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

Focal electrodes were used to record the spontaneous miniature potentials generated on delimited patches of innervated membrane in the Torpedo electric organ. The main population of miniature potentials followed a bell-shaped amplitude distribution. In addition, we observed a second class of spontaneous events that were smaller and whose amplitude distribution was skewed. These subminiatures formed an homogenous population together with the regular miniatures with respect to their time course versus amplitude relationship. They were thus probably generated at the same sites. The proportion of potentials that were subminiature was less than 10% in resting, freshly excised tissue, but it increased markedly: (i) when the tissue was kept for 24-28 h in vitro after excision; (ii) in the period following a brief heat challenger or (iii) stimulation to exhaustion; and (iv) in the presence of dinitrophenol or dinitrofluorobenzene. In all these conditions, we measured the acetylcholine, adenosine 5'-triphosphate and creatine phosphate content of the tissue and found a correlation between the relative number of subminiature potentials and the lack of energy rich molecules. It is concluded that subminiature potentials are present in the electric organ as in neuromuscular junctions. They are probably produced at the same sites as the regular miniature potentials and their relative occurrence seems to increase greatly when the nerve terminals are in a state of energy deficiency.
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PMID:Spontaneous quantal and subquantal transmitter release at the Torpedo nerve-electroplaque junction. 303 36

The mechanism of muscle fatigue was studied by 31P-MRS. During tetanic contraction for 2 minutes(min), the tension measured with a strain gauge and Phosphocreatine(PCr)/Inorganic phosphate(Pi)+ Phosphomonoester(PME) ratio decreased to 31.5 +/- 4.4% of the control value and 0.6 +/- 0.1, respectively. The intracellular pH(pH) also decreased to 6.62 +/- 0.04. Toward the end of the stimulation, the tension decreased to 25.3 +/- 1.9% of the control value. However, during 20min stimulation, the PCr/(Pi+PME) ratio increased to 2.5 +/- 0.5 and the pH to 6.91 +/- 0.04. These results show that muscular fatigue is ascribable not to a decreased level of high energy metabolites required for actomyosin ATPase, but to an increase in the threshold intensity of excitation in excitation-contraction coupling.
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PMID:Observation of fatigue unrelated to gross energy reserve of skeletal muscle during tetanic contraction--an application of 31P-MRS. 319 34

Muscle fatigue, defined as a decreased force generating capacity, develops gradually during exercise and is distinct from exhaustion, which occurs when the required force or exercise intensity can no longer be maintained. We have reviewed several biochemical and ionic changes reported to occur in exercising muscle, and analysed the possible effects these changes may have on the electrical and contractile properties of the muscle. There is no evidence that substrate depletion can account for the decreased force generating capacity, but this factor may be important for the rate of energy turnover and be a major determinant for endurance. Increased concentration of inorganic phosphate and hydrogen ions will depress the force generating capacity, but since fatigue can develop gradually without accumulation of these ions they can only be important when aerobic ATP production is insufficient to support the contractions. Evidence is presented showing that a disturbed balance of K+ alone might cause depolarisation block at high stimulation frequencies, but extracellular K+ accumulation does not increase gradually during prolonged dynamic or static exercise, and is therefore not closely related to fatigue. The repeated release of Ca2+ from the sarcoplasmic reticulum (SR) during muscular activity is suggested of Ca2+ by the mitochondria, increasing with stimulation frequency and duration and possibly also deteriorating mitochondrial function. We therefore speculate that decreased Ca2+ availability for release from SR might contribute to a gradual decline in force generating capacity during all types of exercise.
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PMID:Biochemical correlates of fatigue. A brief review. 328 52

Phosphorus nuclear magnetic resonance (31P NMR) spectroscopy is a non-destructive analytical laboratory technique that, due to recent technical advances, has become applicable to the study of high-energy phosphate metabolism in both animal and human extremity muscles (in vivo). 31P NMR can assay cellular phosphocreatine, ATP, inorganic phosphate, the phosphorylated glycolytic intermediates, and intra-cellular pH in either resting or exercising muscle, in a non-invasive manner. NMR uses non-perturbing levels of radio-frequency energy as its biophysical probe and can therefore safely study intact muscle in a repeated fashion while exerting no artifactual influence on ongoing metabolic processes. Compared with standard tissue biopsy and biochemical assay techniques, NMR possesses the advantages of being non-invasive, allowing serial in situ studies of the same tissue sample, and providing measurements of only active (unbound) metabolites. NMR studies of exercising muscle have yielded information regarding fatigue mechanisms at the cellular level and are helping resolve long-standing questions regarding the metabolic control of glycolysis, oxidative phosphorylation, and post-exercise phosphocreatine re-synthesis. NMR is also being utilized to measure enzymatic reaction rates in vivo. In the near future, other forms of NMR spectroscopy may also permit the non-invasive measurement of tissue glycogen and lactate content.
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PMID:Phosphorus nuclear magnetic resonance: a non-invasive technique for the study of muscle bioenergetics during exercise. 330 42

The goal of these experiments was to investigate the relationship of ATP, phosphocreatine (PCr), inorganic phosphate (Pi), monobasic phosphate (H2PO4-), and pH to human muscle fatigue. Phosphates and pH were measured in adductor pollicis using 31P nuclear magnetic resonance at 2.0 Tesla. The force of muscle contraction was simultaneously measured with a force transducer. The effects of aerobic and anaerobic exercise were compared using two exercise protocols: 4 min sustained maximal voluntary contraction (MVC) and 40 min of repeated intermittent contractions (75% MVC). The sustained maximal contraction produced a rapid decline of MVC and PCr, and was accompanied by a rapid rise of Pi, H+, and H2PO4-. Intermittent exercise produced steady state changes of MVC, pH, and phosphates. No significant changes of ATP were found in either protocol. During fatiguing exercise, PCr and Pi had a nonlinear relationship with MVC. H+ showed a more linear correlation, while H2PO4- showed the best correlation with MVC. Furthermore, the correlations between MVC and H2PO4- were similar in sustained (r = 0.70) and intermittent (r = 0.73) exercise. The highly significant linear relationship between increases of H+ and H2PO4- and the decline of MVC strongly suggests that both H+ and H2PO4- are important determinants of human muscle fatigue.
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PMID:31P nuclear magnetic resonance studies of high energy phosphates and pH in human muscle fatigue. Comparison of aerobic and anaerobic exercise. 335 Sep 69

The pathophysiology of the myopathy in dysthyroid states is poorly understood. We therefore tested the effects of thyroid hormones on muscle bioenergetics in humans and rats, using in vivo 31P NMR. Two hypothyroid patients had: low phosphocreatine to inorganic phosphate ratio (PCr/Pi) at rest, increased PCr depletion during exercise and delayed postexercise recovery of PCr/Pi. Eight thyroidectomized rats did not show abnormalities at rest, but muscle work induced by nerve stimulation resulted in a significantly (P less than 0.0001) lower PCr/Pi (35-45% of control) at each of the three stimulation frequencies tested (0.25, 0.5, and 1.0 Hz). Recovery rate was markedly slowed to one-third of normal values. Thyroxine therapy reversed these abnormalities in both human and rat muscle. Five patients and six rats with hyperthyroidism did not differ from normal controls during rest and exercise but had an unusually rapid recovery after exercise. The bioenergetic abnormalities in hypothyroid muscle suggest the existence of a hormone-dependent, reversible mitochondrial impairment in this disorder. The exercise intolerance and fatigue experienced in hypothyroid muscle may be due to such a bioenergetic impairment. The changes in energy metabolism in hyperthyroid muscle probably do not cause the muscular disease in this disorder.
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PMID:Effects of thyroid hormones on skeletal muscle bioenergetics. In vivo phosphorus-31 magnetic resonance spectroscopy study of humans and rats. 338 46

Magnetic resonance spectroscopy is a non-invasive and repeatable method of studying muscle metabolism. Magnetic resonance spectroscopy uses specific radiofrequency pulses in a strong magnetic field to determine the relative concentrations of chemical compounds in the sample. 31P Magnetic resonance spectroscopy provides indirect measures of phosphate compounds such as adenosine triphosphate (ATP), phosphocreatine and inorganic phosphate. Muscle intracellular pH can also be determined. Exercise tests can be performed in the magnet such that the metabolic response to steady-state exercise can be measured. The ratio of inorganic phosphate to phosphocreatine reflects the relative metabolic rate of mitochondrial respiration (V) and the extrapolated maximum capacity of oxidative metabolism (Vm). Normal humans vary considerably in their metabolic response to exercise. These differences are reflected in their Vms and the degree of acidosis during exercise. Active muscles in endurance trained athletes have higher Vms and faster recovery rates than normal controls. Preliminary studies have been done to assess muscle glycolytic capacity by measuring the degree of acidosis during ischaemic exercise. Exercise-induced muscle injury can be detected as an increased inorganic phosphate to phosphocreatine ratio in resting muscle. The increase in the inorganic phosphate to phosphocreatine ratio with injury reaches a peak 1 to 2 days after the injury and lasts for up to a week. Similar increases in the inorganic phosphate to phosphocreatine ratio occur in patients with destructive neuromuscular diseases. Thus changes in the resting inorganic phosphate to phosphocreatine ratio may be used to detect the degree of muscle injury following exercise. Levels of H2PO4- in muscle are thought to be important in causing muscle fatigue during exercise. As 31P magnetic resonance spectroscopy can measure H2PO4-, magnetic resonance spectroscopy has become a useful technique in the study of the metabolic causes of muscle fatigue. It may also be possible to identify the relative populations of fast twitch and slow twitch fibres in a skeletal muscle using pH changes measured with 31P magnetic resonance spectroscopy. Magnetic resonance spectroscopy using other nuclei, such as 1H, 13C and 23Na, have the potential to provide information on other metabolic changes which occur with exercise. Magnetic resonance spectroscopy has shown promise as a technique to monitor the effects of training, including overtraining, in specific muscle groups in athletes.
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PMID:Application of 31P magnetic resonance spectroscopy to the study of athletic performance. 338 35

The content of glucose 1,6-bisphosphate (G-1,6-P2), an in vitro activator of phosphofructokinase (a rate-limiting enzyme for glycolysis), and the glycolytic rate in skeletal muscle during isometric contraction have been determined. Subjects contracted the knee extensor muscles at two-thirds maximal voluntary force to fatigue. Biopsies from the quadriceps femoris muscle were obtained before and immediately after contraction. G-1,6-P2 increased in all subjects from a mean of 101 +/- 15 (SE) mumol/kg dry wt at rest to 128 +/- 24 at fatigue (P less than 0.05). Muscle glucose did not change significantly, whereas hexosemonophosphates were significantly increased after contraction. The glycogenolytic and glycolytic rate averaged 70.0 +/- 13.8 and 47.3 +/- 6.7 mmol.kg dry wt-1.min-1, respectively, and the glycolytic rate was positively correlated with the accumulation rates of fructose 6-phosphate (F-6-P) (r = 0.95, P less than 0.01) and G-6-P (r = 0.96, P less than 0.01). Phosphocreatine and ATP decreased by 87 and 17%, respectively, whereas ADP increased by 31% after contraction. These data demonstrate that intense, short-term isometric contraction results in an elevation of the muscle content of G-1,6-P2. The increase in G-1,6-P2 could not be accounted for by the side reactions of phosphoglucomutase or phosphofructokinase. It remains to be determined whether the observed increase in G-1,6-P2 is sufficient to account for the high glycolytic rate during intense exercise. The lack of increase in muscle glucose while G-6-P increased (which will inhibit hexokinase) suggests that the debranching enzyme complex was not active during contraction.
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PMID:G-1,6-P2 in human skeletal muscle after isometric contraction. 340 60

Significant interest for orthopedic surgical applications of hydroxyapatite compounds is based on a number of reasons including the elemental chemistry of the primarily calcium and phosphate ion substances, the controllability of the crystalline and physical structures to provide a wide range of in vivo interactions, the existing literature on biocompatibility and the possibility for use as a surface coating, and the opportunity for bonding to bone and enhancing mechanical force transfer. A wide range of crystalline and structural forms can be constituted from reactions between calcium oxide and phosphorous pentoxide. These ceramics can be made in at least eight crystallographic forms with multiple opportunities to introduce other elements or structural defects. Microstructures and densities also can be varied to provide properties from relatively stable to completely biodegradable. One limitation has been the relatively low shear and fatigue strengths of the calcium phosphate-based ceramics. Although experimental for human orthopedic applications at this time, coatings are now in clinical trials using a range of substances, and active research is continuing on combinations of ceramics with higher strengths, cermets, and composites.
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PMID:Hydroxyapatite coatings. 341 27

To study changes in muscle energy state during prolonged exercise, especially in relation to fatigue, muscle biopsies were obtained from seven healthy males working until exhaustion on a cycle ergometer at 68% (63-74%) of their maximal oxygen uptake. Biopsies were taken at rest, after 15 and 45 min of exercise and at exhaustion, and analysed for ATP, ADP, AMP, inosine monophosphate (IMP) and hypoxanthine content by high performance liquid chromatography (HPLC), and for creatine phosphate (CP), lactate and glycogen by enzymatic fluorometric techniques. Glycogen content at exhaustion was approximately 30% of the pre-exercise level. The CP content decreased steeply during the first 15 min of exercise (P less than 0.01) and continued to decrease during the rest of the exercise period (P less than 0.05). Pronounced increases in contents of IMP (64% P less than 0.001) and hypoxanthine (69%, P less than 0.05) were found when exhaustion was approaching. Furthermore, energy charge [EC; (ATP + 0.5 ADP)/(ATP + ADP + AMP)] was decreased at exhaustion (P less than 0.05). The increases in IMP and hypoxanthine which occurred when exhaustion was approaching during prolonged submaximal exercise together with the decrease in EC during this phase of exercise suggest a failure of the exercising skeletal muscle to regenerate ATP at exhaustion.
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PMID:ATP breakdown products in human skeletal muscle during prolonged exercise to exhaustion. 342 83


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