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

Thoroughbred horses were exercised to fatigue at 40, 85, and 100% of their maximal oxygen consumption (VO2max) on a treadmill and completed a 1,600-m gallop on a track to identify the effect of exercise of various durations and intensities on the ultrastructure of mitochondria and sarcoplasmic reticulum (SR) from the middle gluteal muscle. The percentage of the total area occupied by mitochondria and SR increased in electron micrographs of muscle samples collected at the termination of exercise and at 30 and 60 min of recovery compared with those collected before exercise. Mitochondrial area increased 3- to 4-fold and SR area approximately 1.6-fold after exercise at the intensities greater than 40% of the VO2max. Smaller increases occurred in response to exercise at 40% of the VO2max. Areas were not different from rest in samples collected after 60 min of recovery. The reversal of ultrastructural alterations paralleled the trend toward normalization of muscle temperature, muscle pH, and the concentrations of selected muscle metabolites.
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PMID:Ultrastructural changes in skeletal muscle after fatiguing exercise. 845 22

Evidence is adduced to support the proposal that pathological fatigue is a consequence of impaired capillary blood flow resulting in inadequate oxygen delivery, which is in accordance with physiological concepts of fatigue. Case reports are presented.
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PMID:Chronic tiredness and idiopathic chronic fatigue--a connection? 157 97

Multiple compensatory mechanisms operate to preserve exercise tolerance in patients with left ventricular failure. Exercise capacity of most patients with chronic heart failure is limited by dyspnea or fatigue, or both. Maximal stress testing with direct assessment of peak O2 uptake is an essential measurement in planning exercise conditioning programs, which are now attracting patients with chronic heart failure. The biochemical and histologic patterns of skeletal muscle changes seen in chronic heart failure patients are consistent with the effects of long-term exercise deconditioning in normal subjects. Recent studies have suggested beneficial effects of training in subjects with moderate or even severe left ventricular dysfunction by showing increased exercise tolerance or peak O2 consumption, anaerobic threshold, peak leg blood flow, peak central arteriovenous oxygen difference and decreased lactate accumulation. However, a number of questions remain unanswered. Exercise training for the treatment of chronic heart failure should be determined on an individual basis and used with caution.
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PMID:Physical training in patients with congestive heart failure. 157 63

To determine the effect of blood flow on diaphragm fatigue independent of oxygen delivery, the left hemidiaphragm was vascularly isolated in 14 pentobarbital-anesthetized, mechanically ventilated dogs. Fatigue (decline in tension generation) of the left diaphragm was induced by phrenic nerve stimulation at 10 Hz, 12/min, duty cycle of 0.5 for 8 min. Two stimulation periods separated by 30 min of rest were performed in each animal. Diaphragmatic O2 delivery during the two periods was the same. In Group 1 (n = 8), the diaphragm was autoperfused from the femoral artery (high O2-low flow) during the first stimulation period. The tension generated by the diaphragm during this period declined progressively to 47.7% of initial values. In the second period in this group, the diaphragm was pump perfused with arterial blood, diluted with an equal volume of 6% dextran at a flow rate twice that of the first period (low O2-high flow). Tension in this period declined to 76% of initial tension (p less than 0.05 compared with high O2-low flow). In Group 2 (n = 6), stimulation performed while perfusing the diaphragm in the first period with diluted arterial blood at a flow rate twice that recorded during autoperfusion (low O2-high flow) produced a decline in tension to 70% of the initial values. In the second period, the diaphragm was perfused with undiluted arterial blood at a flow rate equal to 50% of that of the first period (high O2-low flow). Tension during this period declined to 56% of initial values (p less than 0.05 compared with low O2-high flow).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Oxygen delivery-independent effect of blood flow on diaphragm fatigue. 158 47

Most animals move intermittently, yet many proposed performance limitations of terrestrial locomotion are based on steady-state measurements and assumptions. We examined the effect of work-rest transitions by exercising the ghost crab, Ocypode quadrata (28.1 +/- 8.1 g), intermittently on a treadmill at 0.30 m/s, a supramaximal speed [i.e., greater than the speed that elicits the maximal rate of oxygen consumption (VO2)]. Duration of the exercise and pause periods, ratio of exercise to pause, and speed during the exercise period were varied to determine the effect on performance. Crabs fatigued after 7.5 min of continuous running, a distance capacity (i.e., total distance traveled before fatigue) of 135 m. When the task was done intermittently with 2-min exercise and 2-min pause periods, the crabs fatigued after 87 min (a total distance of 787 m), representing an 5.8-fold increase in distance capacity compared with continuous exercise at the same absolute speed (0.30 m/s) and a 2.2-fold increase in distance capacity compared with continuous exercise at the same average speed (0.15 m/s). Pause periods less than 30 s did not result in greater distance capacity compared with continuous exercise at the same average speed. Longer (3-5 min) and shorter exercise periods (less than or equal to 30 s) decreased distance capacity. Leg muscle lactate increased 10-fold to 15 mumol/g leg during intermittent exercise. However, significant amounts of lactate were cleared from the leg during the brief pause periods.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Intermittent exercise alters endurance in an eight-legged ectotherm. 159 Apr 78

The purpose of the study was to analyse the effect of arm-shoulder fatigue on manual performance. Ten experienced carpenters performed three standardized tasks (nailing, sawing and screwing). Electromyographic activity was recorded from six arm-shoulder muscles and the performances were video-filmed. After 45 min of standardized arm-cranking (arm-shoulder-fatiguing exercise of approximately 70%-80% maximal oxygen consumption), the tasks were repeated. The number of work movements and the time taken for each task were recorded and the quality of the work performed was compared. After the fatiguing exercise, only nailing was perceived as being harder and more mistakes were made during nailing and sawing. Movement performance was not influenced during nailing but was slightly slower during sawing and faster during screwing. However, there were increased mean EMG amplitudes in the upper trapezius and biceps muscles during nailing, in the upper trapezius, anterior deltoid and infraspinatus muscles during sawing and in the anterior deltoid muscle during screwing. Of the muscles studied the upper trapezius and anterior deltoid muscles increased their activity most after the arm-shoulder-fatiguing exercise.
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PMID:Effect of arm-shoulder fatigue on carpenters at work. 161 78

Silent myocardial ischaemia is now well-recognised in patients with symptomatic coronary artery disease. Its pathogenesis remains speculative, though diminished sensitivity to pain is thought to be one of the mechanisms involved. Because cardiovascular autonomic dysfunction occurs frequently in diabetic patients, we postulate that it contributes towards painless myocardial ischaemia among them. Forty consecutive diabetic (type II) male patients and ten normal volunteers were studied. Using 5 previously-validated noninvasive tests for autonomic dysfunction, 14 of these diabetic men had definite autonomic neuropathy (at least 2 abnormal tests). All 50 subjects were then exercised on a motor-driven treadmill to either exhaustion or chest pains. Thirty-three diabetic subjects were tested positive, with significant (greater than 1 mm) ST segment depression over at least 2 contiguous leads. Of these, 18 were associated with typical angina but the other 15 stopped because of fatigue or exhaustion (ie painless). Thirteen subjects who had definite autonomic neuropathy (AN+) had positive exercise ECG tests-10 had painless ischaemia, and only 3 had angina. This contrasted with 15 patients who had painful ischaemia and 5 who had painless ischaemia among the group without (AN-)autonomic dysfunction (p = 0.0047, Fisher's exact test). There were no significant differences among the various groups for peak rate-pressure-product, all subjects attaining similar maximal oxygen consumption states during which ischaemic ST segment changes were noted (painful AN+: 21917 +/- 4753; painless AN+: 20117 +/- 6752; painful AN-: 16544 +/- 4063; painless AN-: 22220 +/- 4341, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Association of diabetic autonomic neuropathy with painless myocardial ischaemia induced by exercise. 162 Nov 24

This review examines the lung and chest wall adaptation to exercise in health in persons of widely varying degrees of fitness. First we examine the regulation of breathing and gas exchange in the sedentary young adult who shows a near perfect regulation of alveolar gases, ventilation to perfusion distribution, diffusion equilibrium in the lung during all levels of exercise. This individual's respiratory muscles are also ideally recruited both tonically and phasically so as to meet multi-faceted postural, locomotory and respiratory demands. The topic of plasticity in the pulmonary system is discussed with specific reference to the effects of physical training and athleticism. The key point made here is that both homeostasis of gas transport and mechanical efficiency, with which the pulmonary system meets the demands of muscular exercise will depend upon the ability to maintain a significant margin between demand vs. structural capacity. Pulmonary diffusion capacity and at least some aspects of respiratory muscle function seem to be "overbuilt" in the young untrained adult. This margin of safety no longer prevails as the athlete becomes fitter. The cause is to be found in the relative lack of adaptability of the lung and chest wall to the training stimulus. Examples of demand coming very close or exceeding the capacity of the pulmonary system include the highly trained young endurance athlete and the aged athlete. Examples of "failure" or near failure in the pulmonary system's response to exercise include: a) exercise induced arterial hypoxemia via diffusion limitation; b) diaphragmatic fatigue in endurance exercise; c) expiratory flow limitation at VO2max.; d) achieving the capacity of inspiratory muscles for pressure generation at VO2max. and e) oxygen cost of breathing which is in excess of 15% of VO2max. in those athletes who experience the most mechanical limitation.
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PMID:Demand vs. capacity in the healthy pulmonary system. 162 72

Celiprolol is a new-generation beta-blocker with ancillary properties that include partial beta 2-agonism and direct vasodilating activity. The effects of atenolol and celiprolol on maximal exercise capacity and on both respiratory variables and subjective indices of breathlessness and fatigue during submaximal exercise were compared in a placebo-controlled crossover study of 12 trained volunteers. Both atenolol and celiprolol equally and significantly reduced exercise capacity and maximal oxygen consumption. During constant submaximal exercise at 70% maximal oxygen uptake, however, differences emerged between the two beta-blockers. Atenolol was associated with a significantly higher minute ventilation than placebo. In contrast, values for minute ventilation and respiratory exchange ratio with celiprolol were similar to values with placebo. During the early stages of exercise, treatment with atenolol was also associated with higher scores for the subjective indices of breathlessness and fatigue. Thus submaximal exercise, which may be physiologically more relevant to the everyday activities of patients, may demonstrate potentially useful differences between drugs that are not seen during maximal exercise testing.
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PMID:Submaximal, but not maximal, exercise testing detects differences in the effects of beta-blockers during treadmill exercise: a study of celiprolol and atenolol. II. 167 Nov 88

beta-Adrenoceptor blockers are widely used clinically and can be classified as nonselective (beta 1 and beta 2) or selective (beta 1). Impairment of exercise performance is a well-known side effect of this group of drugs. This paper reviews mechanisms that could potentially be responsible for this impairment. In addition to cardiovascular and metabolic effects, beta-blockade inhibits Na(+)-K+ ATPase pumps controlling ion movement between muscle and plasma and thus may contribute to muscle fatigue through this mechanism. To investigate the relationship between the change in plasma [K+] and exercise performance, we studied healthy male subjects taking propranolol. Eight subjects performed maximal incremental cycle ergometer exercise tests during control (no drug), low dose (LD) (40 mg daily), and high dose (HD) (265 +/- 4.3 (SE) mg daily) of propranolol. The control plasma [K+] (5.8 +/- 0.12 mequiv./L) during exercise was significantly lower than either the LD (6.4 +/- 0.05 mequiv./L) or HD (6.1 +/- 0.16 mequiv./L) values. There was no significant difference between plasma [K+] for the LD and HD of propranolol. However, maximum oxygen uptake was reduced only while taking the HD of propranolol. Six of the subjects also performed three 30-s bouts of high intensity exercise on an isokinetic cycle ergometer while taking the LD and HD of propranolol. There was no significant difference between doses for the increase in plasma [K+] (LD, 7.8 +/- 0.35 mequiv./L vs. HD, 7.6 +/- 0.36 mequiv./L) during exercise. However, exercise performance was significantly reduced during HD compared with LD. These results suggest that the increases in plasma [K+] with propranolol did not play a direct significant role in the reduced performance observed during the HD.
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PMID:Factors contributing to increased muscle fatigue with beta-blockers. 167 29


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