Discrimination of muscle tension in chronic pain patients and healthy controls.

The purpose of this study was to assess the perception of muscle tension in chronic pain patients and healthy controls. Twenty chronic back pain patients, 20 patients who suffered from temporomandibular pain and dysfunction, and 20 healthy controls were instructed to produce eight different levels of muscle contraction in either the m. masseter or the m. erector spinae. Each level was produced three times; trials were presented in random order. Analyses of the accuracy and the sensitivity of discrimination of muscle tension levels revealed that the patients were less able to perceive muscle contraction levels correctly and that they underestimated their actual levels of muscle tension. Patients and controls did not differ in the extent to which they contracted muscles not involved in the task. Patients suffering from musculoskeletal disorders seem to display a genuine deficit in discrimination of muscle tension that is related to neither local physiological changes at the site of pain, lack of motivation, in-attention, nor fatigue.     

Deficient Discrimination of EMG Levels and Overestimation of Perceived Tension in Chronic Pain Patients

Twenty chronic low back pain patients (CBP), twenty tension headache (THA) patients, and twenty healthy controls (HC) participated in a tension production task where subjects had to attain four levels (4, 8, 12, 16 V) of muscle tension at the m. frontalis and the m. erector spinae. Ratings of perceived tension, pain, and aversiveness as well as EMG, heart rate, and skin conductance levels were recorded. Signal detection and correlational methods revealed that the patients were deficient in muscle tension discrimination at high tension levels in both muscles. They generally overestimated low and underestimated high levels of muscle tension, especially in the CBP group. At low muscle tension levels, both healthy controls and patients showed deficient discrimination ability. Perceived muscle tension, aversiveness, and pain ratings during the tasks were higher in the patient groups. These data confirm and clarify previous reports of deficient tension perception and show concurrent overestimation of bodily symptoms in chronic musculoskeletal pain patients.     

The effectiveness of EMG biofeedback training in low back pain

Eighteen patients with chronic low back pain(lbp) of muscle tension origin were given an EMG biofeedback training. Compared to seven controls they showed a significant decrease during training in muscle tension and subsequently in pain. However, at follow-up EMG levels dropped to the initial(high) level. Pain scores of patients with high pain decrements during training showed further improvement during follow-up, which was not the case with patients showing less substantial improvement. The importance of cognitions was discussed.We wish to express our thanks to Marijke Höweler-van Dalen for supervising this investigation, to Arnold Goedhart for statistical advice, to Dr. Orlebeke for his critical remarks, and to Dr. Penders for referring the patients in Amsterdam. We are particularly indebted to the general practitioners Paul Kreutzer and Jan Huls for referring the Andijk patients. Without their support this investigation would not have been possible.     

Activation imbalances in lumbar spine muscles in the presence of chronic low back pain.

Paraspinal electromyographic (EMG) activity was recorded bilaterally from three lumbar levels during 30-s isometric trunk extensions [40 and 80% of maximum voluntary contraction (MVC)] in 20 healthy men and 14 chronic low back pain patients in pain. EMG parameters indicating neuromuscular fatigue and contralateral imbalances in EMG root-mean-square amplitude and median frequency were analyzed. Patients in pain showed less fatigue than controls at both contraction levels and produced only 55% of their MVC. Patients in pain likely did not produce a "true" maximum effort. A low MVC estimate would mean lower absolute contraction levels and less neuromuscular fatigue, thus explaining lower scores in the patients. Contralateral root-mean-square amplitude imbalances were present in both categories of subjects although such imbalances, when averaged across lumbar levels, were significantly larger in patients. Median frequency imbalances were significantly larger in the patients, at segmental as well as across lumbar levels. These results suggest that the presence of pain in these patients caused a redistribution of the activation behavior between synergistic muscles of the lumbar back.     

The effectiveness of EMG biofeedback training in low back pain.

Eighteen patients with chronic low back pain (lbp) of muscle tension origin were given an EMG biofeedback training. Compared to seven controls they showed a significant decrease during training in muscle tension and subsequently in pain. However, at follow-up EMG levels dropped to the initial (high) level. Pain scores of patients with high pain decrements during training showed further improvement during follow-up, which was not the case with patients showing less substantial improvement. The importance of cognitions was discussed.     

Muscle discrimination ability at three muscle sites in three headache groups

The present study examined the ability of three headache groups (migraine, mixed migraine/tension, and tension) to accurately discriminate subjective levels of muscle tension at the forearm flexor, frontalis, and trapezius muscle sites. Discrimination ability was assessed at pre- and posttreatment using a psychophysical method of magnitude production. Results show that the ability to discriminate muscle tension levels at pretreatment varied across the headache groups, with migraineurs being the most accurate (r=.854), followed by the mixed headache group (r=.785), and finally the tension headache group (r=.732). Discrimination ability significantly increased at the posttreatment assessment. A multiple regression analysis showed that pretreatment performance on the muscle discrimination task significantly predicted outcome (r=.75) from relaxation and biofeedback training for migraine patients but not for the mixed or tension headache groups.This research was supported by a grant from NINCDS, NS-15235.     

兔膈肌力学模式对慢性电刺激的适应性改变和细胞外Ca …

目的：研究兔膈肌肌条力学对不同频率慢性电刺激（ＣＥＳ）的适应性变化特征和细胞外Ｃａ＾２＋变化夺其力学特征的影响。方法：测定正常对照组和ＣＥＳ组的颤搐收缩张力（Ｐｔ）、峰值张力时间（ＴＰＴ）、１／２松弛时间（１／２ＲＴ）、强直颤搐收缩张力（Ｐｏ）、疲劳指数（ＦＩ）和疲劳恢复指数（ＦＲＩ）;观察在无Ｃａ＾２＋Ｈａｎｋ’ｓ液和标准Ｈａｎｋ’ｓ液时肌条收缩张力消失和恢复的时间差异。结果：①同对照组作比较,     

The discrimination of polarized light by the tarantula

Summary The present experiment compared the establishment of a position habit and three subsequent response shifts with and without discriminative stimuli. The discriminative stimuli employed were (a) 90° and 180° polarization patterns and (b) high and low intensity levels. A significant difference (0.05) was found between the running time performance of the polarization discrimination group and the uniform illumination and bright-dark discrimination groups. No similar difference was found with errors as the dependent measure, and no significant between group differences were found during the response shifts. The conclusion was drawn that the extra-ocular hypothesis could not account for the significant difference.This paper is taken from a Master's Thesis submitted to the Florida State University by the senior author, under the direction of the junior author, in partial fulfillment of the requirements for the degree of Master of Science. A portion of this paper was presented at the 1965 meeting of the American Psychological Association.This research was partially supported by a grant from the Florida State University Research Council. The statistical analyses were made possible in part by a National Science Foundation grant (# GP 671) to the Florida State University Computation Center. The authors are indebted to Dr. F. J. King, Institute of Human Learning, Florida State University, for his contribution to the data analysis.     

Heterogeneity of psychophysiological stress responses in fibromyalgia syndrome patients

Dysregulated psychophysiological responses have been observed in patients with fibromyalgia syndrome (FMS), although the results are inconsistent. Surface electromyographic (EMG), systolic and diastolic blood pressure, heart rate (HR), and skin conductance levels (SCLs) were continuously recorded at baseline, and during a series of stress and relaxation tasks in 90 FMS patients and 30 age and sex matched healthy controls (HCs). The patient sample demonstrated lower baseline EMG levels compared to the HCs on all tasks. In contrast, the patients displayed elevated HR and SCL (sympathetic vasomotor and sudomotor indices, respectively) during both stress tasks. A cluster analysis identified four psychophysiological response patterns: 63.3% of HCs showed increased muscle tension and stable cardiovascular responses; 34.8% of FMS patients showed a pattern of increased sympathetic vasomotor reactivity with stable sudomotor and reduced muscular response; 12.2% of FMS patients showed a pattern of increased sympathetic sudomotor reactivity connected with increased sympathetic vasomotor response and reduced muscular response; and, in contrast, 46.7% of FMS patients showed a pattern of parasympathetic vasomotor reactivity and reduced sudomotor as well as muscular response. The identification of low baseline muscle tension in FMS is discrepant with other chronic pain syndromes and suggests that unique psychophysiological features may be associated with FMS. The different psychophysiological response patterns within the patient sample support the heterogeneity of FMS.     

High levels of N-palmitoylethanolamide and N-stearoylethanolamide in microdialysate samples from myalgic trapezius muscle in women

Background

N-acylethanolamines (NAEs) are endogenous compounds that regulate inflammation and pain. These include the cannabinoid ligand anandamide (AEA) and the peroxisome proliferator-activated receptor-α ligand palmitoylethanolamide (PEA). Little is known as to the levels of NAEs in pain states in human, particularly in the skeletal muscle. The aim of this study was to investigate the levels of these lipid mediators in muscle dialysate from women with chronic neck-/shoulder pain compared to healthy controls.

Methods

Eleven women with chronic neck-/shoulder pain and eleven healthy women participated in this study. All participants went through microdialysis procedures in the trapezius muscle. Muscle dialysate samples were collected during four hours and analysed by nano liquid chromatography tandem mass spectrometry (nLC-MS/MS).

Results

We were able to detect AEA, PEA, N-stearoylethanolamine (SEA) and 2-arachidonoylglycerol (2-AG) in a single chromatographic run. Of the NAEs studied, PEA and SEA were clearly detectable in the muscle microdialysate samples. The muscle dialysate levels of PEA and SEA were significantly higher in myalgic subjects compared to healthy controls.

Conclusion

This study demonstrates that microdialysis in combination with mass spectrometry can be used for analysing NAE''s in human muscle tissue regularly over time. Furthermore the significant group differences in the concentration of PEA and SEA in this study might fill an important gap in our knowledge of mechanisms in chronic myalgia in humans. In the long run this expanded understanding of nociceptive and anitinociceptive processes in the muscle may provide a base for ameliorating treatment and rehabilitation of pain.     

Heterogeneity of psychophysiological stress responses in fibromyalgia syndrome patients

Dysregulated psychophysiological responses have been observed in patients with fibromyalgia syndrome (FMS), although the results are inconsistent. Surface electromyographic (EMG), systolic and diastolic blood pressure, heart rate (HR), and skin conductance levels (SCLs) were continuously recorded at baseline, and during a series of stress and relaxation tasks in 90 FMS patients and 30 age and sex matched healthy controls (HCs). The patient sample demonstrated lower baseline EMG levels compared to the HCs on all tasks. In contrast, the patients displayed elevated HR and SCL (sympathetic vasomotor and sudomotor indices, respectively) during both stress tasks. A cluster analysis identified four psychophysiological response patterns: 63.3% of HCs showed increased muscle tension and stable cardiovascular responses; 34.8% of FMS patients showed a pattern of increased sympathetic vasomotor reactivity with stable sudomotor and reduced muscular response; 12.2% of FMS patients showed a pattern of increased sympathetic sudomotor reactivity connected with increased sympathetic vasomotor response and reduced muscular response; and, in contrast, 46.7% of FMS patients showed a pattern of parasympathetic vasomotor reactivity and reduced sudomotor as well as muscular response. The identification of low baseline muscle tension in FMS is discrepant with other chronic pain syndromes and suggests that unique psychophysiological features may be associated with FMS. The different psychophysiological response patterns within the patient sample support the heterogeneity of FMS.     

Oxygenation and Hemodynamics Do Not Underlie Early Muscle Fatigue for Patients with Work-Related Muscle Pain

Patients suffering from work-related muscle pain (WRMP) fatigue earlier during exercise than healthy controls. Inadequate oxygen consumption and/or inadequate blood supply can influence the ability of the muscles to withstand fatigue. However, it remains unknown if oxygenation and hemodynamics are associated with early fatigue in muscles of WRMP patients. In the present study we applied near-infrared spectroscopy (NIRS) on the extensor carpi radialis (ECR) and trapezius (TD) muscles of patients with WRMP (n = 18) and healthy controls (n = 17). Our objective was to determine if there were group differences in endurance times for a low-level contraction of 15% maximal voluntary contraction (MVC) – sustained for 12–13 min, and to see if these differences were associated with differences in muscle oxygenation and hemodynamics. At baseline, oxygen saturation (StO₂%) was similar between groups for the ECR, but StO₂% was significantly lower for TD for the WRMP patients (76%) compared to controls (85%) (P<0.01). Also, baseline ECR blood flow was similar in the two groups. For both muscles there were a larger number of patients, compared to controls, that did not maintain the 15% MVC for the allotted time. Consequently, the endurance times were significantly shorter for the WRMP patients than controls (medians, ECR: 347 s vs. 582 s; TD: 430 s vs. 723 s respectively). Responses in StO₂% during the contractions were not significantly different between groups for either muscle, i.e. no apparent difference in oxygen consumption. Overall, we interpret our findings to indicate that the early fatigue for our WRMP patients was not associated with muscle oxygenation and hemodynamics.     

The relationship between muscle discrimination ability and response to relaxation training in three kinds of headaches

Accurate discrimination of changes in physiological response has been noted as an important element in learning to control that response. Using a magnitude production procedure involving forearm isometric contractions, it was found that the ability to discriminate muscle tension varied across headache groups, with the no-headache control group (r=.76) being most accurate, followed by the tension group (r=.68), the mixed tension and migraine group (r=.60), and finally the migraine group (r=.51). The most important result, however, was that muscle discrimination ability significantly predicted clinical outcome from treatment by relaxation training for tension headache subjects (r=.50) but did not predict outcome for migraine or mixed headache subjects.This research was supported by a grant from NINCDS, NS-15235.     

A comparison of treatment modes in the management of myofascial pain dysfunction syndrome

This research compares different treatment regimes for the management of chronic facial pain associated with the masticatory musculature. Twenty-one females meeting specific criteria were randomly assigned to one of three treatment conditions: a dental splint and physiotherapy program; a relaxation program utilizing progressive muscle relaxation, biofeedback, and stress management techniques; or a minimal treatment program involving transcutaneous electrical nerve stimulation. Improvement was assessed through a dental examination, self-monitoring of pain, and an assessment of EMG activity during resting and task conditions. Significant changes were obtained in response to all treatment programs. The treatment programs differed only in the relative pattern of treatment effects obtained from the self-report monitoring of pain. The data are consistent with the concept of MPD as a psychological response to stress which maintains chronic pain through increased muscle tension in the jaw.This article is based on a thesis submitted in partial fulfillment of the requirement for a master's degree from the University of British Columbia by the second author. This research was facilitated by National Health and Welfare Grant NAHS 30-9625 and provincial government Youth Employment Program project #1225-01 made to Drs. Crockett and Alden, respectively. The authors would like to thank J. Dory, D.D.S., M.Sc. and B. Lundgren, B.P.T. for their help in completing this project. The authors also would like to thank S. Edwards and J. Snyder for their assistance in the preparation of this paper.     

Evidence that a higher ATP cost of muscular contraction contributes to the lower mechanical efficiency associated with COPD: preliminary findings

Impaired metabolism in peripheral skeletal muscles potentially contributes to exercise intolerance in chronic obstructive pulmonary disease (COPD). We used (31)P-magnetic resonance spectroscopy ((31)P-MRS) to examine the energy cost and skeletal muscle energetics in six patients with COPD during dynamic plantar flexion exercise compared with six well-matched healthy control subjects. Patients with COPD displayed a higher energy cost of muscle contraction compared with the controls (control: 6.1 ± 3.1% of rest·min(-1)·W(-1), COPD: 13.6 ± 8.3% of rest·min(-1)·W(-1), P = 0.01). Although, the initial phosphocreatine resynthesis rate was also significantly attenuated in patients with COPD compared with controls (control: 74 ± 17% of rest/min, COPD: 52 ± 13% of rest/min, P = 0.04), when scaled to power output, oxidative ATP synthesis was similar between groups (6.5 ± 2.3% of rest·min(-1)·W(-1) in control and 7.8 ± 3.9% of rest·min(-1)·W(-1) in COPD, P = 0.52). Therefore, our results reveal, for the first time that in a small subset of patients with COPD a higher ATP cost of muscle contraction may substantially contribute to the lower mechanical efficiency previously reported in this population. In addition, it appears that some patients with COPD have preserved mitochondrial function and normal energy supply in lower limb skeletal muscle.     

Surface electromyography assessment of back muscle intrinsic properties.

The purpose of this study was to assess (1) the reliability and (2) the sensitivity to low back pain status and gender of different EMG indices developed for the assessment of back muscle weakness, muscle fiber composition and fatigability. Healthy subjects (men and women) and chronic low back pain patients (men only) performed, in a static dynamometer, maximal and submaximal static trunk extension tasks (short and long duration) to assess weakness, fiber composition and fatigue. Surface EMG signals were recorded from four (bilateral) pairs of back muscles and three pairs of abdominal muscles. To assess reliability of the different EMG parameters, 40 male volunteers (20 controls and 20 chronic low back pain patients) were assessed on three occasions. Reliable EMG indices were achieved for both healthy and chronic low back pain subjects when specific measurement strategies were applied. The EMG parameters used to quantify weakness and fiber composition were insensitive to low back status and gender. The EMG fatigue parameters did not detect differences between genders but unexpectedly, healthy men showed higher fatigability than back pain patients. This result was attributed to the smaller absolute load that was attributed to the patients, a load that was defined relative to their maximal strength, a problematic measure with this population. An attempt was made to predict maximal back strength from anthropometric measurements but this prediction was prone to errors. The main difficulties and some potential solutions related to the assessment of back muscle intrinsic properties were discussed.     

Interaction of biofeedback-assisted relaxation and diuretic in treatment of essential hypertension

Thirty patients with essential hypertension participated in a study designed to compare two treatments: diuretic medication alone (n=10) and biofeedback assisted relaxation combined with diuretic (n=20). One of 10 patients lowered BP with diuretic alone and 11 of 20 patients lowered BP with diuretic combined with biofeedback-assisted relaxation. The addition of the behavioral intervention to the diuretic therapy produced a decrease in blood pressure beyond that associated with the diuretic alone. The decreases in BP mediated by diuretic were related to high entry levels of BP, low anxiety, forehead muscle tension, anger expression and plasma renin activity. The BP decrease mediated by combined diuretic and biofeedback-assisted relaxation was associated with high pretreatment BP, anger controlled, low finger temperature and high/normal plasma renin activity.This work supported by the Northwestern Ohio Heart Association under grant No. 93132 to Dr. McGrady.     

Investigation of trunk muscle co-contraction and its association with low back pain development during prolonged sitting

Previous work has shown muscle activation differences between chronic low back pain patients and healthy controls in sitting postures, and between asymptomatic individuals who do (PDs: pain developers) and do not (NPDs: non-pain developers) develop transient back pain during prolonged standing (as determined using a visual analog scale). The current study aimed to investigate differences in trunk muscle co-contraction between PD and NPD individuals over 2 h of prolonged sitting. Ten healthy males sat continuously for 2 h while performing tasks that simulated computer-aided-drafting; four were classified as PDs, and six as NPDs. Co-contraction indices were calculated from EMG data collected from eight trunk muscles bilaterally, and compared between pain groups and over time. PDs exhibited higher levels of co-contraction than NPDs. Additionally, co-contraction tended to increase over time, and was significantly correlated to pain development. The relationship between co-contraction and back pain development may actually be circular, in that it is both causal and adaptive: high co-contraction initially predisposes to pain development, following which co-contraction further increases in an attempt to alleviate the pain, and the cycle perpetuates. Further work will be required to elucidate the exact nature of this relationship, and to confirm the generalizability to other populations.     

Is Altered Central Pain Processing Related to Disease Stage in Chronic Pancreatitis Patients with Pain? An Exploratory Study

Background

The most dominant feature in chronic pancreatitis is intense abdominal pain. Changes in spinal and/or supraspinal central nervous system pain processing due to visceral nociceptive input play an important role in this pain. How altered pain processing is related to disease stage still needs study.

Methodology/Principal Findings

Sixty chronic pancreatitis patients were compared to 15 healthy controls. Two subgroups of pancreatitis patients were defined based on the M-ANNHEIM severity index of chronic pancreatitis; i.e. moderate and severe. Pain detection and tolerance thresholds for pressure and electric stimuli were measured in six selected dermatomes (C5, T4, T10, L1, L4 and T10BACK). In addition, the conditioned pain modulation response to cold pressor task was determined. These measures were compared between the healthy controls and chronic pancreatitis patients. Severe pancreatitis patients showed lower pain thresholds than moderate pancreatitis patients or healthy volunteers. Healthy controls showed a significantly larger conditioned pain modulation response compared to all chronic pancreatitis patients taken together.

Conclusions/Significance

The present study confirms that chronic pancreatitis patients show signs of altered central processing of nociception compared to healthy controls. The study further suggests that these changes, i.e. central sensitization, may be influenced by disease stage. These findings underline the need to take altered central pain processing into account when managing the pain of chronic pancreatitis.     

Muscle discrimination ability at three muscle sites in three headache groups

The present study examined the ability of three headache groups (migraine, mixed migraine/tension, and tension) to accurately discriminate subjective levels of muscle tension at the forearm flexor, frontalis, and trapezius muscle sites. Discrimination ability was assessed at pre- and posttreatment using a psychophysical method of magnitude production. Results show that the ability to discriminate muscle tension levels at pretreatment varied across the headache groups, with migraineurs being the most accurate (r = .854), followed by the mixed headache group (r = .785), and finally the tension headache group (r = .732). Discrimination ability significantly increased at the posttreatment assessment. A multiple regression analysis showed that pretreatment performance on the muscle discrimination task significantly predicted outcome (r = .75) from relaxation and biofeedback training for migraine patients but not for the mixed or tension headache groups.