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PubMed1981

Basal and reflex human tear analysis. II. Chemical analysis: lactoferrin and lysozyme.

Unstimulated basal tears and stimulated tears were collected from normal controls, keratoconjunctivitis sicca (KCS) patients, and contact lens (CL) wearers. Basal tear volume (Periopaper) and reflex tear volume (Schirmer Strip) were measured and tears eluted from their respective strip with a TMED-acetic acid buffer. Lactoferrin and lysozyme concentrations were measured in the eluates. Concentration of lysozyme in basal tears was: 65 +/- 43 mg% in normals; 44 +/- 26 mg% in KCS, and 81 +/- 50 mg% in CL wearers. Concentration of lysozyme in reflex tears was: 160 +/- 73 mg% in normals, 74 +/- 41 mg% in KCS, and 186 +/- 83 mg% in CL wearers. Concentration of lactoferrin in basal tears was 137 +/- 102 mg% in normals, 154 +/- 82 mg% in KCS, and 157 +/- 80 mg% in CL wearers. Concentrations of lactoferrin in reflex tears was: 327 +/- 187 mg% in normals; 171 +/- 69 mg% in KCS, and 302 +/- 160 mg% in CL wearers. The lactoferrin concentration in all tear samples was consistently higher (1.6-3.5 times) than lysozyme. In basal tears, lactoferrin concentrations were not significantly different in the three groups. In reflex tears, however, lactoferrin was significantly lower in KCS than normal or CL wearers. The concentration of lysozyme in both basal and reflex tears was significantly lower in the KCS when compared to normal or CL wearers. Lysozyme and lactoferrin concentrations in both basal and reflex tears were similar in CL wearers and normal controls. The sampling and elution of basal and reflex tears as described appears to be a feasible technique for analysis of lysozyme and lactoferrin concentrations by the electroimmunodiffusion technique and has potential diagnostic value.

Contact Lenses↗
PubMed2002

Identification of intrinsic and reflexive components of human arm dynamics during postural control.

In this study a new methodology to quantify reflexive feedback gains from the mechanical behavior of the human arm during posture maintenance is proposed. Disturbance experiments were carried out on human subjects using continuous random force inputs. The task instruction was 'minimize displacements', prescribing a maximum performance task. For the separation of intrinsic and reflexive components, system identification in the frequency domain is applied. From the time records of position and force, frequency response functions (FRFs) are estimated. Given a model structure and an appropriate estimate of the intrinsic component, an estimate of the reflex gains for length and velocity are obtained from the FRFs. The feedback gains vary considerably with the frequency content of the disturbance signal. The results show that reflexive dynamics are substantial for narrow-band and especially low-frequency input signals. It is likely that high reflex gains are most effective for low-frequency inputs (< 3 Hz) that do not excite the closed-loop system's eigenfrequency. Also significant negative reflex gains are estimated for near-sinusoidal inputs (> 1.5 Hz). It is concluded that this new methodology can offer interesting insights into the ability of the central nervous system to modulate reflexive feedback gains.

Adult↗
PubMed2002

Acoustic reflex thresholds at varying click rates in children.

OBJECTIVE: Previous studies conducted with young adults have shown that ipsilateral acoustic reflex thresholds improve with an increase in the click-rate. Older adults also show an improvement in acoustic reflex thresholds with an increase in the click-rate. However, the click-rate induced facilitation (RIF) of acoustic reflex thresholds is significantly reduced in older adults. These results suggest that slower temporal processing in older adults can be documented by measuring the click-RIF of acoustic reflex thresholds. Thus, the click-RIF of acoustic reflex thresholds may prove to be a valuable tool for the assessment of temporal processing disorders in young children. However, click-RIF of ipsilateral acoustic reflex thresholds has not been studied in young normal children. The purpose of this study was to evaluate and document the click-RIF in young normal children to provide normative data for this age-group. METHODS: The study included a total of 30 participants (12 male and 18 female) with normal hearing between the ages of 6 and 10 years. Children with outer, middle ear, or neurological disorders were excluded from the study. Ipsilateral acoustic reflex thresholds were determined in the left and right ears with clicks presented at the rate of 50 and 100 per s. The frequency of the probe tone was 226 Hz and intensity was 85 dB SPL. A statistical analysis using a three factor mixed MANOVA was planned to explore differences between ears, click rates and gender. RESULTS: The MANOVA revealed a significant effect (P=0.0000) for the click-rate. There were no differences between ears or gender and no interactions. The mean click-RIF with an increase in the rate from 50 to 100 per s was 10.50 dB. CONCLUSION: Comparison of these results with previous results obtained from young adults suggests that young normal children show click-RIF that is similar to that apparent in young adults.

Acoustic Stimulation↗
PubMed2002

Relationship of the 'fear-inhibited light reflex' to the level of state/trait anxiety in healthy subjects.

RATIONALE: It has been shown that the amplitude of the pupillary light reflex response decreases when subjects anticipate an aversive stimulus (i.e. electric shock), compared to periods when subjects are resting ('fear-inhibited light reflex'). OBJECTIVE: To examine whether the sensitivity of the pupillary light reflex to the threat of an electric shock is related to the pre-existing levels of state and trait anxiety. METHODS: Thirty-two healthy volunteers participated in one experimental session. The possibility of an electric shock to the wrist was signalled by a tone. There were six blocks of three light stimuli: three SAFE blocks (no tone applied) and three THREAT blocks (tone applied). The State-Trait Anxiety Inventory was completed at the beginning and at the end of each session. RESULTS: There was a positive correlation between the state anxiety scores and the within-subject (SAFE-THREAT) difference in light reflex amplitude (P<0.05). There was no significant correlation between the trait anxiety scores and the within-subject differences in light reflex amplitude. CONCLUSIONS: Individual differences in state anxiety associated with the threat of an electric shock are reflected in the amplitude of the pupillary light reflex response. This observation strengthens the validity of the fear-inhibited light reflex as a model of human anxiety.

Adolescent↗
PubMed2002

Test-retest reliability of the somatosensory blink reflex and its inhibition.

Prepulse inhibition (PPI) involves inhibition of the blink reflex by a weak stimulus or prepulse presented immediately prior to the blink reflex-eliciting stimulus. Ten subjects were tested for PPI two times each day with a 60 min pause between tests, for 4 days spaced 1 week apart. Both the somatosensory blink reflex and its inhibition by an acoustic prepulse, presented 50, 100, 200, 400 and 800 ms prior to the reflex-eliciting stimulus, were investigated. The results showed very high reliability for the blink reflex across all eight tests (Chronbach's alpha=0.98). Inhibition of the reflex by a prepulse displayed alphas of >0.94, and percentage of PPI also displayed significant reliability. Blink latency also displayed high reliability. In sum, the reliability of the somatosensory blink reflex and its inhibition is very high.

Adult↗
PubMed2000

Interaction between cutaneous and muscle afferent activity in polysynaptic reflex pathways: a human experimental study.

Interactions between the input from cutaneous and nociceptive muscle afferents in polysynaptic reflex pathways were investigated in man. Interaction was tested by evoking reflexes before, during, and after a period of muscle pain induced by intramuscular injection of hypertonic saline. Muscle pain was induced either in the ankle flexor (tibialis anterior, TA) or in the extensor (soleus, SOL) muscles by injection of 1 ml hypertonic saline. Electrical skin stimulation (1.1 x initial reflex threshold) at the dorsum of the foot over the tarsal joint was used to elicit cutaneo-muscular polysynaptic reflexes in the knee flexor semitendinosus (ST). The injected hypertonic saline evoked a robust muscle pain (the subjects made a continuous score of the muscle pain on a 0-10 cm VAS scale, and the mean VAS area was 1229+/-251 cm x s and lasting 390+/-30 s). In five of 12 subjects, the infusion of hypertonic saline into TA evoked referred pain to the dorsal aspect of the ankle. A significant inhibition (17+/-8.2%, P<0.05) of the ST-reflex by pain in SOL was observed. Pain in TA facilitated (92+/-36%, P<0.05) the short-latency part (50-70 ms post stimulation) of the reflex. The muscle pain did not modulate the perceived sensory intensity of the electrical stimuli. The findings indicate an interaction of input from thin muscle afferents and cutaneous group A-fibre afferents in polysynaptic segmental reflex pathways, which seems to depend on the location of the muscle pain.

Adult↗
PubMed2001

Medullary reticulospinal tract mediating the generalized motor inhibition in cats: parallel inhibitory mechanisms acting on motoneurons and on interneuronal transmission in reflex pathways.

The present study was designed to elucidate the spinal interneuronal mechanisms of motor inhibition evoked by stimulating the medullary reticular formation. Two questions were addressed. First, whether there is a parallel motor inhibition to motoneurons and to interneurons in reflex pathways. Second, whether the inhibition is mediated by interneurons interposed in known reflex pathways. We recorded the intracellular activity of hindlimb motoneurons in decerebrate cats and examined the effects of medullary stimulation on these neurons and on interneuronal transmission in reflex pathways to them. Stimuli (three pulses at 10-60microA and 1-10ms intervals) delivered to the nucleus reticularis gigantocellularis evoked inhibitory postsynaptic potentials in alpha-motoneurons (n=147) and gamma-motoneurons (n=5) with both early and late latencies. The early inhibitory postsynaptic potentials were observed in 66.4% of the motoneurons and had a latency of 4.0-5.5ms with a segmental delay of more than 1.4ms. The late inhibitory postsynaptic potentials were observed in 98.0% of the motoneurons and had a latency of 30-35ms, with a peak latency of 50-60ms. Both types of inhibitory postsynaptic potentials were evoked through fibers descending in the ventrolateral quadrant. The inhibitory postsynaptic potentials were not influenced by recurrent inhibitory pathways, but both types were greatly attenuated by volleys in flexor reflex afferents. Conditioning medullary stimulation, which was subthreshold to evoke inhibitory postsynaptic potentials in the motoneurons, neither evoked primary afferent depolarization of dorsal roots nor reduced the input resistance of the motoneurons. However, the conditioning stimulation often facilitated non-reciprocal group I inhibitory pathways (Ib inhibitory pathways) to the motoneurons in early (<20ms) and late (30-80ms) periods. In contrast, it attenuated test postsynaptic potentials evoked through reciprocal Ia inhibitory pathways, and excitatory and inhibitory pathways from flexor reflex afferent and recurrent inhibitory pathways. The inhibitory effects were observed in both early and late periods. The present results provide new information about a parallel inhibitory process from the medullary reticular formation that produces a generalized motor inhibition by acting on alpha- and gamma-motoneurons, and on interneurons in reflex pathways. Interneurons receiving inhibition from flexor reflex afferents and a group of Ib interneurons may mediate the inhibitory effects upon motoneurons.

Animals↗
PubMed2003

Effects of reversible shutdown of the monkey flocculus on the retention of adaptation of the horizontal vestibulo-ocular reflex.

There are two different proposals regarding the role of the cerebellar flocculus in the adaptation of the vestibulo-ocular reflex: that the flocculus is the site for both the induction and retention of the adaptation, or that the flocculus plays an important role in the induction, but the vestibular nuclei to which the flocculus issues its efferents are the site of retention. To locate the memory trace for the adaptation of the vestibulo-ocular reflex, we determined effects of acute pharmacological shutdown of the bilateral cerebellar flocculi in four Macaca fuscata. The gain of the horizontal vestibulo-ocular reflex was measured by sinusoidal oscillation of the turntable by 10 degrees (peak-to-peak) at 0.33 Hz in the dark. Two hours of 0.33 Hz-10 degrees sinusoidal oscillation of the turntable while viewing the stationary checked-pattern screen through a x2.2 magnifying lens adaptively increased the horizontal vestibulo-ocular reflex gain by 0.2 on the average. The gain increase lasted for 1 h when the monkeys were left with their heads fixed in darkness, but it disappeared within 24 h after the monkeys were returned to their cages where they had free movements. The effects of injections of 5 or 10% lidocaine chloride into the bilateral floccular areas (8 microl for each side) immediately after adaptation occurred were determined in nine sessions. The gain of the horizontal vestibulo-ocular reflex immediately decreased to the level before the adaptation. These effects of lidocaine lasted for at least 1 h. On the contrary, injections of the same amount of Ringer's solution, tested in eight sessions, hardly affected gain of the horizontal vestibulo-ocular reflex over 1-h period. These depressant effects of lidocaine injections were specific to the gains increased by adaptation. These results suggest that the memory trace for the short-term adaptation of the horizontal vestibulo-ocular reflex gain induced by 2 h of sustained visual-vestibular interactions resides within the flocculus.

Adaptation, Physiological↗
PubMed1999

Differences in opioidergic inhibition of spinal reflexes and Fos expression evoked by mechanical and chemical noxious stimuli in the decerebrated rabbit.

Noxious mechanical and chemical stimuli were applied to the toes of the left hind limb of decerebrated, spinalized rabbits and their effects on a hind limb spinal withdrawal reflex and expression of Fos-like immunoreactivity in the spinal cord were measured. The animals were prepared so as to minimize nociceptive inputs arising from surgery. A single crush stimulus applied with a pair of haemostatic forceps caused long-lasting (c. 20 min) inhibition of reflexes evoked in medial gastrocnemius motoneurons by electrical stimulation of the skin at the heel. Naloxone (0.25 mg/kg i.v.) increased reflexes to more than 1000% of pre-drug controls and reversed crush-evoked inhibition. Mustard oil applied to the toes had no consistent effects on the heel-gastrocnemius reflex before or after naloxone. Both crush and mustard oil stimuli gave rise to unilateral increases in the number of Fos-immunopositive profiles in the superficial dorsal horn of spinal segments L7 and S1. There were significantly more Fos-immunoreactive elements in the central and lateral parts of lamina I of both segments in animals receiving the crush stimulus than there were in animals receiving the mustard oil stimulus. Immunochemical localization of enkephalins in rabbit spinal cord showed a dense network of fibres and terminals in laminae I and II, accompanied by infrequent but distinctly stained neuronal cell bodies. The same pattern, with increased numbers of visible cell bodies, was seen after treatment with colchicine. The present data show that tonic and stimulus-evoked opioidergic inhibition of the heel-gastrocnemius reflex of the rabbit are not epiphenomena of surgical preparation of the hindlimb. Opioid-mediated inhibition of the heel-gastrocnemius withdrawal reflex of the rabbit was evoked by noxious mechanical but not by chemical stimulation of the toes. Of these stimuli, the former gave rise to greater activation of neurons in central and lateral lamina I of segments L7 and S1, the region of termination of afferent fibres from the heel and the location of some enkephalin-positive neuronal cell bodies. Thus, noxious mechanical stimulation of the toes elicits inhibition of the heel-gastrocnemius withdrawal reflex, probably via activation of enkephalinergic neurons in the lateral half of lamina I in the L7 and S1 segments.

Animals↗
PubMed1995

The role of bone scintigraphy in diagnosing reflex sympathetic dystrophy.

Three-phase bone scintigraphy is used often to diagnose reflex sympathetic dystrophy of the hand. This study presents an analysis of the literature relating three-phase bone scanning to reflex sympathetic dystrophy in the upper extremity. The data show a wide variability in scintigraphic accuracy in patients with clinically obvious reflex sympathetic dystrophy. The results of bone scintigraphy correlate best with the clinical diagnosis of reflex sympathetic dystrophy within the first 20-26 weeks of onset. Even then, the sensitivity in the most recent series approximates 50%. After 26 weeks, there is a poor correlation between three-phase bone scanning and reflex sympathetic dystrophy. Consequently, three-phase bone scintigraphy should not be used as a major criterion in diagnosing reflex sympathetic dystrophy. The diagnosis of reflex sympathetic dystrophy remains a clinical diagnosis made by an experienced hand surgeon.

Bone and Bones↗
PubMed1980

Interaction of upper airway reflexes on protective laryngeal closure.

Reflex responses evoked in the adductor branches of recurrent laryngeal nerve (RLN) by stimulation of the afferent nerves in the upper respiratory tracty were studied on anesthetized cats for the purpose of elucidating the mechanisms of the protective laryngeal closure reflex. A single pulse stimulation to each of the infraorbital branch of the trigeminal nerve (ION), the glossopharyngeal nerve (GPN) and the superior laryngeal nerve (SLN) elicited reflex responses in RLNs on both sides. The frequency-dependent attenuation of reflex responses in right RLN elicited by repetitive stimulation of ipsilateral SLN began at frequencies of 40-50/sec; on the other hand, that elicited by repetitive stimulation of ipsilateral GPN or ION was attenuated at frequencies of 5-10/sec. Furthermore, interactions among the reflexes in right RLN elicited by stimulation of ipsilateral ION, GPN and SLN were observed by using the technique of double shock stimulation (the "conditioning-testing" technique). The effect of conditioning stimulation of ION was a short facilitation followed by a long-lasting inhibition of RLN reflex responses elicited by test stimulation of SLN and GPN. conditioning stimulation of GPN elicited a similar effect on RLN reflex responses evoked by test stimulation of SLN. These results indicate an important role of the interactions among upper airway afferent activities for the performance of laryngeal defense action.

Animals↗
PubMed2002

Increased reflex activation of the peroneus longus following application of an ankle brace declines over time.

Two experiments were performed to document the time-dependent characteristics of the peroneus longus short latency stretch reflex amplitude following application of an ankle brace. In Experiment 1, stretch reflexes were induced in 15 weightbearing subjects during an unbraced condition and braced condition. In Experiment 2, stretch reflexes were induced in 15 weightbearing subjects before and after 3 h of wearing the brace. In Experiment 1. the amplitude of the stretch reflex increased in the braced condition by about 25% relative to the non-braced condition (p = 0.006). In Experiment 2 the amplitude of the stretch reflex increased about 18% immediately after application of the brace relative to the non-braced condition (p = 0.037). After 3 h, the stretch reflex amplitude was not different from that of initial non-braced condition. Given the importance of the peroneus longus muscle in ankle complex stability, further attention should be directed to whether the increased stretch reflex gain can be exploited during rehabilitation from ankle complex injuries. The findings provide a framework by which the effect of ankle braces on ankle joint proprioception, muscle activation profiles and balance may be physiologically interpreted.

Adult↗
PubMed1996

The Hering-Breuer reflex in ventilated children.

The authors tested the hypothesis that, in the paediatric population, the Hering-Breuer reflex would be provoked by the positive pressure inflation of mechanical ventilation (IPPV), and that the strength of the reflex would relate to the child's age and compliance of the respiratory system (CRS). During IPPV, changes in air flow, volume and airway pressure were recorded simultaneously. From the traces, expiratory times and CRS were calculated. The mean expiratory time (Te1) prior to each inflation and the mean expiratory time (Te2) immediately following an inflation were determined. The presence of the reflex was indicated by Te2 being longer than Te1, and the strength of the reflex was calculated as the difference between Te2 and Te1 expressed as a percentage of Te1. Twenty children were studied who had a mean age of 0.7 years (range 0.1-9.8 years). The reflex was provoked in 19 of the 20 patients and was not seen in the oldest patient. The strength of the reflex varied from 22 to 144% and was inversely related to postnatal age significantly (r = -0.73) but not CRS or inflation volume. It is concluded that the Hering-Breuer reflex is provoked during IPPV in young children; whether, as in neonates, this influences the efficacy of ventilation deserves investigation.

Aging↗
PubMed2002

Cruciate ligament reflexes.

The idea of muscular reflexes elicited from sensory nerves of the cruciate ligaments is more than 100 years old, but the existence of such reflexes has not been proven until the recent two decades. First in animal experiments, a muscular excitation could be elicited in the hamstrings when the anterior cruciate ligament (ACL) was pulled, and tension in the ligament caused activity of the gamma motor neurones of the muscles around the knee. Impulses from the sensory nerves in ACL were activated during motion of the knee, in particular overstretching and combined extension and rotation. In humans, proprioception in the knee is decreased after ACL rupture. By mechanical or electrical stimulation of the ACL, an excitation in the hamstrings muscles can be elicited. During muscular activity, stimulation of the ACL or PCL results in a clear inhibition of the ongoing activity, both during static isometric and isokinetic muscle work, and also during dynamic activity (gait). This inhibitory reflex subjectively resembled giving way. The latency of the reflex was short in animals (about 3 ms) and long in humans (60-120 ms), probably caused by differences in the experimental setup and between species. The long latency in humans makes it unlikely that it is a directly protective reflex. Instead it may be involved in the updating of motor programs. Further research may characterize the reflex in details and map its pathways. The existence of this reflex indicate that the cruciate ligaments have an afferent function, which influences knee dynamics.

Animals↗
PubMed2003

Identification and functional characterization of the trigeminal ventral cervical reflex pathway in the swine.

OBJECTIVE: Trigeminal motor reflexes are clinically useful for diagnosing brain stem lesions. We identified and functionally characterized the neuronal circuit of a new variant of the trigemino-cervical reflex involving the ventral cervical muscles in the swine. METHODS: The distribution and functional properties of the field potentials of the trigeminal reflex elicited by electrical stimulations of the snout were determined with electrodes in different regions of the brain. The generator of the reflex was determined from scanning evoked magnetic fields over the brainstem. The neuronal circuit was determined with electrodes placed along the trigeminal reflex pathway. RESULTS: The reflex produced a large positive potential in the brain (up to 200 microV in the primary somatosensory cortex) with a latency of about 14ms. Its amplitude declined rapidly with stimulation rate above 0.5Hz and was abolished by a muscle relaxant. The accompanying magnetic field was produced by a generator ventral to the pons. This generator was found to be the ventral cervical muscles that were activated by a circuit involving the brainstem trigeminal nuclei and cervical motor nuclei. CONCLUSIONS: It is not known whether this new variant of the trigeminal cervical reflex is species-specific or it also exists in humans. It should be possible to test this possibility in humans, since it produces strong characteristic electrical potentials and magnetic fields in the swine. If it exists in humans, then it may be useful as a clinical tool for testing the integrity of the brainstem and C1 and C2 since the circuit is now identified and characterized in the animal model.

Action Potentials↗
PubMed2003

Soleus H-reflex measures in patients with focal and generalized dystonia.

OBJECTIVE: The purpose of this study was to examine neurophysiological characteristics of dystonia patients using electromyographic soleus H-reflex methods. METHODS: Thirty normal healthy individuals were compared to 27 patients with focal (cervical) or generalized dystonia. Three H-reflex assessment methods were included: the ratio of maximum H-reflex to direct muscle potential (H/M ratio); vibration inhibition (H(v)/H(c) ratio); and H-reflex recovery curves (HRRC). RESULTS: Average H/M ratios between groups were not statistically significant. The average H(v)/H(c) ratio for the generalized dystonia group was significantly greater than the focal dystonia and normal groups. Average values of the HRRC showed the generalized dystonia group had significantly greater disinhibition than the focal dystonia and control groups during the early inhibition phase. The HRRC for the focal dystonia group was greater than normal and more similar to the generalized dystonia group during the late phases of the recovery curve. The average value of the localized late facilitation phase for the focal dystonia group was significantly greater than the control group and less than the generalized dystonia group. No differences were observed between groups for the average localized late inhibition phase of the recovery curve. CONCLUSIONS: Soleus H-reflex measures identified neurophysiologic differences between generalized dystonia, cervical dystonia and normal conditions. SIGNIFICANCE: This methodology enables analysis of the underlying characteristics of dystonic pathologies using soleus H-reflex methods rather than upper extremity H-reflex techniques.

Adult↗
PubMed2003

Effects of transcranial magnetic stimulation on the H reflex and F wave in the hand muscles.

OBJECTIVE: In 14 healthy subjects, we studied the effects of transcranial magnetic stimulation (TMS) on the excitability of spinal motoneurons in the abductor pollicis brevis muscle (ABP), by testing the F wave and H reflex. METHODS: TMS pulses were delivered with the subjects at rest and at various motor threshold (Mth) intensities. Electrical stimuli were delivered to the median nerve at the wrist at two different intensities. High-intensity pulse was used to evoke an F wave and low-intensity paired pulse to evoke an H reflex in the ABP muscle. The effects of TMS were studied using a conditioning-test paradigm. The tests F wave and H reflex were conditioned by TMS (120% Mth) at various interstimulus intervals (ISIs) (30-100ms) and intensities (90-200% Mth). RESULTS: At 30ms but not at ISIs from 40 to 100ms, conditioning TMS (120% Mth) significantly increased the F-wave area. At the 30ms ISI, conditioning TMS at 120% Mth intensity significantly increased the F-wave area whereas higher intensities (140-180% Mth) did not. At 200% Mth intensity, the F-wave area decreased significantly. At 30 and 40ms ISIs, conditioning TMS at 120% Mth significantly reduced the H-reflex area. At 50-100ms ISIs, the H-reflex area almost matched the control value. At the 30ms ISI, conditioning TMS at >or=100% Mth intensity significantly decreased the H-reflex area. CONCLUSIONS: In conclusion, our findings suggest that the distinct changes in the TMS-conditioned F wave and H reflex reflect changing excitability in the motoneuronal populations activated by the cortical input.

Adult↗
PubMed1999

The influence of experimental muscle pain on the human soleus stretch reflex during sitting and walking.

OBJECTIVES: The stretch reflex is functionally important during human locomotion. Muscle pain has been found to increase the stretch reflex amplitude during sitting, possibly due to an altered fusimotor drive. To further study the importance of altered fusimotor activity due to muscle pain we investigated the combined effect of muscle pain and motor task on the soleus stretch reflex. METHODS: Stretch reflexes were elicited before, during and after experimentally induced muscle pain in soleus (i.m. infusion of 6% saline) in 3 experiments: (1) in the relaxed soleus muscle and before, during and after an isometric ramp contraction (500 ms, 0-10 Nm), (2) at 3 different time periods during walking, and (3) at matched pain intensity and soleus activity during sitting and walking. RESULTS: Infusion of hypertonic saline into the soleus muscle caused a significant facilitated stretch reflex in the relaxed muscle (P<0.01), but not during walking or during sitting and walking at matched soleus EMG and matched pain levels. The infusion of isotonic saline (non-painful) did not cause any changes (P = 0.75). CONCLUSIONS: The main findings of the present study were that experimental muscle pain facilitated the stretch reflex during pain in the relaxed muscle, but caused no changes in stretch reflex amplitude during sitting and walking at higher "functional" background EMG levels.

Adolescent↗