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

Indices of electrically stimulated and maximal voluntary isometric muscle torgue and the phosphate content of myosin phosphorylatable light chains (P light chains) were studied during recovery following a 60-s maximal voluntary isometric contraction (MVC) in 21 human subjects. Analysis of muscle biopsy samples revealed that immediately after the 60-s MVC there were significant decreases in ATP (-15%) and phosphocreatine (-82%), and lactate concentration increased by 17-fold. All indices of muscle torque production were reduced by the 60-s MVC, but the twitch torque and torque at 10 Hz were relatively less reduced compared with the torque at 20 and 50 Hz or a 1-s MVC. Between 3 and 6 min of recovery, twitch torque and torque at 10 Hz stimulation were significantly potentiated, reaching peak values of 125 and 134%, respectively, compared with rest. Phosphate content of the fast and two slow P light chains was significantly increased over rest levels immediately after and 4 min after the 60-s MVC. These results suggest that myosin P light-chain phosphorylation could provide a mechanism to increase human muscle torque under conditions of submaximal contractile element activation following fatigue.
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PMID:Torque potentiation and myosin light-chain phosphorylation in human muscle following a fatiguing contraction. 205 43

To elucidate the origin of the reduction in force during prolonged muscle fatigue, the dependency of Ca2+ uptake and release on MgATP and P(i) concentration was studied in saponin-skinned fast skeletal muscle fibers of the iliofibularis muscle of Xenopus laevis at 3 degrees C. The sarcoplasmic reticulum was loaded with Ca2+ for 5 min at pCa 7.0. The amount of Ca2+ released was derived from the area of the caffeine-induced force response. Ca2+ uptake increased with the MgATP concentration present during loading. It was half maximal at 20 microM and saturated at higher concentrations. The kinetics of Ca2+ release were affected for MgATP concentrations between 0.1 and 0.5 mM or less, but the amount of Ca2+ released by caffeine in ATP-free solutions was substantial. Phosphate (15 mM) only slightly reduced Ca2+ uptake when the loading period was short (1 min). It is unlikely, therefore, that the reduction in MgATP concentration contributes to the depression of Ca2+ released from the sarcoplasmic reticulum during fatigue. The increase in P(i) concentration could play a small role by reducing Ca2+ uptake.
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PMID:Uptake and caffeine-induced release of calcium in fast muscle fibers of Xenopus laevis: effects of MgATP and P(i). 821 21

High-intensity contractile activity causes a rapid fall in peak tension or force, a reduced shortening velocity, decline in power, prolonged twitch duration, a sarcolemma action potential with a prolonged duration, reduced amplitude, and a conduction velocity that may result in conduction block. The calcium transient is characterized by a reduced amplitude and prolonged duration. What is the role of hydrogen in high-intensity exercise? It may affect E-C coupling but we do not think so. It definitely inhibits the rate of force development and calcium binding to TN-C. It also definitely inhibits the cross-bridge transition from the low to high force state. It inhibits velocity or the cross-bridge cycle rate and, therefore, decreases power and, importantly, prolongs the rate of calcium reuptake by inhibiting the sarcoplasmic reticulum calcium ATPase pump. Phosphate inhibits tension by reversing the cross-bridge transition from the low to the high force state, but it does not affect cycle rate; therefore, it does not have an effect on velocity. It may be involved in decreasing the free energy of ATP hydrolysis, which would provide less energy and, most importantly, play a role in inhibiting the sarcoplasmic reticulum calcium reuptake. Finally, what does all this mean to the athlete and how can fatigue be prevented? Basically, we do not have answers to these questions, but it is clear that the athlete is going to have to have a varied training program. If an athlete trains with one particular type of exercise, fatigue will result from other factors. Thus, a heterogeneous training program is essential. Diet is very important, and warm-up and fluid replacement are all factors that are going to be important in triggering peak performance.
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PMID:Muscle fatigue: the cellular aspects. 894 17

The goal of this project was to evaluate the effect of the following variables on shear dentin-bonding test results: mode of testing (cyclic fatigue versus static loading), surface treatments (32% phosphoric acid, 10% phosphoric acid, and no treatment [unetched]), and type of shear test (traditional planar versus push-out). All teeth were stored in distilled water and tested in a shear mode at a loading rate of 2 mm/ min. The specimens were loaded in static or cycled for 1000 cycles using a staircase approach or until fracture, whichever occurred first. On samples with etched dentin surfaces, the push-out test did not demonstrate a significant difference in measured bond strength when compared with results from the planar test, although sample preparation was more labor-intensive. The bond strength resulting from cyclic fatigue of the etched specimens was approximately 51% of the static loading value. Ten percent phosphoric acid was as effective as 32% phosphoric acid for dentin bonding. Finite-element analysis indicated that the traditional planar shear test produces flexure of the specimen and high tensile stress magnitudes within the resin bonding layer. The push-out test produces elevated compressive stresses localized in the composite along the circumference of the punch. Shear stresses in the resin bonding layer are similar for both testing methods at the same loading element contact force.
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PMID:Testing mode and surface treatment effects on dentin bonding. 895 43

The paper deals with the history of development of one of the basic trends in scientific activity of Academician O. V. Palladin and world-known biochemical school created by him: biochemistry and physiology of muscular activity. Retrospective analysis of the works by O. V. Palladin and his pupils, dedicated to the mentioned problem permits judging of realization of his ideas, when studying the process of training, work to fatigue by means of determining the content of energy sources in muscles (creatine, creatine phosphoric acid, carnosine cholesterin, glycogen), some redox enzymes (catalase, dehydrogenases), lactic acid, vitamins (ascorbic acid, B1). It is emphasized that the scientific legacy of O. V. Palladin's school is of great practical importance for rational substantiation of regimes of physical loads of sportsmen and physical culture men, production sphere workers. The works of this school have exerted considerable influence on the solution of labour physiology problem.
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PMID:[Research of Academician O.V. Palladin and his school in the field of biochemistry and physiology of muscles]. 922 45

The aim of the study was to determine the bond strength of glass ionomer and resin-modified glass ionomer sealants compared to Bis-GMA sealants using both static and cyclic fatigue shear testing. Four materials were evaluated: D, a Bis-GMA sealant with 10% phosphoric acid etchant; FC, a resin-modified glass ionomer sealant with 20% polyacrylic acid etchant; FD, a resin-modified glass ionomer sealant with 10% polyacrylic acid etchant; and FSC, a self-cured glass ionomer sealant with no etchant. Gelatin capsules filled with the sealant material were bonded to the enamel surfaces of bovine teeth after appropriate surface conditioning and then tested in shear static and cyclic fatigue. Static and cyclic shear bond strengths, respectively, for each group were (MPa): FC: 21.1+/-2.8 and 17.1+/-3.1; FD: 14.6+/-5.9 and 8.5+/-3.1; D: 10.8+/-4.9 and 4.7+/-2.6; FSC: 8.7 (1.0 and 2.9+/-0.6. The resin-modified glass ionomer sealants had better fatigue bond strength than both Bis-GMA and self-cured glass ionomer sealants with the surface conditioning affecting the bond strength of the resin-modified glass ionomer sealants.
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PMID:Bond strength of Bis-GMA and glass ionomer pit and fissure sealants using cyclic fatigue. 952 61

Phosphate depletion is associated with neuromuscular dysfunction due to changes in mitochondrial respiration that result in a defect of intracellular oxidative metabolism. Phosphate diabetes causes phosphate depletion due to abnormal renal re-absorption of phosphate be the proximal renal tubule. Most of the symptoms presented by patients with phosphate diabetes such as myalgia, fatigue and mild depression, are also common in patients with chronic fatigue syndrome, but this differential diagnosis has not been considered. We investigated the possible association between chronic fatigue syndrome and phosphate diabetes in 87 patients who fulfilled the criteria for chronic fatigue syndrome. Control subjects were 37 volunteers, who explicitly denied fatigue and chronic illness on a screening questionnaire. Re-absorption of phosphate by the proximal renal tubule, phosphate clearance and renal threshold phosphate concentration were the main outcome measures in both groups. Of the 87 patients with chronic fatigue syndrome, nine also fulfilled the diagnostic criteria for phosphate diabetes. In conclusion, we report a previously undefined relationship between chronic fatigue syndrome and phosphate diabetes. Phosphate diabetes should be considered in differential diagnosis with chronic fatigue syndrome; further studies are needed to investigate the incidence of phosphate diabetes in patients with chronic fatigue syndrome and the possible beneficial effect of vitamin D and oral phosphate supplements.
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PMID:Phosphate diabetes in patients with chronic fatigue syndrome. 1019 6

The aim of this in vitro study was to compare quasistatic and cyclic fatigue dentin bond strength of modern adhesive systems representing different generations. One hundred and fifty cavities were made in discs of freshly extracted human third molars and filled with direct resin composite restorations. Dentin adhesives of different generations (SY = Syntac Classic, multi-step system with self-etching primer; SE = Syntac Classic with additional phosphoric acid etching prior to application of the self-etching primer; SB = Scotchbond Multi-Purpose Plus, multi-step system with total etching; PE = Prime & Bond 2.1, single-step system with and without [PB] total etching) were used in combination with one hybrid composite. After 21 days of storage, 10 specimens for each adhesive system were subjected to thermocycling (1150 cycles) for 24 h and were afterwards debonded in a push-out test. Another 20 specimens were tested with cyclic fatigue according to the staircase method with 5000 cycles for each specimen. Static and cyclic push-out bond strengths, respectively, for each group were (MPa): SY 16.9 +/- 0.9 and 14.2 +/- 1.7, SE 17.5 +/- 1.8 and 14.8 +/- 3.4, SB 18.5 +/- 1.7 and 13.9 +/- 2.1, PB 14.6 +/- 2.2 and 7.2 +/- 2.4, PE 13.4 +/- 2.2 and 6.8 +/- 1.8. Both quasistatic and dynamic bond strengths revealed better values for the multi-step systems (P < 0.05). All adhesive systems tested revealed a significant fatigue behaviour which was more pronounced for the one-bottle system with a decrease of about 50% independent of additional dentin etching.
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PMID:Fatigue behaviour of different dentin adhesives. 1052 87

A component of ATP, phosphate is at the hub of the energy-related mechanisms operative in muscle cells. Together with calcium, phosphate is involved in bone tissue mineralization: thus, a chronic alteration in the metabolism of phosphate can induce bone and joint disorders. Diagnosis of chronic hypophosphatemia. Serum phosphate, calcium, and creatinine should be assayed simultaneously. Serum calcium is increased in hypophosphatemia caused by hyperparathyroidism and decreased in osteomalacia. Urinary phosphate excretion should be measured in patients with a normal serum calcium level and a serum phosphate level lower than 0.80 mmol/L. A decrease in urinary phosphate excretion to less than 10 mmol/24 h strongly suggests a gastrointestinal disorder, such as malabsorption, antacid use, or chronic alcohol abuse. In patients with a urinary phosphate excretion greater than 20 mmol/24 h, the maximal rate of tubular reabsorption of phosphate (TmPO4) and the ratio of TmPO4 over glomerular filtration rate (GFR) should be determined to look for phosphate diabetes. Manifestations and causes of phosphate diabetes in adults. Moderately severe phosphate diabetes in adults manifests as chronic fatigue, depression, spinal pain, and polyarthralgia, with osteoporosis ascribable to increased bone resorption. Although many cases are idiopathic, investigations should be done to look for X-linked vitamin D-resistant rickets missed during childhood, a mesenchymatous tumor, or Fanconi's syndrome with renal wasting of phosphate, glucose, and amino acids. Management of phosphate diabetes. Phosphate supplementation and, in patients with normal urinary calcium excretion, calcitriol produce some improvement in the symptoms and increase the bone mineral density. Whether dipyramidole is clinically effective remains unclear.
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PMID:Phosphate, the renal tubule, and the musculoskeletal system. 1139 20

1. Phosphate ions (P(i)) enter intracellular Ca2+ stores and precipitate Ca2+. Since transport pathways for P(i) across the membrane of intracellular calcium stores have not been identified and anion channels could provide such a pathway, we have examined the P(i) conductance of single anion channels from the sarcoplasmic reticulum (SR) of rabbit skeletal muscle using the lipid bilayer technique. 2. Two anion channels in skeletal muscle SR, the small conductance (SCl) and big conductance (BCl) chloride channels, were both found to have a P(i) conductance of 10 pS in 50 mM P(i). The SCl channel is a divalent anion channel which can pass HPO4(2-) as well as SO4(2-) (60 pS in 100 mM free SO4(2-)). The BCl channel is primarily a monovalent anion channel. The SCl and BCl channels are permeable to a number of small monovalent anions, showing minor selectivity between Cl-, I- and Br- (Cl- > I- > Br-) and relative impermeability to cations and large polyatomic anions (Cs+, Na+, choline+, Tris+, Hepes- and CH3O3S-). 3. The P(i) conductance of SCl and BCl channels suggests that both channel types could sustain the observed P(i) fluxes across the SR membrane. Comparison of the blocking effects of the phosphonocarboxylic acids, ATP and DIDS, on the anion channels with their effects on P(i) transport suggests that the SCl channel is the more likely candidate for the SR P(i) transport mechanism. 4. The SCl channel, with previously unknown function, provides a regulated pathway for P(i) across the SR membrane which would promote P(i) entry and thereby changes in the rapidly releasable Ca2+ store during onset and recovery from muscle fatigue. Anion channels may provide a pathway for P(i) movement into and out of Ca2+ stores in general.
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PMID:Phosphate ion channels in sarcoplasmic reticulum of rabbit skeletal muscle. 1155 70


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