EMG Levels Research Articles

EMG scanning: Normative data

Surface EMG was recorded from both right and left aspects of 18 muscle groups for the purpose of establishing a data base of normative EMG levels. A scanning electrode permitted easy and rapid EMG measurement from 52 male and 51 female college students, both sitting and standing. Several a posteriori analyses of variance revealed sex differences in the masseter, occipital, posterior cervical, upper trapezius, latissimus dorsi, and anterior tibialis. Similarly, there were side differences for the anterior temporalis, occipitalis, splenius capitus, trapezius, paraspinalis, and soleus. The analyses also revealed interactions among sex, position, and side for various measures on the trapezius. The data show that females tend to muscle brace more than males in the upper extremities. The study provides data for normative comparisons and helps to plan and interpret future EMG studies.

Significance of EMG surface electrode placement models and headache findings.

SYNOPSISShould muscle contraction headache be measured and treated from the traditional bifrontal muscle sites? Fivestudies report significant positive correlations between headache parameters and frontalis surfaceelectromyogram (EMG) levels. In contrast, four sets of authors who analyzed the relationship failed to find asignificant relationship.The purpose of this study is to investigate whether headache and nonheadache EMG levels in chronic musclecontraction headache patients were higher than in nonheadache‐matched controls using both conventional andmore inclusive EMG electrode placement sites.Twenty‐five patients experiencing chronic muscle contraction headache (experimental group) and twenty‐fiveage‐matched nonheadache subjects (control group) comprised this study. Experimental group subjects weremonitored twice while having a headache and twice while not having headache prior to beginning therapy. Datafrom the experimental group were compared with that of the control group who indicated “seldom if everexperiencing headache.” EMG data were collected and statistically compared using the conventional bifrontalmodel, the Cram‐Scan model and a Schwartz‐Mayo profiling method on all persons in this study.Results indicate the Schwartz‐Mayo placement followed by the Cram‐Scan model were superior indisciminating between the headache and nonheadache groups. The most conclusive finding is that the bifrontalplacement model appears antiquated in its ability to provide meaningful diagnostic information and may not besufficient for patient assessment and efficient therapy. Determining the existence of muscle contraction andmodes of treatment may be more effectively reached using multisite EMG monitoring rather than the traditionalbifrontal placement.

Application of EMG biofeedback to patients with mandibular dysfunction. Part 2. Validity of frontal EMG biofeedback

The purpose of this study was to investigate the mean integral EMG level of the masseter muscle, which was obtained from the EMG biofeedback of the frontal muscle of those patients whom once had a case of mandibular dysfunction, and to use this as an effective means of treatment. Furthermore, the correlation between the psychological characteristics of mandibular dysfunction patients and EMG biofeedback of the frontal muscle were examined.Results showed;1. EMG biofeedback of the frontal muscle of a normal group to decrease in mean integral EMG level of the masseter muscle, indicating that it was controllable and a learned effect.2. Patients whom once had a case of mandibular dysfunction also showed similar results, but its inhibitory effect was not to the extent of the normal group.3. When patients were further divided into those having psychological problems and those who have not'a decrease in the mean integral EMG level of the masseter muscle after Biofeedback Training and a low and stable EMG level even before BFT that did not vary between and during the session were observed.The findings above, thus suggest a clinical value for EMG biofeedback of the frontal muscle of mandibular dysfunction patients.

Detection of noncontingent feedback in EMG biofeedback.

Noncontingent feedback is frequently used as a placebo control procedure in biofeedback research. Researchers, however, have criticized this procedure for lacking credibility because of easy detection. The present study examined detection of false feedback in biofeedback with EMG. Contingent feedback (CF), truly random false feedback (FF), and controlled false feedback (CFF) groups were compared for changes in EMG levels, report of inaccurate feedback, and report of learning muscle activity reduction. The results indicated that FF procedures are easily detected; therefore, difference found between the FF and CF groups may be influenced by extraneous variables. The CFF group did not detect false feedback, but subjects reported some suspicions in later trials. With more trials, CFF may have also been detected. These results indicate a need for more attention to appropriate placebo control procedures in evaluating the parameters and efficacy of biofeedback.

Relaxation training affects success and activation on a teaching test

We studied the effects of an audiocassette-relaxation training period (ART) and its timing on success at a teaching test (lecture type), on observed tension and on a number of physiological responses. The electrical activity of the upper trapezius muscle (EMG), heart rate (HR) and blood pressure (BP), of female and male instructor candidates, were examined before, during and after the teaching test as well as during its critique. The relaxation period (18 min) was presented either on the preceding night (ARTnt) or immediately before the teaching test (ARTimm). The influence of personality (types A-B and extrovert-introvert) was also studied. ART improved success at the teaching test in both sexes. In males (but not in females), ARTimm decreased EMG level during the test, but ARTnt increased EMG at the test period as compared to the control group. In females, both ARTnt and ARTimm lowered HR more than in the control group. ARTimm lowered systolic BP in both sexes. Personality types affected the ART responses; ART was more beneficial for type A than B subjects.

Progressive relaxation as a function of procedural variations and anxiety level

Progressive relaxation is subject to many procedural variations. Although most investigators follow the 5-7 s tension interval advocated by Bernstein and Borkovec (1973), longer tension intervals may contribute to greater relaxation effects. This study compared tension intervals of 5, 15, and 45 s. Since the development of control over muscle tension requires attention to feedback signals, a focus on internal proprioceptive sensations was contrasted with an external condition in which the subjects silently subtracted numbers immediately following the tension-release cycle. Longer periods of tension resulted in lower EMG levels, with the 45-s tension interval producing the greatest relaxation. Those individuals who focused on physiological sensations during training were able to achieve greater levels of relaxation after the training phase was completed. There was a significant interaction between tension interval duration and focusing; subjects in the 45-s interval who focused on physiological functioning showed the greatest arousal reduction. Anxiety level did not differentially influence the effects of procedural variations in training. Clearly, additional parametric studies in relaxation training are needed.

Intensity and character of pain and muscular activity levels elicited by maintained extreme flexion position of the lower-cervical-upper-thoracic spine : Harms-Ringdahl K. Ekholm J, Scand J Rehabil Med 1986; 18: 117–126

The aim of this study was to find out whether maintained extreme flexion position of the lower-cervical-upper-thoracic spine in a sitting posture could induce pain, and thus possibly play a role in work related disorders with cervico-brachial pain. Ten healthy subjects assessed pain intensity of experimentally-induced pain on a Visual Analogue Scale (VAS). The quality and location of the pain was indicated on a drawing of the body. The load moment induced by the weight of the head-and-neck was calculated. The EMG activity levels were recorded from the splenius, thoracic erector spinae-rhomboid, and descending part of trapezius muscles. This posture, which resembles the posture in some common work, caused pain in all subjects. The pain was experienced within 15 min, increased with time, disappeared within 15 min after the end of provocation, but was again experienced by nine subjects the same evening or next morning and lasted up to four days. The primary location was in the dorsal part of the lower cervical and upper thoracic spine; three subjects also reported pain in the arms and one in the head. The recorded EMG levels were very low, but they increased somewhat during provocation. It is suggested that thorough recordings of work postures should be included in ergonomic analyses to provide a basis for the avoidance of such positions which might provoke pain.

Psychophysiologic response patterns in tension headache: effects of tricyclic antidepressants.

Tension headache (TH) and control subjects (n = 22, 11 in each group) were evaluated within a habituation experimental design, in which psychophysiologic responses to auditory stimulation were measured. Auditory stimuli were 20 80-dB, 1000-Hz tones, each lasting 2 sec and sounded at irregular intervals. Subjects were evaluated twice, with a 6-month interval. At the time of the first session TH subjects were being treated with tricyclic antidepressant, yielding a positive clinical effect. Medication was withdrawn 3 weeks before the second session. Phasic responses in heart rate and temporal artery pulse amplitudes and averaged EMG levels from the frontal muscles were measured. Significantly lower heart rate reactivity and significantly less pronounced left temporal artery pulse amplitude responses were found in non-medicated TH subjects than in controls. TH patients showed a pulse amplitude increase in response to stimulation, whereas control subjects showed a decrease. The pulse amplitude response pattern was normalized in medicated TH patients. EMG levels were similar in TH patients and controls when patients were receiving medication, whereas TH patients showed significantly higher frontal EMG levels than control when medication had been withdrawn.

EMG biofeedback in the treatment of tinnitus: An experimental evaluation

Abstract Twenty-six tinnitus patients received either EMG biofeedback with counterdemand instructions, EMG biofeedback with neutral demand instructions or no treatment. Assessment was conducted on self-report measures of the distress associated with tinnitus, the loudness, annoyance and awareness of tinnitus, sleep-onset difficulties, depression and anxiety. Audiological assessment of tinnitus was also conducted and EMG levels were measured (the latter only in the two treatment groups). No significant treatment effects were found on any of the measures. There was a significant decrease in the ratings of tinnitus awareness over the assessment occasions, but the degree of change was equivalent for treated and untreated groups. The results do not support the assertion that EMG biofeedback is an effective treatment for tinnitus. It is recommended that future research be directed towards the evaluation of broader treatment approaches.

Soleus muscle electromyographic activity and ankle dorsiflexion range of motion during four stretching procedures.

Volitional muscle contractions are used frequently in some combination with muscle stretching to promote muscle relaxation and to increase range of motion. In this study, muscle lengthening procedures were evaluated in the ankle plantar flexors. Four soleus muscle stretching procedures--static stretch (SS), hold relax (HR) (isometric plantar flexor contraction before stretch), agonist contract (AC) (dorsiflexor contraction assisting stretch), and hold relax-agonist contraction (HR-AC)--were performed in the sagittal plane by 12 physically active adults. The dorsiflexion angle, soleus muscle electromyogram, and soleus muscle motoneuron excitability as determined by the Hoffmann-reflex (H-reflex) amplitude were measured throughout the duration of each stretch. The range of dorsiflexion achieved at the end of the stretch did not differ significantly between stretching procedures, although in 8 of the 12 subjects and in the subject group as a whole, the AC and HR-AC procedures were associated with higher levels of soleus muscle EMG than the levels in the SS and HR procedures (p less than .01). The H-reflex amplitudes during the AC and HR-AC procedures were smaller than the amplitudes during the SS and HR procedures (p less than .001), suggesting the possibility of reciprocal inhibition during the agonist contraction. Increased tonic EMG levels produced by input from other neural pathways affecting alpha motoneurons in the AC and HR-AC procedures may have masked this inhibitory reflex. In healthy adults, a complicated procedure, involving muscle contractions for decreasing active resistance to stretch, may be unnecessary because active resistance to stretch is minimal and muscle relaxation during stretch appears to have little or no direct effect on the ROM achieved.

Long-term peripheral nerve and muscle recordings from normal and dystrophic mice

A method for long-term recording of electrical activity from small mammalian nerves and muscles is described. Electrodes for stimulating and recording activity were implanted on nerves and muscles subserving ankle flexion and extension in normal and dystrophic mice. Activity was monitored on a regular basis for up to 200 days following implantation. Neural compound action potentials, compound EMG potentials and twitch tension were recorded. Shortly after implantation, evoked EMG and twitch tension declined, but recovered progressively to values measured at the time of implantation and subsequently remained steady in normal mice. However, while dystrophic mice did recover, with EMG levels reaching 50-60% of the values recorded at implantation, tension eventually dropped to 10% in flexor muscles and 25% in extensors.

Nocturnal electromyographic evaluation of masseter muscle activity in the complete denture patient

Nocturnal oral activity was evaluated in 12 complete denture wearers by means of EMG measurements of the masseter muscle. Patients who had worn dentures for at least 6 months were selected. EMG levels were compared when subjects slept with and without the dentures in the mouth. Three subjects appeared to have reduced EMG values when sleeping with the dentures. However, no overall group trends or significant differences were obtained. High variability in nightly EMG values could not be explained by a post hoc analysis of patient oral symptoms or denture characteristics. Efforts should be directed at improved methodology to study the specific mechanism of the effect of denture wearing on nocturnal muscle activity levels. Additional knowledge is needed on the occurrence and effects of parafunctional habits in the edentulous patients.

Reliability of lumbar paravertebral EMG assessment in chronic low back pain.

The reliability of lumbar paravertebral EMG assessment was investigated in a sample of 70 patients with chronic low back pain, (CLBP). Dual-site EMG monitoring was employed during both static postures and movements. Flexion and rotation indices were divided to assess the reliability of patterning of paravertebral EMG during movement. Within-session reliabilities computed for the full sample ranged from 0.66 to 0.97, and between-session reliabilities, computed on a subset of 29 patients retested after varying intervals, ranged from 0.26 to 0.92. Average EMG levels, flexion, and rotation indices showed no statistically significant differences between surgical (n = 40) and nonsurgical patients (n = 30), although EMG variability was consistently greater for surgical patients across the postures and movements. These results indicate that lumbar paravertebral EMG can be reliably measured and therefore has potential utility as an assessment and treatment variable in CLBP.

Ocular and stabilization feedback: an evaluation of two EMG biofeedback control procedures.

This study evaluated the adequacy of two novel EMG biofeedback control procedures. During a single training session, 36 subjects received either contingent EMG feedback from the frontal region (Veridical), contingent feedback for vertical eye movements (Ocular), or a feedback condition where the signal increased with deviations in any direction from baseline EMG levels (Stabilization). The results supported the use of Ocular but not Stabilization feedback as a control procedure in frontalis EMG biofeedback studies. Ocular feedback did not produce reductions in frontalis EMG but did lead to changes in subjective measures of nonspecific treatment effects that were at least comparable to those obtained with Veridical feedback. Stabilization subjects produced small but significant reductions in EMG, felt the most bored as a result of their feedback training, and were the most likely to rate themselves as having received false feedback. The implications of attribution theory and multiprocess relaxation theory for the evaluation of nonspecific treatment effects are discussed.

Physiological changes after biofeedback and relaxation training for multiple-pain tension-headache patients.

This paper is concerned with the psychophysiology of "muscle-contraction" headaches in a group of Compensation patients suffering from multiple pain problems in addition to headaches. A total of 55 of these patients were divided into 4 groups which received frontalis EMG biofeedback, relaxation training, combined biofeedback-relaxation training, or no treatment. Differences were observed among the 3 experimental treatments and the control group with respect to headache changes, but there were no differences among groups with respect to the changes observed in four underlying physiological responses as a function of time or practice. While the subjects who showed the largest changes in headache characteristics were those who exhibited the largest decreases in frontalis EMG, these were also the subjects whose initial frontalis EMG levels were the highest. It is concluded that, in keeping with a growing literature, the link between frontalis EMG and "muscle-contraction" headaches is a tenuous one and that the changes brought about in headache symptomatology through biofeedback or relaxation training are most likely attributable to a generalization of feelings of mastery over the environment or of self-efficacy brought about in the subjects through apparent success at the task.

Intensity and character of pain and muscular activity levels elicited by maintained extreme flexion position of the lower-cervical-upper-thoracic spine

The aim of this study was to find out whether maintained extreme flexion position of the lower-cervical-upper-thoracic spine in a sitting posture could induce pain, and thus possibly play a role in work related disorders with cervico-brachial pain. Ten healthy subjects assessed pain intensity of experimentally-induced pain on a Visual Analogue Scale (VAS). The quality and location of the pain was indicated on a drawing of the body. The load moment induced by the weight of the head-and-neck was calculated. The EMG activity levels were recorded from the splenius, thoracic erector spinae-rhomboid, and descending part of trapezius muscles. This posture, which resembles the posture in some common work, caused pain in all subjects. The pain was experienced within 15 min, increased with time, disappeared within 15 min after the end of provocation, but was again experienced by nine subjects the same evening or next morning and lasted up to four days. The primary location was in the dorsal part of the lower cervical and upper thoracic spine; three subjects also reported pain in the arms and one in the head. The recorded EMG levels were very low, but they increased somewhat during provocation. It is suggested that thorough recordings of work postures should be included in ergonomic analyses to provide a basis for the avoidance of such positions which might provoke pain.

On hip and lumbar biomechanics A study of joint load and muscular activity

Loading moment of force about the hip and lumbo-sacral joints during straight and flexed knee lifting was calculated at regular intervals during the lifts, using a computerized sagittal plane model. Lift with flexed knees and burden moved close to the body was found to induce lower load. Important parameters influencing the induced joint load are discussed. EMG levels from three trunk and seven hip muscles were recorded with surface electrodes and normalized, i.e. expressed as a percentage of the recorded level of each muscle during an isometric voluntary contraction. The erector spinae, gluteus maximus and adductor magnus muscles were more activated initially in the flexed knee lifts than in the straight knee lift, while the hamstrings were more and earlier activated in the flexed knee lifts. In order to estimate what proportion of the maximum hip extensor muscle moment was used to counteract the induced load moments about the hip, assessments of maximum hip extensor muscle moments were made: the highest extensor muscle moment was exerted at 90 degrees hip flexion, decreasing with decreasing hip angle. The knee angle did not significantly influence the muscle moments exerted by the hip extensor muscles. To calculate the magnitude and direction of the hip compressive load from known load moments, the length of the moment arms of three hip extensors was determined at every fifth degree of flexion at hip flexion angles between 0 degrees and 90 degrees by combining data from autopsy specimens and patients, the latter examined by computed tomography. There were significant differences in moment arm length between men and women but there was low correlation between subject's height and length of muscular moment arms. The calculated compressive force during the lifts was about three times body weight and the direction of the compressive force passed through the area described by others as having the most severe osteoarthrotic lesions on the femoral head. Hip joint load moments and normalized EMGs from five hip muscles were assessed during rising exercises for the lower limb in order to determine to what extent joint load and EMG is influenced by adaptive adjustments of the exercise. A multicomponent force-measuring platform and pictures on cine-film were used in the calculations of load moments. Posterior foot position lowered the load moment and slightly increased the level of muscular activity in the hip extensors. The design and use of a force prediction diagram for estimating induced hip extensor muscular forces is described.(ABSTRACT TRUNCATED AT 400 WORDS)

The use of bilateral EMG equalization training in the treatment of temporomandibular joint dysfunction—A case report

This paper describes a single-subject experiment testing two methods of using EMG biofeedback in the treatment of TMJ dysfunction. Following a baseline period, electrodes were placed on the left and right masseter muscles, and the subject was taught general relaxation of this area using visual biofeedback. Although data supported the conclusion that the subject had indeed learned to relax, this was not associated with any change in the report of pain or dysfunction. Equalization training, the goal being to equalize the levels of EMG in the right and left masseter muscles, was then begun. Once the patient had learned to maintain equal levels of EMG, relaxation was then re-introduced. This produced substantial decreases in her reported pain, both within the session and averaged across days for the time between sessions. These treatment gains were maintained at 2-month follow-up.

Palatoglossus activity during oral/nasal vowels of Hindi

Palatoglossus EMG potentials and voice were recorded while a native speaker of Hindi produced CVC nonsense utterances where C was /s/ and V was one of the vowels /iιeɛəɑɔoɷu,ĩι̃ẽɛ̃ə̃ɑ̃õñɷ̃Ũ/. Preliminary results show low levels of EMG activity for the front oral vowels, whereas for the central and back oral vowels the EMG activity is considerable. All nasal vowels exhibit a high level of EMG activity, except /ẽ, ɛ̃/ for which the EMG activity is minimal. EMG levels for the central and back nasal vowels are considerably higher than those for the front nasal vowels. EMB levels for the nasal vowels /õ, ñ, ɷ̃, Ũ/ are comparable to those for the oral vowels /ɔ, o, ɷ, u/, respectively. However, the EMG levels for the nasal vowels /ĩ, ι̃, ə̃, ã/ are considerably greater than for the comparable oral vowels /i, ι, ə, ɑ/. Furthermore, the patterns of EMG potentials for the long vowels differ from those for the short vowels irrespective of their being oral or nasal. [Work supported by NIH Grant NS-13617 and BRS Grant PR-05596 to Haskins Laboratories.]

Task performance and electromyopotential as functions of task difficulty and EMG feedback.

The dearth of empirical research in the application of biofeedback is discussed. Exp. 1 assessed relationships among biofeedback EMG training, EMG levels, cognitive task performance, and task difficulty. 72 subjects (male or female college students) were administered 1 trial on an iconic memory task with either EMG audio feedback, sham EMG audio feedback, or no feedback. Three levels of task difficulty were used. One 20-min. training session significantly lowered EMG responses, and task performance was inversely related to task difficulty. No relationship between EMG level and task performance was observed. Exp. 2 investigated the effect of increased EMG responses on cognitive task performance for one level of difficulty. One biofeedback training session did not significantly increase frontalis EMG, and there was no relationship between increased EMG and task performance.