EMG activity and pain development in fibromyalgia patients exposed to mental stress of long duration.
ABSTRACT To examine the distribution of stress-induced upper-body pain in fibromyalgia patients, and the possible association of pain with electromyographic activity in muscles near the sites of pain development.
Fifteen fibromyalgia patients and 15 pain-free subjects were exposed to low-level mental strain over a one-hour period. EMG was recorded from frontalis, temporalis, trapezius, and splenius capitis. Pain in the corresponding locations was recorded before the test, every 10 minutes during the test, and the 30-minute posttest period.
The fibromyalgia patients developed pain during the test in all the above body locations. Pain development in all locations associated with trapezius EMG activity, but not with EMG activity in underlying muscles for forehead, temples, and neck.
Stress-induced pain in fibromyalgia patients is not generally caused by muscle activity. The trapezius EMG response may be part of a general stress response that cause pain independently of motor activity in muscles.
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ABSTRACT: Experience of stress may lead to increased electromyography (EMG) activity in specific muscles compared to a non-stressful situation. The main aim of this study was to develop and validate a stress-EMG paradigm in which a single uncontrollable and unpredictable nociceptive stimulus was presented. EMG activity of the trapezius muscles was the response of interest. In addition to linear time effects, non-linear EMG time courses were also examined. Taking into account the hierarchical structure of the dataset, a multilevel random regression model was applied. The stress paradigm, executed in N = 70 subjects, consisted of a 3-minute baseline measurement, a 3-minute pre-stimulus stress period and a 2-minute post-stimulus phase. Subjects were unaware of the precise moment of stimulus delivery and its intensity level. EMG activity during the entire experiment was conform a priori expectations: the pre-stimulus phase showed a significantly higher mean EMG activity level compared to the other two phases, and an immediate EMG response to the stimulus was demonstrated. In addition, the analyses revealed significant non-linear EMG time courses in all three phases. Linear and quadratic EMG time courses were significantly modified by subjective anticipatory stress level, measured just before the start of the stress task. Linking subjective anticipatory stress to EMG stress reactivity revealed that subjects with a high anticipatory stress level responded with more EMG activity during the pre-stimulus stress phase, whereas subjects with a low stress level showed an inverse effect. Results suggest that the stress paradigm presented here is a valid test to quantify individual differences in stress susceptibility. Further studies with this paradigm are required to demonstrate its potential use in mechanistic clinical studies.PLoS ONE 01/2014; 9(4):e95215. · 3.53 Impact Factor
- Der Schmerz 01/2008; 22(5). · 1.50 Impact Factor
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ABSTRACT: Objectives: The aim of the present study was to investigate autonomic regulation at rest and in response to functional laboratory tests in patients with chronic low back pain [CLBP], as well as its possible relations to different characteristics of the clinical picture. Methods: Ninety-three CLBP patients [47 females, 45 males; age 38 ± 7 years] and 32 healthy normal control subjects [15 females, 16 males; 36 ± 9 years] participated. Subjects were examined according to the McKenzie procedure, and filled in Short Form 36 and Oswestry Disability Questionnaires in addition to self-reports of pain. An electrocardiogram, finger plethysmogram, respiration, and skin conductance were recorded. Functional tests included the Stroop Color-Word test, orthostatic test, paced breathing, and handgrip. A five-minute baseline recording was followed by four counterbalanced functional tests, separated by two- to three-minute long pauses. Results: An analysis of variance revealed higher baseline heart rate [P = 0.011 in females only], low frequency spectral power [P = 0.001] and electrodermal activity [P = 0.048], and lower high frequency spectral power [P = 0.001]. Each functional test evoked a response, without any group differences in physiological reactivity. There were no significant differences with respect to physiological reactivity between subgroups formed on the basis of prior diagnoses, McKenzie evaluation, VAS pain estimates, Short Form 36, and Oswestry Disability Questionnaire data. The patients did not show high levels of individual response specificity. Conclusions: Presented data show that patients with CLBP exhibit increased sympathetic tonus in comparison with the control group, regardless of CLBP patients' level of pain, functional disability, or clinical status indices.Journal of Musculoskeletal Pain 03/2007; 15(1):29-40. · 0.32 Impact Factor