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

Classic renal tubular acidosis is characterized by a primary defect in establishment of a large hydrogen ion gradient across the distal renal tubule. Thus the development of hyperchlorenic metabolic acidosis follows. In addition, hypokalemia results from renal potassium wasting secondary hyperaldosteronism from sodium wasting and contraction of the extracellular fluid. The presenting signs and symptoms are growth retardation, fatigue, periodic paralysis, polyuria, polydipsia, vomiting and constipation as well as nephrocalcinosis and nephrolithiasis. It is suggested that effective treatment with alkali therapy requires markedly higher doses than formerly recommended, and may related to a higher rate of endogenous acid production from (1) intermediary metabolism of sulfur amino acids and organic acids, (2) impaired tubular reabsorption of bicarbonate and (3) hydrogen ion release from hydroxyapatite formation. It is also suggested that acidosis may interfere with vitamin D metabolism and thus play an important role in the pathoetiology of the growth failure in children with this disorder.
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PMID:Acid-base, calcium, potassium and aldosterone metabolism in renal tubular acidosis. 3 60

There is considerable debate regarding the ergogenic effects of sodium bicarbonate (NaHCO3) on racing performance in horses. Anecdotal evidence suggests that NaHCO3 improves performance by increasing the buffering capacity of the blood and delaying the onset of hydrogen ion-induced fatigue. In a cross-over study, 16 Thoroughbred racehorses were given an aqueous solution of NaHCO3 (0.4 g/kg in 1 litre H2O) or a control treatment (1 litre H2O) before a 1600-m race. Treatments were administered 3 h before the race, which was the time to peak buffering capacity (2.5-3.0 h) determined in a separate study. Before the race, there was a significant increase in venous HCO3- and pH in the NaHCO3-treated horses. After the race, there was a significant increase in venous blood pH and lactate in the NaHCO3-treated horses. Collectively, the data suggest an improved buffering capacity of the blood after NaHCO3 treatment. However, there was no change in race times or venous partial pressure of carbon dioxide. Therefore, the administration of NaHCO3 provided no ergogenic benefit to horses competing in a 1,600-m race.
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PMID:Effects of induced alkalosis on performance in thoroughbreds during a 1,600-m race. 131 65

There are at least 5 metabolic causes of fatigue, a decrease in the phosphocreatine level in muscle, proton accumulation in muscle, depletion of the glycogen store in muscle, hypoglycaemia and an increase in the plasma concentration ratio of free tryptophan/branched-chain amino acids. Proton accumulation may be a common cause of fatigue in most forms of exercise and may be an important factor in fatigue in those persons who are chronically physically inactive and also in the elderly: thus, the aerobic capacity markedly decreases under these conditions, so that ATP must be synthesized by the much less efficient anaerobic system. A marked increase in the plasma fatty acid level, which may occur when liver glycogen store is depleted and when hypoglycaemia results, or during intermittent exercise when the rate of fatty acid oxidation may not match the mobilisation of fatty acids, could be involved indirectly in fatigue. This is because such an increase in the plasma level of fatty acids raises the free plasma concentration of tryptophan, which can increase the entry of tryptophan into the brain, which will increase the brain level of 5-hydroxytryptamine: there is evidence that the latter may be involved in central fatigue. In this case, provision of branched-chain amino acids in order to maintain the resting plasma concentration ratio of free tryptophan/branched-chain amino acids should delay fatigue--there is prima facie evidence in support of this hypothesis. This hypothesis may have considerable clinical importance.
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PMID:Physical and mental fatigue: metabolic mechanisms and importance of plasma amino acids. 136 Mar 9

Muscular fatigue is manifested by a decline in force- or power-generating capacity and may be prominent in both submaximal and maximal contractions. Disturbances in muscle electrolytes play an important role in the development of muscular fatigue. Intense muscular contraction is accompanied by an increased muscle water content, distributed in both intracellular and extracellular spaces. This water influx will modify ionic changes in both compartments. Changes in muscle intracellular electrolyte concentrations with intense contraction may be summarised as including decreases in potassium (6 to 20%) and in creatine phosphate (up to 70 to 100%) and increases in lactate (more than 10-fold), sodium (2-fold) and small, variable increases in chloride. The net result of these intracellular ionic concentration changes with exercise will be a reduction in the intracellular strong ion difference, with a consequent marked rise in intracellular hydrogen ion concentration. This intracellular acidosis has been linked with fatigue via impairment of regulatory and contractile protein function, calcium regulation and metabolism. Potassium efflux from the contracting muscle cell dramatically decreases the intracellular to extracellular potassium ratio, leading to depolarisation of sarcolemmal and t-tubular membranes. Surprisingly little research has investigated the effects of intense exercise training on electrolyte regulation and fatigue.
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PMID:The roles of ionic processes in muscular fatigue during intense exercise. 137 45

The effects of aging on the in situ buffering capacity of fast-twitch muscle fibers was examined in the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles of specific pathogen free Fischer 344 rats. Muscles were electrically stimulated with trains of impulses lasting 100 ms at a frequency of 80 Hz. Trains were delivered at a rate of 1 Hz for 1 min with the hindlimb circulation occluded. Muscle hydrogen ion (H+) release during stimulation was estimated from the accumulation of metabolites. The free [H+] was measured using an homogenate technique. Muscle buffering capacity (Slykes) was estimated as delta mmol H+/l muscle water/delta pH unit. Muscle pH was unaffected by age both at rest and following stimulation in the TA and EDL. H+ release and buffering capacity were significantly reduced in aged TA muscle but unaffected by age in the EDL. Reduced buffering through metabolic processes accounted for only a small portion of the lower buffering capacity in aged TA. Most of the decrease in buffering capacity appeared to be due to reduced protein buffering. Therefore, aged TA muscle was less able to buffer a given H+ load when compared to adult controls. A more rapid accumulation of H+ during intense stimulation may lead to a earlier onset of fatigue in the aged muscle. It is not clear why the EDL buffering capacity was unaffected by age when the fiber mass profiles of the EDL and TA muscles appear similar (approximately 80% fast glycolytic fibers). It is possible that alterations in activity patterns with aging could have differential effects on the two muscles. Detailed activity pattern and fiber mass analyses are required in adult and aged EDL and TA muscles of Fischer 344 rats to answer this question.
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PMID:Effect of aging on the buffering capacity of fast-twitch skeletal muscle. 192 15

Recent investigations using direct (microneurographic) recordings of MSNA have provided a substantial amount of new information on the regulation of sympathetic nervous system control of nonactive skeletal muscle blood flow during exercise in humans. Some of the new conclusions from these studies discussed in this review include: 1. The direction, pattern and magnitude of the MSNA response to exercise depend on the collective influence of a number of factors, including the mode (isometric or rhythmic), intensity, and duration of the exercise, the size of the contracting muscle mass, and possibly the level of conditioning (physical training) of the exercising muscles. The MSNA response also appears to be tightly coupled with the onset and progression of muscle fatigue, at least during sustained, isometric contractions. 2. Increases in MSNA evoked during exercise with the arms are fairly uniform among different skeletal muscle nerves, and these responses correlate strongly with changes in venous plasma norepinephrine concentrations, limb vascular resistance and arterial blood pressure. Thus, increases in this neural activity during exercise are associated with the expected physiological responses. 3. The MSNA response to the same level of exercise varies markedly among healthy subjects but appears to be consistent over time within a particular subject. 4. The muscle metaboreflex (muscle chemoreflex) is the primary-mechanism by which MSNA is stimulated during small-muscle, isometric exercise in humans. In contrast, central command has a relatively weak influence on MSNA during this type of exercise. 5. Muscle metaboreflex-stimulation of MSNA also occurs during dynamic exercise, but only at or above moderate, submaximal intensities (i.e., not during mild exercise). 6. Muscle metaboreflex-evoked increases in MSNA during exercise are strongly associated with glycogenolysis and the consequent cellular accumulation of hydrogen ions in the contracting muscles. 7. Sympathoinhibitory cardiopulmonary reflexes do not appear to modulate the MSNA responses to isometric exercise in the healthy human. However, arterial baroreflexes exert a potent inhibitory effect on MSNA during this form of exercise. The mechanisms involved in the regulation of MSNA during large-muscle, dynamic leg exercise is an important topic for future investigations, as is the relationship between MSNA and sympathetic outflow to other regional circulations (e.g., heart, viscera, skin) during various forms of exercise.
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PMID:Regulation of muscle sympathetic nerve activity during exercise in humans. 193 89

The plasma concentration of lisuride and prolactin have been measured in twelve healthy male volunteers after IV, IM or SC injection of 25 micrograms lisuride hydrogen maleate as an aqueous solution. After IV administration the plasma lisuride fell in two phases with half-lives of 14 min and 1.5 h. Total clearance was 13 ml.min-1.kg-1. After IM and SC injection the plasma concentrations peaked at 12 to 15 min and the profiles were similar to that found after IV administration. The systemic availabilities were 90% and 94%, respectively. Prolactin concentrations were reduced by a maximum of 60% relative to the normal circadian rhythm after all three routes of administration. The treatments were well tolerated, the only adverse reactions reported by some of the volunteers being mild, transient dizziness, tiredness, and nausea.
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PMID:The pharmacokinetics and pharmacodynamics of lisuride in healthy volunteers after intravenous, intramuscular, and subcutaneous injection. 205 Jan 75

Twenty-two Standardbred horses in race training were used in a crossover experiment to determine the effect of oral sodium bicarbonate (NaHCO3) administration on performance and metabolic responses to a 1.6-km (1-mile) race. Horses were paired and one horse in each pair was treated with either NaHCO3 (300 mg/kg BW) or a placebo, 2.5 h before they raced against each other. Each horse was scheduled to compete in two races, approximately 1 wk apart, one on each treatment. Horses always raced in the same pairs. Fourteen horses successfully completed both races. Jugular blood samples were obtained 1.5 h after treatment (rest), immediately before racing, 5 min post-race and 15 min post-race. In six horses, blood samples also were obtained 30 min post-race. Race times averaged 1.1 s faster after NaHCO3 treatment (P less than .1). Sodium bicarbonate treatment also elevated blood pH (P less than .05). In the horses sampled 15 and 30 min post-race, blood lactate disappearance was faster with the NaHCO3 treatment (P less than .05). The NaHCO3 may delay the fatigue precipitated by i.m. acidosis. Because other factors may limit performance (musculoskeletal soundness, cardiovascular and respiratory ability), NaHCO3 would not be expected to enhance the performance of all horses. However, the effect of NaHCO3 on lactate clearance may have implications for all intensively worked horses; because lactate and the associated hydrogen ions are believed to cause muscle damage and soreness, any mechanism to increase their removal rate could benefit the equine athlete.
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PMID:Effect of sodium bicarbonate on racing Standardbreds. 215 89

Substrate depletion and end product accumulation are two important factors in exercise fatigue. Fatigue during long-term exercise results from a depletion of muscle and liver glycogen and coincides with an inability to maintain blood glucose levels. During high intensity exercise, the rapid catabolism of carbohydrate and the resultant production of lactate and hydrogen ions cause a reduction in muscle pH that inhibits maximum force generation. Dietary manipulations that can influence carbohydrate status or lactate accumulation may be beneficial to performance. In human athletes, carbohydrate loading and carbohydrate supplementation can enhance endurance time during long-term exercise. These practices have not been explored extensively in the equine athlete, although glycogen loading does not enhance the performance of horses during short-term intense work. Short-term work can be detrimentally affected if glycogen levels are inadequate. The most marked effect of exercise on nutrient requirements is in the energy requirement. Horses in heavy training may require more energy than they can consume on a conventional diet. Fat has been added to horse diets to increase energy density, usually at levels between 6% and 12% of the total diet. Although protein requirements may be slightly increased in the working horse, supplementing protein as a means of adding calories is not an efficient practice. In addition, although studies with horses are not available, human studies indicate that there are no benefits to vitamin supplementation above required levels. At this point, more is unknown than is known about feeding performance horses. Most information on fuel utilization is extrapolated from studies with rats and humans. Areas that have received little attention but are critical to optimizing feeding practices are the timing of pre-event feeding and the determination of ideal body composition in equine athletes of different types.
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PMID:Nutrition and fuel utilization in the athletic horse. 220 99

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


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