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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Physiological and biochemical responses of skeletal muscle fibres to enhanced neuromuscular activity under conditions of maximum activation can be studied experimentally by chronic low-frequency stimulation of fast muscles. Stimulation-induced changes in the expression pattern of the rabbit fast skeletal muscle proteome were evaluated by two-dimensional gel electrophoresis and compared to the altered isoform expression profile of established transformation markers such as the Ca2+-ATPase, calsequestrin and the myosin heavy chain. Sixteen muscle proteins exhibited a marked change in their expression level. This included albumin with a 4-fold increase in abundance. In contrast, glycolytic enzymes, such as enolase and aldolase, showed a decreased expression. Concomitant changes were observed with marker elements of the contractile apparatus. While the fast isoforms of troponin T and myosin light chain 2 were drastically down-regulated, their slow counterparts exhibited increased expression. Interestingly, mitochondrial creatine kinase expression increased while the cytosolic isoform of this key muscle enzyme decreased. The expression of the small heat shock protein HSP-B5/alphaB-crystallin and the oxygen carrier protein myoglobin were both increased 2-fold following stimulation. The observed changes indicate that the conversion into fatigue-resistant red fibres depends on: (i) the optimum utilization of free fatty acids via albumin transportation, (ii) a rearrangement of the creatine kinase isozyme pattern for enhanced mitochondrial activity, (iii) an increased availability of oxygen for aerobic metabolism via myoglobin transport, (iv) the conversion of the contractile apparatus to isoforms with slower twitch characteristics and (v) the up-regulation of chaperone-like proteins for stabilising myofibrillar components during the fast-to-slow transition process.
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PMID:Differential expression of the fast skeletal muscle proteome following chronic low-frequency stimulation. 1614 47

Intraspinal microstimulation (ISMS), a novel rehabilitative therapy consisting of stimulation through fine, hair-like microwires targeted at the ventral spinal cord, has been proposed for restoring standing and walking following spinal cord injury. This study compared muscle recruitment characteristics of ISMS with those produced by peripheral nerve cuff stimulation (NCS). Thirty-three minutes of either ISMS or NCS at 1, 20 or 50 s(-1) and 1.2 x threshold (T) amplitude depleted glycogen from muscle fibres of vastus lateralis and rectus femoris. ISMS and NCS were also carried out at 20 s(-1) and 3.0T. Muscle serial sections were stained for glycogen and for myosin heavy chain (MHC)-based fibre types using a panel of monoclonal antibodies. The results of this study show that ISMS recruited fatigue-resistant (FR) fibres at 2.9, 1.9, 1.7 and 2.5 times their relative MHC content at 1, 20 and 50 s(-1) 1.2T and 20 s(-1) 3.0T, respectively. In contrast, NCS recruited FR fibres at 1.2, 1.0, 2.1 and 0.0 times their MHC content at 1, 20 and 50 s(-1) 1.2T and 20 s(-1) 3.0T, respectively. The proportion of FR fibres recruited by ISMS and NCS was significantly different in the 20 s(-1) 3.0T condition (P < 0.0001). We also report that force recruitment curves were 4.9-fold less steep (P < 0.019) for ISMS than NCS. The findings of this study provide evidence for the efficacy of ISMS and further our understanding of muscle recruitment properties of this novel rehabilitative therapy.
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PMID:Intraspinal microstimulation preferentially recruits fatigue-resistant muscle fibres and generates gradual force in rat. 1623 81

The purpose of this study was to establish if early chronic oral breathing could induce an ultra-structural adaptation of the diaphragm and orofacial muscles related to oral or nasal breathing. Therefore, we performed a bilateral nasal obstruction at day 8 on rat pups and the myosin heavy chain (MHC) composition of the muscles was analyzed at day 21. Nasal obstruction and the related switch to chronic oral breathing were associated with impaired growth, atrophy of olfactory bulbs, hypertrophy of adrenal glands and reduced muscle growth for all muscles studied except the diaphragm. Furthermore, we detected a smaller decrease of MHC 2b compared to MHC 2a and 2x in levator nasolabialis, a muscle involved with nasal breathing. In masseter superficialis and anterior digastric involved with oral breathing, we observed a smaller decrease of MHC 2a compared to MHC 2b or 2x, respectively. No difference was detected in the diaphragm MHC expression of oral breathing animals. Since the relative expression of fatigue resistant MHC fiber types increased in muscles involved with oral breathing, orofacial muscles seem to present a profile in MHC adapted to the transition from nasal to oral breathing, facilitating respiration.
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PMID:Myosin heavy chain expression and muscle adaptation to chronic oral breathing in rat. 1646 73

The absence of dystrophin and resultant disruption of the dystrophin glycoprotein complex renders skeletal muscles of dystrophic patients and dystrophic mdx mice susceptible to contraction-induced injury. Strategies to reduce contraction-induced injury are of critical importance, because this mode of damage contributes to the etiology of myofiber breakdown in the dystrophic pathology. Transgenic overexpression of insulin-like growth factor-I (IGF-I) causes myofiber hypertrophy, increases force production, and can improve the dystrophic pathology in mdx mice. In contrast, the predominant effect of continuous exogenous administration of IGF-I to mdx mice at a low dose (1.0-1.5 mg.kg(-1).day(-1)) is a shift in muscle phenotype from fast glycolytic toward a more oxidative, fatigue-resistant, slow muscle without alterations in myofiber cross-sectional area, muscle mass, or maximum force-producing capacity. We found that exogenous administration of IGF-I to mdx mice increased myofiber succinate dehydrogenase activity, shifted the overall myosin heavy chain isoform composition toward a slower phenotype, and, most importantly, reduced contraction-induced damage in tibialis anterior muscles. The deficit in force-producing capacity after two damaging lengthening contractions was reduced significantly in tibialis anterior muscles of IGF-I-treated (53 +/- 4%) compared with untreated mdx mice (70 +/- 5%, P < 0.05). The results provide further evidence that IGF-I administration can enhance the functional properties of dystrophic skeletal muscle and, compared with results in transgenic mice or virus-mediated overexpression, highlight the disparities in different models of endocrine factor delivery.
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PMID:Systemic administration of IGF-I enhances oxidative status and reduces contraction-induced injury in skeletal muscles of mdx dystrophic mice. 1662 99

The purpose of this study was to investigate whether creatine (Cr) supplementation during 12 weeks of phasic high-frequency voluntary wheel running would result in a faster myosin heavy chain (MHC) isoform profile in the rat mixed fast-twitch plantaris and alter its corresponding isometric contractile properties. The fast-twitch extensor digitorum longus and medial gastrocnemius and slow-twitch soleus were also studied. Forty weanling Sprague-Dawley male rats were assigned to one of four groups: creatine-sedentary (Cre-Sed); creatine-voluntary running (Cre-Run); control-sedentary (Con-Sed); control-voluntary running (Con-Run). Daily running distance was similar between Cre-Run and Con-Run. Average daily Cr ingestion was also similar being 2.4+/-0.17 and 3.0+/-0.14 g/kg in Cre-Sed and Cre-Run, respectively. Total creatine (TCr) content was elevated (P<0.03) in the plantaris of Cre-Run [211.4+/-16.9 mmol/kg dry weight (dw)], compared with Con-Run (175.1+/-5.69). In the plantaris, MHCIIb was 13% greater (P<0.00001) in Cre-Run compared with Con-Run, while MHCIId/x and MHCIIa were lower in Cre-Run by 7 and 6% (P<0.0002), respectively. No differences were observed in twitch force, time-to-peak tension, half-rise time or half-fall time. Greater tetanic force production (P<0.05) in Cre-Sed compared with Con-Sed corresponded to a 12% increase in MHCIId/x (P<0.0001) and a 12% decrease in MHCIIb (P<0.0006). The fatigue index of the plantaris at 10 s (FI(10s)) was reduced only after running (Cre-Run vs Con-Run), while in all other muscles the FI(10s) was lower only in the Cre-Sed group. In conclusion, Cr supplementation had differential effects on MHC isoform content and fatigability that depended on the level of contractile activity. Cr feeding combined with running exercise resulted in a faster MHC-based phenotype in the rat plantaris but the impact on associated isometric contractile properties was minimal.
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PMID:Effects of long-term creatine feeding and running on isometric functional measures and myosin heavy chain content of rat skeletal muscles. 1668 65

Previously, we showed that artificial rearing using the "pup in a cup" model results in decreased tongue activity and caused some minor alterations in the tongue retrusor musculature. However, the artificial rearing time frame previously chosen was brief (11 days). The purpose of the present investigation was to extend the artificial rearing period from postnatal days 3 to 21 (P21) to determine whether significant alterations occur as a result of this reduced tongue use. Several changes in contractile properties due to the artificial rearing process were observed, which fully recovered by postnatal days 41 to 42 (P41-2). These changes included a shorter twitch contraction time, shorter twitch half-relaxation time, and decreased fatigue resistance. Styloglossus muscle exhibited more neonatal myosin heavy chain (MHC) isoform at P21 for the artificially reared (AR) group. Changes that were persistent at P41-2 were also observed. Maximum tetanic tension was lower for the AR group at P21 and P41-2 compared with their dam-reared counterparts. Twitch tension was also lower by P41-2 in the AR group. At P41-2, the AR group exhibited an increase in MHC IIa and a decrease in MHC IIb for the styloglossus muscle. In addition, the AR group exhibited a decreased MHC IIb for the long head of the biceps brachii at P41-2. Our results are similar to other models of hindlimb immobilization and suspension. By extending our artificial rearing period, this reduced tongue activity induced acute changes and alterations in the tongue retrusor musculature that persisted into early adulthood.
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PMID:Contractile properties and myosin heavy chain composition of rat tongue retrusor musculature show changes in early adulthood after 19 days of artificial rearing. 1680 31

Discovering approaches to maintain or improve muscle function (fatigue resistance) in patients with cachexia, postoperative weakness, and sarcopenia is of clinical importance. beta(2)-Agonist treatment increases muscle mass, yet it alters fiber proportions such that the net consequences on muscle function remain unclear. In the present study, we focus on the contractile and metabolic consequences of chronic treatment with the beta(2)-agonist prodrug BRL-47672 (BRL). Gastrocnemius-plantaris-soleus (GPS) muscles were harvested at rest and studied for fatigue characteristics during 4 and 20 s of isometric stimulation (30 Hz; 10 V; 200 ms) using the perfused hind limb model. BRL treatment increased GPS mass by 21% (P < 0.05), whereas greater fatigue occurred during 20 s of contraction (45% less work; P < 0.05). Phenotypically, BRL resulted in 17% more type IIb myosin heavy chain protein expression (P < 0.001) and greater adenine nucleotide catabolism during 20 s of contraction (P < 0.05). Chronic BRL treatment impaired maximal lipid oxidation capacity by 30% (P < 0.05) and reduced glutamate dehydrogenase activity by 15% (P < 0.05). We conclude that beta(2)-agonist induced muscle hypertrophy may be clinically limited as impaired energy metabolism and function occur, presumably as a consequence of the shift in muscle phenotype.
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PMID:Chronic treatment with the beta(2)-adrenoceptor agonist prodrug BRL-47672 impairs rat skeletal muscle function by inducing a comprehensive shift to a faster muscle phenotype. 1684 43

Recognition of the adaptive capacity of mammalian skeletal muscle has opened the way to a number of clinical applications. For most of these, the fast, fatigue-susceptible fibres need to be transformed stably to fast, fatigue-resistant fibres that express the 2A myosin heavy chain isoform. The thresholds for activity-induced change are size-dependent, so although the requisite patterns of electrical stimulation are known for the rabbit, in humans these same patterns would produce type 1 fibre characteristics, with an undesirable loss of contractile speed and power. We have used histochemistry, immunohistochemistry and electrophoretic separations to evaluate a possible conditioning regime in a large animal model. Stimulation of the porcine latissimus dorsi muscle with a phasic 30-Hz pattern for up to 41 days converted all type 2X and 2A/2X fibres to 2A with only a small increase in the type 1 population, from 17% to 22%. Stimulation for longer periods increased the proportion of type 1 fibres to 52%. Based on this model, stimulation regimes designed to achieve a stable 2A phenotype in humans should deliver fewer stimulating impulses, possibly by a factor of 2, than the pattern assessed here. Any such pattern needs to be tested for at least 8 weeks.
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PMID:Adaptive conditioning of skeletal muscle in a large animal model (Sus domesticus). 1687 97

Mammals suckle from a nipple during the early neonatal period to obtain nourishment. The genioglossus muscle helps position and move the tongue for efficient suckling. The purpose of this study was to examine the contractile properties and myosin heavy chain (MHC) phenotype of the genioglossus following an early period of artificial rearing, which reduced nutritive suckling. Beginning at 3 days of age, rats were fed via gastric cannula until postnatal day 14 (P14). At P14, artificially reared rat pups were either allowed to grow to postnatal day 42 (P42) or anaesthetised and prepared for experimentation. Comparisons were made between artificially reared and dam reared groups at P14 and P42. At P14 maximum tetanic tension and fatigue index were lower in the artificially reared group than the dam reared group. By P42, artificially reared rats had a higher fatigue index and lower percentage of MHCIIa than dam reared rats. The artificial rearing technique employed in this study was adequate to produce chronic changes in fatigue resistance and MHC distribution in genioglossus muscle of rat; the changes observed here may be similar to changes that occur in premature human infants requiring early artificial feedings.
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PMID:Effects of artificial rearing on contractile properties of genioglossus muscle in Sprague-Dawley rat. 1704 55

The aims of this work were to analyze the effects of a chronic (14 days) increase in the functional demand imposed on the triceps brachii and to evaluate the changes of the cortical representation of forelimb to this increased activity. The activation of triceps brachii was obtained by the hindlimb unloading (HU) model. Electromyographic activity changed from a phasic to a tonic pattern. Response amplitude increased during the first days of hyperactivity and then stabilized at an intermediate level. A transient decrease (-13% to -36% on day 2) in the mean frequency of motor units was observed. Content in myosin heavy chain of muscle fibers showed a reduction in IIb+IIx fibers in HU rats, whereas IIa+IIx fibers were more numerous. Thus, fibers tend to be more resistant to fatigue. Taken together, these observations reveal a dual plastic process. First, the nervous system reacts immediately to an environmental change, and second it reorganizes its motor command to impose a pattern of activity that is more adapted to a postural function. The extent of the cortical forelimb representation was delimited by oxidase histochemistry. No differences were detectable between control and HU animals for the period corresponding to enlarged receptive fields in the HU condition. Our observation lends support to our hypothesis that activation patterns contribute to the maintenance of neuronal properties in the somatosensory cortex. Moreover, the new tonic pattern resulting from the long contact of the paw with the floor may contribute to the adaptation of the central control of motoneuronal activity.
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PMID:Effect of hindlimb suspension on activation and MHC content of triceps brachii and on the representation of forepaw on the sensorimotor cortex. 1705 86


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