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

The bioenergetic correlates of skeletal muscle fatigue were assessed in vivo with phosphorus-31 nuclear magnetic resonance (31P-NMR) spectroscopy. After surgical construction of latissimus dorsi muscle ventricles, seven beagles underwent 31P-NMR spectroscopy during 12-min exercise protocols at 25- and 85-Hz stimulation frequencies and during both isovolumetric and dynamic contractions. Exercise at 85 Hz was associated with significantly greater fatigue than exercise at 25 Hz. At both frequencies, the onset of exercise was associated with a marked increase in inorganic phosphate (Pi) and a decrease in phosphocreatine (PCr). As the muscle fatigued at 85 Hz but not at 25 Hz, the phosphorus spectra returned to near baseline with a decrease in Pi and increase in PCr. For a given amount of force generated, the Pi-to-PCr ratio was higher for dynamic contractions than for isovolumetric contractions. This study indicates that high-frequency fatigue is unlikely to result from the direct effects of high-energy phosphate metabolism and that contractions producing external work consume more metabolic energy than equally forceful isometric contractions.
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PMID:Skeletal muscle bioenergetics during frequency-dependent fatigue. 200 85

Skeletal muscle activity is invariably associated with a decline in force-generating capacity (fatigue). The build-up of metabolic by-products such as intracellular H+ and inorganic phosphate (Pi) has been shown to be one of the potential mechanisms of muscle fatigue. The use of phosphorus magnetic resonance spectroscopy is a repeatable and useful tool to study the effect of pH and Pi on force development. When maximal exercise is preceded by submaximal exercise to reduce the starting muscle pH and increase Pi, the degree of muscle fatigue correlates more strongly with H2PO4- than pH or Pi alone. However, other studies in humans have found that H2PO4- does not always correlate well with fatigue. The use of ramp exercise protocols allow repeatable and sensitive measurement of changes in muscle metabolism in response to endurance training. Chronic electrical stimulation in dogs and endurance training in humans results in reduced pH and Pi changes at the same exercise intensities. This means that the effect of pH and Pi in depressing force development is reduced, which could partially explain the increased fatigue resistance seen following endurance training.
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PMID:Biochemical adaptations to training: implications for resisting muscle fatigue. 205 44

The fields of muscle physiology and biochemistry have already identified some of the key components of ATPase hydrolysis products that are involved in muscle fatigue. The concentration of the relevant chemical species can be readily measured by nuclear magnetic resonance techniques in muscle. Now the question is: is alteration of cellular energy balance and the normal balance between supply and demand disturbed in fibromyalgia? Since these chemical events account for a very large amount of muscle reduced performance as well as reduction in both velocity and force, at the very least one ought to identify how large these changes are in any patient in whom we are trying to assess the degree to which these chemical changes might be associated with muscle fatigue. An objective chemical criteria for muscle performance is possible with modern noninvasive phosphorus magnetic resonance spectroscopy.
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PMID:Muscle energy metabolism, nuclear magnetic resonance spectroscopy and their potential in the study of fibromyalgia. 260 14

Neurological symptoms including lethargy, obtundation, and confusion are early and common findings in patients with sepsis. The etiology of the mental status changes that occur during severe infection is not known. We investigated the effects of sepsis on the levels of high-energy phosphates to determine whether decreased energy metabolism was a factor in the depressed neurological state. The time course of changes in brain pH and brain high-energy phosphate metabolites during an Escherichia coli infusion was determined from sequential phosphorus-31 nuclear magnetic resonance (31P-NMR) spectra of ketamine-xylazine-anesthetized rats. A second group of rats received 0.9% saline infusion and served as a control group. Despite severe obtundation and near loss of righting reflex, the rats in the septic group had no significant differences in the brain pH, the ratio of phosphocreatine (PCr) to beta-adenosine 5'-triphosphate (beta-ATP), or in the ratio of PCr to Pi. The only significant decrease in brain high-energy phosphates or pH occurred terminally in the septic rat group and corresponded with a rapidly falling arterial blood pressure. We conclude that the severe neurological depression that is characteristic of sepsis is not due to decreased levels of brain high-energy phosphates or brain acidosis.
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PMID:An in vivo examination of rat brain during sepsis with 31P-NMR spectroscopy. 261 Feb 45

1. The relationship between intracellular metabolites and the generation of force during fatigue has been examined in the first dorsal interosseous muscle of the hand. With the arm made ischaemic, the muscle was fatigued by three bouts of maximal voluntary contraction, leaving approximately three minutes ischaemic rest between contractions. During one series of experiments intracellular phosphorus metabolites were measured by nuclear magnetic resonance during the intervals between the fatiguing contractions: in the second series contractile properties were tested with brief electrical stimulation during the rest intervals. 2. The relationships between loss of force and change in metabolite concentrations obtained with four normal subjects were compared with those from one subject with myophosphorylase deficiency (MPD) who could not utilize muscle glycogen and therefore produced no hydrogen ion from glycolysis during exercise. 3. For both the MPD and normal subjects the relationship between relative force loss and inorganic phosphate (Pi) concentration was curvilinear, force changing little in the early stages of the contraction when the intracellular Pi was accumulating rapidly but falling faster when the Pi was above 25 mM and increasing relatively slowly. 4. In the normal subjects intracellular pH fell from a mean of 7.03 +/- 0.01 (mean +/- S.E. of mean, n = 19) in the fresh muscle to 6.51 +/- 0.02 at the end of the fatiguing exercise; force, as a percentage of the initial value, fell in proportion to the increase in H+ concentration. In the MPD subject pH did not change and force loss was therefore independent of H+ accumulation. In the normal subjects the force of the fatiguing muscle showed an approximately linear relationship with the concentration of the monobasic form of inorganic phosphate. However, the MPD subject showed a quite different relationship, with force loss being much greater for a given concentration of monobasic phosphate. This result indicates that monobasic phosphate is not a unique determinant of force loss in fatigued muscle. 5. During the first 60 s of recovery in the normal subjects, pH remained low while force recovered, indicating a mechanism of force loss that was independent of H+ accumulation. However, the recovery of force was not complete, so that for comparable phosphocreatine contents the recovering, more acid, muscle generated less force than the muscle that was being fatigued. It was estimated that H(+)-dependent and independent mechanisms contributed roughly equally to the observed force loss. The relationship between force and the concentration of monobasic phosphate differed in fatiguing and recovering muscle.
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PMID:Changes in force and intracellular metabolites during fatigue of human skeletal muscle. 262 21

A review of metabolic pathways is presented, which are involved in muscular energy production during hypoxia according to recent experimental findings. By means of own exercise examinations the course of reactions providing ATP anaerobically in the muscles of limbs with poor circulation is analysed. Therefore, the arteriovenous differences in the concentrations of lactate, pyruvate, ammonia, hypoxanthine and alanine in the femoral blood of patients with stage II AOD were determined. In addition, the intracellular phosphorus compounds ATP, PCr and Pi as well as the tissue pH were measured noninvasively in the calf muscles using 31P magnetic resonance spectroscopy. The results give evidence for marked activation of the creatine kinase reaction, of glycolysis, of the myokinase reaction and of the purine nucleotide cycle in the ischaemic musculature at loads of short duration, which are in total sufficient to maintain the concentration of ATP even during claudication pain. In spite of salvage pathways like alanine formation, the end products of these "emergency reactions", Pi, H+ and NH4+, accumulate and exert deleterious cytotoxic effects, which are thought to be responsible for rapid muscle fatigue and claudication pain in PAOD.
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PMID:[Regulation of ischemic muscle metabolism in peripheral arterial occlusive disease]. 267 1

Many factors have been proposed to contribute to the development of muscle fatigue, but as yet a definitive assessment of their relative contributions has not been possible. To determine whether changes in bioenergetic factors are determinants of muscle force during the development of fatigue, simultaneous measurements were made during fatiguing exercise of the decline in muscle force and changes in phosphorus (31P) nuclear magnetic resonance (NMR) spectra. The results showed that the decline in force strongly correlated with a rise in inorganic phosphate (Pi) concentration; in contrast, fatigue correlated less strongly with intracellular pH. Similar results were found in different muscles and with different exercise protocols. They suggest that the rise in [Pi] is a mechanism that produces progressive inhibition of the force-generating reaction, while energy availability is not limiting. Down-regulation of force and energy utilization are consistent with fatigue being not simply a disruptive process, but an adaptive response that establishes an equilibrium between energy supply and demand.
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PMID:Investigations of muscle bioenergetics with 31P NMR. 269 38

We used phosphorus magnetic resonance spectroscopy to study skeletal muscle metabolism of trained vs. untrained humans. The forearms of highly trained rowers (n = 10) and age-matched controls were placed in a 1.9-T magnet so that the wrist flexor muscles were placed over a 4-cm transmitting and receiving coil. The subjects performed work by depressing a handle attached to an isokinetic ergometer. Relative concentrations of Pi, phosphocreatine (PCr), and ATP were measured along with intracellular pH. Measurements were made at rest, during steady-state and ramp exercise protocols, and during recovery from exercise. At rest the rowers had Pi/PCr that were not different from control. During steady-state exercise rowers (n = 4) had lower Pi/PCr at the same relative power levels, and the slope of the power vs. Pi-PCr curve was significantly greater than for controls. Rowers (n = 4) also had faster rates of PCr recovery after exercise than controls (T1/2 of 24 +/- 2.0 s for rowers and 47 +/- 8.4 s for controls) when power level was adjusted so that all subjects recovered from the same level of Pi/PCr. During a ramp exercise protocol, the initial slope of the power vs. Pi-PCr curve was greater in three of six rowers compared with controls and at the highest power level rowers had lower Pi/PCr values with less drop in pH. At the end of the ramp test, the same degree of muscle fatigue was associated with much lower levels of H2PO-4 (5.7 +/- 0.70 mM) in rowers compared with controls (13.0 +/- 1.8 mM).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Wrist flexor muscles of elite rowers measured with magnetic resonance spectroscopy. 279 23

Patients with heart failure frequently report leg fatigue during exercise. At present, however, there is no objective method of detecting leg muscle abnormalities in such patients. To determine if phosphorus-31 nuclear magnetic resonance spectroscopy can provide such information, this technique was used to compare calf responses to stair climbing and plantarflexion in 20 patients with heart failure (peak oxygen consumption (VO2) of 13.6 +/- 5 ml/kg/min, ejection fraction 20 +/- 5%) and 9 age-matched normal subjects. Work was quantified by measuring VO2. At rest, both groups exhibited similar inorganic phosphorus to phosphocreatine (Pi/PCr) ratios (patients with heart failure 0.21 +/- 0.07, normal subjects 0.21 +/- 0.06, difference not significant) and pH levels (patients with heart failure 7.06 +/- 0.17, normal subjects 7.05 +/- 0.11, difference not significant). In both normal subjects and patients with heart failure, exercise resulted in a progressive rise in Pi/PCr as VO2 increased. However, examination of the relation of VO2 versus Pi/PCr revealed steeper slopes in patients with heart failure during both stair climbing and plantar-flexion. Neither form of exercise decreased calf pH in normal subjects. In the patients with heart failure, significant decreases in pH were noted during the highest work level of plantarflexion (pH of heart failure patients 6.86 +/- 0.20, pH of normal subjects 7.07 +/- 0.14, p less than 0.01). Metabolic recovery time was also prolonged in the patients with heart failure versus normal subjects (3.3 +/- 0.8 vs 2.1 +/- 0.5 minutes, respectively, p less than 0.002). These findings indicate that phosphorus-31 nuclear magnetic resonance provides objective evidence of leg muscle abnormalities in patients with heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Detection of abnormal calf muscle metabolism in patients with heart failure using phosphorus-31 nuclear magnetic resonance. 319 84

In 10 patients with chronic renal failure (CRF), undergoing hemodialysis, we studied respiratory muscle strength and endurance. The data obtained was compared with those acquired from 10 age-, sex-, weight- and height-matched normal volunteers. Maximal static inspiratory pressures (PImax) measured at residual volume and maximal static expiratory pressure (PEmax) measured at total lung capacity were significantly lower in the CRF group, 58.2 +/- (SD)24.9 and 50.8 +/- (SD)24.2% of predicted, respectively (p less than 0.005, p less than 0.01). There was a significant correlation between PImax and PEmax (r = 0.827, p less than 0.001), indicating similar involvement of both inspiratory and expiratory muscle groups. Maximal voluntary ventilation (MVV), although 84.4% of the predicted value in the CRF group, was significantly lower than in the control group, where it was 114% of predicted (p less than 0.001). MVV also correlated significantly with PImax and PEmax (r = 0.764, p less than 0.001 and r = 0.807, p less than 0.001, respectively). All but one CRF patient had elevated erum inorganic phosphorus levels, and a significant correlation was found between the serum inorganic phosphorus levels and PImax and PEmax (r = 0.718, p less than 0.001). These data indicate that there is an impairment of respiratory muscle strength and endurance in patients with CRF which may predispose the patient to respiratory muscle fatigue.
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PMID:Effect of chronic renal failure on respiratory muscle strength. 324 15


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