Cervical multisegmental motor responses in healthy subjects.

STUDY DESIGN: Experimental design. OBJECTIVES: This descriptive design study presents multisegmental motor responses in the upper extremities after stimulation of cervical spinal vertebrae. SETTING: Neuro Lab of Texas Woman's University, School of Physical Therapy, Texas, USA. METHODS: In trial 1, C7 spinal segment was electrically stimulated in 13 healthy subjects using surface electrodes while recording responses from abductor digiti minimi (ADM), abductor pollicis brevis (APB), flexor carpi radialis (FCR) and biceps brachii (BB) in the right upper extremity. In trial 2, C7 stimulation was carried out while recording responses from the APB and BB bilaterally. In trial 3, C7 stimulation was carried out while recording responses from the flexor hallucis brevis (FHB), soleus, vastus medialis (VMO) and gluteus medius (GM) in the right lower extremity. The amplitude of the signal and the deflection latency were the measured parameters. Descriptive statistics were completed on the data. RESULTS: Results showed response amplitudes in all muscles of the upper extremities ranging from 328 to 1239 µV, with the largest recorded from the APB and ADM, then the FCR and BB. Muscular responses were recorded simultaneously in bilateral muscles. Response latency was comparable, in bilateral similar muscles, and was varied from 6 to 16.5 msec, being longer in the ADM and APB, shorter in FCR and shortest in the BB. No lower limb muscles responded to C7 spinal stimulation, using current setup/method. CONCLUSION: These responses appear to be caused by stimulating the dorsal roots or motor nuclei of the cervical region and could be useful in testing patients with cervical spinal disorders.

Thoracolumbar multisegmental motor responses in the upper and lower limbs in healthy subjects.

STUDY DESIGN: Experimental design. OBJECTIVES: This descriptive study presents muscular responses from both the upper and the lower extremities during T11-12 segmental stimulation. SETTING: Neuro Lab of the Texas Woman's University (School of Physical Therapy, TX, USA). METHODS: A total of 13 healthy subjects were electrically stimulated using surface electrodes. In trial 1, signals were recorded from the flexor hallucis brevis, soleus, vastus medialis and gluteus medius in the lower right extremity. In trial 2, responses were recorded from the abductor digiti minimi, abductor pollicis brevis (APB), flexor carpi radialis and biceps brachii in the right upper extremity. In trial 3, stimulation was carried out and signals were recorded for both the upper and the lower extremities simultaneously, using different muscle combinations. Five traces per muscle were averaged for each step of the testing. Amplitude and deflection latency were the measured parameters and were compared using descriptive statistics. RESULTS: Results showed signal amplitudes ranging from 85 to 821 µV in the upper extremity and from 582 to 3927 µV in the lower extremity, with the largest signal recorded in the soleus muscle and the APB. Response latency varies between 5.5 and 14 ms in the upper limbs and between 7.7 and 27 ms in the lower limbs and was comparable in bilateral recording. CONCLUSION: These muscular responses seem to be elicited from electrical stimulation of motor nuclei in lower limb muscles or from pathways to those nuclei in upper limb muscles, and could be useful in testing patients with spinal disorders.

The proportion of patients with non-specific low back pain and neural compromise.

Lack of sensitivity in clinical evaluation and imaging techniques often result in the potential misdiagnosis of the nerve root compromise in patients with non specific low back pain (NSLBP). H-reflex is reliable, valid, and sensitive electrophysiological procedure in detecting neural impingement in patients with low back pain of neurological origin and, thus, could be used to detect nerve root compromise in NSLBP To date, this has not been studied. The purpose of this study was to estimate the proportion of patients with NSLPB and neural compromise using the soleus H-reflex. Soleus H-reflex was measured bilaterally in 30 NSLBP patients with no radicular symptoms during prone lying and standing upright relaxed postures. Five traces were measured and averaged. Side-to-side amplitude (HIH) ratios were then calculated. Inference statistic estimated the proportion and 95% confidence intervals of patients with NSLBP and neural involvement. Soleus H-reflex asymmetry was detected in 17% and 20% of patients with NSLBP during lying and standing, respectively. In some patients, NSLBP may be associated with small degree of nerve root compromise, although the neural compromise is insufficient to cause distal radiculopathy. For these patients, treatment strategies to address such possible underlying mechanism of pain should be considered.

Using standing postures as a practical alternative to gait analysis for assessing normal neuromotor activity variation of the ankle muscle antagonists: a soleus H-reflex and EMG activity study / Uso de posturas erguidas como alternativa al análisis de marcha para evaluar la variación en la actividad neuromotora de los músculos antagonistas del tobillo: un estudio utilizando el reflejo H del músculo sóleo y EMG

Soleus and tibialis anterior muscle EMG and soleus H-reflex are widely used to study ankle motor control during gait. Normally, the soleus H-reflex amplitude and EMG activity varies greatly through the course of walking. The examining of these events during walking requires space and resources that are generally found only in research oriented facilities, making difficult a more practical use. Earlier reports have suggested that normal variation of the soleus H-reflex and EMG could be determined from standing postures. Therefore, the main purpose of this study was to examine and determine which standing postures would reproduce the normal neuromotor variation of the ankle muscle antagonists. A total of five postures were investigated. The results of this study demonstrated that the normal variation in the soleus H-reflex amplitude and the associated EMG activity can be comparably reproduced from two selected standing postures (PO and SW). The described method presents a practical and functional alternative to gait analysis when the goal is determining normal ankle neuromotor control.

La actividad electromiográfica (EMG) de los músculos tibial anterior y sóleo junto al reflejo H del sóleo han sido extensamente usados en el estudio del control motor del tobillo durante la marcha. Normalmente, la amplitud del reflejo H del sóleo y EMG varía ampliamente durante el curso de la marcha. El estudio de estos eventos durante la marcha requiere de espacio y equipamiento generalmente sólo disponible en laboratorios de investigación, por lo que resulta difícil su aplicación práctica. Previos estudios han sugerido que la variación normal del reflejo H del sóleo y EMG pudiese ser obtenida utilizando posturas en la posición de pie. El propósito principal de este estudio fue examinar y determinar qué posturas reproducirían la variación neuromotora normal en los músculos antagonistas del tobillo. Un total de cinco posturas fueron investigadas. Los resultados de este estudio demostraron que la variación normal de la amplitud del reflejo H del sóleo y EMG asociada, puede ser similarmente reproducida a partir de dos posturas (PO y SW). El método descrito presenta una alternativa práctica y funcional a la marcha, cuando el objetivo es la determinación del control neuromotor normal en el tobillo.

Medial and lateral gastrocnemius H-reflex intersession reliability during standing and lying postures at varied foot positions in healthy participants.

Available H-reflex procedures do not allow a reliable or valid examination for the L5 radiculopathy. However, recording the gastrocnemius H-reflex may allow a reliable and valid method for examination of the L5 nerve root. Therefore, the purpose of this study was to examine the intersession reliability of the medial gastrocnemius (MG) and lateral gastrocnemius (LG) H-reflexes recordings during standing and lying postures at varied ankle positions in healthy participants. The MG and LG H-reflexes of eight healthy participants were elicited by stimulating the tibial nerve and recording the resultant muscle response using surface electrodes. The stimulation parameters were 1.0 ms, 0.2 PPS, with incremented stimulus intensity. Four traces of the maximum amplitude H-reflex and M-wave were recorded during lying and standing with the ankle in neutral, full dorsiflexion, and full plantarflexion over two consecutive days. The averaged traces were used to calculate the intersession intraclass correlation coefficients (ICC) among conditions. Intersession ICCs (2, 1) of MG and LG during standing and lying with varied ankle positions were moderate to high (ranging from 0.58 to 0.94). The MG was more stable than LG and the ICCs were greater during standing (ranging from 0.76 to 0.94) than during lying (ranging from 0.58 to 0.85), indicating higher sensitivity of the MG H-reflex when the limb is engaged in functional standing However, the LG H-reflex reliability was robust and, thus, could be recorded consistently in the examination of the L5 nerve root.

Test-retest reliability of the soleus H-reflex in three different positions.

PURPOSE: H-reflex has been clinically useful in the diagnosis of radiculopathies, developmental disorders, and measurement of motoneuron excitability. However, variability of the H-reflex precluded its routine application. The purpose of this study is to evaluate the test-retest and within-subject reliability of the soleus H-reflex tested in three different positions. SUBJECTS: Seven men and eight women healthy volunteered (20-50 y) with no history of significant low back pain or radiculopathy consented to the study. METHODS: The soleus H-reflexes for both lower extremities were elicited and recorded using Cadwell 5200-A EMG unit and surface recording. The tibial nerve was electrically stimulated at the popliteal fossa using 0-5 ms., 0.2 pps pulses at intensity equivalent to H-max. Each subject was tested randomly in three different positions: pronelying, free standing, and standing while lifting 20% of his/her body weight. Signal were amplified (1-5 K) using surface electrodes applied on the soleus muscle at midline and 3 cm below the gastrocnemius musculotendinous junction. The peak-to-peak amplitude and onset latencies of four separate traces were averaged for each trial. Subjects were re-tested within 10 days by the same tester following the same protocol. RESULTS: Test-retest reliability of the H-reflex amplitude ranged from r = .29 in prone position to r = .56 in the loading position. Within day reliability of the H-amplitude was high between the three different positions and ranged from r = .56 to r = .97. The test-retest reliability of the H-latency were extremely high and robust, with the coefficients ranged from r = .92 to r = .94. Also the within day reliability of the H-latency ranged from r = .96 to r = .99. CONCLUSIONS: Results indicated that, when the H-amplitude is the measure of choice, testing the H-reflex in standing and loading positions is more reliable than testing in pronelying. Also testing the subject during various procedures in the same session is more reliable than testing subject in different days/sessions. The H-latency is highly reliable in all three testing positions.

H-reflex changes under spinal loading and unloading conditions in normal subjects.

OBJECTIVE: The soleus H- reflex is usually tested clinically in patients lying prone, with the H-latency always the criterion of choice for detecting abnormality. However, stresses on the spine vary during lying, standing, loading (weight lifting) and unloading. So the objective of this study was to measure changes in the H-reflex under 4 different loading conditions and to investigate whether mechanical loading of the spine would affect the H-reflex parameters. METHODS: Twenty healthy volunteers (22-46 years) with no history of significant low back pain or radiculopathy participated in the study. A Cadwell Excel electromyography unit was used to elicit and record the soleus H-reflex. The tibial nerve was stimulated at the popliteal fossa using 1 ms pulses at 0.2 pps of H-max. Each subject was tested under 4 different conditions: prone lying, free standing, standing while lifting 20% of his or her body weight, and standing while unloaded by 25% of his/or her body weight by a ZUNI II unloading system. For each subject, the peak-to-peak amplitudes of the maximum obtained H- reflex and the onset latencies of 8 separate traces were averaged for both lower extremities. Two-factor, repeated-measures ANOVAs were used to test the effect of the condition and side on the H-reflex amplitude and latency with ( approximately =0.025). RESULTS: The H-reflex was inhibited during standing, loading and unloading as compared with prone lying. The H-reflex was recovered during loading as compared with during standing. There were no significant changes in the H-reflex latency under the 4 different conditions. Both lower extremities showed similar pattern of changes in the H-reflexes. CONCLUSIONS: These results imply a significant interplay between peripheral and central mechanisms and their effects on the spinal motoneurons. This in turn suggests that testing of the H-reflex amplitude and latency under functional conditions, such as standing may be useful in detecting subtle changes in root impingement.

Electromyographic analysis of neck muscle fatigue in patients with osteoarthritis of the cervical spine.

Median frequency parameters of myoelectric signals were studied in 25 patients with osteoarthritis of the cervical spine and in 25 normal subjects. The median frequency parameters included initial median frequency and slope of the median frequency during 20%, 50%, 80%, and 100% of maximum voluntary contractions (MVC). The subjects performed sustained, isometric constant-force contractions of forward and backward bend of the cervical spine. The median frequency signals were obtained from the anterior (sternocleidomastoid) and posterior (upper trapezius) neck muscles. The results showed that at moderate and high forces (i.e., 50%, 80%, and 100% MVC) the anterior neck muscles in patients with osteoarthritis of the cervical spine fatigued faster than those of normal subjects. The posterior neck muscles in patients fatigued faster compared to normal subjects at high force levels (i.e., 80% and 100% MVC). This indicates a higher fatigue of the anterior and posterior neck muscles associated with arthritic changes of the cervical spine. Rehabilitation programs must consider these muscular changes to obtain optimal outcomes.

Changes in fatigue characteristics of cervical paraspinal muscles with posture.

The median frequency of the myoelectric signal of the cervical paraspinal muscles was studied in 28 normal subjects in prone and sitting positions. Median frequency parameters (initial median frequency and slope of the median frequency) of the myoelectric spectrum were monitored during sustained isometric neck extensions at 20%, 50%, 80%, and 100% of maximum voluntary contractions. Force output of 100% maximum voluntary contractions was also measured in the prone and sitting positions. Reliability of the median frequency parameters for repeated trials at various force levels was computed. There were significant differences (P less than 0.05) in the median frequency parameters between the prone and sitting positions, and there was significantly higher 100% maximum voluntary contractions force production in the prone position than in the sitting position (P less than 0.05). There were also high reliability estimates for the median frequency parameters in both test positions. The cervical paraspinal muscles may use different strategies of recruiting motor units during force production in various postures of the neck. It therefore is necessary to standardize the testing procedures before the median frequency parameters can be considered objectively to measure the muscle function in the neck.

Topical anesthetic-induced improvements in the mobility of patients with muscular hypertonicity: Preliminary results.

Application of a topical anesthetic on the skin of the upper and lower limbs of chronic stroke and head-trauma patients induced considerable improvement in limb mobility within 30 min. We hypothesize that the augmentation of joint mobility and reduction in muscle rigidity are the result of desensitization of skin receptors that interact with the motor system. Physical therapy exercises performed during the effective period of the anesthetic rendered long-lasting improvement in the patients' ability to move their upper limbs and ambulate more effectively.

Do joint receptors modulate the motoneuron excitability?

The purpose of this study was to test the effect of joint receptor afferent discharge, during rest and during small excursion movement on kinesthetic sensation and on the excitability of alpha-motoneurons in the ankle joint in normal subjects. Movement kinesthesia was tested using a specially designed test that measured the delay time between the actual and the perceived movement during slow 5 degrees/sec), passive, 20 degrees movement excursion. These data were correlated to a second kinesthetic test using a visual analog scale in which the subject compared movements of the joint being tested and the contralateral control limb joint. The excitability of alpha-motoneurons was tested using soleus H-M recruitment curve with incremented electrical stimuli to the posterior tibial nerve at the back of the knee joint. The H-reflex recovery curve was also tested using double-identical stimuli of increasing interstimulus intervals. Joint receptors were desensitized by iontophoretic application of 3 cc. of 2% xylocaine using 5 mAmp direct current for 30 min, and movement kinesthesia and H-reflexes were tested over time up to 30 min after termination of iontophoresis. Movement kinesthesia was significantly decreased (p less than 0.05) following anesthesia, and the decrease lasted during the time of the experiment. No statistically significant changes were recorded in the H-M recruitment or H-reflex recovery curves. These results indicate that joint receptor afferents may lack the spontaneous activity recorded in other receptors, such as the skin and muscles, and do not provide position sensation at the ankle joint during rest. These results also indicate that joint receptor afferents may inform the central nervous system about movement sensation in the middle range, but this information has minimal effect on the excitability of the motoneurons as measured by H-reflexes.

Segmental H-reflex studies in upper and lower limbs of healthy subjects.

The H-reflex has been recorded from the flexor carpi radialis muscle in the upper limb and vastus medialis (quadriceps) muscle in the lower limb in relaxed healthy subjects. The characteristics of these reflexes have been compared with those of the soleus H-reflexes, recorded with the same technique, and similar behavior has been reported. The techniques and pitfalls of recording these segmental reflexes and their clinical and neurophysiologic significance are discussed in light of the relevant literature. These segmental reflexes will be useful in studying conduction and integrity of C7, L4, and S1 spinal segments.

Segmental H-reflex studies in upper and lower limbs of patients with radiculopathy.

The H-reflex was recorded from the flexor carpi radialis, vastus medialis, and soleus muscles in patients with radiculopathy at C7, L4, and S1 roots. Reflex parameters were compared to normal standards and correlated with other electrophysiologic (eg, electromyography) and clinical evaluations, as well as magnetic resonance imaging scan reports. The H-reflex had significantly smaller peak-to-peak amplitude and longer latency. The stimulus threshold for eliciting the reflexes was substantially higher than normal standards, and the reflex was polyphasic in most patients. A strong correlation was recorded between the pathologic changes in reflex parameters and electrophysiologic and clinical findings of different segmental lesions. Magnetic resonance imaging reports showed moderate correlation with the H-reflex changes. A test of specificity showed that soleus and vastus medialis H-reflexes were 100% specific for lumbosacral segments; flexor carpi radialis was 90% specific for cervical spinal segments. These results indicate that flexor carpi radialis, vastus medialis, and soleus H-reflexes are useful and valid methods for testing C7, L4, and S1 radiculopathy.

Recovery profile of single motoneurons after electrical stimuli in man.

The H-reflex of 120 soleus motoneurons was recorded using fibre EMG. The recovery profile of these motoneurons was studied during monitoring surface H-reflex records in 28 adult subjects. The spectrum of motoneurons tested was homogeneous with two extremes of neurons having different characteristics. A motoneuron population (forming about 69% of our sample) had a high threshold level for electrical stimuli, short recovery time, and short recovery fringe time (called type A). A second population of motoneurons (forming about 20-30% of our sample) had a low threshold level for electrical stimuli, long recovery fringe time (called type B). During an isometric muscle contraction every motoneuron showed an early shift in recovery time (i.e. each had a shorter recovery time) with shortened recovery fringe time. These changes were larger for motoneurons type B than motoneurons type A. With paired identical electrical stimuli of varying interstimulus intervals a motoneuron may fire in response to the conditioning and test stimuli giving an H2, but not in response to both stimuli. This occurred for interstimulus intervals of 4-11 ms. A strong inhibition period was recorded with interstimulus intervals of 12-80 ms in which all motoneurons did not show any recovery. Most motoneurons recovered in orderly fashion between 80 and 300 ms of interstimulus interval, and this recovery coincided with the fast recovery recorded in surface H-reflex. All motoneurons were recovered by 3000 ms of interstimulus intervals. These findings emphasize the importance of eliciting the H-reflex every 3-5 s in H-reflex methodology in order to be assured that all excited motoneurons have been recovered.

Median frequency of the myoelectric signal. Effects of hand dominance.

A study was performed to investigate the existence of any distinction in the fatiguability of corresponding contralateral muscles in the hand as a function of hand dominance. The first dorsal interosseous muscle was studied. The median frequency of the myoelectric signal was employed to describe the fatigue behavior of the muscle. It was found that during sustained contractions the median frequency decreased faster in the non-dominant hand of right handed individuals, whereas, no statistically significant distinction could be found in left handed individuals. This distinction was evident in both male and female subjects. This study demonstrates that continued preferential usage of a muscle is associated with altered electrical properties of the myoelectric signal and that the median frequency of the signal provides an appropriate measure of the modifications. It is argued that the findings may provide an indication of modifications in the metabolic properties of muscle fibers induced by a lifetime of preferred functional use.

Median frequency of the myoelectric signal. Effects of muscle ischemia and cooling.

A study was performed to investigate the changes that occur in the median frequency of the myoelectric signal during local ischemia or reduction of intramuscular temperature produced by surface cooling. Data was obtained from experiments which involved the first dorsal interosseous muscle of 10 female and 16 male subjects. These subjects were asked to perform isometric constant-force abduction contractions of the index finger at 20% and 80% of maximal voluntary contraction level. The initial median frequency (IMF) of the myoelectric signal during the first 0.5 s of contraction was calculated. Results showed a significant reduction of the IMF in contractions performed under ischemic conditions; upon release, the IMF recovered quickly. At 80% maximal voluntary level of contraction, a greater decrease of the IMF was recorded. Similar results were demonstrated during reduction of intramuscular temperature with gradual recovery of the IMF after cooling. These results demonstrate that the median frequency of the myoelectric signal displays behavior similar to that reported for conduction velocity and this is consistent with the notion that accumulation of metabolic byproducts in muscle tissue causes a decrease in the conduction velocity of the muscle fibers.

Topical anesthesia: modulation of the monosynaptic reflexes by desensitization of the skin.

Skin desensitization by topical anesthesia was studied for its effect on the motoneuron excitability of the soleus muscle. Skin areas overlying calf, tibial, quadriceps and hamstrings muscles and skin dermatomes (L2, L3, L4, L5, S1 and S2) were studied separately. Motoneuron excitabilities were measured by the H-reflex and Achilles tendon reflex (for alpha and gamma motoneurons). It was shown that anesthesia applied to all skin areas and dermatomes, except those overlying the antagonist muscles, resulted in significant facilitation of the soleus H-reflex. In these cases, the ATR showed either slight inhibition or no significant changes. Anesthesia to the skin overlying the anterior tibial antagonistic muscle produced varied and inconsistent modifications in the amplitude of the H-reflex. In these cases the ATR was either slightly facilitated or showed no significant changes. These results appear to indicate the existence of on-going excitatory and inhibitory effects from the skin on the alpha and gamma motoneuron pool probably via segmental and suprasegmental levels. A possible clinical application of these results to modulate the motoneuron pool excitability is proposed.

Age-related changes in monosynaptic reflex excitability.

The excitability of the H-reflex was tested in a younger group (19 to 31 years) and an older group (60 to 72 years) of subjects. The threshold for the H-reflex was higher and the reflex latency was 7 msec longer in the older group of subjects. Also, the H-reflex amplitude was significantly smaller, longer in duration and polyphasic in shape whereas the time delay between the M-response and the H-reflex (central latency) was 5 msec longer in the older group. The H-reflex recovery curves of the older subjects demonstrated a longer primary inhibition period (94 msec in older subjects, 44 msec in younger subjects) and was slower, more inhibited, and took a longer time for maximal recovery. In accordance with previous findings, these results are attributed to possible central as well as peripheral and muscle fiber defects in old subjects. Such changes must be taken into account when using H-reflex tests in the clinic.

Topical anesthesia: a possible treatment method for spasticity.

Topical anesthesia was applied to the skin of the leg and thigh of a hemiparesis patient resulting from embolic infarction in the middle cerebral artery. After application of the anesthesia, the angular displacement of the ankle and knee joints measured during a full gait cycle showed a substantial shift towards normal. This response indicated a reduction in muscle spasticity which was confirmed by clinical tests. Neurophysiologic studies performed on the patient suggested that the reduction in muscular hypertonicity was mediated by reduced cutaneous inputs on the alpha - gamma motoneuron interaction. This conjecture is supported by studies of other investigators performed on animals as well as humans.