Low-level exertions of the neck musculature: a study of research methods.

Musculoskeletal neck discomfort is prevalent in many occupations and has been the focus of much research employing surface electromyography (sEMG). Significant differences in experimental methods among researchers make comparisons across studies difficult. The goal of the current research was to use empirical methods to answer specific methodological questions concerning use of sEMG in evaluation of the neck extensor system. This was accomplished in two studies. In Experiment 1, ultrasound technology was used to: (a) determine accessibility of m. splenius and semispinalis capitis with surface electrodes, (b) identify appropriate electrode locations for these muscles/muscle groups, and (c) illustrate potential benefits of using ultrasound in locating muscles/placing electrodes. Experiment 2 sought to assess effects of posture when normalizing sEMG data. Results from Experiment 1 showed no direct access to semispinalis capitis for surface electrodes; their activity can only be sampled as part of a group of muscles. In most subjects, m. splenius was found to be accessible to surface electrodes. Electrode placement recommendations are provided. Results of Experiment 2 showed significant differences in normalized EMG data between a posture-specific technique and a reference posture technique. Posture-specific normalization is recommended for accurately assessing the relative intensity of contractions of these muscles.     

Influence of test position on neck muscle fatigue in healthy controls

BackgroundIt has been suggested that increased fatigue of neck muscles could be related to neck pain. However, studies on the matter present contradicting results which could be explained by the different test positions used.PurposeThe purpose of this study was to investigate the influence of test position on muscle fatigue of neck flexor and extensor muscles in healthy controls.MethodsTwenty-five women without neck pain sustained neck flexion and neck extension isometric contractions at 25% and 75% of their maximal voluntary contraction (MVC) in two test positions: sitting and supine lying. Using surface electromyography, the change over time of the median frequency of the power spectrum (MDF slope) of the myoelectric signal of the sternocleidomastoid and splenius capitis muscles was measured and compared between both positions.ResultsAt 75% MVC, splenius capitis muscles presented higher fatigue in lying compared to sitting, while sternocleidomastoid demonstrated no difference between positions. No statistically significant effect of test position was found at 25% MVC for both sternocleidomastoid and splenius capitis muscles as they generally did not present myoelectric manifestations of fatigue.ConclusionThese results underline the need to standardise the test position when investigating neck muscle fatigue, especially for neck extensors at high loads.     

Muscle pain induces task-dependent changes in cervical agonist/antagonist activity.

This study examined the effect of experimental neck muscle pain on the EMG-force relationship of cervical agonist and antagonist muscles. Surface EMG signals were detected from the sternomastoid, splenius capitis, and upper trapezius muscles bilaterally from 14 healthy subjects during cervical flexion and extension contractions of linearly increasing force from 0 to 60% of the maximum voluntary contraction (MVC). Measurements were performed before and after injection of 0.5 ml hypertonic and isotonic saline into either the sternomastoid or splenius capitis in two experimental sessions. EMG average rectified value (ARV) of the sternomastoid, splenius capitis, and upper trapezius muscles and the muscle fiber conduction velocity (CV) of the sternomastoid muscle were estimated at 5% MVC force increments. During cervical flexion with injection of hypertonic saline in sternomastoid, ARV of sternomastoid was lower on the side of pain in the force range 25-60% MVC (P < 0.05) and was associated with a bilateral reduction of splenius capitis and upper trapezius ARV (P < 0.01). During cervical extension, injection of hypertonic saline in splenius capitis resulted in lower estimates of splenius capitis ARV on the painful side from 45 to 60% MVC (P < 0.05), which was associated with a bilateral increase in upper trapezius ARV estimates from 50 to 60% MVC (P < 0.001). However, no significant change was identified for estimates of sternomastoid ARV. Experimentally induced neck muscle pain resulted in task-dependent changes in cervical agonist/antagonist activity without modifications in muscle fiber CV.     

Spectral profile of superficial cervical muscles.

The objective of the study was to determine the median frequency (MF) and mean power frequency (MPF) of the stermodeidomastorial, splenius capitis and trapezius in progressively and linearly increasing isometric cervical flexion and extension. There is a dearth of data on spectral parameters of cervical muscles. Such data have been generated from 40 young adult subjects (21 male and 19 female). The subjects were seated upright in an individually adjusted chair and stabilized with a 4-point Velcro restraint system to stabilize the torso. These subjects exerted isometric flexor and extensor forces in a random sequence on an instrumented resistance device (specifically designed for the study) in a gradual and linearly increasing manner with a visual feedback to their maximal voluntary contraction (MVC) within a 5 s period. Surface EMG was sampled from the sternocleidomastoid, the splenius capitis and the trapezius muscles bilaterally at 1 kHz. The EMG signals were subjected to Fast Fourier Transform (FFT) analysis. Spectral profiles of all muscles in the dimensions of frequency, power, and grade of contraction were plotted. The mean median frequency (MF), mean power frequency (MPF), peak power and total power were analyzed. In the sternocleidomastoid, and the splenius the MF increased with the grade of contraction, widening its bandwidth at higher grades. The trapezius maintained a narrow bandwidth and its MF declined with the grade of contraction.     

Force depression in human quadriceps femoris following voluntary shortening contractions.

The purpose of this study was to investigate whether the isometric muscle force, redeveloped following maximal-effort voluntary shortening contractions in human skeletal muscle, is smaller than the purely isometric muscle force at the corresponding length. Isometric knee extensor moments, surface electromyographic (EMG) signals of quadriceps femoris, and interpolated twitch moments (ITMs) were measured while 10 subjects performed purely isometric knee extensor contractions at a 60 degrees knee angle and isometric knee extensor contractions at a 60 degrees knee angle preceded by maximal-effort voluntary shortening of the quadriceps muscles. It was found that the knee extensor moments were significantly decreased for the isometric-shortening-isometric contractions compared with the isometric contractions for the group as a whole, whereas the corresponding EMG and ITM values were the same. This study is the first to demonstrate force depression following muscle shortening for voluntary contractions. We concluded that force depression following muscle shortening is an actual property of skeletal muscle rather than a stimulation artifact and that force depression during voluntary contraction is not accompanied by systematic changes in muscle activation as evaluated by EMG and ITM.     

慢性非特异性颈部不适飞行员与无症状飞行员之间头颈夹肌表面肌电特征的比较

目的:通过对慢性非特异性颈部不适飞行员与无症状飞行员之间头颈夹肌表面肌电特征的比较,为慢性非特异性颈部不适飞行员的早期诊断提供参考依据。方法:用表面肌电仪测量52名慢性非特异性颈部不适飞行员与11名无症状飞行员双侧头颈夹肌的松弛状态、等长收缩以及异长收缩时的表面肌电特征,分析不同状态下双侧头颈夹肌疲劳性肌电指标MFs、MPFs、ZCRs以及平均肌电AEMG值,用统计学软件SPSS 18.0分析实验结果。结果:非特异性颈部不适飞行员与无症状飞行员双侧头颈夹肌在松弛状态时疲劳性肌电指标MFs、MPFs、ZCRs比较均无统计学差异(P0.05),其双侧头颈夹肌在等长收缩和异长收缩时间有统计学差异(P0.05)。头颈夹肌处于松弛状态时,两组间平均肌电AEMG比较无统计学差异(P0.05),而在肌肉等长收缩和异长收缩时,两组间比较有统计学差异(P0.05)。结论:慢性非特异性颈部不适飞行员与无症状飞行员之间头颈夹肌表面肌电相关指标存在统计学差异,慢性颈部不适的飞行员相比无症状飞行员更易出现头颈夹肌的疲劳以及头颈夹肌的功能下降。头颈夹肌表面肌电特征有助于早期诊断慢性非特异性颈部不适飞行员的肌肉功能状态的改变。     

Morphology, histochemistry, and function of epaxial cervical musculature in the horse (Equus caballus).

The semispinalis capitis and splenius muscles of the horse were analyzed for gross morphology, microarchitecture, fiber length, and fiber type. Although these two muscles are similar in size and anatomical position, they are very different from one another in structural design and histochemistry, implying diverse functional roles in the animal's behavior. The histochemical staining profile was limited to two fiber types: slow oxidative and fast glycolytic. The splenius muscle has simple architecture, long fibers, and a 60/40 ratio of SO to FG cross-sectional area. The semispinalis capitis has complex architecture with short-fibered, concentric compartments dorsal to its central tendon and longer-fibered compartments ventrally. The entire dorsal region has an increasing gradient of slow oxidative fiber percentage from caudal to cranial (58-71% SO). In contrast, the ventral region has a decreasing gradient of slow oxidative fibers from caudal to cranial (48-67% FG). These patterns can be interpreted within the context of the cervical musculature during locomotion and posture to indicate the functional advantages of this organization.     

Pain-induced changes in cervical muscle activation do not affect muscle fatigability during sustained isometric contraction

This study investigated whether pain-induced changes in cervical muscle activation affect myoelectric manifestations of cervical muscle fatigue. Surface EMG signals were detected from the sternocleidomastoid and splenius capitis muscles bilaterally from 14 healthy subjects during 20-s cervical flexion contractions at 25% of the maximal force. Measurements were performed before and after the injection of 0.5 ml of hypertonic (painful) or isotonic (control) saline into either the sternocleidomastoid or splenius capitis in two experimental sessions. EMG average rectified value and mean power spectral frequency were estimated throughout the sustained contraction. Sternocleidomastoid or splenius capitis muscle pain resulted in lower sternocleidomastoid EMG average rectified value on the side of pain (P < 0.01). However, changes over time of sternocleidomastoid EMG average rectified value and mean frequency (myoelectric manifestations of fatigue) during sustained flexion were not changed during muscle pain. These results demonstrate that pain-induced modifications of cervical muscle activity do not change myoelectric manifestations of fatigue. This finding has implications for interpreting the mechanisms underlying greater cervical muscle fatigue in people with neck pain disorders.     

The relationship between the electromyogram-amplitude and isometric extension torques of neck muscles at different positions of the cervical spine

A group of 12 healthy men volunteered for the experiment. Electromyograms (EMG) were obtained from semispinalis capitis, splenius capitis, levator scapulae, and trapezius muscles. The flexion angle of the cervical spine was precisely adjusted to 0°, 10°, 20°, and 30° relative to the horizontal, with a constant angle of the atlanto-occipital joint. The subjects made eight short (about 2 s) vertical extension forces (6%, 12%,18%, 24%, 30%, 36%, 42%, and 48% of maximal voluntary peak contraction force). For each position, the centre of pressure under the head was determine as the basis for the calculation of the external lever arm. The presence of motor endplate regions was ascertained by multiple surface electrodes. The slopes of individual linear regression lines for the root mean square (rms)-values were dependent on the existence of endplates in the area of the electrodes — endplates caused smaller rms values per Newton metres of external torque. Significant intersubject differences between regression equations could not be eliminated by the normalization of EMG-parameters and/or torques. The elimination of gravity, the continuous monitoring of positions, and the consideration of localization of motor endplate regions were essential prerequisites for the acquisition of reliable relationships between EMG of different neck muscles and external torques. Two important conclusions were derived for the prediction of torques from EMG measurements: firstly, individual regression equations which take into account the position of the head and neck should be used; secondly, normalization procedures do not justify the application of average regressions to a group of subjects.     

New observations on the splenius capitis and rectus capitis ventralis muscles of the Common Swift Apus apus (Apodidae)

In swifts and hummingbirds (Apodiformes), the splenius capitis muscle displays a characteristic modification, the 'cruciform origin'. The muscle pairs arise from the second vertebra by several slips which criss-cross and interdigitate with each other, before inserting into the skull. In the course of a study on the neck muscles of the Common Swift, we paid special attention to the arrangement of these slips of the splenius capitis muscle, and noted a previously unrecognized individual modification of this muscle. In addition, we observed an incipient cruciform origin of the deep portion (slip) of the rectus capitis ventralis muscle that has not been noticed for swifts or any other avian taxon before. The development and function of these modifications of the splenius capitis and rectus capitis ventralis muscle are discussed.     

Specificity of resistance training responses in neck muscle size and strength

This study examined hypertrophy after head extension resistance training to assess which muscles of the complicated cervical neuromuscular system were used in this activity. We also determined if conventional resistance exercises, which are likely to evoke isometric action of the neck, induce generalized hypertrophy of the cervical muscle. Twenty-two active college students were studied. [mean (SE) age, weight and height: 21 (1) years, 71 (4) kg and 173 (3) cm, respectively]. Subjects were assigned to one of three groups: RESX (head extension exercise and other resistance exercises), RES (resistance exercises without specific neck exercise), or CON (no training). Groups RESX (n = 8) and RES (n = 6) trained 3 days/week for 12 weeks with large-muscle mass exercises (squat, deadlift, push press, bent row and mid-thigh pull). Group RESX also performed three sets of ten repetitions of a head extension exercise 3 days/week with a load equal to the 3 × 10 repetition maximum (RM). Group CON (n = 8) was a control group. The cross-sectional area (CSA) of nine individual muscles or muscle groups was determined by magnetic resonance imaging (MRI) of the cervical region. The CSA data were averaged over four contiguous transaxial slices in which all muscles of interest were visible. The 3 × 10 RM for the head extension exercise increased for RESX after training [from 17.9 (1.0) to 23.9 (1.4) kg, P < 0.05] but not for RES [from 17.6 (1.4) to 17.7 (1.9)␣kg] or CON [from 10.1 (2.2) to 10.3 (2.1) kg]. RESX showed an increase in total neck muscle CSA after training [from 19.5 (3.0) to 22.0 (3.6) cm², P < 0.05], but RES and CON did not [from 19.6 (2.9) to 19.7 (2.9)␣cm² and 17.0 (2.5) to 17.0 (2.4) cm², respectively]. This hypertrophy for RESX was due mainly to increases in CSA of 23.9 (3.2), 24.0 (5.8), and 24.9 (5.3)% for the splenius capitis, and semispinalis capitis and cervicis muscles, respectively. The lack of generalized neck muscle hypertrophy in RES was not due to insufficient training. For example, the CSA of their quadriceps femoris muscle group, as assessed by MRI, increased by 7 (1)% after this short-term training (P < 0.05). The results suggest that: (1) the splenius capitis, and semispinalis capitis and cervicis muscles are mainly responsible for head extension; (2) short-term resistance training does not provide a sufficient stimulus to evoke neck muscle hypertrophy unless specific neck exercises are performed; and (3) the postural role of head extensors provides modest loading in bipeds. Accepted: 15 October 1996     

An evaluation of different protocols for measuring the force-velocity relationship of the human quadriceps muscles

A modified Cybex II isokinetic dynamometer was used to evaluate the problems associated with measuring the concentric force-velocity characteristics of human knee extensor muscles. Three contraction protocols were investigated, simple voluntary contractions (VC); releases from maximal voluntary isometric contractions (VR) and releases from. isometric femoral nerve stimulated contractions (FNR). Percutaneous stimulation of the quadriceps was unsuitable for dynamic contractions as the proportion of the muscle activated varied with the angle of knee flexion. Isometric length-tension relationships and isokinetic contractions at seven angular velocities between 0.5 and 5.2 rad · s^–1 were recorded in five subjects. During isometric and slow dynamic contractions the voluntary forces were often greater than those obtained by femoral nerve stimulation, probably due to subjects stretching the rectus femoris during voluntary manoeuvres. It was found that the VC protocol produced acceptable isokinetic force recordings only at velocities below 3.1 rad · s^–1 in most subjects whilst VR contractions resulted in unexpectedly low forces at velocities below 1.57 rad · s^–1. Of the three techniques employed, FNR, although uncomfortable for subjects, provided the most accurate and reliable method of measuring force-velocity characteristics of knee extensor muscles. FNR contractions produced a force-velocity curve which showed a smooth decline in force with increasing velocity up to 5.2 rad · s^–1. VC contractions appear to be an acceptable alternative for testing the muscles provided the angular velocity is less than 3.1 rad · s^–1 and the subjects can be prevented from stretching the rectus femoris during the movement.     

Homologies of the transversospinalis muscles in the anterior presacral region of Sauria (crown Diapsida)

Homologies of muscles of the m. transversospinalis group in the dorsal and cervical regions in Sauria are established based on detailed dissections and published accounts of lepidosaurs, crocodylians, and birds. Attachments and directions of tendons comprising this muscle group are fairly conserved among the saurian clades, enabling rather robust inferences on muscle homologies. The innervation pattern indicates that mm. ascendentes are the most lateral muscles of the m. transversospinalis group in Aves, and are inferred to be homologous with the crocodylian m. tendinoarticularis based on their topological similarities. It is suggested here that the lepidosaurian articulo-parietalis part of m. longissimus cervico-capitis actually belongs to the m. transversospinalis group because its tendons of origin are shared with those of m. semispinalis. The avian m. complexus and the lateral part of the crocodylian m. transversospinalis capitis have origins and insertions similar to this lepidosaurian muscle, and are proposed to be homologous with the latter. In some birds, m. longus colli dorsalis, pars profunda continues directly into the anterior cervical region as m. splenius accessorius, suggesting a serially homologous relationship. Similarly, m. splenius anticus continues anteriorly from m. longus colli dorsalis, pars cranialis, and both of these muscles lie dorsal to m. splenius accessorius. Therefore, the currently used nomenclature that regards m. splenius accessorius as a part of m. longus colli dorsalis, pars cranialis and that regards m. splenius anticus as a part of the former muscle does not accurately reflect the serial homologies among these muscles and may not be justified.     

Force depression following muscle shortening in sub-maximal voluntary contractions of human adductor pollicis

Mechanical properties of skeletal muscles are often studied for controlled, electrically induced, maximal, or supra-maximal contractions. However, many mechanical properties, such as the force-length relationship and force enhancement following active muscle stretching, are quite different for maximal and sub-maximal, or electrically induced and voluntary contractions. Force depression, the loss of force observed following active muscle shortening, has been observed and is well documented for electrically induced and maximal voluntary contractions. Since sub-maximal voluntary contractions are arguably the most important for everyday movement analysis and for biomechanical models of skeletal muscle function, it is important to study force depression properties under these conditions. Therefore, the purpose of this study was to examine force depression following sub-maximal, voluntary contractions. Sets of isometric reference and isometric-shortening-isometric test contractions at 30% of maximal voluntary effort were performed with the adductor pollicis muscle. All reference and test contractions were executed by controlling force or activation using a feedback system. Test contractions included adductor pollicis shortening over 10 degrees, 20 degrees, and 30 degrees of thumb adduction. Force depression was assessed by comparing the steady-state isometric forces (activation control) or average electromyograms (EMGs) (force control) following active muscle shortening with those obtained in the corresponding isometric reference contractions. Force was decreased by 20% and average EMG was increased by 18% in the shortening test contractions compared to the isometric reference contractions. Furthermore, force depression was increased with increasing shortening amplitudes, and the relative magnitudes of force depression were similar to those found in electrically stimulated and maximal contractions. We conclude from these results that force depression occurs in sub-maximal voluntary contractions, and that force depression may play a role in the mechanics of everyday movements, and therefore may have to be considered in biomechanical models of human movement.     

Older adults are less steady during submaximal isometric contractions with the knee extensor muscles.

This study compared the steadiness of submaximal contractions with the knee extensor muscles in young and old adults. Twenty young and twenty old subjects underwent assessment of isometric maximum voluntary contraction (MVC), one-repetition maximum (1-RM) strength, and steadiness during isometric, concentric, and eccentric contractions with the knee extensor muscles. The old adults displayed 33% lower MVC force and a 41% lower 1-RM load. The coefficient of variation for force was significantly greater for the old adults during isometric contractions at 2, 5, and 10% of MVC but not at 50% MVC. The decline in steadiness at low forces experienced by the men was marginally greater than that experienced by the women. The steadiness of concentric and eccentric contractions was similar in young and old adults at 5, 10, and 50% of 1-RM load. Old subjects exhibited greater coactivation of an antagonist muscle compared with young subjects during the submaximal isometric and anisometric contractions. These results indicate that, whereas the ability to exert steady submaximal forces with the knee extensor muscles was reduced in old adults, fluctuations in knee joint angle during slow movements were similar for young and old adults.     

Guidelines for the intramuscular positioning of EMG electrodes in the semispinalis capitis and cervicis muscles.

The objective of the study was to establish guidelines for the application of fine-wire or needle electrodes in the semispinalis cervicis and semispinalis capitis muscles.First of all, measured data for the puncture angle and puncture depth of each muscle were determined in CT scans. Using a regression approach, a model relation of these data with the neck circumference was established. This made it possible to accurately determine the puncture angle and puncture depth on the basis of the known neck circumference. In a further step, the neck muscles of seven human cadavers were punctured with wires in order to check the workability of these guidelines. At the same time, the wires' positions in relation to important structures (nerves, vessels) were studied.Both muscles can be punctured with a high degree of reliability. However, when puncturing the semispinalis cervicis muscle, one has to pass through a layer that contains vessels, nevertheless the risk of injury is regarded as very small.The technique enables intramuscular EMG measurements of the two muscles in manifold clinical problems.     

Voluntary activation of human quadriceps during and after isokinetic exercise.

The extent of voluntary activation in fresh and fatigued quadriceps muscles was investigated during isometric and isokinetic voluntary contractions at 20 and 150 degrees/s in 23 normal human subjects. The muscles were fatigued by a total of 4 min of maximal knee extension at an angular velocity of 85 degrees/s. Voluntary activation was determined by the superimposition of tetanic electrical stimulation at 100 Hz for 250 ms, initiated at a constant knee angle. The relationship between voluntary and stimulated force was similar to that found with the established twitch superimposition technique used on isometric contractions. In fresh muscle all the subjects showed full voluntary activation during isometric contractions. Some activation failure was seen in five subjects at 20 degrees/s [2.0 +/- 0.9 degrees (SE)] and in two subjects at 150 degrees/s (0.7 +/- 0.5). After fatigue all subjects showed some activation failure at 0 and 20 degrees/s (36.4 +/- 3.1 and 28.8 +/- 4.1 degrees, respectively), but only two showed any at 150 degrees/s (1.4 +/- 5.7). We conclude that brief high-intensity dynamic exercise can cause a considerable failure of voluntary activation. This failure was most marked during isometric and the lower-velocity isokinetic contractions. Thus a failure of voluntary activation may have greater functional significance than previous studies of isometric contractions have indicated.     

Patients with chronic,but not episodic,migraine display altered activity of their neck extensor muscles

The current study aimed to investigate differences in activity of neck flexor and extensor muscles in women with migraine considering the chronicity of their condition. Thirty-one subjects with episodic migraine, 21 with chronic migraine and 31 healthy controls participated. Surface electromyography signals were recorded bilaterally from the sternocleidomastoid, anterior scalene, splenius capitis and upper trapezius muscles as subjects performed 5 stages of cranio-cervical flexion (CCF), representing a progressive increase in range of CCF motion. Comparison of normalized root-mean-square among groups was conducted with 3 × 5 ANCOVA with task level as the within-subject variable, group as the between-subject variable, and the presence of neck pain and disability as co-variates. The group with chronic migraine exhibited increased activity of their extensor muscles compared to the control and episodic migraine groups (splenius capitis: F = 3.149, P = 0.045; upper trapezius: F = 3.369, P = 0.041). No significant between-group differences were found for the superficial neck flexors (sternocleidomastoid: F = 1.161, P = 0.320; anterior scalene: F = 0.135, P = 0.874). In conclusion, women with chronic migraine exhibit increased activity of their superficial neck extensor muscles when acting as antagonists during low-load isometric CCF contractions in comparison to non-headache subjects.     

Observations on force enhancement in submaximal voluntary contractions of human adductor pollicis muscle.

It has been observed consistently and is well accepted that the steady-state isometric force after active muscle stretch is greater than the corresponding isometric force for electrically stimulated muscles and maximal voluntary contractions. However, this so-called force enhancement has not been studied for submaximal voluntary efforts; therefore, it is not known whether this property affects everyday movements. The purpose of this study was to determine whether there was force enhancement during submaximal voluntary contractions. Human adductor pollicis muscles (n = 17) were studied using a custom-built dynamometer, and both force and activation were measured while muscle activation and force were controlled at a level of 30% of maximal voluntary contraction. The steady-state isometric force and activation after active stretch were compared with the corresponding values obtained during isometric reference contractions. There was consistent and reliable force enhancement in 8 of the 17 subjects, whereas there was no force enhancement in the remaining subjects. Subjects with force enhancement had greater postactivation potentiation and a smaller resistance to fatigue in the adductor pollicis. We conclude from these results that force enhancement exists during submaximal voluntary contractions in a subset of the populations and suggest that it may affect everyday voluntary movements in this subset. On the basis of follow-up testing, it appears that force enhancement during voluntary contractions is linked to potentiation and fatigue resistance and therefore possibly to the fiber-type distribution in the adductor pollicis muscle.     

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.