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

We studied changes in muscle proton (1H) transverse relaxation times (T2) by magnetic resonance imaging during exercise and compared these changes with alterations in muscle metabolism measured by phosphorus-31 magnetic resonance spectroscopy (31P-MRS). Eleven subjects completed two trials of intermittent incremental forearm wrist flexion exercise requiring 30 contractions/min for 5 min, 7 min of recovery between stages, and 5-N load increments/stage. Between stages of the first trial, T2 images of muscle 1H were obtained. Muscle T2 increased from 27.3 +/- 1.1 (SD) ms at rest to 35.8 +/- 3.6 ms after volitional fatigue (P < 0.05), whereas less active wrist extensor muscle T2 remained unchanged (26.8 +/- 0.9 to 28.8 +/- 1.6 ms; P > 0.05). After localizing the predominant muscle recruited from the T2 images, subjects completed an identical trial at least 1 wk later but involving surface coil 31P-MRS of the T2-enhanced muscle to measure the H+ concentration ([H+]). Intramuscular [H+] of T2-enhancing muscle increased from 1.1 +/- 0.1 x 10(-7) M at rest to 4.1 +/- 2.0 x 10(-7) M after volitional fatigue. Both muscle T2 and intramuscular [H+] increased in a bimodal manner, with T2 increasing before muscle [H+] (P < 0.05). The correlation coefficient between the percent change in T2 and muscle [H+] during exercise was +0.74 (range 0.48-0.98; P < 0.05) and +0.47 during recovery. After 12 min of recovery, muscle [H+] decreased to 1.4 +/- 0.3 x 10(-7) M (P < 0.05), and T2 remained close to postexercise values (32.2 +/- 3.1 ms, P > 0.05). The data indicate that 1) the T2 increases during increases in exercise intensity are nonlinear, 2) the T2 increases during exercise are significantly correlated with increases in [H+], and 3) the slow recovery of T2 compared with [H+] indicates that [H+] has a minor contribution to the recovery in T2.
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PMID:Changes in muscle proton transverse relaxation times and acidosis during exercise and recovery. 856 85

The most attractive feature of nuclear magnetic resonance spectroscopy (MRS) is the noninvasive and nondestructive measurement of chemical compounds in intact tissues. MRS already has many applications in comparative physiology, usually based on observation of 31P, since levels of phosphorus compounds indicate tissue energy status and are changed during exercise, fatigue, recovery, hypometabolism, anesthesia, hypoxia, hypercapnia, and osmotic and acid stress. Nuclei other than 31P may also be monitored, such as 1H, 13C, 15N, 19F, or 23Na, and applied in biological research. Particularly, 13C-MRS is interesting because it allows the analysis of metabolic pathways in living systems. Applications of MRS in comparative physiology and biochemistry are comprehensively discussed in this review. The main focus is on anaerobic metabolism during hypoxia, ischemia, and exercise. Species as widely different as slime molds, nematodes, frogs, turtles, and ducks have been studied by 31P-MRS. It is not surprising that striking species differences do occur, but many similarities are also observed. Unique is the occurrence of six different phosphagens with different values of Gibbs free energy in polychete worms The presence of a particular phosphagen may be related to the average oxygen tension within the tissues. Phosphagens and their kinases are also discussed in relation to hypercapnia and acid stress. Other topics discussed in this paper are enzyme kinetics, anesthetics, development and growth, parasitism, and the detection of previously unknown compounds.
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PMID:Nuclear magnetic resonance spectroscopy of living systems: applications in comparative physiology. 875 89

Dimethylformamide (DMF) is widely used as an industrial solvent in spite of well-established hepatotoxicity and adverse effects on in vitro muscle contractility. The doses used in the studies describing these effects were higher than the doses required to solubilize drugs to be injected at very low levels and the potential effects of DMF at very low levels has not yet been explored. The goal of this work was to study the effects of an acute, low dose of DMF (3 mu/100 g body weight, administered i.p.) on mechanical parameters and energy metabolism of contracting rat skeletal muscle. Metabolic changes were followed by 31P nuclear magnetic resonance spectroscopy. Tension was significantly lower during the fatigue test in DMF-treated rats than in controls. Phosphomonoesters and inorganic phosphorus level were lower, and intracellular pH was higher in DMF-treated rats than in controls, showing that energy metabolism was activated to a lesser degree, in relation with the lower mechanical performance, after DMF. Skeletal muscle is a target organ for dimethylformamide which has a major effect on muscle contractility by decreasing the tension developed. The effects of DMF suggest that it is unsuitable for use as a drug vehicle for in vivo injections, even at a very low nonhepatotoxic doses.
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PMID:Effects of dimethylformamide on in vivo fatigue and metabolism in rat skeletal muscle measured by 31P-NMR. 878 91

The objective of this paper was to propose a mathematical model for the fatigue and recovery phases of a paraplegic's quadriceps muscle subjected to intermittent functional electrical stimulation (FES). The model is based on in vivo, noninvasive, recording of fatigue related metabolic parameters recorded during stimulation and recovery. Records of the time variations of the muscle's phosphorus metabolites, particularly the phosphocreatine (PCr) and inorganic phosphorus (Pi), obtained from 31P magnetic resonance spectroscopy (MRS), were used to calculate the intracellular pH level in the muscle and this latter parameter was incorporated in a musculo-tendon model. The fatigue-recovery model allows the transition from the fatiguing phase to the recovery phase as soon as the stimulation terminates and vice versa. This model was incorporated into a Huxley type muscle model expressing the dynamics of the muscle. Two ordinary differential equations describing the musculo-tendon dynamics and the dynamics of the activation were solved simultaneously and records of the force trajectory during intermittent stimulations were obtained. Study cases ranging from 5 to 30 s for each of the stimulation and recovery alternating phases were stimulated. The force and the total impulse in the modeled quadriceps muscle were computed. It was found that the greatest impulse was produced in intermittent stimulation of 40-50 s duty cycle, with a 50 percent ratio between the stimulation and recovery intervals. An additional series of six runs, including two contractions, one of 3 min and one of 1 min, separated by rest periods of 3, 6, 9, 12, 15, and 30 min was performed. From the predicted force trajectories obtained, the maximal force values served for comparison with measured values made on one patient.
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PMID:A model of fatigue and recovery in paraplegic's quadriceps muscle subjected to intermittent FES. 887 58

Using 31P nuclear magnetic resonance (NMR) spectroscopy, the bioenergetics of paralyzed muscles activated by functional electrical stimulation (FES) were studied in vivo during fatigue and recovery on paraplegic subjects. During the activation phase of the muscle, the muscle force was also monitored. The phosphorus metabolites were found to vary systemically during the fatigue and to recover slowly to their rest state values after cessation of FES. During fatigue, a good correlation was found between the decaying force and each of the profiles of phosphocreatine, inorganic phosphorus, and intracellular pH. A musculotendon 5 element model was proposed for the activated muscle to predict its force generation capacity. A fatigue recovery function, based on the metabolic profiles, was introduced into the model. This model allowed us to predict the force expected to be developed as a function of the time after recovery of given time durations. Validation experimental measurements of force were carried out and included recurrent fatigue tests, both in the initially unfatigued state and at various times in the postfatigue stage of the muscle. Comparison of the predicted and measured forces indicated satisfactory agreement of the results. The developed model of muscle dynamics should help to design a strategy for reducing muscle fatigue under FES.
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PMID:Predicted and measured muscle forces after recoveries of differing durations following fatigue in functional electrical stimulation. 914 14

Eighty-six workers exposed to zinc phosphide (Zn3P2) pesticide were studied for evidence of neuropsychiatric manifestations. They were evaluated clinically, by electroencephalography (EEG), and, in some cases, by electromyography (EMG). All were males (mean age, 35.8 years; mean duration of exposure to zinc phosphide, 11.3 years). Most presented with one (or more) neuropsychiatric symptom(s), including fear of poisoning, anxiety, impotence, and easy fatigue. About half showed evidence of neuropsychiatric signs, including hyperreflexia, polyneuropathy, lumber radiculopathy, and cervical myelopathy, as well as anxious mood, impaired attention, and psychomotor stimulation. EEG recordings showed abnormal findings in 17.4% of the subjects. The mean age in that group was 39.1 years; mean duration of exposure to Zn3P2 was 15.1 years. EMG studies showed evidence of partial denervation of the anterior tibial group of muscles and flexor digiti minimi in 2 of the 30 workers (6.7%) who underwent EMG examination. Serum levels of zinc (Zn) and cadmium (Ca) were significantly higher in exposed workers than in controls (P < 0.005). Serum copper (Cu), iron (Fe), phosphorus (P), and magnesium (Mg) were significantly lower in exposed workers than in controls. Electrophoretic pattern of globulin showed that gammaglobulin fraction was significantly increased (P < 0.005); alpha2 and beta-globulin were decreased (P < 0.005) in exposed workers. Lipoprotein pattern showed that the total lipids, B-lipoprotein, and B/alpha ratio were significantly increased (P < 0.005) in exposed workers; the alpha1 lipoprotein was decreased. Triglycerides and cholesterol were significantly increased (P < 0.001), and phospholipids and phospholipid/cholesterol ratio were significantly decreased (P < 0.005) in exposed workers compared to controls. The study findings indicated that exposure to Zn3P2 not only caused mild acute and subacute liver cell damage, but also affected renal function and perhaps B-cells of the pancreas. A total of 68.6% of the exposed workers had chest symptoms; only 24.4% presented with chest or cardiac signs. Ventilatory functions were abnormal in 70% of the exposed workers; abnormal ECG findings were present in 12.8%.
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PMID:Neuropsychiatric syndromes and occupational exposure to zinc phosphide in Egypt. 931 48

The nephrology nurses in collaboration with the nephrologist worked closely to avoid severe symptomatology related to calcium phosphorus imbalance. The surgical team support was discontinued 48 hours after the removal of the autotransplant. The patient exhibited classic signs of secondary hyperparathyroidism, as indicated by laboratory tests, anemia, and pruritus. Despite the level of anemia, the patient did not complain of fatigue or dyspnea. A hypocalcemic crisis was avoided by the ongoing assessment and intervention the patient received from the nursing staff. Four of the five stated goals were met. The patient is free of disability as evidenced by steady gait, normal range of motion, and adequate muscle strength. The calcium and phosphorus levels and the calcium phosphorus product are within acceptable ranges (see Figure 1). J.I. has always had information about diet and medication management but has demonstrated variable adherence to the regimen. However, the nephrology nurses plan to continue with counseling and education as needed.
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PMID:Patient, nurses, and physicians collaborating in the management of a patient following autotransplant parathyroidectomy. 932 98

The metabolism of the human masseter muscle was investigated using phosphorus (31p) magnetic resonance spectroscopy (MRS) during long periods of exercise and recovery. Eleven subjects aged 19 to 28 yr were examined by 31p MRS during four consecutive periods of 13 min each: rest, exercise, recovery 1 and 2. For each subject, a biting force equal to 20% of maximum voluntary biting force was applied and controlled during the exercise period to produce maximum fatigue. 31p MR spectra were localized from a 24 cm3 volume of interest using an image selected in vivo spectroscopy (ISIS) sequence and a 6 cm diameter surface coil placed on the left masseter. Compared to the resting level, the phosphocreatine (PCr) content decreased by 26% during exercise, while the inorganic phosphate (Pi) concentration increased by 65%. During the two recovery periods, the Pi content remained decreased compared with the resting level by 36% and 30%, respectively. The Pi/PCr ratio was increased from 0.30+/-0.04 at rest to 0.63+/-0.13 during exercise while the adenosine triphosphate (ATP)/Pi ratio was decreased. The pH decreased from 7.02+/-0.03 to 6.93+/-0.04 during exercise and returned to control level (7.09+/-0.08) only during the second recovery period. These results suggest that the masseter muscle is characterized by high ATP turnover and, therefore, high oxidative phosphorylative activity in agreement with its constitution of predominantly fatigue resistant type I fibers.
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PMID:A metabolism study of human masseter muscle by 31P magnetic resonance spectroscopy during long periods of exercise and recovery. 952 54

We studied the physiologic adaptation of patients with mitochondrial myopathies to aerobic training. Ten patients underwent individually supervised, moderate-intensity aerobic training on a treadmill for 8 weeks. Biochemical and functional measures improved with training. Estimated aerobic capacity increased by 30%. Blood lactate concentrations at rest and after exercise decreased by 30%. Muscle phosphorus magnetic resonance spectroscopy measurements of adenosine diphosphate recovery after exercise improved by more than 60%. Fatigue and tolerance to daily activities also improved. Although the improvement in exercise tolerance may be due in part to reversal of the effects of secondary deconditioning, this uncontrolled clinical trial suggests that aerobic training can benefit patients with mitochondrial myopathies.
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PMID:Effects of aerobic training in patients with mitochondrial myopathies. 956 94

It has been shown previously that some patients with chronic fatigue syndrome show an abnormal increase in plasma lactate following a short period of moderate exercise, in the sub-anaerobic threshold exercise test (SATET). This cannot be explained satisfactorily by the effects of 'inactivity' or 'deconditioning', and patients with abnormal lactate responses to exercise (SATET +ve) have been found to have significantly fewer Type 1 muscle fibres in quadriceps biopsies than SATET -ve patients. We performed phosphorus magnetic resonance spectroscopy on forearm muscles of 10 SATET +ve patients, 9 SATET -ve patients and 13 sedentary volunteers. There were no differences in resting spectra between these groups but at the end of exercise, intracellular pH in the SATET +ve patients was significantly lower than in both the SATET -ve cases and controls (P < 0.03), and the SATET +ve patients also showed a significantly lower ATP synthesis rate during recovery (P < 0.01), indicating impaired mitochondrial oxidative phosphorylation. These observations support other evidence which indicates that chronic fatigue syndrome is a heterogeneous disorder, and confirms the view that some chronic fatigue syndrome patients have a peripheral component to their fatigue.
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PMID:Heterogeneity in chronic fatigue syndrome: evidence from magnetic resonance spectroscopy of muscle. 963 3


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