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

A continuous electrical 8 Hz impulse pattern imposed directly via implanted electrodes on denervated fast twitch muscle induced changes in its contractile characteristics. Compared with non-stimulated denervated muscle, stimulated muscle showed slowing of contraction time and improved fatigue resistance. The reaction for succinic dehydrogenase was more intense in the denervated stimulated muscle, indicating an increased capacity of oxidative enzymes. The rate of atrophy was not influenced by stimulation. The 8 Hz frequency pattern is the mediator for these changes in the characteristics of denervated muscles. It demonstrates a comparable effect on innervated muscle. The contralateral normal innervated muscle was also influenced by the electrical stimulation. Contraction time as well as twitch tension were increased. This finding is important when using the normal muscle as intraindividual control.
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PMID:Influence of direct low frequency stimulation on contractile properties of denervated fast-twitch rabbit muscle. 405 36

Alterations in enzyme activities involved in muscle energy metabolism and the muscle fiber type distribution were investigated in six subjects, ranging in age from 19-23 years, following short-term, high intensity exercise. Changes in the vastus lateralis muscle were studied prior to exercise and approximately 24 h after each of 2 consecutive days of supramaximal cycling exercise (120% VO2 max) performed intermittently as 1-min work to 4-min rest until fatigue or until 24 repetitions had been completed. The results indicated that there were no changes (P greater than 0.05) in maximal in vitro activities for representative enzymes of beta-oxidation (3-hydroxyacyl CoA dehydrogenase, HAD), the citric acid cycle (succinic dehydrogenase, SDH), glucose phosphorylation (hexokinase, HK), glycogenolysis (total phosphorylase, PHOSPH), or glycolysis (phosphofructokinase, PFK; pyruvate kinase, PK; lactate dehydrogenase, LDH) in spite of the large increase in carbohydrate utilization and glycolytic flux rate. In addition, although no change in fiber type distribution was found in the pre-exercise biopsy between days, an acute reduction (P less than 0.05) in type I fiber distribution occurred with exercise. It is concluded that supramaximal exercise performed on a short-term basis does not alter the enzymatic profile or the fiber type distribution when measured 24 h following the activity.
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PMID:Fiber type distribution and maximal activities of enzymes involved in energy metabolism following short-term supramaximal exercise. 609 Mar 24

Hypocaloric dieting and fasting alter the contraction-relaxation characteristics of skeletal muscle and result in low frequency fatigue. We report the metabolic and structural changes in skeletal muscle in five morbidly obese female subjects who had biopsies of the gastrocnemius muscle on a base-line diet (2500 kcal/day) followed by a repeat biopsy after 2 wk of a 400-kcal/day carbohydrate diet. Hypocaloric dieting resulted in a significant increase in the intracellular muscle calcium content (p less than 0.05), which may account for the observed changes in muscle function. There were no significant changes in muscle glycogen, lactate, pyruvate, or free energy stores. There was a significant decrease in muscle enzymes [phosphofructokinase (p less than 0.05), succinate dehydrogenase (p less than 0.02)] and some muscle amino acid levels [glutamine (p less than 0.025), glycine (p less than 0.01), and alanine (p less than 0.02)], while muscle histochemistry showed type II fiber atrophy (p less than 0.025). However, these changes reflect a generalized response to hypocaloric dieting and probably do not explain the specific functional changes. Change in the muscle calcium content is probably an important mediator of the adverse functional effects of malnutrition.
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PMID:Metabolic and structural changes in skeletal muscle during hypocaloric dieting. 620 Oct 62

The contractile, histochemical, morphological and electrophysiological properties of two rat laryngeal muscles, the cricothyroid and posterior cricoarytenoid, have been measured. Both muscles act during respiration to maintain upper airway patency and an even distribution of air in the lungs. The cricothyroid and posterior cricoarytenoid are fast-twitch muscles, having contraction times of 3.4 and 7.2 ms respectively, high myosin ATPase activity, abundant sarcoplasmic reticulum (with average volumes of 9% and 15%, respectively, of the fibre volume) and T-system membrane (with average areas of 0.4 and 0.5 micron 2 micron -3 of fibre). The large areas of T-tubule membrane are reflected in the average specific membrane capacities of 6.5 muF cm-2 to 10.5 muF cm-2, which are high considering the small diameter of the fibres (20-30 micron). Of the two muscles, the posterior cricoarytenoid has the faster contraction time and the more abundant sarcoplasmic reticulum content. In addition, the posterior cricoarytenoid is less resistant to fatigue and demonstrates lower succinic dehydrogenase activity. The fatigability of this muscle, coupled with its general lack of functional reserve, suggest that its failure may contribute to upper airway obstruction during respiratory distress.
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PMID:The contractile properties, histochemistry, ultrastructure and electrophysiology of the cricothyroid and posterior cricoarytenoid muscles in the rat. 621 35

Leg muscles of adult rats were stimulated chronically at a low-frequency, and the histochemical reactions of various enzymes (succinic dehydrogenase, mitochondrial alpha-glycerophosphate dehydrogenase, phosphorylase, alkali-ATPase and acid-ATPase), capillary density, resistance to fatigue, and contractile properties were studied. Following stimulation, the histochemical properties of muscle fibres in the fast extensor digitorum longus (EDL) and tibialis anterior (TA) muscles became similar to those of the majority of fibres in the slow soleus muscle. In the soleus muscle, the histochemical properties of the few fast type fibres became similar to the majority of 'slow' fibres so that its fibre composition was homogeneously 'slow'. The stimulated fast muscles also had higher capillary density and were more resistant to fatigue than normal. Despite the prolonged stimulation, the twitch duration of the fast muscles was little changed. This result differs from the findings obtained previously for the rabbit and cat, which show that slowing of contraction can be achieved by low-frequency activity of similar duration. Thus it may be that there is a species difference regarding the readiness with which the transformation of fast to slow muscles can be brought about.
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PMID:Effects of low-frequency electrical stimulation on fast and slow muscles of the rat. 621 64

Transversal sections of the inferior oblique muscle from kittens of various ages and from adult cats were stained for myofibrillar ATP-ase at Ph 9.4 and 4.35, succinic dehydrogenase (SDH) and fat. The same muscles had previously been submitted to studies of contractional and fatigue properties. With ATPase the fibers could be differentiated into types I, II and II C. The percentages of each fiber type remained approximately the same from birth onwards. In the inner, global layer of the muscle, type I fibers showed a linear increase in size, but types II and IIC fibers an accelerated growth after age 20 weeks. In the outer, orbital layer, where no type I fibers were seen, type II and II C fibers showed the same growth pattern as in the global layer. The fiber content of SHD and fat was low at birth but increased after two weeks of age. Type I fibers were poor and type II C fibers rich in SDH and fat. Type II fibers showed varying amounts of these substances. Provided that type I fibers are slow, type II fast and type II C intermediate in speed of contraction, like in other muscles, the findings on fiber growth and SDH content seem to support the idea that slow, fatigue resistant components in eye muscles reach maturity earlier than fast components.
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PMID:The postnatal development of the inferior oblique muscle of the cat. III. Fiber sizes and histochemical properties. 644 74

Lizard skeletal muscle fiber types were investigated in the iliofibularis (IF) muscle of the desert iguana (Dipsosaurus dorsalis). Three fiber types were identified based on histochemical staining for myosin ATPase (mATPase), succinic dehydrogenase (SDH), and alphaglycerophosphate dehydrogenase (alphaGPDH) activity. The pale region of the IF contains exclusively fast-twitch-glycolytic (FG) fibers, which stain dark for mATPase and alphaGPDH, light SDH. The red region of the IF contains fast-twitch-oxidative-glycolytic (FOG) fibers, which stain dark for all three enzymes, and tonic fibers, which stain light for mATPase, dark for SDH, and moderate for alphaGPDH. Enzymatic activities of myofibrillar ATPase, citrate synthase, and alphaGPDH confirm these histochemical interpretations. Lizard FG and FOG fibers possess twitch contraction times and resistance to fatigue comparable to analogous fibers in mammals, but are one-half as oxidative and several times as glycolytic as analogous fibers in rats. Lizard tonic fibers demonstrate the acetylcholine sensitivity common to other vertebrate tonic fibers.
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PMID:Histochemical, enzymatic, and contractile properties of skeletal muscle fibers in the lizard Dipsosaurus dorsalis. 645 26

This study was designed to determine the influence of a long-term, moderate-intensity treadmill training program on the distribution of blood flow within and among muscles of rats during exercise. One group (T) of male Sprague-Dawley rats trained for 1 h/day for 13-17 wk at 30 m/min on a motor-driven treadmill. A second group (UT) of rats was conditioned for 10 min/day for 4 wk at the same speed. Muscle succinate dehydrogenase activities were higher in T than UT rats indicating a significant training effect. Blood flows (BFs) in 32 hindlimb muscles or muscle parts and other selected organs were measured in the two groups with radiolabeled microspheres during preexercise and while the rats ran for 30 s, 5 min, or 15 min at 30 m/min on the treadmill. The data indicate 1) there were no differences in total hindlimb muscle BF between UT and T rats at any time; however, 2) T rats had higher preexercise heart rates and higher muscle BFs in the deep red extensor muscles, suggesting a greater anticipatory response to the impending exercise; 3) T rats demonstrated more rapid elevations in BF in the red extensor muscles at the commencement of exercise; 4) T rats had higher BFs in red extensor muscles during exercise, whereas UT rats had higher BFs in white muscles; and 5) T rats maintained higher BFs in the visceral organs during exercise. These findings demonstrate that exercise training results in changes in the distribution of BF within and among muscles and among organs during exercise. Specifically, data indicate the high-oxidative motor units that are primarily recruited in the muscles during the initial stages of moderate treadmill exercise receive higher blood flows in the trained rats; this presumably contributes to increased resistance to fatigue.
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PMID:Exercise blood flow patterns within and among rat muscles after training. 669 89

Tenotomy of the rat soleus muscle is followed by a central degeneration of slow, fatigue-resistant muscle fibers. Previous experiments showed that fast, fatigable fibers of the gastrocnemius when transformed to slow, fatigue-resistant fibers by cross-reinnervation also develop lesions after tenotomy. The experiments described in this communication were carried out to discover whether the susceptibility of fibers to lesions was determined by their fiber type or the nature of their innervation. Rats were rendered hyperthyroid by the administration of sodium 3,3',5-triiodo-L-thyronine (T3) for 7 to 10 weeks. Tenotomy of the soleus muscles was then carried out and the experimental and contralateral muscles were removed and stained for myosin ATPase activity after a further 2 weeks. The hyperthyroid state of each animal was confirmed by the assay of succinate dehydrogenase activity of liver and the contralateral muscle. After acid preincubation, whole muscle fiber type counts of contralateral muscles showed a statistically significant change from a predominantly acid-stable population of fibers to acid-labile fibers. In addition, many fibers of intermediate staining properties were seen. When the experimental muscles were examined, all three varieties of fiber showed central degeneration. The nature of the fiber type change induced by T3 and the role that innervation might play in this is discussed. It was concluded that the susceptibility of fibers to the lesions that follow tenotomy is dependent on the nature of their innervation rather than their fiber type.
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PMID:Central core degeneration after tenotomy in soleus muscles of hyperthyroid rats. 688 81

Biopsies from the vastus lateralis muscle were obtained from three astronauts before and after two 5-day flights and from five astronauts before and after one 11-day flight (space shuttle flights: STS-32, -33, and -34). Muscle fibers from two separate samples from each biopsy were classified as type I and II or as type I, IIA, and IIB by using qualitative myofibrillar adenosinetriphosphatase (ATPase) staining. Cross-sectional area (CSA), number of capillaries per fiber, and the activities of succinate dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (GPD), and myofibrillar ATPase were determined from one sample of fibers of each myofibrillar ATPase type. Postflight biopsies had 6-8% fewer type I fibers than preflight. Mean fiber CSAs were 16-36% smaller after the 11-day flight with the relative effect being type IIB > IIA > I. Mean fiber CSAs were 11 and 24% smaller in type I and II fibers after 5 days of flight. Myofibrillar ATPase activities increased in type II but not in type I fibers after flight, whereas SDH activity was unaffected in either fast or slow fibers. GPD activity in type I fibers was approximately 80% higher (P > 0.05) postflight compared with preflight. Myofibrillar ATPase/SDH ratios in type II fibers were higher after than before flight, suggesting that some fast fibers were more susceptible to fatigue after flight. The GPD/SDH ratios were elevated in some type I fibers after spaceflight. The number of capillaries per fiber was 24% lower after than before flight, whereas the number of capillaries per unit CSA of muscle tissue was unchanged. These data suggest that adaptations in the size, metabolic properties, and vascularity of muscle fibers can occur rapidly in the space environment. These adaptations were qualitatively similar to those observed in animals after actual or simulated spaceflight conditions for short periods.
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PMID:Human fiber size and enzymatic properties after 5 and 11 days of spaceflight. 764 6


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