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.

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 comparing patients with hemiplegia to healthy subjects / Uso de posturas erguidas como alternativa práctica al análisis de marcha para evaluar la actividad neuromotora normal de los antagonistas del tobillo: una comparación entre pacientes hemiplégicos y sujetos normales

The purpose of this study was to evaluate and compare the soleus H-reflex amplitudes recorded in three standing postures between a group of patients with stroke and a group of healthy subjects. Nine ambulatory patients were compared with 10 healthy subjects. Measures were recorded during quiet standing (QS), heels raised (PO) and with the foot of the measured leg held just off the ground while standing on the opposite leg (SW). The results showed that patients, as opposed to the healthy group, did not inhibit soleus H-reflex in the SW posture. As opposed to evaluating ankle motor control during gait, the PO and SW standing postures appeared to offer a practical and objective method to assess soleus H-reflex when the purpose is to determine impairment (or recovery) of ankle neuromotor control in stroke survivors.

El propósito de este estudio fue evaluar y comparar la amplitud de el reflejo H en el músculo sóleo en tres posturas en la posición de pie entre un grupo de pacientes con hemiplejia y un grupo de individuos sanos. Nueve pacientes ambulatorios fueron comparados con diez individuos sanos. Registros fueron obtenidos en la posición de pie bipedal (QS), bipedal con talones elevados (PO), y unipedal manteniendo el pie afectado ligeramente elevado sin contacto con el piso (SW). Los resultados mostraron que los pacientes, en contraste con el el grupo sano, no presentaron inhibición del reflejo H en la postura SW. Comparado a registros del reflejo H obtenidos durante la marcha, aquellos obtenidos con las posturas PO y SW aparecen como un método más práctico y objetivo para evaluar el reflejo H del soleus si el propósito es determinar nivel de pérdida (o recuperación) de el control neuromotor del tobillo en pacientes con hemiplejia.

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.

Methods of H-reflex evaluation in the early stages of Parkinson's disease.

Differentiating the early stages of Parkinson's disease from the normal consequences of aging or from other common neurologic conditions can be diagnostically problematic. The purpose of this study was to compare methodologies for measuring motor neuron excitability of Parkinson's disease patients with a control group. H-reflexes were monitored in 16 patients diagnosed in the early stages of Parkinson's disease (Hoehn & Yahr stages I and II) compared with 30 subjects who were disease free. Methods of measurement included H-reflex latencies, the relative values of maximum H-reflexes to maximum direct motor responses (H-to-M ratio), the relative values of H-reflex amplitudes during vibration compared with control H-reflex amplitudes (Hv-to-Hc ratio), and double-stimulation H-reflex recovery curves using different interstimulus interval parameters. No significant differences were observed for the H-to-M or Hv-to-Hc ratios, or for the H-reflex latencies. The H-reflex recovery curves for the patients with Parkinson's disease demonstrated significantly greater ratio amplitudes than the control group during the double-stimulus responses between the 150-msec and 700-msec interstimulus intervals. Although comparisons of simple H-reflexes and H-reflexes during vibration did not differentiate the patients in the early stages of Parkinson's disease from the control group, the double-stimulation paradigm was a sensitive method for detecting early diagnoses of this disease.

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.

Neck retractions, cervical root decompression, and radicular pain.

STUDY DESIGN: Two-group repeated measures. OBJECTIVES: To evaluate the changes in the flexor carpi radialis H reflex after reading and neck retraction exercises and to correlate reflex changes with the intensity of radicular pain. BACKGROUND: Repeated neck retraction movements have been routinely prescribed for patients with neck pain. METHODS AND MEASURES: Ten nonimpaired subjects (mean age, 27 +/- 4 years) and 13 patients (mean age, 35 +/- 9 years) with C7 radiculopathy volunteered for the study. The flexor carpi radialis H reflex was elicited by electrical stimulation of the median nerve at the cubital fossa before and after 20 minutes of reading and after 20 repetitive neck retractions. Subjective intensity of the radicular pain was reported before and after each condition using an analog scale. RESULTS: For patients with radiculopathy, a repeated-measures analysis of variance showed a significant decrease in the H reflex amplitude (from 0.81 +/- 0.4 to 0.69 +/- 0.39 mV), an increase in radicular symptoms after reading (from 4.2 +/- 1.3 to 5.6 +/- 1.4 on the visual analog scale), an increase in the H reflex amplitude (from 0.69 +/- 0.39 to 1.01 +/- 0.49 mV), and a decrease in pain intensity (from 5.6 +/- 1.4 to 1.5 +/- 1.3) after repeated neck retractions. There was an association between cervical root compression (smaller H reflexes) and increased pain during reading and between cervical root decompression (larger H reflex) and reduced pain (r = -0.86 to -0.60). Exacerbation of symptoms was found with a reading posture. There were no significant changes in the H reflex amplitude in the nonimpaired group. No changes were found in reflex latency for either groups. CONCLUSIONS: Neck retractions appeared to alter H reflex amplitude. These exercises might promote cervical root decompression and reduce radicular pain in patients with C7 radiculopathy. The opposite effect (an exacerbation of symptoms) was found with the reading posture.

Correlation of spasticity with hyperactive stretch reflexes and motor dysfunction in hemiplegia.

OBJECTIVES: To study the correlation between spasticity and motor dysfunction in the wrist-hand unit of adult hemiplegic patients, and to investigate the correlation between clinical spasticity and hyperactive stretch reflexes. STUDY DESIGN: A survey study with a sequential case series of subjects. SETTING: Neuromuscular Research Laboratory, School of Physical Therapy, Texas Woman's University, Houston, TX. SUBJECTS: Sequential sample recruited from local stroke support groups: 10 patients with chronic hemiplegia caused by cerebral vascular accident who had various degrees of spasticity in the wrist joint. OUTCOME MEASURES: Modified Ashworth Scale, amplitudes of stretch reflexes for wrist flexors, grip strength, active range of motion of the wrist joint, and Fugl-Meyer test. RESULTS: Strong reverse correlation was found between spasticity and grip strength, the Fugl-Meyer test scores, and the Box and Blocks test scores (p = .001 to .005). Results also indicated a strong and consistent correlation between spasticity and reflexive electromyographic activities of the stretch reflex recorded from active muscles (p = .005 and .007), but not between spasticity and torque response of the stretch reflex. CONCLUSIONS: The degree of wrist spasticity is associated with impaired hand function in hemiplegic patients, and hyperactive electromyographic response of the stretch reflex, recorded from active muscles, is a valid indicator of spasticity.

Cervical root compression monitoring by flexor carpi radialis H-reflex in healthy subjects.

STUDY DESIGN: One-group, pretest-postest experimental research with repeated measures. OBJECTIVE: To determine the effect of head postural modification on the flexor carpi radialis H-reflex in healthy subjects. SUMMARY OF BACKGROUND DATA: H-reflex testing has been reported to be useful in evaluating and treating patients with lumbosacral and cervical radiculopathy. The idea behind this technique is that postural modification can cause further H-reflex inhibition, indicating more compression of the impinged nerve root, or recovery, indicating decompression of the root. Such assumptions cannot be supported unless the influence of normal head postural modification on the H-reflex in healthy subjects is studied. METHODS: Twenty-two healthy subjects participated in this study (14 men, 8 women; mean age, 39 +/- 9 years). The median nerve of the subjects at the cubital fossa was electrically stimulated (0.5 msec; 0.2 pulses per second [pps] at H-max), whereas the flexor carpi radialis muscle H-reflex was recorded by electromyography. The H-reflexes were recorded after the subject randomly maintained the end range of head-forward flexion, backward extension, rotation to the right and the left, lateral bending to the right and the left, retraction and protraction. These were compared with the H-reflex recorded during comfortable neutral positions. Data were recorded after the subject maintained the position for 30 seconds, to avoid the effect of dynamic postural modification on the H-reflex. Four traces were recorded in each position. During recording, the H-reflex was monitored by the M-response to avoid any changes in the stimulation-recording condition. RESULTS: Repeated multivariate analysis of variance was used to evaluate the significance of the difference among the H-reflex, amplitude, and latency, in various head positions. The H-reflex amplitude showed statistically significant changes (P < 0.001) with head postural modification. All head positions, except flexion, facilitated the H-reflex. Extension, lateral bending, and rotation toward the side of the recording produced higher reflex facilitation than the other positions. These results indicate that H-reflex changes may be caused by spinal root compression-decompression mechanisms. It may also indicate that relative spinal root decompression occurs in most head-neck postures except forward flexion. CONCLUSIONS: Head postural modification significantly influences the H-reflex amplitude but not the latency. This indicates that the H-reflex is a more sensitive predictor of normal physiologic changes than are latencies. The H-reflex modulation in various head positions may be-caused by relative spinal root compression-decompression mechanisms.

The H-reflex modulation in lying and a semi-reclining (sitting) position.

OBJECTIVE: The purpose of this study was to compare motor pool excitability as measured by the H-reflex during lying prone and sitting in a semi-reclining position. DESIGN AND METHOD: Twelve volunteer subjects were measured for maximum M-wave and H-wave during sitting and prone lying to determine an H/M ratio. Latency of each H-reflex was also measured. H-reflex responses were recorded during a control and a vibration condition in the two positions. A double-stimuli H-reflex recovery curve was also plotted for each subject in each relaxed position of sitting and lying. RESULTS: No significant differences were observed between the prone lying and sitting positions for the any of the variables measured. CONCLUSIONS: The present results showed no difference in H-reflex responses between sitting or lying and it is suggested that the subject/patient should be tested in a position which is most comfortable.

The aging effects on the EMG and mechanical responses of the human wrist flexor stretch reflexes.

The purpose of this study is to investigate the effects of aging on the human stretch reflexes. The EMG and torque responses of the stretch reflex of the wrist flexors were evoked by ramp-and-hold mechanical perturbations. The stretch reflexes were recorded at seven test conditions with different stretch velocity and muscle preload. The test results from young and older healthy adult subjects were compared. In average, the absolute amplitude of the short-latency (20-40 ms) EMG (recorded from flexor carpi radialis) reflex response was significantly lower in the older group. If the data were normalized and expressed in percentage of the maximal voluntary EMG activity, however, this group difference was not significant. There was no change in the reflex gain of the short-latency reflex with aging. For the long-latency (50-90 ms) EMG reflex response, both the normalized amplitude and the reflex gain were significantly enhanced with aging, probably through supraspinal mechanisms. There was no significant difference in the threshold velocity for the evoked EMG reflexive activities between age groups. There were also no changes in the reflexive wrist flexion torque with aging. These results suggested that the number of motor units recruited during the stretch reflex activity declined with aging although the percentage of motor units recruited was not affected by aging. It is concluded that the central regulating mechanisms of the spinal motoneuron excitability are not compromised by aging. The automatic gain compensation phenomenon is also preserved with aging.

Functional assessment of tibial-nerve recovery in the cat using gait analysis: preliminary study.

The purpose of this study was to investigate gait-pattern changes after complete tibial nerve lesion in the cat, and to observe whether nerve repair could reverse some of the changes. In six cats, a 5-cm segment of the tibial nerve was transected. The nerve gap was then repaired with nerve autograft in three animals and was unrepaired in three as controls. The walking patterns of the cats were videotaped, and the hip, knee, ankle, and metatarsophalangeal joint angles were measured at the beginnings of the F, E1, E2, and E3 phases of the step cycle. Two weeks after surgery, abnormal gait patterns were observed, and four gait parameters (E3.Hip, E3.Ankle, E3.M-P, and F.Ankle) were found to be statistically significantly different from normal. Six months after surgery, the nerve-graft group had gait-parameter values approaching normal, while the control group showed no measurable improvement. Correspondingly, electrophysiologic testing revealed considerable nerve regeneration in the nerve-graft group but not in the control group. It was concluded that these gait parameters can be used as valid functional indices to evaluate the degree of tibial nerve recovery in the cat model.

Ankle stance angle: a functional index for the evaluation of sciatic nerve recovery after complete transection.

This study attempted to develop a motor functional index, ankle stance angle (ASA), to assess rat sciatic nerve regeneration subsequent to autografting. ASA, 50 degrees in normal rats, is the ankle joint angle at the mid-stance phase of the gait cycle. In a nerve graft group, a 1-cm segment of the right sciatic nerve was transected and then repaired with nerve autograft. In an ungrafted group, the nerve gap was left unrepaired. ASA measured 4 months after surgery was statistically significantly larger in the nerve graft group (36 degrees) than in the ungrafted group (22 degrees). The results suggest that ASA is more sensitive than sciatic function index in detecting functional recovery after a complete sciatic nerve lesion. ASA also showed a significant correlation with the passive range of ankle joint motion and gastrocnemius muscle weight. The study concluded that ASA is a reliable index for assessment of regeneration of rat sciatic nerve after a complete lesion. The intra-rater reliability (r = 0.97 and 0.90) and inter-rater reliability (r = 0.85) tests performed support the conclusions.

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.