Ageing and surface EMG activity patterns of masticatory muscles

P>The purpose of this study was to evaluate the influence of age on the electromyographic activity of masticatory muscles. All volunteers were Brazilian, fully dentate (except for Group I - mixed dentition), Caucasian, aged 7-80, and divided into five groups: I (7-12 years), II (13-20 years), III (21-40 years), IV (41-60 years) and V (61-80 years). Except for Group V, which comprised nine women and eight men, all groups were equally divided with respect to gender (20 M/20 F). Surface electromyographic records of masticatory muscles were obtained at rest and during maximal voluntary contraction, right and left laterality, maximal jaw protrusion and maximal clenching in the intercuspal position. Statistically significant differences (P < 0 center dot 05) were found in all clinical conditions among the different age groups. Considerably different patterns of muscle activation were found across ages, with greater electromyographic activity in children and youth, and decreasing from adults to aged people.

Activated satellite cells in medial rectus muscles of patients with strabismus

PURPOSE. The goal of this study was to determine whether the medial rectus muscles of patients with a history of medial rectus underaction or overaction show alterations in the process of satellite cell activation when compared with normal age-matched control muscles. METHODS. Medial rectus muscles were obtained with consent from adult patients undergoing surgical resection due to medial rectus underaction or overaction and were prepared for histologic examination by fixation and paraffin embedding. Control muscles were obtained from cornea donor eyes of adults who had no history of strabismus or neuromuscular disease. Cross sections were obtained and stained immunohistochemically for the presence of activated satellite cells, as identified by MyoD immunoreactivity, and the presence of the total satellite cell population, as identified by Pax7 immunoreactivity. The percentages of MyoD- and Pax7-positive satellite cells per 100 myofibers in cross section were calculated. RESULTS. As predicted from results in the literature, MyoD-positive satellite cells, indicative of activation, were present in both the control and resected muscles. In the underacting medial rectus muscles, the percentages of MyoD- and Pax7-positive satellite cells, based on the number of myofibers, were approximately twofold higher than the percentages in the control muscles. In the overacting medial rectus muscles, the percentage of MyoD- positive satellite cells was twofold less than in the control muscles, whereas the percentage of Pax7-positive satellite cells significantly increased compared with that in the control specimens. CONCLUSIONS. The presence of an increased number of activated satellite cells in the resected underacting medial rectus muscles and the decreased numbers of activated satellite cells in the overacting muscles was unexpected. The upregulation in the number of MyoD- positive satellite cells in underacting muscles suggests that there is potential for successful upregulation of size in these muscles, as the cellular machinery for muscle repair and regeneration, the satellite cells, is retained and active in patients with medial rectus underaction. The decreased number of activated satellite cells in overacting MR muscle suggests that factors as yet unknown in these overacting muscles are able to affect the number of satellite cells and/or their responsiveness compared with normal age-matched control muscles. These hypotheses are currently being tested.

Degeneration of dystrophic or injured skeletal muscles induces high expression of Galectin-1

Muscle degenerative diseases such as Duchenne Muscular Dystrophy are incurable and treatment options are still restrained. Understanding the mechanisms and factors responsible for muscle degeneration and regeneration will facilitate the development of novel therapeutics. Several recent studies have demonstrated that Galectin-1 (Gal-1), a carbohydrate-binding protein, induces myoblast differentiation and fusion in vitro, suggesting a potential role for this mammalian lectin in muscle regenerative processes in vivo. However, the expression and localization of Gal-1 in vivo during muscle injury and repair are unclear. We report the expression and localization of Gal-1 during degenerative-regenerative processes in vivo using two models of muscular dystrophy and muscle injury. Gal-1 expression increased significantly during muscle degeneration in the murine mdx and in the canine Golden Retriever Muscular Dystrophy animal models. Compulsory exercise of mdx mouse, which intensifies degeneration, also resulted in sustained Gal-1 levels. Furthermore, muscle injury of wild-type C57BL/6 mice, induced by BaCl(2) treatment, also resulted in a marked increase in Gal-1 levels. Increased Gal-1 levels appeared to localize both inside and outside the muscle fibers with significant extracellular Gal-1 colocalized with infiltrating CD45(+) leukocytes. By contrast, regenerating muscle tissue showed a marked decrease in Gal-1 to baseline levels. These results demonstrate significant regulation of Gal-1 expression in vivo and suggest a potential role for Gal-1 in muscle homeostasis and repair.

Implant-supported prosthesis following Branemark protocol on electromyography of masticatory muscles

This research evaluated the effects of Branemark protocol on electromyography of the masseter and temporal muscles. The patients were divided into two groups: Group 1: patients who wore an implant-supported prosthesis in the mandibular arch following Branemark protocol, and maxillary removable complete dentures; Group II: dentate individuals (control). Electromyography was carried out at rest, right (RL) and left (LL) laterality, protrusion and maximum voluntary contraction (MVC). Data were compared by t-test. At rest, a higher electromyographic (EMG) activity was observed in Group I, and the values were significant in the right masseter and left temporal muscles. In RL, there were statistically significant differences for right masseter (P < 0.01), left masseter and temporal muscles and for the left temporal muscle in LL (P < 0.05). In protrusion, Group I presented a higher EMG activity, and there was a statistically significant difference for the right masseter muscle (RM) (P < 0.05). In MVC, the EMG values were higher in Group II (control), but significant just for the right temporal muscle (P < 0.05). In conclusion, individuals with mandibular fixed dentures supported according to the Branemark protocol and maxillary removable complete dentures showed a higher activity of masticatory muscles during the mandibular postural clinical conditions examined; however, in the MVC, Group I presented lower values when compared to dentate group. Despite presenting different EMG values in all of the clinical conditions, both groups showed similar EMG patterns of muscle activation which demonstrates that the proposed treatment can be considered as a good option for oral rehabilitation.

Immunolocalization of the 38.3 kDa calponin-like protein in stratified muscles of the tail of Schistosoma japonicum cercariae

Calponins are proteins present in vertebrate smooth musculature where they occur in association with thin myofilaments. Calponins are not present in vertebrate or invertebrate striated muscles. The blood fluke Schistosoma japonicum expresses a 38.3-kDa protein that bears substantial homology with vertebrate calponin and occurs entirely within smooth musculature of adults. Calponin-like immunoreactivity has been demonstrated in smooth muscles of many invertebrate phyla. The Schistosoma japonicum calponin has been localised in smooth myofibrils of adults where it is associated with myofilaments and sarcoplasmic reticulum. In this study, the ultrastructural localisation of the protein in muscles of S. japonicum cercariae is described. The protein is present in smooth muscles of the forebody and the stratified muscle of the tail. Within the stratified layer, the protein occurs predominantly in transverse arrays of sarcoplasmic reticulum. The localisation data suggest that the calponin-like protein of S. japonicum is involved in contraction of the stratified tail muscle. Furthermore, the presence of a calponin system in the stratified muscle suggests that this muscle is simply a superior form of muscle, closely related to smooth muscles that use a caldesmin-calponin system in contraction. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.

Influence of the menstrual cycle on the pressure pain threshold of masticatory muscles in patients with masticatory myofascial pain

Objective. The aim of this study was to investigate the influence of the menstrual cycle and oral contraceptive (OC) intake on the pressure pain threshold (PPT) of masticatory muscles in patients with masticatory myofascial pain (MFP). Study design. The sample was composed of 36 women, divided into 4 groups, according to the presence of MFP and the intake of OC (15 patients had MFP [7 taking OC] and 21 were pain-free controls [8 taking OC]). The algometer-based PPT of masseter and temporalis, and the record of subjective pain by visual analog scale (VAS) were determined during 2 consecutives menstrual cycles at 4 phases (menstrual, follicular, periovulatory, and luteal). A 3-way ANOVA for repeated measurements, Kruskal-Wallis, Friedman, and Dunn tests, with a 5% significant level analyzed the data. Results. PPT was significantly lower in MFP patients when compared with controls throughout the experiment (P < .001). The menstrual phases did not influence PPT (P > .05), while the intake of OC seems to raise PPT levels for the left temporalis (P = .01) and right masseter (P = .04). VAS was, in general, higher at the menstrual phase Conclusions. Different phases of the menstrual cycle have no influence on PPT values, regardless of the presence of a previous condition, as masticatory myofascial pain, while the intake of OC is associated with decreased levels of reported pain.

Back, chest and abdominal pain: How good are spinal signs at identifying musculoskeletal causes of back, chest or abdominal pain?

Background: Spinal signs found in association with atypical chest and abdominal pain may suggest the pain is referred from the thoracic spine. However, the prevalence of such signs in these conditions has rarely been compared with that in those without pain. In this study, the prevalence of spinal signs and dysfunction in patients with back, chest and abdominal pain is compared with that in pain free controls. The aim of the study is to determine the significance of spinal findings in patients with such pain. Methods: A general practitioner blinded to the patients' histories performed a cervical and thoracic spinal examination on general practice patients with back, chest and/or abdominal pain and on controls without pain. Thoracic intervertebral dysfunction was diagnosed on the basis of movement and palpation findings. Results: Seventy three study patients plus 24 controls, were examined. For cervical spinal signs, pain in the back, chest and/or abdomen was associated with pain with active movements and overpressure at end range and with loss of movement range. For thoracic spinal signs, this association held for pain with active movements and overpressure, but not with loss of movement range. The prevalence of thoracic intervertebral dysfunction was 25.0% in controls, 65.5% with chest/abdominal pain, 72.0% with back pain and 79.0% with back pain with chest/abdominal pain. This prevalence was higher with chest pain than with abdominal pain. Conclusions: The results show an association, but not a causal link between thoracic intervertebral dysfunction and atypical chest/abdominal pain. A spinal examination should be performed routinely assessing these conditions. The minimum examination for the detection of intervertebral dysfunction is testing for pain with spinal movements and palpation for tenderness. The interpretation of positive signs requires knowledge of their prevalence in pain free controls and in patients with visceral disease

Adult mouse intrinsic laryngeal muscles express high levels of the myogenic regulatory factor, MYF-5

The intrinsic laryngeal muscles display unique structural and functional characteristics that distinguish them from the skeletal muscle of the trunk and limbs. These features include relatively small muscle fibers, super-fast contraction speed, and fatigue resistance. The molecular basis of tissue-specific functions and other characteristics is differential gene expression. Accordingly, we have investigated the molecular basis of the functional specialization of the intrinsic laryngeal muscles by examining the expression of two key genes in the larynx, known to be important for skeletal muscle development and function: (a) the muscle regulatory factor, Myf-5, and (b) the superfast-contracting myosin heavy chain (EO-MyHC). We have found that the adult thyroarytenoid muscles express much higher levels of both Myf-5 and EO-MyHC messenger ribonucleic acid (mRNA), compared to lower hindlimb skeletal muscle where Myf-5 mRNA levels are very low and EO-MyHC is not detectable. These findings suggest that the unique functional characteristics of the intrinsic laryngeal muscles may be based in laryngeal muscle-specific gene expression directed by a unique combination of muscle regulatory factors. Such laryngeal muscle-specific genes may allow the future development of new treatments for laryngeal muscle dysfunction.

Postural control of the trunk in response to lateral support surface translations during trunk movement and loading

The postural response to translation of the support surface may be influenced by the performance of an ongoing voluntary task. This study was designed to test this proposal by applying lateral perturbations while subjects handled a load in the frontal plane. Measurements were made of medio-lateral displacement of the centre of pressure, angular displacement of the trunk and thigh in the frontal plane and intra-abdominal pressure. Subjects were translated randomly to the left and right in a variety of conditions that involved standing either quietly or with a 5 kg load in their left hand, which they were required either to hold statically or to lift or lower. The results indicate that when the perturbation occurred towards the loaded left side the subjects were able to return their centre of pressure, trunk and thigh rapidly and accurately to the initial position. However, when the perturbation occurred towards the right (away from the load) this correction was delayed and associated with multiple changes in direction of movement, suggesting decreased efficiency of the postural response. This reduced efficiency can be explained by a conflict between the motor commands for the ongoing voluntary task and the postural response, and/or by the mechanical effect of the asymmetrical addition of load to the trunk.

Repeatability of maximal voluntary force and of surface EMG variables during voluntary isometric contraction of quadriceps muscles in healthy subjects

The repeatability of initial values and rate of change of EMG signal mean spectral frequency (MNF), average rectified values (ARV), muscle fiber conduction velocity (CV) and maximal voluntary contraction (MVC) was investigated in the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles of both legs of nine healthy male subjects during voluntary, isometric contractions sustained for 50 s at 50% MVC. The values of MVC were recorded for both legs three times on each day and for three subsequent days, while the EMG signals have been recorded twice a day for three subsequent days. The degree of repeatability was investigated using the Fisher test based upon the ANalysis Of VAriance (ANOVA), the Standard Error of the Mean (SEM) and the Intraclass Correlation Coefficient (ICC). Data collected showed a high level of repeatability of MVC measurement (normalized SEM from 1.1% to 6.4% of the mean). MNF and ARV initial values also showed a high level of repeatability (ICC > 70% for all muscles and legs except right VMO). At 50% MVC level no relevant pattern of fatigue was observed for the VMO and VL muscles, suggesting that other portions of the quadriceps might have contributed to the generated effort. These observations seem to suggest that in the investigation of muscles belonging to a multi-muscular group at submaximal level, the more selective electrically elicited contractions should be preferred to voluntary contractions. (C) 2001 Elsevier Science Ltd. All rights reserved.

Repeatability of surface EMG variables in the sternocleidomastoid and anterior scalene muscles

In this study we examined the repeatability and reliability of the surface electromyographic (sEMG) signal mean frequency (MNF), average rectified value (ARV) and conduction velocity (CV) measured for the sternocleidomastoid (SCM) and the anterior scalene (AS) muscles in nine healthy volunteers during 15-s isometric cervical flexion contractions at 50% of the maximal voluntary contraction level over 3 non-consecutive days. Repeatability and reliability estimates were obtained for the initial values and rates of change of each sEMG variable by using both the Intraclass Correlation Coefficient (ICC) and the normalised standard error of the mean (nSEM). Results from SCM indicated good levels of repeatability for the initial value and slope of ARV (ICC > 65%). For the AS, high levels of repeatability were identified for the initial value of MNF (ICC > 70%) and the slope of ARV (ICC > 75%). Values of nSEM in the range 2.8-7.2% were obtained for the initial values of MNF and CV for both SCM and AS, indicating clinically acceptable measurement precision. The low value obtained for the nSEM of the initial value of MNF for the AS, in combination with the high ICC, indicates that of all of the variables examined, this variable could offer the best normative index to distinguish between subjects with and without neck pain, and represents the sEMG variable of choice for future evaluation purposes.

Location of innervation zones of sternocleidomastoid and scalene muscles - a basis for clinical and research electromyography applications

Objectives: Advances in surface electromyography (sEMG) techniques provide a clear indication that refinement of electrode location relative to innervation zones (IZ) is required in order to optimise the accuracy, relevance and repeatability of the sEMG signals. The aim of this study was to identify the IZ for the sternocleidomastoid and anterior scalene muscles to provide guidelines for electrode positioning for future clinical and research applications. Methods: Eleven volunteer subjects participated in this study. Myoelectric signals were detected from the sternal and clavicular heads of the stemocleidomastoid and the anterior scalene muscles bilaterally using a linear array of 8 electrodes during isometric cervical flexion contractions. The signals were reviewed and the IZ(s) were identified, marked on the subjects' skin and measurements were obtained relative to selected anatomical landmarks. Results: The position of the IZ lay consistently around the mid-point or in the superior portion of the muscles studied. Conclusions: Results suggest that electrodes should be positioned over the lower portion of the muscle and not the mid-point, which has been commonly used in previous studies. Recommendations for sensor placement on these muscles should assist investigators and clinicians to ensure improved validity in future sEMG applications. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.

Outcomes after trans-tibial amputation: The relationship between quiet stance ability, strength of the hip abductor muscles and gait

Background and Purpose Previous research regarding the symmetry of trans-tibial amputees has examined weight distribution and various gait parameters between prosthetic and sound limbs. However, to date, no known research has determined if asymmetry is present in the strength of the hip abductor muscles or if correlations exist between these categories of symmetry. The purpose of the present study was, therefore, to document asymmetry present in stance, strength and gait measures, and to determine the relationship between these variables. Method Twenty-three elderly, unilateral trans-tibial amputees stood on two adjacent forceplates whilst the weight distribution and standard deviation (SD) of the anterior-posterior and the medio-lateral centre of pressure excursion (COPE) under each limb was recorded during four 40 s trials: quiet stance (QS), with eyes open and eyes closed; and even stance (ES), with eyes open and eyes closed. Gait measures (velocity, cadence, step and stride lengths, stance:swing ratio and period of double support) over 10 m of fast, yet safe walking and measures of the strength of hip abductor muscles were also obtained by use of a stride analyser and a dynamometer, respectively. Results No significant differences were found between QS and ES measures. However, significantly more weight was taken on the sound limb than on the amputated limb. Notably, more anterior-posterior movement occurred under the sound limb than the amputated limb, with this becoming more apparent with the eyes closed. Movement in the medio-lateral direction was found to be the same between sides. No differences in muscle strength or gait measures between limbs were demonstrated. However. strong hip abductor muscles were correlated with increased weight-bearing on the amputated limb, improved gait parameters and reduced medio-lateral COPE under the amputated limb. Conclusions This research confirms the asymmetrical nature of amputee stance and demonstrates symmetry of strength and gait measures between limbs. The correlations between hip abductor muscle strength, weight distribution and gait measures illustrates the importance of pre- and postoperative training of these muscles. Copyright © 2002 Whurr Publishers Ltd.