that the effects of arm movement features on H-reflexes in the leg would be similar and hypothesized that the Soleus H-reflex suppression evoked by arm movement would therefore be specifically related to: (1) phase of the movement; (2) the locus of the movement (i.e., ipsilateral or contralateral arm); (3) range of arm motion; and (4) frequency of arm cycling. Participants performed bilateral arm cycling at 1 and 2 Hz with short and long-crank lengths. Ipsilateral and contralateral arm cycling was also performed at 1 Hz with a long-crank length. Soleus H-reflexes were evoked at four equidistant phases and comparisons were made while maintaining similar evoked motor waves and Soleus activation. Our results show that comparable suppressive effects were seen at all phases of the arm movement: there was no phase-dependence. Further, bilateral or unilateral (whether ipsi- or contralateral arm) cycling yielded equivalent suppression of the H-reflex amplitude. Cycling at 2 Hz resulted in a significantly larger suppression than with 1 Hz cycling. We conclude that a general, rather than a specific, signal related to the command to produce rhythmic arm muscle activity mediates the suppression of Soleus H-reflex during arm cycling.

Adult↗
PubMed1997

The functional effectiveness of neck muscle reflexes for head-righting in response to sudden fall.

Reflex head-righting in normal and labyrinthine-defective (LD) subjects was compared to identify the relative functional effectiveness of vestibular-collic and cervico-collic myotactic reflexes. To restrict stimuli largely to the head and neck, subjects lay supine, supported up to the shoulders on a horizontal bed with their head supported in a sling over the edge. The head fell freely as the sling was released with an electromagnetic catch. Head drops were delivered with the subjects instructed to relax and accept the fall passively or to actively right the head as fast as possible. With both instructions, righting responses in normal subjects commenced with electromyographic (EMG) bursts in the sternocleidomastoid (SCM) at 24.5 ms latency, which was reflected in a deceleration of the downwards head velocity. The latency of the earliest EMG responses in LD subjects was 67.4 ms, accompanied by similar deceleration. It is assumed that the earliest response in normal subjects is vestibular, whereas in LDs the SCM stretch reflex is the earliest response. These reflexes are followed at circa 100 ms by more intense EMG activity due to voluntary movement, but braking of head fall is evident before voluntary activity takes effect. Righting was more effective in normal subjects than in LDs, and when "active" normal subjects made more vigorous righting responses than when "passive"; whereas active righting in LDs was no better than passive. The results demonstrate that reflex responses contribute significantly to head-righting. The vestibular contribution gives an advantage over stretch reflexes alone and also assists in voluntary enhancement of reflex responses.

Acceleration↗
PubMed1999

Dependence of stretch reflexes on amplitude and bandwidth of stretch in human wrist muscle.

The tonic stretch reflex was investigated using small-amplitude displacements (<4.2 degrees ) of the wrist while subjects maintained average contraction levels of 25% of maximum in flexor carpi radialis. The wrist displacements were designed to preclude voluntary following but at the same time were confined to the frequency range most relevant to voluntary movements. They included a broad-frequency band (0-12 Hz) signal as well as sets of narrow-band signals spanning the range from 0 to 10 Hz. The maximum frequency was set so as to remain within the linear encoding bandwidth of the reflex system and thereby minimize distortion. The effects of frequency bandwidth and amplitude of the displacement perturbations were tested in separate experiments. The coherence square, gain and phase between the EMG and angular displacement were calculated in order to characterize the stretch reflex under these conditions. It was found that the phase of the reflex response was dependent on both bandwidth and amplitude. For narrow-band displacements, the phase advance was about 30 degrees greater over the frequency range tested than for broad-band displacements, suggesting that the reflex response may be influenced by the predictability of the perturbation. At the smallest amplitude of 0.3 degrees, the peak phase advance was about 20 degrees greater than at the largest amplitude of 4.2 degrees. The gain was also higher and rose more steeply with frequency at smaller amplitudes. In the frequency range up to 12 Hz, the tonic stretch reflex responds most effectively to smaller-amplitude, more regular, higher-frequency inputs and this is consistent with a role for the reflex in counteracting small-amplitude oscillations, tremors and errors of voluntary movement.

Adult↗