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PubMed2003

Gait-dependent integration of neck muscle afferent input.

We investigated the integration of neck muscle afferents during walking and running. Subjects walked or ran straight ahead, with or without an additional mass (20% of body weight). They performed all trials without vibration and with continuous vibration (80 Hz) applied to the lateral aspect of the neck. Vibration systematically caused body deviation toward the side opposite to the stimulation. The amplitude of vibration-induced body deviations was dramatically larger for walking (21.6 +/- 4.6 degrees ) than for running (8.0 +/- 2.5 degrees ). The additional mass marginally straightened body trajectory (average 5.6%), indicating that the gait-dependent effect of neck vibration cannot solely be attributed to differences in body inertia between walking and running. We concluded that neck muscle afferences are selectively gated according to the gait performed.

Adult↗

PubMed1999

Changes of visual localization induced by eye and neck muscle vibration in normal and strabismic subjects.

BACKGROUND: It has been reported that vibratory activation of eye- and neck-muscle proprioception can induce eye position changes in normal and strabismic subjects. This study investigated the effects of proprioception in the eye and neck muscles on space localization. METHOD: Vibration was applied to either the eye or neck muscle in normal subjects, intermittent exotropes, and constant exotropes/esotropes. The subjects pointed at the immediately remembered position of an extinguished visual target with the hand both before and immediately after vibration of the muscles under binocular and monocular viewing conditions. The hand-pointing performance in darkness was recorded by an infrared camera, and the pointing shifts were analyzed qualitatively and quantitatively. RESULTS: With vibration of the vertically moving muscles of the eye and neck, the direction of the pointing shifts was the same in all groups of the subjects and under all viewing conditions. With vibration of the horizontally moving muscles of the eye and neck, the directions were the same in the normals and in most of the intermittent exotropes. However, in the constant exotropes and esotropes, the directional shifts were dependent on which eye was vibrated, and the directions were more variable, always directed only to one side. CONCLUSION: Proprioception in the eye and neck muscles participates in visual space localization, but the effects of proprioceptive activation were differed in normal subjects from those in patients having constant strabismus. The differences may be related to the level of binocular function.

Adaptation, Ocular↗

PubMed2005

Issues in relation to the repeatability of and correlation between EMG and Borg scale assessments of neck muscle fatigue.

INTRODUCTION: The repeatability of subjective and objective assessments of neck muscle fatigue is very important with regard to the clinical applicability of these methods. METHOD: To establish between-days reliability, 33 healthy volunteers performed a 60% maximum voluntary isometric contraction test from a standing position in all neck movements. Cervical muscle fatigue was assessed on three separate occasions from the spectral (median frequency, MF) and amplitude (root mean square, RMS) analysis of the electromyogram (EMG) signal recorded from the cervical paraspinal group, splenius capitis, levator scapulae and sternocleidomastoid. Subjective assessment of fatigue was rated by employing the Borg scale. Intraclass correlation coefficient ICC((1,1)), standard error of measurement (SEM), smallest detectable difference (SDD) indices and Pearson's correlation co-efficient were calculated for the analysis of the results. RESULTS: Normalised median frequency (MF) slope had low repeatability and large between-day error (ICC((1,1))=0.28-0.61; SEM=0.33-0.60%/s; SDD=132.7-703.2%) for the protagonist muscles of each movement. Initial median frequency (IMF) had moderate to good reliability and small error (ICC((1,1))=0.64-0.81; SEM=2.8-8.8Hz; SDD=19.9-38.5%). The RMS slope yielded also poor repeatability. The Borg assessment was more reliable than the EMG estimate though variability between sessions was still quite high (SDD=29.2-136.5%). No correlation was found between the EMG and Borg assessment of neck muscle fatigue (r=-0.01-0.39). CONCLUSION: The protocol used for assessing neck muscle fatigue proved to be reliable only for the IMF but the clinical usefulness of this measure remains questionable. The lack of correlation between objective and subjective estimation of neck muscle fatigue was possibly a consequence of the poor measurement repeatability. Further research is needed to identify the factors responsible for these results on neck area.

Adult↗

PubMed2002

Neck muscle vibration induces lasting recovery in spatial neglect.

OBJECTIVES: To evaluate whether neck muscle vibration is an effective technique for neglect rehabilitation, with lasting beneficial effects. METHODS: The effects of differential treatment of visual exploration training alone or in combination with neck muscle vibration were evaluated in a crossover study of two matched groups of 10 patients suffering from left sided neglect. Each group received a sequence of 15 consecutive sessions of exploration training and combined treatment. The effects of treatment were assessed with respect to different aspects of the neglect disorder such as impaired perception of the egocentric midline, exploration deficits in visual and tactile modes, and visual size distortion. The transfer of treatment effects to activities of daily living was examined by a reading test and a questionnaire of neglect related everyday problems. All variables were measured six times: three baseline measurements, two post-treatment measurements, and one follow up after two months. RESULTS: The results showed superior effects of combination treatment. A specific and lasting reduction in the symptoms of neglect was achieved in the visual mode, which transferred to the tactile mode with a concomitant improvement in activities of daily living. The improvement was evident two months after the completion of treatment. In contrast, isolated exploration training resulted in only minor therapeutic benefits in visual exploration without any significant transfer effects to other tasks. CONCLUSIONS: Neck muscle vibration is a decisive factor in the rehabilitation of spatial neglect and induces lasting recovery when given as a supplement to conventional exploration training.

Activities of Daily Living↗

PubMed1991

Corticobulbar and corticospinal projections to neck muscle motoneurons in man. A functional study with magnetic and electric transcranial brain stimulation.

The cortical projections to neck muscle motoneurons were studied in normal subjects by electrical and magnetic transcranial brain stimulation. After magnetic stimulation with a large coil, motor evoked potentials were present in about 20% of relaxed and 100% of contracting neck muscles. The latency of these responses was short: about 7 ms in the sternomastoid and splenius and 9 ms in the trapezius muscles. Subtraction of the M-wave latency after stimulation of the accessory nerve at the skull base resulted in a central latency of about 4.5 ms. We suggest that rapid cortical projections connect with neck muscle motoneurons mono or disynaptically. The latency difference between the responses after electrical and magnetic stimulation was smaller in neck than in limb muscles but similar to that seen in masticatory muscles. A small magnetic coil was used to study the pattern of functional lateralization of cortical projections to neck muscle motoneurons; the projections for the sternomastoid and splenius are bilateral but predominantly contralateral, whereas those for the trapezius are exclusively contralateral.

Adult↗

PubMed2005

Long-term potentiation of orofacial sensorimotor processing by noxious input from the semispinal neck muscle in mice.

Tension-type headache is the most common type of primary headaches but no conclusive concept of pathophysiology exists. This may be due to a lack of an appropriate animal model. This study addressed the hypothesis that noxious neck muscle input induces central sensitization of orofacial sensorimotor processing. The effect of hypertonic saline injection into the semispinal neck muscle on the jaw-opening reflex (JOR) was investigated in anaesthetized mice (n = 11). Hypertonic saline injection into the neck muscle facilitated the JOR for at least one hour: integral (+94.5%) and duration (+18.7%) increased, latency decreased (-7.5%). The reflex threshold decreased to 61% after injection. Isotonic saline injection into the neck muscle (n = 11) or hypertonic saline injection into a hindpaw muscle (n = 10) did neither change the reflex integral nor the threshold. Long-term potentiation of the JOR by noxious neck muscle input may be an appropriate model to investigate tension-type headache pathophysiology.

Animals↗

PubMed1984

Reflex effects from high threshold neck muscle afferents on hind limb extensor gamma motoneurones in the cat.

The supra-segmental control of hind limb gamma motoneurones from neck muscle receptors has been studied in decerebrated and in spinal cats. Stretch of individual dorsal neck muscles was not an adequate stimulus for evoking long spinal reflexes to gamma motoneurones of gastrocnemius-soleus (GS) muscles unless the stretch was maximal or excessive. Pressure applied to the neck muscles, or intramuscular injections of KCl solution (0.1 ml, 5%), did affect the discharge of GS gamma motoneurones. Excitation was more evident than inhibition. We conclude that the long spinal reflex effects originate from high threshold mechanoreceptors, or nociceptors, rather than muscle spindles.

Animals↗

PubMed1984

Cardiovascular responses to isometric neck muscle contractions: results after dynamic exercise with various headgear loading configurations.

Experiments were conducted to quantify the cardiovascular response (blood pressure and heart rate) elicited by sustained isometric contractions of the neck muscles. The response was secondary to dynamic exercise with various headgear loading combinations. The neck muscles were loaded by the head itself (CON), the standard U.S. Army SPH-4 helmet (HEL), and a combination of the SPH-4 helmet with Night Vision Goggles (H/NVG). During two exercise periods of 5 min and 35 min, each of the five subjects would rotate the head from side-to-side in the CON, HEL, or H/NVG configuration. Immediately thereafter, the subject would position his head in an isometric head dynamometer and exert a sustained right lateral (LAT) neck contraction or forward (FOR) neck contraction at 70% of a maximal voluntary contraction (MVC). During this isometric neck muscle contraction, the subject's endurance time to fatigue was recorded, the blood pressure was manually recorded, and the heart rate was continuously recorded. Characteristic increases in the systolic and diastolic blood pressure and heart rate occurred with sustained isometric neck muscle contractions. There was an average 40% increase in the systolic blood pressure, an average 50% increase in the diastolic blood pressure, and an average 45% increase in the heart rate from resting to the end of a fatiguing 70% MVC (p less than 0.05). These responses appear to be relatively independent of the duration of the exercise period, the loading during the exercise period, and the specific muscle mass involved. The mechanisms for the pressor response and the heart rate response are reviewed.

Adult↗

PubMed1995

Noninvasive analysis of human neck muscle function.

STUDY DESIGN: Muscle use evoked by exercise was determined by quantifying shifts in signal relaxation times of T2-weighted magnetic resonance images. Images were collected at rest and after exercise at each of two intensities (moderate and intense) for each of four head movements: 1) extension, 2) flexion, 3) rotation, and 4) lateral flexion. OBJECTIVE: This study examined the intensity and pattern of neck muscle use evoked by various movements of the head. The results will help elucidate the pathophysiology, and thus methods for treating disorders of the cervical musculoskeletal system. SUMMARY OF BACKGROUND DATA: Exercise-induced contrast shifts in T2 has been shown to indicate muscle use during the activity. The noninvasive nature of magnetic resonance imaging appears to make it an ideal approach for studying the function of the complex neuromuscular system of the neck. METHODS: The extent of T2 increase was examined to gauge how intensely nine different neck muscles or muscle pairs were used in seven subjects. The absolute and relative cross-sectional area of muscle showing a shift in signal relaxation was assessed to infer the pattern of use among and within individual neck muscles or muscle pairs. RESULTS: Signal relaxation increased with exercise intensity for each head movement. The absolute and relative cross-sectional area of muscle showing a shift in signal relaxation also increased with exercise load. Neck muscles or muscle pairs extensively used to perform each head movement were: extension--semispinalis capitis and cervicis and splenius capitis; flexion--sternocleidomastoid and longus capitis and colli; rotation--splenius capitis, levator scapulae, scalenus, semispinalis capitis ipsilateral to the rotation, and sternocleidomastoid contralateral; and lateral flexion--sternocleidomastoid CONCLUSION: The results of this study, in part, agree with the purported functions of neck muscles derived from anatomic location. This also was true for the few selected muscles that have been examined in human electromyographic studies. Neck muscle function and morphology can be studied at a detailed level using exercise-induced shifts in magnetic resonance images.

Adult↗

PubMed1987

Effects of interception of snout sensory input on murine neck muscles: an electron microscopic study.

To examine whether the interference of the snout sensory input causes neuromuscular dysfunction in the murine neck muscles, the fine structure of the dorsal neck muscles was studied by electron microscopy. The infraorbital nerves were bilaterally transected in the adult ICR mice (one-month-old), and the animals were sacrificed after postoperative periods ranging from six to 18 months. Alpha motor end-plates showed remarkable changes characterized by shrunken synaptic boutons containing abundant lysosomes and/or disappearance of the synaptic boutons. The changes in the muscle spindles were characterized by the sarcolemmal undulation of the intrafusal muscle fibers and the frequent appearance of lysosomes in their sensory terminals. These degenerative changes were observed between nine months and 18 months after neurotomy and intensified with the length of the postoperative period. From the results of the present study, it was concluded that a reflex pathway exists between the snout receptor organs and the dorsal neck muscles.

Afferent Pathways↗

PubMed2002

Neck muscle strength across the sagittal and coronal planes: an isometric study.

OBJECTIVE: To determine the maximal isometric strength of neck muscles across different anatomical positions in the body sagittal and coronal planes. DESIGN: A descriptive study involving maximal isometric strength measurements of the cervical musculature in extension, flexion, and left and right lateral bending. Before measurements, the new device was tested for reliability. BACKGROUND: The literature contains only a few studies on cervical musculature strength assessment. Of these, measurement methods have displayed weak reliability. No studies existed reporting neck strength at various positions in the body coronal plane. METHODS: A new device incorporating local population anthropometry was developed for neck strength assessment on an isokinetic dynamometer. The device's repeatability attributes at measuring the strength of functionally different groups of neck muscles were first evaluated. The isometric apparatus was next used to determine the maximal strength of the cervical musculature of 17 healthy volunteers at different anatomical positions across the body sagittal and coronal motion planes. RESULTS: The results showed good intratester repeatability for intraday and day-to-day studies for all measured parameters. Strength values demonstrated that extensor muscles yielded the greatest torque and that flexor muscles provided the least torque. Linear regression analyses showed strong association of isometric strength with anatomical positions in the two body planes. CONCLUSIONS: Maximal isometric strength of neck muscles in four directions was quantified. Cervical musculature strength levels vary in discernible patterns with head-neck positions and contraction directions. RELEVANCE: Knowledge of normative values of neck muscle strength is essential for designing and implementing appropriate rehabilitation programmes. Results from the present study contribute to such literature.

Adult↗

PubMed1983

Neck muscle loading and fatigue: systematic variation of headgear weight and center-of-gravity.

An extensive series of experiments has been conducted to quantify the fatigue of neck muscles as measured by isometric endurance time. The neck muscles were dynamically and statically loaded by systematic variation of 15 headgear configurations consisting of 5 different centers-of-gravity (forward-low, center-low, center-high, right-lateral-low and afterward-low) and 3 different weights (3.2 lb, 5.0 lb, 9.0 lb, 1.45, 2.27, 4.09 kg). Each of six subjects would rotate his head laterally (from side-to-side) for 30 min in each of the 15 headgear loading combinations. Immediately thereafter, the subject would position his head in an isometric head dynamometer and exert a sustained right lateral neck contraction at 70% of his maximum strength (MVC), during which endurance time (to fatigue) was recorded. The results indicate that there were no significant differences (p greater than 0.05) in endurance time between the 3.2 lb/forward-low, 3.2 lb/lateral-right-low, and 9.0 lb/afterward-low compared to controls (endurance time for at 70% MVC isometric neck contraction in which there was no prior head loading). All other head loading configurations (weight and center-of-gravity combinations) did result in a significant reduction (p less than or equal to 0.05) in endurance times (compared to controls). These results are significant since they provide useful insights into the optimal trade-off between various centers-of-gravity and helmet weight combinations which result in the optimization of neck muscle endurance.

Adult↗

PubMed2006

Brainstem and cervical spinal cord Fos immunoreactivity evoked by nerve growth factor injection into neck muscles in mice.

Although myofascial tenderness is thought to play a key role in the pathophysiology of tension-type headache, very few studies have addressed neck muscle nociception. The neuronal activation pattern following local nerve growth factor (NGF) administration into semispinal neck muscles in anaesthetized mice was investigated using Fos protein immunohistochemistry. In order to differentiate between the effects of NGF administration on c-fos expression and the effects of surgical preparation, needle insertion and intramuscular injection, the experiments were conducted in three groups. In the sham group (n=7) cannula needles were only inserted without any injection. In the saline (n=7) and NGF groups (n=7) 0.9% physiological saline solution or 0.8 microm NGF solution were injected in both muscles, respectively. In comparison with sham and saline conditions, NGF administration induced significantly stronger Fos immunoreactivity in the mesencephalic periaqueductal grey (PAG), the medullary lateral reticular nucleus (LRN), and superficial layers I and II of cervical spinal dorsal horns C1, C2 and C3. This activation pattern corresponds very well to central nervous system processing of deep noxious input. A knowledge of the central anatomical representation of neck muscle pain is an essential prerequisite for the investigation of neck muscle nociception in order to develop a future model of tension-type headache.

Animals↗

PubMed1992

Electromyographic studies of neck muscles in the intact cat. I. Patterns of recruitment underlying posture and movement during natural behaviors.

Natural head movements in alert, unrestrained cats were studied using video-filming, videofluoroscopy and electromyographic (EMG) recording methods. In each cat, up to sixteen neck muscles or neck-muscle compartments were implanted with recording electrodes. Patterns of muscle recruitment were examined during systematically-selected behavioral epochs in which the cat held a range of stationary postures, and when it performed volitional and exploratory behaviors such as flexion-extension or turning, grooming, eating, or headshaking. Patterns of muscular activity were interpreted with reference to simultaneous video images of head and neck movements. In separate, videofluoroscopic analysis, flexion-extension movements were examined to gain insight into the underlying movements of the skull and cervical vertebrae. These and other movements were found commonly to depend upon changes in joint angles between lower as well as upper cervical joints. Stationary postures in which the neck was held vertically were consistently associated with tonic EMG activity in only two long dorsal muscles, biventer cervicis and occipitoscapularis. Less consistent activity was also present in dorsal intervertebral muscles crossing lower cervical joints. When the neck was held horizontally, the long dorsal muscles increased their EMG activity and moderate activity was also recorded in deeper intervertebral and suboccipital muscles. When flexion-extension occurred around upper cervical joints, greatest activity was recorded in rectus capitis posterior and complexus, but when it involved the lower cervical joints, large changes in EMG activity could also be detected in biventer cervicis, occipitoscapularis, and the intervertebral muscles crossing lower cervical joints. During specialized, sagittal-plane movements such as grooming, well-defined patterns of synergy could be recognized that varied according to the degree of involvement of upper and lower cervical joint-sets. Movements in the horizontal plane were associated with EMG activity in a largely different subset of neck muscles including splenius, longissimus capitis and obliquus capitis inferior. The levels of EMG activity during flexion-extension or turning movements were much lower than those observed during other more vigorous behaviors, such as head shaking. Some neck muscles, such as clavotrapezius and sternomastoideus, could only be recruited during forceful or ballistic head movements. Results showed that the patterns of muscular activation were linked not only to the speed and trajectory of the movements of the skull, but also to the kinematics of the motion occurring across different parts of the cervical column.

Animals↗

PubMed2003

Neck muscle vibration alters visually perceived roll in normals.

The objective of this study was to determine whether vibration of dorsal neck muscles or of the mastoid bone or of both modified the perception of visual orientation in the head roll-tilt plane in normal subjects. Measurements of the subjective visual vertical (SVV) were obtained from 26 normal human subjects. Subjects reported the SVV in the upright and in the left and right 30 degrees static head roll-tilt positions. Subjects then reported the SVV while vibration was applied to the left or right dorsal neck or left or right mastoid. Both head position and vibration independently modified settings of the SVV. In head-tilted positions, vibration of the upper dorsal neck muscles (on the side of the head opposite to the head tilt) caused a significantly greater shift of the SVV in the opposite direction of head roll-tilt compared to vibration of the lower dorsal neck muscles or of the mastoid. These results support a role for cervical somatosensory information in perception of visual orientation in the roll plane. Our findings may help explain the differences observed in visual orientation perception in normal subjects between head alone and whole-body roll-tilt. Finally, vibration of neck muscles in the head roll-tilted plane may be a useful method to test cervical somatosensory function possibly by increasing their response to external stimulation.

Adult↗

PubMed1986

Fear conditioning, pre-pulse inhibition and drug modulation of a short latency startle response measured electromyographically from neck muscles in the rat.

The present study evaluated if startle measured electromyographically in the neck muscles (having a 5 msec latency) would exhibit behavioral and pharmacological plasticity known to alter startle measured in a stabilimeter device. A total of 15 rats were implanted with bilateral EMG electrodes in the dorsal neck muscles and subsequently exposed to a variety of manipulations known to affect the whole-body startle response. The peak-to-peak EMG response that occurred within 10 msec of startle stimulus onset displayed pre-pulse inhibition, enhancement by prior fear conditioning, inhibition by clonidine, and enhancement by strychnine. The data are discussed in terms of modulation of neural transmission along a primary startle-mediating pathway.

Animals↗

PubMed1992

Electromyographic studies of neck muscles in the intact cat. II. Reflexes evoked by muscle nerve stimulation.

Short-latency reflexes were studied in the neck muscles of four alert cats following electrical stimulation of nerves supplying biventer cervicis (BC), splenius (SP) or rectus capitis posterior (RCP). Reflexes were assessed by comparing levels of EMG activity of muscles before and after each stimulus, as the cats lapped milk, licked their paws or walked on a treadmill. When BC or SP nerves were stimulated at 1.5-4 times threshold (T) for their motor axons, no short-latency heteronymous reflexes could be identified in most neck muscles. However, stimulation of RCP nerves produced inhibitory effects as early as 3-4 ms in the ipsilateral BC, CM, and SP muscles and 6 ms in contralateral BC. At stimulus strengths above 4xT, a more complex pattern of inhibitory or excitatory effects was observed in CM, SP and the intervertebral muscle spinalis dorsi. The reflex effects were attenuated or abolished by partial or complete C1 dorsal rhizotomy (2 cats). Cervicocollic reflex data may need to be reevaluated to consider the possible effects of disinhibition rather than excitation in short-latency reflex pathways.

Afferent Pathways↗

PubMed2006

The healthy worker survivor effect in a study of neck muscle performance measures in call-centre operators.

BACKGROUND: The healthy worker survival effect is a complex and poorly controlled bias affecting occupational studies. Little is known about its behaviour in samples of computer based workers. This descriptive study examined the healthy worker effect in relation to muscle performance and neck pain in call-centre operators. METHODS: 28 call-centre workers were examined for postural muscle performance. Neck pain was measured using a validated questionnaire. Analysis was by multivariate regression of the cohort, stratified by years of employment. RESULTS: Analysis using the entire sample failed to display any relationship between neck pain and muscle performance. Further examination revealed survival/secondary selection within the sample, with pain and poor muscle performance reduced after 6 years employment. Stratified analysis demonstrated that deep flexor muscle performance and posture were statistically significantly associated with neck pain. Each stratum explained a greater percentage of the variance in questionnaire scores, increasing from 42.3% for the entire sample to 95.1% for the 4 years employed subgroup. CONCLUSION: The healthy worker survival effect is demonstrable in occupations with lower physical demands. It should be considered in analysis since it may obscure causal associations. There is no single method for controlling this bias and greater understanding of its components is required.

Adolescent↗