Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The purposes of this investigation were to determine the validity of critical power (CP) as a measure of the work rate that can be maintained for a very long time without fatigue and to determine whether this corresponded with the maximal lactate steady-state (lass,max). Eight highly trained endurance cyclists (maximal oxygen uptake 74.1 ml.kg-1.min-1, SD 5.3) completed four cycle ergometer tests to exhaustion at pre-determined work rates (360, 425, 480 and 520 W). From these four co-ordinates of work and time to fatigue the regression of work limit on time limit was calculated for each individual (CP). The cyclists were then asked to exercise at their CP for 30 min. If CP could not be maintained, the resistance was reduced minimally to allow the subject to complete the test and maintain a blood lactate plateau. Capillary blood was sampled at 0,5,10,20 and 30 min into exercise for the analysis of lactate. Six of the eight cyclists were unable to maintain CP for 30 min without fatigue. In these subjects, the mean power attained was 6.4% below that estimated by CP. Mean blood lactates (n = 8) reached a steady-state (8.9 mmol.l-1 SD 1.6) during the last 20 min of exercise indicating that CP slightly overestimated lass,max, Individual blood lactates during the last 20 min of exercise were more closely related to the gamma-intercept of the CP curve (r = 0.78, P less than 0.05) than either CP (0.34, NS) or mean power output (r = 0.42, NS).
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PMID:Blood lactate in trained cyclists during cycle ergometry at critical power. 228 14

Previous investigators have demonstrated that 5-10 min of fatiguing exercise would lead to respiratory muscle fatigue in normal subjects. The purpose of this study was to determine if there was a differential inspiratory pressure response to maximal cycle ergometer exercise in trained and untrained subjects. Six highly trained cross country skiers and five untrained college students were studied prior to and 10, 60, and 120 s postexercise (incremental VO2max to exhaustion). On each occasion, maximal inspiratory pressure (MIP) was measured at the mouth from residual volume. Prior to exercise, the two groups had similar MIP values. After exercise, the sedentary subjects experienced significant decreases in MIP compared to the preexercise values. These decreases averaged 10%, 17%, and 13% at 10, 60, and 120 s postexercise, respectively. The skiers, on the other hand, showed no evidence of a decrease in MIP postexercise, with the postexercise values being slightly, but not significantly, higher than the preexercise values. From these results, we conclude that maximal exercise results in inspiratory muscle dysfunction in normal subjects but not in athletes training at or near elite levels. Thus, it appears that endurance exercise training induces an adaptive change in the inspiratory muscles that protects them from the acute loss of strength seen following exercise in normal subjects.
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PMID:Maximal inspiratory pressure following maximal exercise in trained and untrained subjects. 228 59

We examine whether muscle oxygen consumption (VO2) increases gradually during repeated submaximal isometric contractions. Six subjects made two-legged isometric quadriceps contractions at 30% maximal voluntary contraction for 6 s with 4 s of rest between until exhaustion (58 +/- 8 min). Blood samples were taken from the femoral vein and artery, and blood velocity was recorded by ultrasound-Doppler technique in the femoral artery. Blood flow was calculated from velocity and artery diameter values. Leg VO2 increased sixfold within the 1st min of exercise. A further doubling of the VO2 was seen during the remainder of the exercise, reaching 307 +/- 22 ml/min at exhaustion. This latter increase was due to a 54% increase in blood flow and a 34% increase in oxygen extraction. After 20 min of recovery VO2 was still 75% higher than preexercise values. The results show a twofold increase in energy demand of the working muscle during repeated constant-force isometric contractions. The increased energy cost of contraction is probably localized at the cellular level, and it parallels fatigue determined as decreased force-generating capacity.
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PMID:Gradual increase in leg oxygen uptake during repeated submaximal contractions in humans. 234 40

Metabolic events were followed by 31-P NMR spectroscopy during mechanical exhaustion of directly stimulated rat gastrocnemius. During mechanical fatigue, phosphocreatine (PCr) and pH first declined but although stimulation continued high values were recovered without mechanical recovery. Total recovery was only observed after cessation of stimulation. Partial mechanical recovery was elicited by lowering stimulation rhythm; it was accompanied by decrease in PCr to a steady-state level without pH alteration. When exhaustive exercise was induced immediately after nonexhaustive exercise, failure of mechanical function occurred without decrease in pH. Major findings were: first, during exhaustive stimulations, the greater the muscle fatigue, and the higher the PCr level at the end of stimulation. Secondly, PCr and force levels did not depend on preceding levels of PCr and pH. Thirdly, acidosis was observed transiently during the first minutes of the first exercise period. These findings strongly suggested that electrical events and/or excitation-contraction (EC) coupling play a crucial role in this type of fatigue.
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PMID:Muscle fatigue unrelated to phosphocreatine and pH: an "in vivo" 31-P NMR spectroscopy study. 234 61

Heart rate (HR) and oxygen uptake (VO2) at the mechanical power (W) corresponding to the capillary blood lactate ([la]cap) of 4 mmol.l-1 (Wlt) were measured in 34 healthy male subjects during incremental exercise (Winc). On the basis of these measurements, the subjects were asked to cycle at Wlt for 60 min (steady-state exercise, Wss). Twenty subjects could not reach the target time (mean exhaustion time, te, 38.2 min, SD 5.3), while 6 of the 14 remaining subjects declared themselves exhausted at the end of exercise. The final [la]cap if the two groups of exhausted subjects were 5.3 mmol.l-1, SD 2.3 and 4.3 mmol.l-1, SD 1.1, respectively. At the end of Wss, [la]cap and HR were significantly lower in the 8 unexhausted subjects than in the other subjects. This group also had a lower HR at Wlt during Winc. The HR and VO2 appeared to be higher during Wss than during Winc. When all subjects were ranked according to their te during Wss, Wlt (expressed per kilogram of body mass) was found to be negatively related to te. In conclusion, during Winc, measurements of physiological variables at fixed [la]cap give a poor prediction of their trends during Wss and of the relative te; at the same work load [la]cap can be quite different in the two experimental conditions. Furthermore, resistance to exercise fatigue at Wlt seems lower in the fitter subjects.
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PMID:Physiological responses during prolonged exercise at the power output corresponding to the blood lactate threshold. 235 77

The purpose of this investigation was to determine the effect of glycogen depletion and supercompensation on the physical working capacity at the fatigue threshold (PWCFT). Ten adult males (mean age 23 years, SD 3) volunteered as subjects for this study. During the first laboratory visit the subjects performed a maximal bicycle ergometer test for the determination of maximum oxygen consumption (VO2max). Between 48 and 72 h later, the subjects pedaled to exhaustion at a power output which corresponded to a mean of 76% of VO2max (range, 72-80%) for the purpose of glycogen depletion. For the next 3 days, the subjects were fed a 10.5 MJ.day-1 low carbohydrate diet which consisted of 7.5% carbohydrates, 22.0% protein and 70.5% fat. The subjects then performed an incremental cycle ergometer test to the onset of fatigue or PWCFT, which was estimated from integrated electromyographic voltages of the vastus lateralis muscle. For the next 3 days the subjects were fed a 10.5 MJ high carbohydrate diet which consisted of 72.2% carbohydrates, 12.4% protein and 15.4% fats for the purpose of glycogen supercompensation. The subjects then performed a second PWCFT test. A paired t-test indicated that there was no significant (p greater than 0.05) difference between the means of the PWCFT values (depletion 246 W, SD 30; supercompensation 265 W, SD 28) and they were highly correlated at r = 0.884. The results of this investigation suggested that the methods commonly used to affect glycogen depletion or supercompensation had no effect on PWCFT.
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PMID:The effect of glycogen depletion and supercompensation on the physical working capacity at the fatigue threshold. 236 12

We report on the distress associated with physical symptoms in 761 male hypertensive patients enrolled in a clinical trial of the effects of captopril, methyldopa or propranolol on quality of life. Educational level at entry into the trial showed a negative association with a series of physical symptom distress items among patients not previously treated with antihypertensive medications but no association with symptoms among the previously treated. Over the 24 weeks of therapy captopril as monotherapy was associated with no change from baseline in distress in all symptoms examined. In contrast, distress increased in the methyldopa treated patients for dry mouth and blurred vision. Propranolol treated patients had increased "trouble getting breath," bradycardia, shortness of breath or wheezing, and blurred vision. Between group comparisons revealed significant differences favorably comparing captopril to both methyldopa and propranolol in regard to fatigue, and blurred vision, as well as to methyldopa alone for dry mouth and "feeling worn out." There were significant differences as well between captopril and propranolol with patients on propranolol worsening in bradycardia. Other comparisons of patients on propranolol and methyldopa monotherapy showed propranolol patients worsening in bradycardia and loss of taste, but methyldopa patients reported more dry mouth and feeling worn out than those on propranolol. The addition of hydrochlorothiazide to therapy worsened total physical symptom distress scores for methyldopa and propranolol patients. This study confirms the value of methods which assess the degree of distress associated with symptoms commonly reported by hypertensive patients receiving antihypertensive medications. This approach can be useful in establishing a treatment regimen least likely to cause distress and can be of value in preserving quality of life, preventing noncompliance, and withdrawal from treatment.
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PMID:Self-reported side effects from antihypertensive drugs. A clinical trial. Quality of Life Research Group. 240 65

In an earlier occupational study the EMG was found to be unchanged during a whole working day. The purpose of this study was therefore to examine EMG changes during experiments in a laboratory environment comparable to occupational work. The surface EMG of the quadriceps muscle of 16 subjects was analysed during 3 experiments: (I) 10% maximal voluntary contraction (MVC) sustained for 1 h, and with a constant work intensity of the muscle; (II) 20% MVC for 5 sec alternating with a rest of 5 sec for 1 h; (III) 20% MVC was sustained until exhaustion. In the latter the endurance time decreased with increasing MVC. The results indicated that the methods used in this study can be trusted to reveal changes in EMG due to fatigue in a group of subjects but not in the individual subject. The decrease in mean power frequency (MPF) and the increase in root mean square amplitude (RMS) were most pronounced during the first 10 min of the 10% sustained contraction, indicating a decrease in the conduction velocity along the muscle fibres or synchronization of motor unit firing. In contrast, at 20% intermittent contraction the MPF was unchanged. Between 10 and 60 min of contraction time the increase in RMS amplitudes associated with none or only slight changes in MPF indicated recruitment of new motor units for both types of contraction. The lack of EMG fatigue during a whole day in an earlier occupational study may be because the work performed required varying degrees of muscle force.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Quantitative surface EMG during sustained and intermittent submaximal contractions. 245 30

In 12 dogs the effect of experimental laminectomy on the structure of motor and sensitive neurons, as well as on the structure of the conductive pathways in the spine cord has been investigated. The experimental laminectomy with a subsequent durotomy results in an increase (in 1.5-5 days of the experiment) of both hyperchromatophilic and hyperchromatophobic neurons. This demonstrates their functional reconstruction (inhibitory chromophilia, inhibited activity, fatigue and exhaustion chromatophobia). Restoration of the neuronal structure and that of the spinal cord nervous fibers takes place by the end of 10 days after the experimental laminectomy with residual foci of reversible changes in the conductive pathways system.
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PMID:[Effect of experimental laminectomy on the structure of neurons and conductive pathways of the spinal cord]. 255 78

Changes in femoral vein pH, lactate, glucose and potassium were studied in a double-blind randomized, short-term, dynamic cycle ergometry exercise test on six healthy male subjects after administration of non-selective (timolol), beta-1-selective (atenolol) beta blocker or placebo. The exercise intensity was increased in steps of 200 kpm/min every 2 min until exhaustion. During submaximal exercise, potassium concentrations in blood from the exercising leg muscles increased progressively with increasing exercise intensity, and was significantly higher for any given exercise level following timolol as compared to placebo administration. The potassium concentrations following atenolol were in-between those of timolol and placebo. Despite reduced working capacity after non-selective beta blockade, almost identical potassium concentrations were reached at exhaustion irrespective of treatment regimens (placebo: 6.3, range 5.8-6.8 mmol/l; atenolol: 6.5, range 6.1-7.3 mmol/l and timolol: 6.4, range 6.2-6.8 mmol/l). The increase in s-lactate concentrations was similar across all treatments, and rose in proportion to the increase in the exercise intensity. A biphasic increase in lactate was observed with identical breaking points (anaerobic threshold) irrespective of treatment regimens. There was no difference in glucose concentrations between the treatment regimens. The marked increase in serum potassium during maximal exercise coincides with leg muscle fatigue and may, by its effect on the muscle cell membrane potential, limit the maximal working capacity following beta blockers. The rise in serum potassium may curtail the use of maximal exercise test as an index of cardiac performance in healthy young subjects.
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PMID:The importance of potassium and lactate for maximal exercise performance during beta blockade. 257 96


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