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

The fatigue characteristics of a zinc phosphate cement were examined. Using a split mould made of stainless steel, 12 mm x phi 6 mm column shape specimens were prepared. Fatigue tests were done by loading partially repeated pulsating diametrical tensile stress of 1-20 Hz, minimum stress was 0.2 MPa (2.0 kgf/cm2) and maximum stress was 3.5-5.4 MPa (36-55 kgf/cm2). During testing, the specimen was kept under distilled water. The existence of a fatigue was confirmed and there were marked signs of fatigue on the fracture surface. The relation between maximum stress and the number of cycles to fracture (S-N diagram) was obtained. Therefore the following equation and fatigue parameter (n) were deduced. logS + 0.0775.logN = 0.8931 n = 12.9 The fatigue characteristics depended on the frequency, that is, a time to fracture was shorter at the loading frequency of 20 Hz than that of 1 Hz.
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PMID:[Fatigue of dental zinc phosphate cement]. 213 51

Vanadate (Na3VO4) action of the isometric force of maximal Ca2(+)-activated fibre has been studied at pH from 6.3 to 7.3. Acidification was shown to decrease the force declining vanadate effect: appearance of the dissociation constant estimated from force--H2VO4--dependence increases about two-fold following the pH decreasing from 7.3 to 6.3. Therefore the well-known decline of the force at acidification is accompanied by a decrease of the sensitivity to vanadate. These both phenomena can have a common nature and reflect, for example, a decreasing complex AM.ADP+ responsible for the force and interaction with vanadate. Our findings permit to think that the changes in pH with fatigue increasing the diprotonated form of phosphate simultaneously reduce the sensitivity of the contractile system to this form.
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PMID:[Reduced sensitivity of glycerinated rabbit m.psoas fibers to diprotonated vanadate during decrease in pH]. 216 24

A rat model was used to study the effects of endotoxemic shock in vivo on diaphragmatic tension generation and diaphragmatic metabolism in vitro. Animals were injected with E. coli lipopolysaccharide (30 mg/kg) and killed at fixed times after injection. The hemidiaphragms were isolated in an organ bath, and tension generation was measured during electrical stimulation of the phrenic nerve or diaphragmatic muscle. Diaphragmatic oxygen consumption was measured in vitro during rest and during in vivo stimulation. Adenosine triphosphate and glycogen concentrations were measured in vivo before the animals were killed and in vitro. Tension generation was reduced in a time-dependent fashion after endotoxin at all stimulation frequencies. Both contractile fatigue and transmission fatigue were present. Glycogen stores were reduced but not depleted. ATP concentration was reduced in vivo but recovered in vitro. Diaphragmatic oxygen consumption was reduced in vitro at rest and during stimulation. The results suggest that endotoxemic shock results in diaphragmatic fatigue in a time-dependent fashion, that impaired neural or neuromuscular transmission is present in vitro, and that impaired oxygen consumption in the shocked diaphragm is associated with reduced high-energy-phosphate stores.
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PMID:Diaphragmatic fatigue after endotoxemic shock in rats: in vitro function and metabolism. 221 69

We examined the relationships between muscle force and both phosphate and hydrogen ion concentrations in muscles with differential fatigability and in different types of exercise. We measured force and 31phosphorus nuclear magnetic resonance spectra from the tibialis anterior (a slow-contracting, fatigue resistant, postural leg muscle) during a sustained maximum contraction (anaerobic exercise) and during intermittent contractions (aerobic exercise). We observed similar relationships between the decline in muscle force during fatigue and changes in both phosphate and hydrogen ion concentrations during both aerobic and anaerobic exercise in tibialis anterior. Furthermore, these relationships were similar to those previously observed in the adductor pollicis. The demonstration of constant relationships between muscle contraction force and metabolism under different exercise conditions and in muscles of different function supports the view that both phosphate and hydrogen ions are important regulatory factors in the fatigue of human muscle.
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PMID:Constant relationships between force, phosphate concentration, and pH in muscles with differential fatigability. 224 39

Metabolic fatigue is a characteristic muscle response to intense exercise that has outstripped the rate of ATP replacement. The accumulation of metabolic by-products, namely hydrogen ions and diprotonated phosphate, interferes with actin-myosin interaction, effectively preserving muscle ATP levels by preventing further ATP hydrolysis. Muscle force and metabolite concentrations return to normal in about 5 minutes. Less intense exercise causes a more subtle, non-metabolic fatigue due to a still-undefined disturbance of excitation-contraction coupling, which can last for several hours. In this type of fatigue, greater effort is required to generate submaximal forces. Endurance exercise is mainly limited by the size of muscle glycogen stores and how efficiently they are used. Endurance training permits an athlete to work aerobically at high rates, consuming a mixture of lipid and carbohydrate fuels. When muscle glycogen is used up, exercise can only continue at the relatively low rate supportable by lipid metabolism. Anaerobic exercise is also limited by subjective factors such as dyspnoea and muscle pain, which have objective determinants. Extremely prolonged exercise can lead to general collapse because of dehydration, hyperthermia, or hypoglycaemia. None of these factors explains the phenomenon of asthenia, a subjective sense of exhaustion that produces no objective impairment of physical performance. The metabolic myopathies are experiments of nature that promise to shed new light on the biochemical basis of muscle fatigue. This will require quantitative studies of the kind provided by topical magnetic resonance spectroscopy, correlating physiology and metabolism in vivo.
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PMID:Muscle metabolism during fatigue and work. 226 24

Reductions in work output during repeated contractions of rat medial gastrocnemius muscles (37 degrees C) were compared with changes in muscle metabolite concentrations. Three different exercise protocols were used in which the total number of stimuli and the length excursion were the same. The muscles performed a series of either 10, 25 or 40 repeated contractions at velocities of 20, 50 and 80 mm/s for groups A, B and C, respectively. In group A work output decreased steadily to 66% of the output in the first contraction. In groups B and C work output decreased to less than 10% of the first contraction. Changes in phosphocreatine and lactate concentrations were similar for all groups. However, very low ATP concentrations (approximately 35% of the resting value) were observed in groups B and C, compared with approximately 65% in group A. Inosine 5'-monophosphate (IMP) production was 9.9 mumol/g dry wt in group A and approximately 18 mumol/g dry wt in groups B and C. The results suggest fatigue does not depend on changes in intracellular inorganic phosphate and pH but possibly on changes in nucleotide metabolism.
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PMID:High-energy phosphates and fatigue during repeated dynamic contractions of rat muscle. 227 Nov 63

In vivo nuclear magnetic resonance (NMR) spectroscopy was used to define several intracellular high energy phosphate variables of the gastrocnemius muscle of normal subjects during rest, graded plantar flexion exercise to exhaustion, and recovery. There were nine males and eight females with an average age of 34 +/- 8 years. At rest, pH averaged 7.09 +/- 0.03 and the energy cost index (ECI)--the ratio of inorganic phosphate to phosphocreatine--averaged 0.13 +/- 0.03. At peak exercise, the ECI increased markedly to 2.71 +/- 2.0 (P less than 0.001) and pH fell precipitately to 6.76 +/- 0.17 (P less than 0.001), indicating the high intensity of the exercise. Exercise endurance averaged 12 +/- 5 mins; it was not highly correlated with sex, age (r = 0.35), rest pH (r = 0.26), rest ECI (r = 0.38), peak exercise pH (r = 0.23) or peak exercise ECI (r = 0.38), nor exercise changes in pH (r = 0.17) and ECI (r = 0.28). At 23 mins post exercise all variables were similar to rest. Rest pH was the only variable different between males (7.10 +/- 0.03) and females (7.07 +/- 0.03) (P less than 0.05). Thus, dynamic exercise of large skeletal muscles in normal subjects was characterized by marked temporal changes in high energy phosphate profiles and very low pH at exhaustion. No single metabolic variable correlated highly with exercise endurance, suggesting that the intracellular pathophysiology of exhaustive muscle exercise and clinical fatigue may be multifactorial.
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PMID:Metabolism of normal skeletal muscle during dynamic exercise to clinical fatigue: in vivo assessment by nuclear magnetic resonance spectroscopy. 227 74

We investigated the metabolic basis of human muscular fatigue and recovery utilizing 31P magnetic resonance spectroscopy and measurements of maximum voluntary contraction (MVC). We produced fatigue by sustained MVC for 4 minutes in 2 different muscles (adductor pollicis, tibialis anterior) and obtained similar results in both muscles. During fatiguing exercise, there was a nonlinear relationship between MVC and both phosphocreatine and total inorganic phosphate. By contrast, there was a roughly linear relationship between the decline in MVC and the accumulation of both H+ and H2PO4-. However, during recovery after exercise, MVC rapidly returned to control levels while H+ recovered with a much slower time course. On the other hand, H2PO4- rapidly returned to control values with a time course similar to MVC. In addition, the relationship of H2PO4- to MVC was similar during both fatigue and recovery. Thus, during fatigue as well as during recovery, changes in MVC correlate best with H2PO4-, suggesting that this metabolite is an important factor in human muscle fatigue.
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PMID:The metabolic basis of recovery after fatiguing exercise of human muscle. 230 Feb 42

Subjective fatigue was quantified before and 20 days after uncomplicated elective abdominal surgery in 12 patients and compared with changes in heart rate, enzyme activities and skeletal muscle substrates before and after bicycle exercise for 10 min at 65 per cent of patients' preoperative maximum work capacity. Fatigue increased from a mean(s.e.m.) preoperative level of 2.5(0.5) arbitrary units to 4.6(0.5) on postoperative day 20 (P less than 0.01). Body-weight, triceps skinfold thickness and arm circumference decreased postoperatively (P less than 0.02). Postoperative values of muscle enzyme activities indicative of oxidative phosphorylation capacity (citrate synthase and 3-OH-acyl coenzyme A dehydrogenase) were lower than preoperative values (P less than 0.05). Lactate dehydrogenase was unaltered and resting values of muscle glycogen and adenosine triphosphate were higher after operation (P less than 0.05). In response to exercise, heart rate, muscle glucose, glucose-6-phosphate and lactate increased (P less than 0.05), while muscle glycogen and creatine phosphate decreased (P less than 0.05). Increase in postoperative fatigue correlated with the increase in heart rate (P less than 0.05), while no significant correlations were found between fatigue and muscle parameters. Our results suggest that lack of exercise and malnutrition may be of importance in the decrease in work capacity and in fatigue after operation.
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PMID:Skeletal muscle enzyme activities and metabolic substrates during exercise in patients with postoperative fatigue. 232 98

A 64-year-old female patient was admitted to our department for fatigue, pain in the right upper abdomen, obstipation, and meteorism. The laboratory findings showed total calcium and ionized calcium elevated, phosphate close to lower limit, and parathyroid hormone increased. T1-201/Tc-99m subtraction scintiscan of the neck and upper mediastinal region did not give any evidence of isolated enhanced uptake suggesting the presence of parathyroid adenoma. After further increases in calcium and parathyroid hormone level T1-201 whole-body scan and single photon emission computed tomography of the thoracic region were performed. These revealed a circumscribed T1-201 uptake in the mediastinum immediately cranial ventral to the heart base. The postcontrast transmission computed tomography of this area confirmed the finding of the T1-201 scintigraphy with a 4 x 3 x 2 cm tumor. After sternotomy and surgical removal of the mediastinal parathyroid adenoma (chief cell adenoma), calcium and parathyroid hormone levels returned to normal values.
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PMID:Localization of mediastinal parathyroid adenoma by T1-201 scintiscan and SPECT. 235 26


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