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

The lactate concentration in different muscle fibre types was determined in biopsy specimens from human vastus lateralis muscle after 30 and 60 s of maximal dynamic leg exercise. In addition, muscle fibre type distribution, total lactate dehydrogenase (LDH) activity, and isozymes of LDH were determined. In accordance with previous studies (Thorstensson and Karlsson 1976, Nilsson et al. 1977) it was found that an increasing proportion of slow twitch (ST) fibres corresponded to better sustained muscle force. Lactate was found preferentially in fast twitch (FT) fibres after 30 s, but after 60 s this difference was abolished. Differences between the two main muscle fibre types in muscle lactate, total LDH activity, and M-LDH activity were correlated to muscle fatigue. It was concluded that lactate or associated pH changes primarily in FT fibres could be one factor responsible for the impaired muscle function.
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PMID:Muscle fatigue and its relation to lactate accumulation and LDH activity in man. 71 62

Estimation of lactate oxidation in vivo was carried out by a tracer technique in the muscles of the lower hindleg of the dog during tetani of different duration. The fractional (%) rate of lactate oxidation increased markedly, compared with that of the resting muscle, after the first 2 min of stimulation. Lactate oxidation afforded a large contribution to the total oxygen consumption. Fatigue appeared to play a role in limiting lactate oxidation in the later phase of sustained contraction.
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PMID:Lactate oxidation by skeletal muscle during sustained contraction in vivo. 103 26

The relationship between lactic acid concentration and twitch tension was reevaluated in electrically stimulated frog sartorius muscle. In muscles stimulated under anaerobic conditions at a rate of 30 stimuli/MIN CONTRACTILE FORCE DECREASED TO 36% OF THE INITIAL VALUE IN 15 MIN, Concomitantly lactate increased from 3.3 to 18.7 mumol/g of muscle. The correlaiton between the increase in lactate and the decrease in contractile force was significant (r = -0.99, P less than 0.000001). Recovery occurred in two phases. A rapid increase in contractile force, which represented 20% of the total recovery, took place during the first 15 s and occurred concomitantly with an increase in ATP from 3.9 to 4.6 mumol/g. Lactate concentration did not change significantly during this period. The second phase of recovery of contractile force was complete in 50 min. Lactate concentration and contractile force were significatly correlated during recovery (r = -0;92, P less than 0.00001). However, recovery of contractile force lagged behind the decrease in lactate; a given concentration of muscle lactate was associated with a higher contractile force early during development of fatigue than late during recovery.
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PMID:Lactate and contractile force in frog muscle during development of fatigue and recovery. 108 70

The purpose of this study was to determine the concentration of ATP, phosphocreatine (PC), Pi, lactate, and glycogen in single frog skeletal muscle fibers and assess their role in the etiology of muscle fatigue. The frog semitendinosus (ST) muscle was fatigued, quick frozen at selected time points of recovery, and freeze-dried, and single fibers were dissected, weighed, and assayed for ATP, PC, lactate, Pi, and glycogen. The fatigue protocol reduced peak tetanic force (Po) to 8.5% of initial, while ATP and PC decreased from 45.18 to 33.16 and 128.90 to 28.76 mmol/kg dry wt, respectively. Lactate and Pi increased from 29.36 to 100.84 and 33.04 to 142.50 mmol/kg dry wt, respectively. It is doubtful that the small decline in ATP limited cross-bridge force production. Although a significant correlation between the recovery of PC and Po was demonstrated (r = 0.994), the time period showing the fastest rate of force recovery coincided with little change in PC. A significant correlation was demonstrated between the recovery of both total and the H2PO4- form of Pi and Po. In conclusion, the results of this study are incompatible with the hypothesis that the high-energy phosphates (ATP and PC) mediate muscle fatigue. The large increase in Pi with stimulation and the high correlation between the recovery of both total and the H2PO4- form of Pi and Po support a role for Pi in the production of skeletal muscle fatigue.
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PMID:Muscle fatigue in the frog semitendinosus: role of the high-energy phosphates and Pi. 141 69

All exercise draws first on intramuscular stores of ATP and creatine phosphate; initially these are replenished by anaerobic glycolysis. The lactic acid produced contributes to the rapid development of fatigue in high intensity exercise. Aerobic metabolism (at first mainly of glycogen, later increasingly of fat) is the principal route of ATP resynthesis in activities lasting longer than 2 min, but can only maintain work-rates about 1/4 of those possible in very brief bursts. Blood lactate rises at the higher aerobic work rates. 'Lactate threshold' (LT: approximately 2 mmol/l) is almost exactly the speed at which endurance races are won, and close to those apparently providing optimal aerobic training. This training, predominantly of muscle aerobic capacity, elevates LT more than maximum oxygen consumption. LT is not now thought to indicate oxygen-deprivation, but intracellular adjustments driving oxidative phosphorylation faster. Ventilatory breakpoints, formerly considered to indicate LT, correlate more closely with the accumulation of potassium than lactate.
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PMID:Aerobic exercise, anaerobic exercise and the lactate threshold. 145 Aug 85

The development of fatigue was investigated by electrical stimulation in 15 domestic pigs (1 yr old, 70-90 kg body weight) and seven adult dogs (3 yr old, 45 kg body weight). After anaesthesia, silver electrodes were implanted in the anterior and posterior parts of the right masseter muscles. The contralateral muscle was used as control. The bite force was measured. Muscle biopsies were obtained from the anterior, central and posterior parts, and were immediately frozen in liquid nitrogen. A fluorometrical analysis by enzymatic methods for glycogen, glucose, creatine phosphate, NAD, NADH, lactate and pyruvate was made. Blood flow was measured by 133Xe wash-out; oxygen consumption was monitored with an oxygen electrode. The porcine masseter was continuously stimulated for 60 min (100 V, 4 Hz and 2 ms). The canine masseter was intermittently stimulated (100 V, 20 Hz and 2 ms). The contraction was repeated four times, with a 10-min rest between. The porcine masseter could sustain longer endurance times than the canine masseter, which was easily fatigued. A marked substrate depletion was evident. The precontractional contents of glycogen, glucose and creatine phosphate were reduced. Lactate accumulation was evident (2-4 times more in the porcine and 4-8 times more in the canine masseter). The NADH concentration increased and the NAD content decreased. Blood-flow impairment (80% reduction in the dog, 60% in the pig) was observed. After the contraction phase, there was a hyperaemia (58% elevation of blood flow in the pig masseter, 45% in the canine). The oxygen tension followed in magnitude and time the blood-flow changes. These circulatory variables returned to normal after recovery. The high degree of substrate depletion, blood-flow impairment and a simultaneous decrease in oxygen transport to the contracted muscle, in combination with a prominent lactate accumulation, may induce a decrease in bite-force production.
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PMID:Bite-force development, metabolic and circulatory response to electrical stimulation in the canine and porcine masseter muscles. 147 60

A 50-year-old man complained of lumbar pains, lack of energy, dysarthria and ataxic gait. Investigation revealed progressive anaemia (haemoglobin initially 10.5 g/dl, later 6.8 g/dl) and thrombocytopenia (initially 67,000/microliters, later 25,000/microliters). In addition he had unexplained pyrexia of up to 39.8 degrees C. Lactate dehydrogenase was 780 U/l and fragmented red cells were noted in the blood film. Because of suspicion of thrombotic thrombocytopenic purpura, treatment with fresh plasma by infusion was immediately initiated. On the third day of treatment he developed left ventricular failure; auscultation revealed a blowing early diastolic murmur over Erb's point together with a spindle-shaped early diastolic murmur over the right second intercostal space. Computed tomography of the skull showed recent haemorrhage into the left half of the cerebellum and an older right posterior infarct. The abdominal ultrasound scan suggested a haemorrhagic spleen infarct. In view of these findings the diagnosis was revised to embolizing aortic endocarditis with aortic reflux (confirmed by colour Doppler echo-cardiography). Aortic valve replacement was performed immediately, and the patient was treated with gentamycin 80 mg/d and teicoplanin 400 mg/d for four weeks. Postoperatively he was given 12 units of platelet concentrate and the platelet count remained stable thereafter (greater than 100,000/microliters). Splenectomy became necessary because the splenic haematoma increased in size during oral anticoagulant therapy. After a 6 week hospital stay the patient was discharged in good condition.
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PMID:[Embolizing aortic valve endocarditis in the differential diagnosis of thrombotic thrombocytopenic purpura]. 153 83

The effect of preexercise muscle glycogen content on the metabolic responses to exercise has been investigated. Seven men cycled at a work load calculated to elicit 75% of maximal oxygen uptake [211 +/- 17 (SE) W] on two occasions: 1) to fatigue (37.2 +/- 5.3 min) and 2) at the same work load and for the same duration as the first. Biopsies were obtained from the quadriceps femoris muscle before and after exercise. Before the first experiment, muscle glycogen was lowered by exercise and diet, and before the second experiment, muscle glycogen was elevated. In the low-glycogen condition (LG), muscle glycogen decreased from 182 +/- 15 at rest to 7 +/- 4 mmol glucosyl units/kg dry wt at fatigue, while in the high-glycogen condition (HG), glycogen decreased from 725 +/- 31 at rest to 353 +/- 53 mmol glucosyl units/kg dry wt at the end of exercise. Hexose monophosphates were not increased after LG exercise but increased approximately fivefold after HG exercise. Lactate increased more during HG exercise (LG = 16 +/- 5, HG = 61 +/- 7 mmol/kg dry wt; P less than or equal to 0.001), whereas IMP increased more during LG (LG = 2.8 +/- 0.6, HG = 0.9 +/- 0.2 mmol/kg dry wt; P less than or equal to 0.05). The increases in the sum of tricarboxylic acid cycle intermediates (TCAI; citrate+malate+fumarate) and acetylcarnitine (which is in equilibrium with acetyl CoA) were significantly greater during HG exercise (P less than or equal to 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of low glycogen on carbohydrate and energy metabolism in human muscle during exercise. 156 23

1. Peak isometric force of single fast (type 1) and slow (type 3) muscle fibres of Xenopus decreased when fibres were stimulated intermittently above their predicted sustainable duty cycle at 20 degrees C. Type 1 fibres could be fatigued to zero force. In most type 3 fibres force did not decrease below 50% of the original (P0) before activation failure, as indicated by irregular contractions. 2. Fibres were rapidly frozen at different force levels and analysed by high-performance liquid chromatography (HPLC) for ATP, IMP, phosphocreatine (PCr) and creatine (Cr). Lactate was determined enzymatically in type 1 fibres only. The relationships between force and PCr, and between force and ATP during fatigue were, apart from the range of values obtained, the same for both fibre types. When force had fallen to about 60-80% of original, PCr was fully reduced. At lower force levels, the ATP content-decreased, and a concomitant rise of IMP content was found. At zero force, ATP had fallen to about 25% of its value in rested type 1 fibres, and up to 200 mumol lactate (g dry weight)-1 had accumulated. 3. Recovery from fatigue was studied in fibres where force had fallen to 0.6 P0 (both fibre types) and 0.2 P0 (type 1 only). After 1 h of recovery ATP had in all cases returned to the level measured in rested fibres. In fibres fatigued to 0.6 P0, force almost returned to its original value. However, in type 1 fibres fatigued to 0.2 P0, it returned to only 0.3 P0. After 1 h of recovery the PCr/Cr ratio in type 1 fibres was lower (probability, P less than 0.05) than in control fibres, whereas in type 3 fibres it was not significantly different from controls. 4. The relationship between peak force and stimulus frequency, which had a sigmoid shape in fully rested fibres, was drastically changed by fatiguing stimulation. Immediately after fatiguing stimulation of type 1 fibres, force hardly increased with stimulus frequency, corresponding to the observation that calcium efflux from the sarcoplasmic reticulum was decreased at high stimulus frequencies. The force-frequency relationship of type 3 fibres was the same before and after intermittent stimulation.
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PMID:Metabolic changes with fatigue in different types of single muscle fibres of Xenopus laevis. 159 75

1. The differential effects of beta-adrenoceptor subtypes on potassium fluxes and exercise capacity were compared in eight healthy young men using single oral doses of the selective beta 2-adrenoceptor antagonist ICI-118551, the selective beta 1-adrenoceptor antagonist atenolol or the non-selective beta-adrenoceptor antagonist propranolol. The study was randomized, double-blind and placebo controlled. 2. Potassium in the venous effluent from the exercising muscles increased progressively with increasing exercise intensity. This response was augmented by propranolol, whereas neither atenolol nor ICI-118551 modified the response. After exercise potassium concentration fell exponentially with no difference between the treatment regimens. 3. Cumulative work was significantly reduced by ICI-118551 (6.4%, P = 0.04) and by propranolol (12.4%, P less than 0.01), whereas the reduction with atenolol (5.6%) did not reach statistical significance. 4. Atenolol and propranolol reduced peak heart rate by 23% and 29%, and peak systolic blood pressure by 9% and 11% respectively during maximal exercise. ICI-118551 caused a non-significant reduction in heart rate during submaximal exercise, with a significant reduction at maximum exercise (6% reduction), whereas systolic blood pressure was not different from placebo. Diastolic blood pressures were similar across all treatment regimens. 5. Similar glucose concentrations were obtained at baseline and at exhaustion during all treatment regimens. Lactate concentrations were comparable for any given exercise intensity irrespective of treatment regimens. Propranolol reduced lactate concentrations from the exercising muscles at maximum exercise in proportion to the reduction of maximal exercise capacity. 6. The subjective perception of fatigue was not affected by either beta 1- or beta 2-adrenoceptor blockade.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of selective beta 2-adrenoceptor blockade on serum potassium and exercise performance in normal men. 168 47


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