Pain induced by low-grade stress in patients with fibromyalgia and chronic shoulder/neck pain, relation to surface electromyography

Pain-sensorimotor interactions: New perspectives and a new model

How pain and sensorimotor behavior interact has been the subject of research and debate for many decades. This article reviews theories bearing on pain-sensorimotor interactions and considers their strengths and limitations in the light of findings from experimental and clinical studies of pain-sensorimotor interactions in the spinal and craniofacial sensorimotor systems. A strength of recent theories is that they have incorporated concepts and features missing from earlier theories to account for the role of the sensory-discriminative, motivational-affective, and cognitive-evaluative dimensions of pain in pain-sensorimotor interactions. Findings acquired since the formulation of these recent theories indicate that additional features need to be considered to provide a more comprehensive conceptualization of pain-sensorimotor interactions. These features include biopsychosocial influences that range from biological factors such as genetics and epigenetics to psychological factors and social factors encompassing environmental and cultural influences. Also needing consideration is a mechanistic framework that includes other biological factors reflecting nociceptive processes and glioplastic and neuroplastic changes in sensorimotor and related brain and spinal cord circuits in acute or chronic pain conditions. The literature reviewed and the limitations of previous theories bearing on pain-sensorimotor interactions have led us to provide new perspectives on these interactions, and this has prompted our development of a new concept, the Theory of Pain-Sensorimotor Interactions (TOPSMI) that we suggest gives a more comprehensive framework to consider the interactions and their complexity. This theory states that pain is associated with plastic changes in the central nervous system (CNS) that lead to an activation pattern of motor units that contributes to the individual's adaptive sensorimotor behavior. This activation pattern takes account of the biological, psychological, and social influences on the musculoskeletal tissues involved in sensorimotor behavior and on the plastic changes and the experience of pain in that individual. The pattern is normally optimized in terms of biomechanical advantage and metabolic cost related to the features of the individual's musculoskeletal tissues and aims to minimize pain and any associated sensorimotor changes, and thereby maintain homeostasis. However, adverse biopsychosocial factors and their interactions may result in plastic CNS changes leading to less optimal, even maladaptive, sensorimotor changes producing motor unit activation patterns associated with the development of further pain. This more comprehensive theory points towards customized treatment strategies, in line with the management approaches to pain proposed in the biopsychosocial model of pain.

Stress and pain: modality-specific opioid mediation of stress-induced analgesia

Preclinical research has demonstrated that exposure to acute stress is associated with attenuated pain perception, so called stress-induced analgesia (SIA). Mechanisms of SIA in humans have not been reliably demonstrated. This study examined the role of the endogenous opioid system in the impact of combined interpersonal and mental stressors on evoked pain responses in 84 participants (34 women). Using a within-subject, double-blinded, counterbalanced design, participants were administered either oral placebo or the opioid antagonist naltrexone (50 mg) across two testing sessions. In each session, they experienced two evoked pain stimuli (cold pressor test [CPT], heat pain) after an extended rest period (rest condition) and after exposure to an acute stressor (a combination of public speaking and mental arithmetic challenge; stress condition). Results showed that both stress and opioid blockade produced significant changes in hormonal and cardiovascular measures, consistent with successful induction of acute stress. Stress was associated with attenuated pain perception (SIA) as indicated by significantly increased CPT tolerance. These effects were particularly pronounced in individuals experiencing the stress condition first. More importantly, SIA effects on CPT tolerance were abolished by opioid blockade. There were no significant SIA effects on heat pain responses. This study demonstrates that the endogenous opioid system may mediate effects of acute stress on pain perception, although this effect seems to be qualified by the type of evoked pain stimuli experienced.

Blunted Pain Modulation Response to Induced Stress in Women with Fibromyalgia with and without Posttraumatic Stress Disorder Comorbidity: New Evidence of Hypo-Reactivity to Stress in Fibromyalgia?

There is evidence regarding the presence of alterations in both the stress response and the endogenous pain modulation systems of people with fibromyalgia (FM). However, research on pain modulation under induced stress on FM patients is scarce and contradictory. The present study analyzes stress-induced changes in pain and intolerance thresholds among FM patients, examining the possible existence of differences linked to PTSD comorbidity and gaining insights into the role of cardiovascular reactivity. Eighteen women diagnosed with FM and comorbid PTSD (FM + PTSD), 18 women diagnosed with FM and no PTSD (FM-PTSD), and 38 healthy women (HC) were exposed to the Social Stress Test task. Pressure pain thresholds and intolerance thresholds were measured before and during stress induction, and after a recovery period, while systolic blood pressure and heart rate were simultaneously recorded. Overall, while pain thresholds decreased during stress and recovery for HC, no significant changes were observed for women with FM. The intolerance threshold decreased for HC during stress, but was maintained at basal level during recovery. FM-PTSD women exhibited a delayed response, with a drop at recovery. For FM + PTSD, tolerance levels remained unchanged. In addition, cardiovascular reactivity did not seem to explain these results. This performance of the pain modulation system seems to follow the same pattern of hypoactive responsiveness under stressors that has previously been observed in FM patients on the autonomic and neuroendocrine axes. Such a hypoactive pattern may involve a non-adaptive response that may contribute to the development and maintenance of chronic pain.

Fibromyalgia: A Critical and Comprehensive Review

Fibromyalgia is a disorder that is part of a spectrum of syndromes that lack precise classification. It is often considered as part of the global overview of functional somatic syndromes that are otherwise medically unexplained or part of a somatization disorder. Patients with fibromyalgia share symptoms with other functional somatic problems, including issues of myalgias, arthralgias, fatigue and sleep disturbances. Indeed, there is often diagnostic and classification overlap for the case definitions of a variety of somatization disorders. Fibromyalgia, however, is a critically important syndrome for physicians and scientists to be aware of. Patients should be taken very seriously and provided optimal care. Although inflammatory, infectious, and autoimmune disorders have all been ascribed to be etiological events in the development of fibromyalgia, there is very little data to support such a thesis. Many of these disorders are associated with depression and anxiety and may even be part of what has been sometimes called affected spectrum disorders. There is no evidence that physical trauma, i.e., automobile accidents, is associated with the development or exacerbation of fibromyalgia. Treatment should be placed on education, patient support, physical therapy, nutrition, and exercise, including the use of drugs that are approved for the treatment of fibromyalgia. Treatment should not include opiates and patients should not become poly pharmacies in which the treatment itself can lead to significant morbidities. Patients with fibromyalgia are living and not dying of this disorder and positive outlooks and family support are key elements in the management of patients.

Analysis of scapular muscle EMG activity in patients with idiopathic neck pain: a systematic review

It is proposed that altered scapular muscle function can contribute to abnormal loading of the cervical spine. However, it is not clear if patients with idiopathic neck pain show altered activity of the scapular muscles. The aim of this paper was to systematically review the literature regarding the differences or similarities in scapular muscle activity, measured by electromyography ( = EMG), between patients with chronic idiopathic neck pain compared to pain-free controls. Case-control (neck pain/healthy) studies investigating scapular muscle EMG activity (amplitude, timing and fatigue parameters) were searched in Pubmed and Web of Science. 25 articles were included in the systematic review. During rest and activities below shoulder height, no clear differences in mean Upper Trapezius ( = UT) EMG activity exist between patients with idiopathic neck pain and a healthy control group. During overhead activities, no conclusion for scapular EMG amplitude can be drawn as a large variation of results were reported. Adaptation strategies during overhead tasks are not the same between studies. Only one study investigated timing of the scapular muscles and found a delayed onset and shorter duration of the SA during elevation in patients with idiopathic neck pain. For scapular muscle fatigue, no definite conclusions can be made as a wide variation and conflicting results are reported. Further high quality EMG research on scapular muscles (broader than the UT) is necessary to understand/draw conclusions on how scapular muscles react in the presence of idiopathic neck pain.

Oral electromyography activation patterns for speech are similar in preschoolers who do and do not stutter

PURPOSE

In this study, the authors determined whether basic patterns of muscle activation for speech were similar in preschool children who stutter and in their fluent peers.

METHOD

Right and left lower lip muscle activity were recorded during conversational speech and sentence repetition in 64 preschool children diagnosed as stuttering (CWS) and in 40 children who do not stutter (CWNS). Measures of electromyography (EMG) amplitude, right-left asymmetry, and bilateral coordination were computed for fluent speech. The potential presence of tremor-like oscillations during disfluencies of CWS was assessed, and EMG amplitudes of fluent and disfluent speech were compared in CWS.

RESULTS

Across both speaking tasks, lip muscle activation was similar in CWS and CWNS in overall amplitude, bilateral synchrony, and degree of right-left asymmetry. EMG amplitude was reduced during disfluent compared with fluent conversational speech of CWS, and there was no evidence of tremor in the disfluencies of CWS.

CONCLUSION

These results support the assertion that stuttering in young children arises not from basic features of muscle contraction but rather from the command signals that control the timing and amplitude of muscle activity. The results indicate that no frank abnormality is present in muscle activation patterns in preschoolers who stutter.

Painful effects of auditory startle, forehead cooling and psychological stress in patients with fibromyalgia or rheumatoid arthritis

OBJECTIVE

The aim of this study was to determine whether the clinical pain associated with rheumatoid arthritis or fibromyalgia would increase during standard laboratory tasks and, if so, whether these increases were linked with individual differences in psychological distress.

METHODS

Twenty-three patients with fibromyalgia and 16 patients with rheumatoid arthritis rated changes in clinical pain after an acoustic startle stimulus, during painful forehead cooling, and during stressful mental arithmetic. In addition, pain tolerance was assessed during a submaximal effort tourniquet test, and patients provided ratings of distress on a standard Depression, Anxiety and Stress Inventory.

RESULTS

Pain at rest was associated with depression scores in patients with rheumatoid arthritis, and was associated with stress scores in the fibromyalgia group. However, pain tolerance was unrelated to individual differences in psychological distress in either group. In patients with fibromyalgia, clinical pain increased after the acoustic startle stimulus and painful forehead cooling, and increased during stressful mental arithmetic. Arthritic pain also increased during forehead cooling and mental arithmetic in association with indices of psychological distress.

CONCLUSIONS

These findings suggest that processes linked with individual differences in distress aggravate pain in rheumatoid arthritis, whereas some other mechanism (e.g., failure of stress-related pain modulation processes or an aberrant interaction between nociceptive afferent and sympathetic efferent fibers) triggers stress-induced pain in fibromyalgia.

Trapezius activity of fibromyalgia patients is enhanced in stressful situations, but is similar to healthy controls in a quiet naturalistic setting: a case-control study

Background

Muscle activity and pain development of fibromyalgia (FM) patients in response to mental stress show inconsistent results, when compared to healthy controls (HCs). A possible reason for the inconsistent results is the large variation in stress exposures in different studies. This study compares muscle responses of FM patients and HCs for different modes and levels of imposed stress, to elucidate features in stress exposures that distinguish stress responses of FM patients from HCs.

Methods

Upper trapezius (clavicular and acromial fibers), deltoid, and biceps surface electromyographic (sEMG) activity was recorded in FM patients (n=26) and HCs (n=25). Heart rate (HR) was recorded and used as indicator of autonomic activation. Tests included inspiratory breath holding (sympathetic activation procedure), mental stress tests (color-word test and backward counting; 28 min), instructed rest prior to stress test (30 min TV watching), and controlled arm movement. sEMG and HR was also recorded during an unrestrained evening stay at a patient hotel. The 5-min period with lowest trapezius muscle activity was determined. Pain (shoulder/neck, low back pain) and perceived tension were scored on VAS scales at the start and the end of the stress test and at bedtime.

Results

Trapezius sEMG responses of FM patients were significantly higher than HCs during sympathetic activation, mental stress, and instructed rest, but similar during arm movement and unrestrained evening activity. HR of FM patients and HCs was similar during mental stress and in the evening, including the 5-min period with lowest trapezius activity. Muscle activity of FM patients during the stress test (with shoulder/neck pain development) and the evening stay (no pain development) was similar.

Conclusions

FM patients show elevated muscle activity (in particular trapezius activity) in situations with imposed stress, including sympathetic activation, and putative anticipatory stress. Muscle activity and HR were similar to HCs in instructed arm movement and in a situation approaching low-stress daily living. Pain development of FM patients during the stress test may be due to activation of several stress-associated physiological systems, and not obviously caused by muscle activity in isolation.

Effect of experimental stress in 2 different pain conditions affecting the facial muscles

Chronic facial muscle pain is a common feature in both fibromyalgia (FM) and myofascial (MF) pain conditions. In this controlled study, a possible difference in the mode of deregulation of the physiological response to a stressing stimulus was explored by applying an acute mental stress to FM and MF patients and to controls. The effects of the stress test were observed on pain, sympathetic variables, and both tonic and reflex electromyographic activities of masseteric and temporal muscles. The statistical analyses were performed through a generalized linear model including mixed effects. Painful reaction to the stressor was stronger (P < .001) and longer (P = .011) in FM than in MF independently of a higher pain level at baseline. The stress-induced autonomic changes only seen in FM patients did not reach significance. The electromyographic responses to the stress test were strongest for controls and weakest for FM. The stress test had no effect on reflex activity (area under the curve [AUC]) or latency, although AUC was high in FM and latencies were low in both pain groups. It is suggested that FM is characterized by a lower ability to adapt to acute stress than MF.

PERSPECTIVE

This study showed that an acute psychosocial stress triggered several changes in 2 pain conditions including an increase in pain of larger amplitude in FM than in MF pain. Similar stress-induced changes should be explored as possible mechanisms for differentiation between dysfunctional pain conditions.

Biopsychosocial function analyses changes the assessment of the ability to work in patients on long-term sick-leave due to chronic musculoskeletal pain: the role of undiagnosed mental health comorbidity

AIMS

To study the prevalence of somatic and mental health comorbidity and the use of opioid medication among patients on long-term sick-leave due to chronic musculoskeletal pain (CMP); to compare an orthopaedic-based assessment of ability to work with a team assessment; to investigate the relationship between intensity of pain and psychosocial characteristics in this group.

METHODS

A cross-sectional study was carried out with 174 consecutive patients on sick-leave for a mean of 21 months. All were referred from the Social Insurance Office for orthopaedic evaluation and assessment of the ability to work. Of them, only 83/174 patients were referred by the Office for psychiatric evaluation.

RESULTS

Neck pain was the main cause of disability. Patients with neck pain often suffered pain in more than two sites, and greater intensity of pain. Thirty-four percent of all participants had been prescribed opioid medication before consultation. Degrees of disability, unemployment, low degree of education and to be an immigrant were related to intensity of pain. Unrecognized psychiatric disorders changed the main cause of inability to work in 69% of patients who underwent both orthopaedic and psychiatric evaluation.

CONCLUSIONS

An evaluation based on biopsychosocial function is valuable in reaching an accurate assessment of the patient's diagnosis, and ability to work in CMP. Ability to work and degree of sick-leave in patients on long-term sick-leave is determined to a large extent by undiagnosed mental health comorbidities, and not solely somatic complaints.

Relation between muscle activation pattern and pain: an explorative study in a bassists population

OBJECTIVE

To explore the muscle activation patterns in relation to pain complaints in bassists studied during a musical task. This study was based on the assumption that pain complaints are caused by increased muscle activation during playing or relaxation and/or faster onset of fatigue of muscles.

DESIGN

Cross-sectional study.

SETTING

Nonclinical.

PARTICIPANTS

Student bass guitarists (N=36) from conservatories in the Netherlands.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Bassists played a standard music piece for 30 minutes. Muscle activation levels and pain were recorded. Pain was registered with a Numeric Rating Scale (NRS 0-10). The muscle activation level of both the trapezius muscles and flexor carpi radialis was measured with sEMG: sEMG as the percentage of the maximal voluntary isometric contraction (%MVC) and the slope of the sEMG (slope of %MVC) were calculated. The %MVC as a function of time and the slope of %MVC were calculated during playing and for rest periods before and after playing. For statistic analysis, the Mann-Whitney U test and a multilevel multiregression analysis were used for comparing the sEMG data of bassists with and without pain.

RESULTS

No significant differences in %MVC or the slope of %MVC were between the bassists with and without pain complaints.

CONCLUSIONS

The results surprisingly indicate that pain complaints of bassists may not be associated with another muscle activation pattern. It is, therefore, not likely that pain is caused by increased muscle activation during playing and/or relaxation, nor by faster onset of fatigue.

Autonomic activation and pain in response to low-grade mental stress in fibromyalgia and shoulder/neck pain patients

OBJECTIVE

Psychosocial stress is a risk factor for musculoskeletal pain, but how stress affects musculoskeletal pain is poorly understood. We wanted to examine the relationship between low-grade autonomic activation and stress-related pain in patients with fibromyalgia and localised chronic shoulder/neck pain.

METHODS

Twenty-three female patients with fibromyalgia, 29 female patients with chronic shoulder-neck pain, and 35 healthy women performed a stressful task lasting 60min. With a blinded study design, we recorded continuous blood pressure, heart rate, finger skin blood flow and respiration frequency before (10min), during (60min) and after (30min) the stressful task. The physiological responses were compared with subjective reports of pain.

RESULTS

The increase in diastolic blood pressure and heart rate in response to the stressful task were smaller in fibromyalgia patients compared with the healthy controls. Furthermore, fibromyalgia patients had reduced finger skin blood flow at the end of the stressful task compared to healthy controls. We also found an inverse relationship between the heart rate response and development and recovery of the stress-related pain in fibromyalgia patients.

CONCLUSION

We found abnormal cardiovascular responses to a 60min long stressful task in fibromyalgia patients. Furthermore, we found a negative association between the heart rate response and the pain which developed during the stressful task in the fibromyalgia group, possibly a result of reduced stress-induced analgesia for fibromyalgia patients.

Further validation of a model of fibromyalgia syndrome in the rat

We have recently developed an animal model of fibromyalgia syndrome in the rat. In this model, rats exposed to unpredictable sound stress develop a delayed onset enhancement and prolongation of cytokine-induced mechanical hyperalgesia in muscle and skin. In this study, we tested the hypothesis that our model also manifests symptoms of common comorbid diagnoses: irritable bowel syndrome, temporomandibular disorder, and anxiety. Both visceral sensitivity and cytokine hyperalgesia in masseter muscle were present in the stressed rats. Furthermore, in an established model of irritable bowel syndrome-water avoidance-we observed significant muscle hyperalgesia. Finally, using the elevated plus maze to assess for anxiety level, we observed a significantly higher anxiety level in sound stress-exposed rats. Thus, unpredictable sound stress produces a condition in the rat with several features-delayed onset visceral and temporomandibular hyperalgesia and increased anxiety, as well as cutaneous and muscle hyperalgesia-commonly found in patients with fibromyalgia syndrome.

PERSPECTIVE

A stress model-unpredictable sound-in the rat exhibits several features (cutaneous, musculoskeletal, and visceral hyperalgesia, as well as anxiety) that are found in patients with fibromyalgia syndrome. Thus, this model may be used to test hypotheses about the underlying mechanisms and response to therapy in patients with fibromyalgia.

Central motor control failure in fibromyalgia: a surface electromyography study

Background

Fibromyalgia (FM) is characterised by diffuse musculoskeletal pain and stiffness at multiple sites, tender points in characteristic locations, and the frequent presence of symptoms such as fatigue. The aim of this study was to assess whether the myoelectrical manifestations of fatigue in patients affected by FM are central or peripheral in origin.

Methods

Eight female patients aged 55.6 ± 13.6 years (FM group) and eight healthy female volunteers aged 50.3 ± 9.3 years (MCG) were studied by means of non-invasive surface electromyography (s-EMG) involving a linear array of 16 electrodes placed on the skin overlying the biceps brachii muscle, with muscle fatigue being evoked by means of voluntary and involuntary (electrically elicited) contractions. Maximal voluntary contractions (MVCs), motor unit action potential conduction velocity distributions (mean ± SD and skewness), and the mean power frequency of the spectrum (MNF) were estimated in order to assess whether there were any significant differences between the two groups and contraction types.

Results

The motor pattern of recruitment during voluntary contractions was altered in the FM patients, who also showed fewer myoelectrical manifestations of fatigue (normalised conduction velocity rate of changes: -0.074 ± 0.052%/s in FM vs -0.196 ± 0.133%/s in MCG; normalised MNF rate of changes: -0.29 ± 0.16%/s in FM vs -0.66 ± 0.34%/s in MCG). Mean conduction velocity distribution and skewnesses values were higher (p < 0.01) in the FM group. There were no between-group differences in the results obtained from the electrically elicited contractions.

Conclusion

The apparent paradox of fewer myoelectrical manifestations of fatigue in FM is the electrophysiological expression of muscle remodelling in terms of the prevalence of slow conducting fatigue-resistant type I fibres. As the only between-group differences concerned voluntary contractions, they are probably more related to central motor control failure than muscle membrane alterations, which suggests pathological muscle fibre remodelling related to altered suprasegmental control.

Muscle dysfunction in cervical spine pain: implications for assessment and management

SYNOPSIS

There is irrefutable evidence of an association between mechanical neck pain (MNP) and dysfunction of the muscles of the cervical spine. A myriad of impairments have been demonstrated that include changes in the physical structure (cross-sectional area, fatty infiltration, fiber type), as well as changes in behavior (timing and activation level), of the cervical muscles. Such changes suggest an impaired capacity of the cervical muscles to generate, sustain, and maintain precision of the required levels of torque needed for optimal function. In the context of physical support, these changes potentially have deleterious consequences for the cervical region, which relies heavily on its muscles for mechanical stability. While interventions focused on the retraining of cervical muscle function have shown favorable responses in alleviating MNP, the development of best practice strategies for the assessment and management of cervical muscle dysfunction is still a work in progress. One obstacle in researching the efficacy of cervical muscle training is that, as yet, we do not possess the capacity to optimally measure and classify those patients most likely to respond to different methods of training that would enrich clinical practice. While gains in this area are emerging, the ability of a clinician to best identify the need and implement the most appropriate method of training cervical muscle function is still largely dependent on a comprehensive examination of the patient that considers all aspects of the patient's disorder and functional requirements.

LEVEL OF EVIDENCE

Level 5.

Muscle modifications in fibromyalgic patients revealed by surface electromyography (SEMG) analysis

Background

Several studies have been carried out in order to investigate surface electromyography (SEMG) response on fibromyalgic (FM) patients. Some studies failed to demonstrate differences between FM patients and healthy individuals while others found differences in SEMG parameters. Different muscular region have been analyzed in FM patients and heterogeneity is also produced because of the different ways in which the SEMG technique is used.

The aims of this study were to evaluate muscle modifications by SEMG analysis in FM women with respect to a sample of healthy controls and to investigate the relationships between SEMG parameters and the clinical aspects of the disease.

Methods

SEMG was recorded in 100 FM women (48.10 ± 11.96 yr) and in 50 healthy women (48.60 ± 11.18 yr), from the tibialis anterior and the distal part of vastus medialis muscle during isometric contraction. Initial values and rate of change of median spectral frequency (MDF) and conduction velocity (CV) of the SEMG signal were calculated.

The clinical parameters "Fibromyalgia Impact Questionnaire", pain, tender points, tiredness were evaluated and the relationships between these data and the SEMG results were also studied. For the statistical analysis Mann-Whitney test, chi-square test and Spearman correlation were used.

Results

MDF absolute values and the so-called Fatigue Index (FI) were significantly lower (p < 0.001) in both muscles studied in FM patients (MDF: 93.2 μV; FI: 1.10, 0.89) with respect to healthy controls (MDF: 138.2 μV; FI: 2.41, 1.66) and a smaller reduction in the percentage values of MDF was observed in FM patients vs controls (22% vs 38%). A significant correlation was found between the SEMG parameter decrement of normalized median frequency (MNF) (%) and seriousness of FM (evaluated by means of tender points).

Conclusion

We have found some interesting muscle modifications in FM patients with respect to healthy controls, regarding MDF, CV and FI values which resulted significantly lower in FM. Patients might have a different fiber recruitment or a possible atrophy of type II fibers suggesting that they are not able to reach muscle relaxation.

Pain induced by a single simulated office-work session: time course and association with muscle blood flux and muscle activity

The present study aimed to assess the development of pain during computer work with high precision demand and time pressure, and the association between pain and muscle blood fluxes and muscle activity. Twenty-eight healthy subjects (range 22-44 years) performed a 90-min standardized task of correcting a text on a word-processor. Monetary reward was given according to productivity in order to induce time pressure. Pain intensity, general tension, and eye strain were reported on visual analogue scales before, during and after the computer session. Intramuscular trapezius blood fluxes were recorded by laser-Doppler flowmetry (LDF) and analyzed as % of baseline level. Muscle activity was measured from the upper trapezius and forearm extensors by surface electromyography (EMG), analyzed as % of a maximal calibration contraction, %EMG(max). Pain, tension, and eye strain increased considerably during the computer session with different time course for pain and tension. The LDF of the active side of trapezius was elevated for 30 min followed by a falling trend. There was an initial short-lasting increase in the inactive trapezius. The upper trapezius EMG was low (<3 % of EMG(max)) but increased during the work, similar in both the active and passive side. There was a significant time and blood flux interaction effect on pain in the shoulders/neck, but no association with EMG. In conclusion, considerable neck/shoulder pain may develop in healthy pain-free subjects during 90 min of office-work and seems to be related to the regulation of trapezius muscle blood flow.

A unilateral sympathetic blockade does not affect stress-related pain and muscle activity in patients with chronic musculoskeletal pain

OBJECTIVE

Chronic musculoskeletal pain is often exacerbated by mental and social stress. The association between stress and musculoskeletal pain is potentially mediated by peripheral sympathetic nerves, either directly or indirectly through muscle activity. In the present study we wanted to determine whether sympathetic blockade could affect either the pain or the muscular activity experienced during mental stress in patients with chronic musculoskeletal pain.

METHODS

We performed a unilateral anaesthetic blockade of the lower cervical sympathetic ganglion (ganglion stellatum) in 18 patients with chronic musculoskeletal pain (10 with fibromyalgia and eight with chronic shoulder/neck pain). After the blockade the patients performed a 60-minute stressful task with low-grade mental stress that has induced pain and muscle activity in earlier experiments. Surface electromyography (SEMG) of the forehead, temples, neck, and shoulders, and heart rate and blood pressure were recorded together with ratings of pain.

RESULTS

We did not find any side or sidextime effect for pain or muscular activity in any of the four muscle groups (p>0.12).

CONCLUSION

We investigated the potential involvement of peripheral sympathetic nerves in stress-related musculoskeletal pain. A peripheral sympathetic block did not affect pain and muscle responses to a stressful task. Other explanatory models should be implemented and tested experimentally to further investigate the clinical impression that mental stress exacerbates pain in patients with chronic musculoskeletal pain.

Similarities in stress physiology among patients with chronic pain and headache disorders: evidence for a common pathophysiological mechanism?

One common feature of chronic musculoskeletal pain and headaches are that they are both influenced by stress. Among these, tension-type headache (TTH), fibromyalgia (FMS) and chronic shoulder/neck pain (SNP) appear to have several similarities, both with regard to pathophysiology, clinical features and demographics. The main hypothesis of the present study was that patients with chronic pain (TTH, FMS and SNP) had stress-induced features distinguishing them from migraine patients and healthy controls. We measured pain, blood pressure, heart rate (HR) and skin blood flow (BF) during (1 h) and after (30 min) controlled low-grade cognitive stressor in 22 migraine patients, 18 TTH patients, 23 FMS patients, 29 SNP patients and 44 healthy controls. FMS patients had a lower early HR response to stress than migraine patients, but no differences were found among FMS, TTH and SNP patients. Finger skin BF decreased more in FMS patients compared to migraine patients, both during and after the test. When comparing chronic pain patients (chronic TTH, FMS and SNP) with those with episodic pain (episodic TTH and migraine patients) or little or no pain (healthy controls), different adaptation profiles were found during the test for systolic and diastolic blood pressure, HR and skin BF in the chronic group. In conclusion, these results suggest that TTH, FMS and SNP patients may share common pathophysiological mechanisms regarding the physiological responses to and recovery from low-grade cognitive stress, differentiating them from episodic pain conditions such as migraine

Neck movement and muscle activity characteristics in female office workers with neck pain

STUDY DESIGN

Cross-sectional study.

OBJECTIVE

To explore aspects of cervical musculoskeletal function in female office workers with neck pain.

SUMMARY OF BACKGROUND DATA

Evidence of physical characteristics that differentiate computer workers with and without neck pain is sparse. Patients with chronic neck pain demonstrate reduced motion and altered patterns of muscle control in the cervical flexor and upper trapezius (UT) muscles during specific tasks. Understanding cervical musculoskeletal function in office workers will better direct intervention and prevention strategies.

METHODS

Measures included neck range of motion; superficial neck flexor muscle activity during a clinical test, the craniocervical flexion test; and a motor task, a unilateral muscle coordination task, to assess the activity of both the anterior and posterior neck muscles. Office workers with and without neck pain were formed into 3 groups based on their scores on the Neck Disability Index. Nonworking women without neck pain formed the control group. Surface electromyographic activity was recorded bilaterally from the sternocleidomastoid, anterior scalene (AS), cervical extensor (CE) and UT muscles.

RESULTS

Workers with neck pain had reduced rotation range and increased activity of the superficial cervical flexors during the craniocervical flexion test. During the coordination task, workers with pain demonstrated greater activity in the CE muscles bilaterally. On completion of the task, the UT and dominant CE and AS muscles demonstrated an inability to relax in workers with pain. In general, there was a linear relationship between the workers' self-reported levels of pain and disability and the movement and muscle changes.

CONCLUSION

These results are consistent with those found in other cervical musculoskeletal disorders and may represent an altered muscle recruitment strategy to stabilize the head and neck. An exercise program including motor reeducation may assist in the management of neck pain in office workers.

Cardiovascular responses to cognitive stress in patients with migraine and tension-type headache

BACKGROUND

The purpose of this study was to investigate the temporal relationship between autonomic changes and pain activation in migraine and tension-type headache induced by stress in a model relevant for everyday office-work.

METHODS

We measured pain, blood pressure (BP), heart rate (HR) and skin blood flow (BF) during and after controlled low-grade cognitive stress in 22 migraineurs during headache-free periods, 18 patients with tension-type headache (TTH) and 44 healthy controls. The stress lasted for one hour and was followed by 30 minutes of relaxation.

RESULTS

Cardiovascular responses to cognitive stress in migraine did not differ from those in control subjects. In TTH patients HR was maintained during stress, whereas it decreased for migraineurs and controls. A trend towards a delayed systolic BP response during stress was also observed in TTH. Finger BF recovery was delayed after stress and stress-induced pain was associated with less vasoconstriction in TTH during recovery.

CONCLUSION

It is hypothesized that TTH patients have different stress adaptive mechanisms than controls and migraineurs, involving delayed cardiovascular adaptation and reduced pain control system inhibition.

Noradrenaline and cortisol changes in response to low-grade cognitive stress differ in migraine and tension-type headache

The goal of this study was to explore the relationship between indicators of sympathoneural, sympathomedullar and hypothalamic-pituitary-adrenocortical (HPA) activity and stress-induced head and shoulder-neck pain in patients with migraine or tension-type headache (TTH). We measured noradrenaline, adrenaline and cortisol levels before and after low-grade cognitive stress in 21 migraineurs, 16 TTH patients and 34 controls. The stressor lasted for 60 min and was followed by 30 min of relaxation. Migraine patients had lower noradrenaline levels in blood platelets compared to controls. Pain responses correlated negatively with noradrenaline levels, and pain recovery correlated negatively with the cortisol change in migraineurs. TTH patients maintained cortisol secretion during the cognitive stress as opposed to the normal circadian decrease seen in controls and migraineurs. There may therefore be abnormal activation of the HPA axis in patients with TTH when coping with mental stress, but no association was found between pain and cortisol. A relationship between HPA activity and stress in TTH patients has to our knowledge not been reported before. In migraine, on the other hand, both sympathoneural activation and HPA activation seem to be linked to stress-induced muscle pain and recovery from pain respectively. The present study suggests that migraineurs and TTH patients cope differently with low-grade cognitive stress.

Respiratory and stress-induced activation of low-threshold motor units in the human trapezius muscle

The study aimed to characterize trapezius motor unit firing pattern in low-amplitude contractions, with emphasis on respiratory modulated activity. Constant-amplitude contractions with shoulder elevation, controlled by feedback of the root mean square detected surface electromyographic (SEMG) signal, typing with arm movement and tasks with mental stress were performed. Single motor unit activity was recorded by a quadrifilar fine-wire electrode. A surface electrode simultaneously recorded SEMG activity. Contraction amplitudes ranged from 1 to 10% of the SEMG signal at maximum voluntary contraction (1-10% EMG(max)). The majority ( approximately 80%) of motor units recorded during constant-amplitude contractions showed firing rate modulation at the respiratory frequency. Respiratory firing rate modulation was clear for low amplitude contractions (< 3% EMG(max)), but was reduced at higher amplitudes (3-5.9% EMG(max)). Most motor units had peak firing rate at the transition from inspiration to expiration, but peak firing rate at the transition from expiration to inspiration or at the first harmonic frequency was also observed. The SEMG signal showed little or no respiratory modulation, possibly because respiratory phase varied between motor units. Respiratory modulation of firing rates was significantly reduced in experiments with mental stress and was rarely observed in typing experiments. Both central respiratory drive and peripheral afferent input may contribute to respiratory modulation of firing rates; however, animal studies indicate a central source of the respiratory modulated input. We speculate that the reduction in respiratory modulation of motor activity with mental stress is due to activation of alternative pathways providing excitatory input to trapezius motoneurons.