Saturated Fatty Acid-Induced Insulin Resistance Is Associated With Mitochondrial Dysfunction in Skeletal Muscle Cells

Increased plasma levels of free fatty acids (FFA) occur in states of insulin resistance such as obesity and type 2 diabetes mellitus. These high levels of plasma FFA are proposed to play an important role for the development of insulin resistance but the mechanisms involved are still unclear. This study investigated the effects of saturated and unsaturated FFA on insulin sensitivity in parallel with mitochondrial function. C2C12 myotubes were treated for 24 h with 0.1 mM of saturated (palmitic and stearic) and unsaturated (oleic, linoleic, eicosapentaenoic, and docosahexaenoic) FFA. After this period, basal and insulin-stimulated glucose metabolism and mitochondrial function were evaluated. Saturated palmitic and stearic acids decreased insulin-induced glycogen synthesis, glucose oxidation, and lactate production. Basal glucose oxidation was also reduced. Palmitic and stearic acids impaired mitochondrial function as demonstrated by decrease of both mitochondrial hyperpolarization and ATP generation. These FFA also decreased Akt activation by insulin. As opposed to saturated FFA, unsaturated FFA did not impair glucose metabolism and mitochondrial function. Primary cultures of rat skeletal muscle cells exhibited similar responses to saturated FFA as compared to C2C12 cells. These results show that in muscle cells saturated FFA-induced mitochondrial dysfunction associated with impaired insulin-induced glucose metabolism. J. Cell. Physiol. 222: 187-194, 2010. (C) 2009 Wiley-Liss, Inc.

Morphological aspects of rabbit masseter muscle after cervical sympathectomy

The objective of this paper was to study the effect of sympathetic innervation on morphological and histochemical aspects of skeletal muscle tissue. Rabbit masseter muscle was studied using histochemical and immunohistochemical methods for periods of up to 18 months post-sympathectomy. The morphological and enzymatic characteristics of control masseter muscles were similar on both the left and right sides. The main features were muscle fibres with a mosaic pattern and a predominance of type IIa fibres, followed by type I. Type IIb fibres showed very low frequency. Sympathectomized animals showed varying degrees of metabolic and morphological alterations, especially 18 months after sympathectomy. The first five groups showed a higher frequency of type I fibres, whilst the oldest group showed a higher frequency of type lib fibres. In the oldest group, a significant variation in fibre diameter was observed. Many fibres showed small diameter, atrophy, hypertrophy, splitting, and necrosis. Areas with fibrosis were observed. Thus cervical sympathectomy induced morphological alterations in the masseter muscles. These alterations were, in part, similar to both denervation and myopathy. These findings indicate that sympathetic innervation contributes to the maintenance of the morphological and metabolic features of masseter muscle fibres.

Maximal clenching effort influence on the electromyographic activity of the trapezius muscle in healthy subjects

Alteration of the occlusion and the position of the jaw can affect the muscles of the neck, due to a relationship between the masticatory and cervical systems. Thus, the objective of this study was to verify whether the bite in maximal clenching effort, in centric occlusion, in individuals with clinically normal occlusion, and without a history of dysfunction in the masticatory system, influences the electromyographic activity of the upper trapezius muscle. A total of 19 normal individuals participated in the study, 14 of which were women (average age of 25.4 ± 4.14 years), and 5 were men (average age of 24.11 ± 3.28 years). The root mean square (RMS) amplitude and median frequency (MF) of the upper trapezium muscle with 40% and 60% of maximal voluntary contraction were analyzed under pre- and post-maximal clenching effort conditions in centric occlusion. The electromyographic signal was collected with a sampling frequency of 2. kHz and the value in RMS was obtained by a moving window of 200. ms. The paired Student's t-test was used to compare RMS amplitude and MF under pre- and post-maximal clenching effort conditions. The level of significance for each comparison was set to p<0.05. This study concluded that in individuals without a history of dysfunction of the masticatory system, maximum clenching effort in centric occlusion does not alter the electromyographic signal of the upper trapezius. © 2009 Elsevier Ltd.

Clinical assessment of the efficacy of low-level laser therapy on muscle pain in women with temporomandibular dysfunction, by surface electromyography

The use of low-level laser (LLL) may be an useful tool to promote reduction of muscular pain caused by TMD. Aim: This study evaluated the immediate efficacy of low-level laser therapy on women reporting pain and diagnosed with temporomandibular dysfunction (TMD). Methods: Diode laser (GaAlAs) at 790 nm wavelength (infrared spectrum) was applied as experimental treatment. Irradiations of 1.5 J/cm2 were made at 4 points of the temporomandibular joint (TMJ) and of 3 J/cm2 at 3 points in the temporal muscle. An electromyographic (EMG) evaluation of the masseter and anterior temporal was done at the following intervals: before, immediately after, 5 min and 20 min after laser application. Results: Comparison of the electrical activity at the times of measurement revealed a statistically significant difference in masseter muscles before (P=0.025) and immediately after (P=0.013) LLLT. Conclusions: Both masseter and temporal muscles showed a reduction in the measured EMG activities at all times after LLLT, and the temporal muscle showed higher EMG activity than the masseter muscle at all the evaluation times. LLLT caused significant immediate relaxation of the masseter muscles.

Morphological aspects of rabbit masseter muscle after cervical sympathectomy

The objective of this paper was to study the effect of sympathetic innervation on morphological and histochemical aspects of skeletal muscle tissue. Rabbit masseter muscle was studied using histochemical and immunohistochemical methods for periods of up to 18 months post-sympathectomy. The morphological and enzymatic characteristics of control masseter muscles were similar on both the left and right sides. The main features were muscle fibres with a mosaic pattern and a predominance of type IIa fibres, followed by type I. Type IIb fibres showed very low frequency. Sympathectomized animals showed varying degrees of metabolic and morphological alterations, especially 18 months after sympathectomy. The first five groups showed a higher frequency of type I fibres, whilst the oldest group showed a higher frequency of type IIb fibres. In the oldest group, a significant variation in fibre diameter was observed. Many fibres showed small diameter, atrophy, hypertrophy, splitting, and necrosis. Areas with fibrosis were observed. Thus cervical sympathectomy induced morphological alterations in the masseter muscles. These alterations were, in part, similar to both denervation and myopathy. These findings indicate that sympathetic innervation contributes to the maintenance of the morphological and metabolic features of masseter muscle fibres.

Muscle membrane dysfunction in critical illness myopathy assessed by velocity recovery cycles

To test the hypothesis that muscle fibers are depolarized in patients with critical illness myopathy by measuring velocity recovery cycles (VRCs) of muscle action potentials.

Myostatin dysfunction is associated with reduction in overload induced hypertrophy of soleus muscle in mice

Acknowledgements This project was also supported by Marie Curie International Reintegration Grant 249156 (A. Lionikas) and the grants VP1-3.1-SMM-01-V-02-003 (A. Kilikevicius) and MIP-067/2012 (T. Venckunas) from the Research Council of Lithuania as well as the grant from the Ministry of Higher Education of Saudi Arabia (Y. Alhind). We wish also to thank Mrs Indre Libnickiene for her excellent technical assistance provided during the project

Patients with chronic neck pain demonstrate altered patterns of muscle activation during performance of a functional upper limb task

Study Design. Cross-sectional study. Objective. This study compared neck muscle activation patterns during and after a repetitive upper limb task between patients with idiopathic neck pain, whiplash-associated disorders, and controls. Summary of Background Data. Previous studies have identified altered motor control of the upper trapezius during functional tasks in patients with neck pain. Whether the cervical flexor muscles demonstrate altered motor control during functional activities is unknown. Methods. Electromyographic activity was recorded from the sternocleidomastoid, anterior scalenes, and upper trapezius muscles. Root mean square electromyographic amplitude was calculated during and on completion of a functional task. Results. A general trend was evident to suggest greatest electromyograph amplitude in the sternocleidomastoid, anterior scalenes, and left upper trapezius muscles for the whiplash-associated disorders group, followed by the idiopathic group, with lowest electromyographic amplitude recorded for the control group. A reverse effect was apparent for the right upper trapezius muscle. The level of perceived disability ( Neck Disability Index score) had a significant effect on the electromyographic amplitude recorded between neck pain patients. Conclusions. Patients with neck pain demonstrated greater activation of accessory neck muscles during a repetitive upper limb task compared to asymptomatic controls. Greater activation of the cervical muscles in patients with neck pain may represent an altered pattern of motor control to compensate for reduced activation of painful muscles. Greater perceived disability among patients with neck pain accounted for the greater electromyographic amplitude of the superficial cervical muscles during performance of the functional task.

Neck flexor muscle fatigue is side specific in patients with unilateral neck pain

Despite the evidence of greater fatigability of the cervical flexor muscles in neck pain patients, the effect of unilaterality of neck pain on muscle fatigue has not been investigated. This study compared myoelectric manifestations of sternocleidomastoid (SCM) and anterior scalene (AS) muscle fatigue between the painful and non-painful sides in patients with chronic unilateral neck pain. Myoelectric signals were recorded from the sternal head of SCM and the AS muscles bilaterally during sub-maximal isometric cervical flexion contractions at 25% and 50% of the maximum voluntary contraction (MVC). The time course of the mean power frequency, average rectified value and conduction velocity of the electromyographic signals were calculated to quantify myoelectric manifestations of muscle fatigue. Results revealed greater estimates of the initial value and slope of the mean frequency for both the SCM and AS muscles on the side of the patient's neck pain at 25% and 50% of MVC. These results indicate greater myoelectric manifestations of muscle fatigue of the superficial cervical flexor muscles ipsilateral to the side of pain. This suggests a specificity of the effect of pain on muscle function and hence the need for specificity of therapeutic exercise in the management of neck pain patients. (C) 2003 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. All rights reserved.

Magnetic resonance imaging analysis of the upper cervical spine extensor musculature in an asymptomatic cohort: an index of fat within muscle

AIM: To establish a simple method to quantify muscle/fat constituents in cervical muscles of asymptomatic women using magnetic resonance imaging (MRI), and to determine whether there is an age effect within a defined age range. MATERIALS AND METHODS: MRI of the upper cervical spine was performed for 42 asymptomatic women aged 18-45 years. The muscle and fat signal intensities on axial spin echo T1-weighted images were quantitatively classified by taking a ratio of the pixel intensity profiles of muscle against those of intermuscular fat for the rectus capitis posterior major and minor and inferior obliquus capitis muscles bilaterally. Inter- and intra-examiner agreement was scrutinized. RESULTS: The average relative values of fat within the upper cervical musculature compared with intermuscular fat indicated that there were only slight variations in indices between the three sets of muscles. There was no significant correlation between age and fat indices. There were significant differences for the relative fat within the muscle compared with intermuscular fat and body mass index for the right rectus capitis posterior major and right and left inferior obliquus capitis muscles (p = 0.032). Intraclass correlation coefficients for intraobserver agreement ranged from 0.94 to 0.98. Inter-rater agreement of the measurements ranged from 0.75 to 0.97. CONCLUSION: A quantitative measure of muscle/fat constituents has been developed, and results of this study indicate that relative fatty infiltration is not a feature of age in the upper cervical extensor muscles of women aged 18-45 years. (C) 2005 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Effect of gaze direction on neck muscle activity during cervical rotation

Control of the neck muscles is coordinated with the sensory organs of vision, hearing and balance. For instance, activity of splenius capitis (SC) is modified with gaze shift. This interaction between eye movement and neck muscle activity is likely to influence the control of neck movement. The aim of this study was to investigate the effect of eye position on neck muscle activity during cervical rotation. In eleven subjects we recorded electromyographic activity (EMG) of muscles that rotate the neck to the right [right obliquus capitis inferior (OI), multifides (MF), and SC, and left sternocleidomastoid (SCM)] with intramuscular or surface electrodes. In sitting, subjects rotated the neck in each direction to specific points in range that were held statically with gaze either fixed to a guide (at three different positions) that moved with the head to maintain a constant intra-orbit eye position or to a panel in front of the subject. Although right SC and left SCM EMG increased with rotation to the right, contrary to anatomical texts, OI EMG increased with both directions and MF EMG did not change from the activity recorded at rest. During neck rotation SCM and MF EMG was less when the eyes were maintained with a constant intra-orbit position that was opposite to the direction of rotation compared to trials in which the eyes were maintained in the same direction as the head movement. The inter-relationship between eye position and neck muscle activity may affect the control of neck posture and movement.

Further evaluation of an EMG technique for assessment of the deep cervical flexor muscles

A novel surface electromyographic (EMG) technique was recently described for the detection of deep cervical flexor muscle activity. Further investigation of this technique is warranted to ensure EMG activity from neighbouring muscles is not markedly influencing the signals recorded. This study compared deep cervical flexor (DCF) muscle activity with the activity of surrounding neck and jaw muscles during various anatomical movements of the neck and jaw in 10 volunteer subjects. DCF EMG activity was recorded with custom electrodes inserted via the nose and fixed by suction to the posterior mucosa of the oropharynx. Surface electrodes were placed over the sternocleidomastoid, anterior scalene, masseter and suprahyoid muscles. Positioned in supine, subjects performed isometric cranio-cervical flexion, cervical flexion, right and left cervical rotation,jaw clench and resisted jaw opening. Across all movements examined, EMG amplitude of the DCF muscles was greatest during neck movements that would require activity of the DCF muscles, particularly during cranio-cervical flexion, their primary anatomical action. The actions of jaw clench and resisted jaw opening demonstrated significantly less DCF EMG activity than the cranio-cervical flexion action (p < 0.05). Across all other movements, the neighbouring neck and jaw muscles demonstrated greatest EMG amplitude during their respective primary anatomical actions, which occurred in the absence of increased EMG amplitude recorded from the DCF muscles. The finding of substantial EMG activity of the DCF muscles only during neck actions that would require their activity, particularly cranio-cervical flexion, and not during actions involving the jaw, provide further assurance that the majority of myoelectric signals detected from the nasopharyngeal electrode are from the DCF muscles. (C) 2005 Elsevier Ltd. All rights reserved.