Tibialis anterior response to sudden ankle displacements in normal and parkinsonian subjects

It is well known that in Parkinsonian subjects with akinesia, reaction times are increased but reflex latencies remain normal. We have attempted to use this knowledge to distinguish between 'reflex' and 'voluntary' components of the electromyographic (EMG) response to ankle displacement. The EMG and torque responses of tibialis anterior (TA) to randomly applied servo-controlled plantar-flexing displacements of the ankle with and without the subject's intentional opposition were examined in 9 Parkinsonian and 9 age-matched normal humans. To obtain a measure of akinesia, the response latency to a visual stimulus was subsequently measured in the same subjects. Three principal findings emerged. (1) The intermediate latency EMG component (PSR) of the response evoked by ankle displacement with the subject instructed to relax was more regularly evoked and of lower threshold in Parkinsonians than in normals. This finding corresponds to the enlarged M2 component in upper limb muscles. However, the facilitation of PSR was not found to be associated with an increase in torque. In fact, the patients did not exhibit more stiffness than normals under our experimental conditions. (2) Mean latency estimate of the PSR was indistinguishable between Parkinsonians and normals. This finding puts the PSR in the nature of a reflex. Indeed, in accordance with reflex behaviour which is proportional to input characteristics, its area increased linearly with increase in the magnitude of displacement velocity. (3) In contrast, the 'late' EMG response (FSR) evoked by opposing sudden ankle displacement exhibited a significantly longer latency in 6 out of 8 Parkinsonians than normals. In the same patients, the EMG response latency to a visual signal was similarly increased. The delay of FSR in akinesia patients thus argued against its being a stereotyped reflex. The result is discussed with reference to the recent finding that preprogrammed responses are delayed in Parkinsonians.     

Reliability of elbow stretch reflex assessment in chronic post-stroke hemiparesis.

OBJECTIVE: To establish reliability of quantitative measures of elbow joint spastic hypertonia in post-stroke hemiparesis. METHODS: Nine subjects with post-stroke hemiparesis (mn duration: 42 months) were tested on three separate days. Biceps brachii and brachioradialis EMG were recorded during passive ramp-and-hold extensions applied at seven speeds between 30 and 210 degrees /s. EMG burst duration, onset position threshold, and burst intensity were used to evaluate reflex activity. Torque at 40 degrees of elbow flexion was used as a mechanical indicator of spastic hypertonia. RESULTS: Across speeds ICCs were consistent, means ranged between 0.63 and 0.85. Thus, relative reliability was fair to excellent for all parameters. Absolute reliability, determined using standard error of measurement expressed as a percentage of the mean score (%SEM), improved at higher speeds (> or = 120 degrees/s). CONCLUSIONS: These results establish reliability of reflex and mechanical measures of elbow spastic hypertonia post-stroke. The data demonstrate greater reflex detection at high speeds, indicating greater potential to document meaningful changes in these distinct aspects of spastic hypertonia following intervention. SIGNIFICANCE: Based on findings of this study, reliability was demonstrated using four parameters of reflex EMG and torque indicating measurement consistency across sessions. These observations motivate determination of requisite effect sizes for clinical trials that evaluate treatment outcome.     

Reliability of electromyographic and torque measures during isometric axial rotation exertions of the trunk

OBJECTIVE: The aim of the present study was to investigate the between-days reliability of electromyographic (EMG) measurement of 6 bilateral trunk muscles and also the torque output in 3 planes during isometric right and left axial rotation at different exertion levels. METHODS: Ten healthy subjects performed isometric right and left axial rotation at 100, 70, 50 and 30% maximum voluntary contractions in two testing sessions at least 7 days apart. EMG amplitude and frequency analyses of the recorded surface EMG signals were performed for rectus abdominis, external oblique, internal oblique, latissimus dorsi, iliocostalis lumborum and multifidus bilaterally. The primary torque in the transverse plane and the coupling torques in sagittal and coronal planes were measured. RESULTS: For both EMG amplitude and frequency values, good (intraclass correlation coefficient, ICC=0.75-0.89) to excellent (ICC>/=0.90) reliability was found in the 6 trunk muscles at different exertion levels during axial rotation. The reliability of both maximal isometric axial rotation torque and coupling torques in sagittal and coronal planes were found to be excellent (ICC>/=0.93). CONCLUSIONS: Good to excellent reliability of EMG measures of trunk muscles and torque measurements during isometric axial rotation was demonstrated. This provides further confidence of using EMG and triaxial torque assessment as outcome measures in rehabilitation and in the evaluation of the human performance in the work place.     

Alterations in H reflex magnitude by variations in baseline EMG excitability

The effect of systematic variations in the baseline level of electromyographic activity of the flexor carpi radialis muscle on the magnitude of its H reflex was studied in 4 normal subjects. H reflex magnitude increases with variations in the baseline EMG activity corresponding to a range of 0.1-7.4% of the motoneuron pool as estimated by the maximum M response (Mmax) to peripheral nerve stimulation. Variations in H reflex magnitude with changes in baseline EMG activity were evident for all median nerve stimulus voltages examined ranging from 29% to 72% of that necessary to evoke an Mmax. H reflex magnitude increased with increases in baseline EMG activity, or net tension which provided an alternate estimate of pre-existing motoneuron activity. The greatest increase occurred when the H/M ratio was less than 50%, where the H reflex magnitude was found to increase by as much as 400%. The research establishes that baseline EMG activity and/or the net force being exerted by the muscles must be controlled and measured at different H/M ratios in order to interpret unambiguously studies using single stimuli to construct H-M recruitment curves or paired stimuli to evaluate changes in reflex excitability.     

Electrophysiological recording of deep tendon reflexes: normative data in children and in adults.

OBJECTIVE: Latency measurement of myoelectric deep tendon (T) reflex responses is not usually performed in EMG laboratories. We investigated the optimal conditions of reliable recording of T reflex in children and adults. METHODS: Two hundred and sixty-eight normal subjects (139 males, 129 females, age rank 2 days-80 years) were studied. T reflexes were recorded from soleus and rectus femoris muscles (children and adults) and from triceps brachialis, biceps brachialis and flexor carpi radialis (adults). Specially devised hammers were used. They were fitted with a spring switch system in order to trigger the trace display on the EMG machine. Distinct technical options for the synchronisation delay assessment were tested. The nerve conduction velocities along reflex pathways were computed by referring the T wave latencies to subject's height. RESULTS: Reliable recordings could be obtained in all cases, with a strong linear correlation of the response latency with height. T reflex conduction velocities increased as the log value of subject age. Normative data from birth to 80 years are provided. CONCLUSION: T reflex recording represents a painless and easily performed technique. It may be helpful for the assessment of proximal conduction velocities, especially in children during maturation of the peripheral nervous system.     

Continuous wavelet transform in the evaluation of stretch reflex responses from surface EMG

OBJECTIVE: This is the first reported use of the continuous wavelet transform (CWT) of the surface EMG (sEMG) to extract the reflex response to muscle stretch. We used a modulus-based method to estimate instantaneous amplitude-envelopes from ridges of the CWT (referred in this work as sEMG intensity) to extract the dynamic reflex response from sEMG. We tested the method on tendon reflexes where excellent temporal resolution is required to identify the different latency components, and on the tonic stretch reflex (tonic SR) response to an ongoing perturbation that characteristically has a low signal to noise ratio. METHODS: Eight subjects without neurological impairment were subjected to a series of archilles tendon taps and a 2 min continuous perturbation of the ankle using a pseudo-sinusoidal stretch profile containing frequencies from 0.1 to 8.0 Hz. The tendon reflexes were assessed in the soleus muscle at 10% of MVC and the tonic SR in tibialis anterior while the muscle was relaxed, at 5 and 10% of maximal voluntary contraction. Root mean square (RMS) and wavelet ridge extraction was applied to the sEMG signal to extract sEMG amplitudes (RMS) and intensities for all reflexes. To obtain the tonic SR, these estimates and those from the sEMG-RMS were subsequently cross-correlated with the perturbation record to yield 2 sets of estimates of reflex gain and coherence for comparison. RESULTS: The sEMG intensities were highly correlated with the torques resulting from a ramped voluntary contraction. Following tendon taps, the method resolved the M1, M2, M3 response components at accurate latencies and with more complete reconstruction of the components than RMS-derived estimates. The wavelet ridge estimates extracted the tonic SR from resting and contracting muscles with significantly higher coherence than RMS estimates. Reflex gain, when estimated from sEMG intensity or sEMG-RMS, demonstrated similar relationships to the perturbation frequency and background contraction level. When the sEMG intensity reflex gain estimates from different subjects were pooled, they showed significantly lower variance about the mean than gain estimates derived from the rectified sEMG. CONCLUSIONS: Wavelet-ridge extraction provides a valid approach to reflex evaluation from sEMG that does not depend on the absolute amplitude of the potentials measured at the EMG electrodes. This may have substantial advantages in more directly comparing responses between subjects on an absolute frequency scale without the need for normalisation against maximal contraction levels.     

Normalization reduces the spatial dependency of the jaw‐stretch reflex activity in the human masseter muscle

The jaw‐stretch reflex is the short‐latency response in the jaw‐closing muscles after a sudden stretch. The hypothesis whether normalization of the jaw‐stretch reflex amplitude with respect to prestimulus electromyographic (EMG) activity will make the amplitude more independent of the location of the electrodes over the masseter muscle was tested. A 5 × 6 electrode grid was used to record the jaw‐stretch reflex from 25 sites over the right masseter muscle of 15 healthy men. The results showed that there was a significant site dependency of the prestimulus EMG activity and the reflex amplitude. High cross‐correlation coefficients were found between the spatial distribution of mean prestimulus EMG activities and reflex amplitude. When the reflex amplitude was normalized with respect to the prestimulus EMG activity, no site dependency was found. In conclusion, normalization of the jaw‐stretch reflex amplitude by the prestimulus EMG activity strongly reduces its spatial dependency. Muscle Nerve, 2010     

Stretch reflexes in the upper limb of spastic man

The reflex response to stretch has been studied in the upper limb of 20 spastic patients. The amplitude of reflex EMG was found to be closely related to the velocity of stretch. Reflex EMG in biceps and triceps muscles was augmented by increasing the length of the muscle, although minimal inhibition of reflex EMG in biceps was obtained in two patients by extreme stretch. The clasp-knife sensation in the upper limb cannot be related to autogenic inhibition but may be explained by the characteristics of a velocity-dependent reflex in which limb movement is braked by the mechanical effect of increasing muscle tension. It is suggested that this be called the pseudo-clasp-knife reaction to distinguish it from the clasp-knife phenomenon of the quadriceps muscle, since the underlying neurophysiological mechanism is quite different.     

The effect of posture on the normal and pathological auditory startle reflex.

The effect of posture on the EMG pattern of the normal auditory startle reflex was investigated. The startle response to an unexpected auditory tone was studied in eleven normal subjects when standing, and in six normal subjects when sitting relaxed or tonically plantar flexing both feet. Reflex EMG activity was recorded in the tibialis anterior and soleus about twice as frequently when standing, than when sitting relaxed. In addition, the median latencies to onset of reflex EMG activity in the tibialis anterior and soleus were about 40 and 60 ms shorter during standing, than when sitting relaxed. No short latency EMG activity was recorded in the calf muscles during tonic plantar flexion of the feet, while sitting. The effect of posture on the EMG pattern of the pathological auditory startle reflex was studied in five patients with hyperekplexia. In three patients the latency to onset of reflex EMG activity in the tibialis anterior was shorter when standing, than when sitting relaxed. The EMG pattern of the reflex response to sound was studied in detail in two of these patients and consisted of up to three successive components. The expression of each EMG component depended on the postural set of the limbs. In particular, a distinct short latency component was found in posturally important muscles following auditory stimulation. This short latency component was not recorded when sitting relaxed. It is concluded that the EMG pattern of the physiological and pathological auditory startle response is not fixed, but may change with the postural stance of the body. This finding supports the theory that the normal startle reflex and the abnormal startle reflex in hyperekplexia have a common brainstem origin.     

Voluntary supraspinal suppression of spinal reflex activity in paralyzed muscles of spinal cord injury patients

Having previously demonstrated that residual facilitatory brain influence on segmental structures occurs in paralyzed spinal cord injury patients, we sought evidence of suprasegmental suppression in such patients. By recording EMG activity from leg muscles, we studied changes in segmental excitability of the plantar reflex elicited by cutaneous stimulation of the plantar surface. Using surface EMG recordings, 50 paralyzed spinal cord injury patients were examined for their ability to volitionally suppress the plantar reflex on three repeated trials after three baseline trials. The patients, who had no voluntary EMG activity in the monitored muscles, were able to volitionally suppress the plantar reflex responses by 45% in the tibialis anterior, hamstring, and triceps surae muscles and to suppress the quadriceps response by 72%. In this patient group, 73 of 100 tibialis anterior muscle groups showed suppression of more than 20% compared with the control response. On reexamination, these findings were consistent during a period of 2 years in six patients. We conclude that suprasegmental suppression of segmental activity does occur in paralyzed spinal cord injury patients, and that in clinically complete patients, neurological evaluation should include assessment of the degree of preservation of suprasegmental neurocontrol on segmental activity below the lesion.     

Reliability of surface electromyographic measurements.

OBJECTIVES: The aim of the study was to investigate short-term, intermediate-term and long-term reliability of surface electromyographic (EMG) measurements. METHODS: Eighteen healthy subjects performed 810 isometric knee extension tests. Reliability for maximum voluntary contraction (MVC) and 50% MVC was assessed with retest intervals of 3 min, 90 min and 6 weeks. Reliability for sustained contractions was assessed with retest intervals of 90 min and 6 weeks. EMG was recorded from the rectus femoris, vastus lateralis and vastus medialis muscles. The root mean square (RMS) and the median frequency (MF) parameters were extracted. At sustained contraction tasks, estimated linear regression values of both parameters were analyzed. Bland-Altman-plots, coefficient of repeatability, Pearson's coefficient of correlation and intra class correlation (ICC) procedures were applied to assess test-retest reliability. RESULTS: EMG recordings taken at short-term intervals were generally better reproducible than those of the longer-term intervals. Moreover, 50% MVC EMG recordings demonstrated better reproducibility than 100% MVC measurements, and EMG recorded from the rectus femoris were more constant than that from the vastus lateralis or vastus medialis. The MF parameter recorded from the rectus femoris was the only reliable parameter of EMG fatigue change. CONCLUSION: In our set up, EMG measurement is best suited for clinical applications if submaximal MVC measurements are performed and signal is taken from rectus femoris muscle.     

Coexistent Hoffmann reflexes in human leg muscles are commonly due to volume conduction

The existence of "concomitant" (coexistent) electromyographic reflex responses in soleus and tibialis anterior muscles, produced by posterior tibial nerve stimulation, has been cited as evidence for "reciprocal excitation" between these antagonistic muscles normally reflexly linked by reciprocal inhibition. Using the Hoffmann reflex procedure and posterior tibial nerve stimulation, the existence of true reciprocal excitation was tested in six subjects with no neuromuscular impairment. Coexistent EMG responses were observed in all subjects. In no instance, however, could the tibialis anterior EMG volley to posterior tibial nerve stimulation of the soleus muscle be antidromically blocked by common peroneal nerve stimulation applied at 10 to 20 ms offset latencies. A second stimulation pulse applied to the common peroneal nerve at similar offset latencies did antidromically block a tibialis anterior reflex response to common peroneal nerve stimulation. Therefore, volume conduction of reflex activity from the posterior tibial compartment to the anterior tibial compartment was a common observance. We suggest that coexistent EMG reflex responses, presumed to reflect reciprocal excitation, should be tested by the procedure described to reject the possibility of EMG cross-talk as a confounding variable or as the actual variable under investigation.     

Different responses to auditory and somaesthetic stimulation in patients with an excessive startle: a report of pediatric experience.

OBJECTIVES: Children with cerebral injury often exhibit brief muscle contraction to a variety of stimuli. However, it remains to be determined whether or not the pattern of the reaction is stereotypical irrespective of the site stimulated. To answer this question, we studied electromyographic (EMG) responses to three types of stimuli in children. METHODS: The EMG responses of cranial and limb muscles were recorded after acoustic or somaesthetic stimulation in 6 patients and 23 control subjects. RESULTS: Acoustic stimuli evoked patterned motor activity with a rostrocaudal progression. Nose-tapping stimuli elicited reflex EMG activity in the VIIth cranial muscles that was similar to the R1 component of the electrical blink reflex. Sternum-tap stimuli evoked motor activity in the sternocleidomastoid and arm muscles, and this reflex was probably mediated through the cervical cord (H-reflex). Moreover, late reflexes were evoked following these early reflexes in the patients. In particular, atypical forms of myoclonic jerks were evoked on sternum-tap stimuli. CONCLUSIONS: Many types of primitive reflexes were evoked following three types of stimuli. These reflexes included startle reflex, trigeminomotor reflex, H-reflex and atypical forms of myoclonus, and they were enhanced in the patient group. There are many startle-mimicking reflexes.     

Stance and gait perturbations in children: developmental aspects of compensatory mechanisms

The leg muscle EMG responses following perturbations during stance and gait were analysed in children between 1 and 8 years of age in order to study the development of those reflex systems responsible for the compensatory movements necessary to maintain body equilibrium. Single monosynaptic reflex potentials followed by a long-lasting (about 500 msec) polysynaptic gastrocnemius EMG response, along with coactivation of all antagonistic leg muscles, were characteristic of the EMG reactions following a treadmill acceleration impulse in early infancy. From 4 years of age on, the monosynaptic reflex potentials disappeared when perturbations were induced during gait. In addition, the polysynaptic reflex response became shorter (about 100 msec) and a reciprocal mode of leg muscle activation occurred, with a consequently more rapid and effective compensation of perturbation impulses. In older children with a disorder of the motor system acquired at an early age, a partial persistence of the immature motor responses could be observed, irrespective of whether the impairment was a cerebral lesion or a muscular dystrophy. It is concluded that the coactivation pattern is due to the immaturity of those nervous structures mediating afferent information necessary for the control of bipedal stance and gait. Furthermore, the existence of mutual inhibition of monosynaptic and polysynaptic spinal reflex responses, dependent on the function of supraspinal motor centres, can be assumed.     

A method for quantifying reflex responses from intra-muscular and surface electromyogram

Measuring human reflex responses from electromyogram (EMG) traces in an accurate, repeatable and reliable way with a high degree of specificity has traditionally been a difficult task. This paper describes a new method that can be used to quantify reflex responses from both surface and intra-muscular EMG. This technique extends the classical cumulative sum (CUSUM) calculations by defining precise points for the calculation of latencies, durations and strengths to facilitate automatic reflex detection and permit the strength of a reflex to be defined in absolute units. The effect of varying the pre-stimulus time, the number of trials averaged and the amount of filtering used on the identification and classification of reflex parameters are also investigated. Furthermore, the effect of noise on these values, and how to remove it, is discussed. The new method, which is an expansion of the CUSUM analysis, is compared and contrasted with the more common threshold-crossing method in two different muscles: masseter and first dorsal interosseous (FDI), in experiments utilizing both mechanical and electrical stimulation. There are a number of advantages to using the new method; not only does the modified CUSUM method detect reflexes earlier than threshold-crossing methods but also the strength and duration are less susceptible to averaging and filtering parameters while giving a better indication of the reflex size. The data suggests that a pre-stimulus analysis period of at least 100 ms be used to correctly identify the variability inherent in EMG traces. It is also concluded that for subtle reflexes, 50 stimuli should be the minimum number used when spike trigger averaging is employed as lower numbers are associated with much greater pre-stimulus variability. Zero-phase filtering the rectified averaged EMG traces is recommended as this makes it easier to identify significant changes in the electrical activity of the muscle in question. In addition, noise estimation and removal from averaged rectified EMG recordings yields results that are a more accurate representation of the synaptic activity of the motor units in question.     

Reproducibility and adaptation of the EMG responses of the lower leg following perturbations of upright stance

The electromyographic (EMG) response of gastrocnemius, soleus and anterior tibialis muscles to a backwardly directed perturbation of stance was recorded in 12 normal subjects using surface electrodes and studied with regard to its reproducibility (test-retest reliability coefficients, variability coefficients) and to adaptational effects. (1) Reproducibility was shown to be uniformly high and can be interpreted as an index for the high intraindividual constancy of the results. (2) Adaptational effects have been found and should be circumvented, either by pre-adapting the subjects to the motor task, or by restriction of the period of measurement. (3) Variation of the position of the electrodes produced only small effects. The impedance of the surface electrodes was not critical if kept below 5 k omega. EMG investigations with surface electrodes during stance and perturbations of stance provide highly reliable results with respect to intraindividual changes but interindividual variability of the results clearly marks the limits of this method. The interindividual variability observed with surface electrodes is of the same order as that reported in the literature for inserted needle recording.     

Regulation of stretch reflex threshold in elbow flexors in children with cerebral palsy: a new measure of spasticity

The tonic stretch reflex threshold in children with cerebral palsy (CP) was measured to determine its test-retest reliability and its concurrent validity as a potential measure of spasticity. Fourteen children with spastic CP aged 6 to 18 years were tested on three separate occasions for clinical spasticity and stretch reflex thresholds of affected elbow flexors. Electromyographic (EMG) recordings were obtained by surface electrodes for elbow flexors and extensors during mechanical displacements of the passive joint towards extension. Displacements were produced by a torque motor at seven velocities which randomly varied from trial to trial. EMG activity was measured in the stretched flexor muscles to determine threshold angles and velocities for each velocity of stretch. These were plotted on a velocity-angle-phase diagram and regression analysis was used to determine the static stretch reflex threshold for each participant. The measure showed good test-retest reliability for the group (ICC 0.73, p<0.001) whereas a significant correlation between the measure and the clinical spasticity scale was not found. This technique is a potential outcome variable for measuring the efficacy of treatments aimed at decreasing spasticity in children with CP.     

Cortical reflex myoclonus. A study of the relationship between giant somatosensory evoked potentials and motor excitability

The excitability cycles of the N1-P1-N2 waveforms of the scalp-recorded somatosensory evoked potential (SEP) and of the long-latency, cortical loop reflex electromyographic (EMG) activity were studied in two patients with cortical reflex myoclonus. Long-latency cortical loop reflex EMG activity in the thenar muscles and giant SEPs occurred following median nerve stimulation. The excitability cycle of the EMG paralleled that of the SEP. There was an initial period of attenuation of SEP and EMG amplitude at interstimulus intervals (ISIs) of less than 40 ms followed by a period of amplitude enhancement at an ISI of up to 200 ms followed by a second period of attenuation. The excitability cycle is abnormal and the SEP and EMG amplitude changes parallel each other. It is therefore likely that a common mechanism determines the abnormal excitability cycle. The substrate for this mechanism is unknown and may be diffuse or restricted. Oral 5-hydroxytryptophan (5-HTP) in therapeutic doses altered the SEP excitability cycle. 5-HTP did not attenuate the giant SEPs but did attenuate the long-latency reflex EMG. Therefore, 5-HTP's site of action may be different from the substrate underlying the mechanism that results in the giant SEPs. Additionally, spinal latency reflex EMG activity occurred following treatment with 5-HTP but was absent when the patient discontinued 5-HTP.     

CUTANEOUS REFLEX RESPONSES RECORDED IN CHILDREN WITH VARIOUS NEUROLOGICAL DISORDERS

Cutaneous reflex responses were recorded from tibialis anterior or first dorsal interosseous muscles of children with hemiplegia, spinal-cord compression, necrotizing sacroid granulomatosis, acute encephalomyelitis, myalgic encephalomyelitis, and a group of children attending the Learning Difficulties Clinic. Abnormalities of response are reported and are compared with the different reports in the literature of abnormal reflex EMG responses recorded by various methods. It is concluded that cutaneo-muscular reflex testing may have a part to play in the diagnosis of difficult paediatric problems.     

Neurophysiological observations on the effects of botulinum toxin treatment in patients with dystonic blepharospasm.

Botulinum toxin treatment improves dystonic blepharospasm by inducing transient paresis of the orbicularis oculi muscle. It is not known if it also reduces the enhanced brainstem neuronal excitability found in this disorder. We have performed conventional electromyography (EMG) and blink reflex excitability studies on fifteen patients with blepharospasm before and after botulinum toxin treatment. Denervation signs were found with needle EMG in all treated muscles. Amplitude of the facial compound muscle action potential (CMAP) and R1 response was reduced after botulinum toxin injections. In blink reflex excitability studies, the recovery of R2 response was enhanced after treatment even when patients were tested at the time of maximal benefit from botulinum toxin injections. The results suggest that there is little influence of botulinum toxin treatment upon the enhanced excitability of brainstem interneurons in patients with blepharospasm.