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

The work output, energy consumption and efficiency during repetitive dynamic contractions were calculated for rat extensor digitorum longus muscle. The muscles performed 40 successive dynamic contractions at 37 degrees C (with occluded bloodflow) with interval durations of either 500, 250 or 167 ms. The muscle-tendon complexes were allowed to shorten at the velocity at which they could exert their highest power output (50 mm.s-1). Work output in the first contraction was the same among the three groups with different interval durations. The reduction in work output during the series of contractions differed among the groups, mainly in the last part of the exercise period. In the group with the longest interval duration, work output steadily decreased over the whole contraction period and at the end was approximately 72% of the output in the first contraction. In contrast, after the 30th contraction, work output decreased at a significantly higher rate of approximately 3% of each contraction in the groups with the intermediate and the shortest interval duration. After the last contraction, work output in these groups was approximately 52% of the work output in the first contraction. These differences in fatigue coincided with differences in the reduction in adenosine 5'-triphosphate and the production of inosine-5'-monophosphate. Total work output was not significantly different among the three groups with different interval durations, indicating that the different reductions in work output in the last contractions only had a minor influence on total work output of all 40 contractions. Also high-energy phosphate consumption and efficiency were not significantly different over these three exercise periods. Thus with the protocol used no interval dependent pattern of efficiency could be detected.
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PMID:Muscle fatigue and efficiency in relation to interval duration of successive contractions. 173 10

Six thoroughbred horses exercised on a motorised treadmill on two separate occasions at a speed of 11 or 12 m.s-1 for up to 2 min. 4 h prior to exercise each horse was given a 21 test solution of sodium bicarbonate (NaHCO3; 0.6 g.kg-1 body mass) or a control solution of water by nasogastric intubation, the order of administration of the two solutions was randomised. Blood samples (n = 15) were obtained before and during the 4 h after intubation, during exercise and for 30 min after exercise. NaHCO3 ingestion resulted in changes in pre-exercise acid-base status. The changes in blood lactate and base excess with exercise were greater after NaHCO3 administration; after 1 min of exercise in the case of lactate (P less than 0.05) and immediately after exercise in the case of base excess (P less than 0.05). Plasma ammonia levels were lower during (P less than 0.05) and immediately after (P less than 0.05) exercise following NaHCO3 ingestion. The peak change in plasma ammonia with exercise was also lower after NaHCO3 ingestion (P less than 0.05). Following exercise after NaHCO3 ingestion, five horses demonstrated lower muscle adenosine 5-triphosphate loss (P less than 0.05) and inosine 5-monophosphate formation (P = 0.05) and higher glycerol 3-phosphate formation (P less than 0.05). There is evidence to suggest that metabolic alkalosis may delay the onset of fatigue by decreasing the extent of adenine nucleotide loss during high-intensity exercise.
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PMID:The influence of metabolic alkalosis upon exercise metabolism in the thoroughbred horse. 174 3

Dynamic changes in intracellular phosphocreatine (PCr), inorganic phosphate (Pi), and pH in human forearm muscle were studied from rest through heavy exercise by means of a ramp exercise protocol and 31P nuclear magnetic resonance spectroscopy. Eighteen healthy volunteers performed an isotonic wrist flexion exercise of repeated contractions at a frequency of 0.5 Hz. Work rate was increased continuously (ramped) at approximately 0.13 W each minute from 0.34 to 1.5 W or until fatigue. Pi/PCr was used as an estimate of the cellular phosphorylation potential of the muscle. Exercise caused a progressive increase in Pi/PCr with an initial slow and later fast component. The transition between these components was distinct and corresponded to the onset of pH decline in all subjects. These changes in Pi/PCr and pH were best fit (P less than 0.05) by a piecewise linear regression model with a break point or threshold. Repeated ramp testing of six subjects showed that the threshold was reproducible (r = 0.98). The results of this study demonstrate the existence of an intracellular metabolic threshold and suggest that indirect threshold measures (lactate and ventilatory thresholds) may reflect events at the cellular level.
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PMID:Coincident thresholds in intracellular phosphorylation potential and pH during progressive exercise. 175 3

Sheep under general anesthesia had their left and right latissimus dorsi muscles mobilized for paraneuroelectrode and pulse generator implantation. After a 10-day recovery period, the left-side muscles were stimulated with a gradually increasing duration and rate over 3 months. At 4 months after operation, the tendinous end of each latissimus dorsi muscle was freed from its humeral insertion and attached to a strain gauge force transducer. Both left and right latissimus dorsi muscles, from each animal, were stimulated to contract for 2 hours for the fatigue study before being isolated, trimmed, and weighed. Frozen tissue biopsies were used to determine creatine phosphate, adenosine triphosphate, lactate, and glycogen content and muscle myosine ATPase, and succinate dehydrogenase activities. The arterial diameter in the conditioned muscle was 30% larger than that of the control muscle and had a 40% higher blood flow at rest. A three- to fivefold increase in blood flow during the fatigue test was observed. The force decreased 47% for the conditioned muscle and 91% for the control muscle. The mass and cross-sectional area of conditioned and unconditioned muscles were similar. Electric conditioning increased fatigue resistant fiber content from 33% to 92%, as evidenced by myosine ATPase activity. During the early phase of the fatigue test, higher glucose uptake but significantly lower lactate production were found for the conditioned muscle. This study indicates that it is possible to produce fatigue resistant muscle with preserved force and mass. In addition to skeletal muscle fiber transformation, metabolic adaptations appear to be important factors for fatigue resistance of skeletal muscle.
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PMID:Fatigue resistant muscle with preserved force and mass for cardiac assist. 180 6

Continuous electrical stimulation ot canine latissimus dorsi (LD) muscle in situ during 24 weeks induced an increase of immunohistochemically assayed type I fibers from about 30 to 80%. Concomitantly, the activity of fructose-6-phosphate kinase, a key enzyme of the glycolytic pathway, declined markedly, but the capacity for fatty acid oxidation remained unaltered. With respect to myofibrillar and metabolic properties the dog LD muscle initially resembled soleus muscle, and after 24 weeks of stimulation had acquired the properties of gastrocnemius muscle. It is concluded that in the dog, unlike the rat, the LD muscle has an inherently fixed capacity for oxidative energy production. Further expansion of its resistance to fatigue, as induced by chronic stimulation, most likely results mainly from a more efficient coupling between tension development and energy production.
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PMID:Canine-specific adaptation of energy metabolism of latissimus dorsi muscle in response to chronic electrical stimulation. 180 12

Aerial application of organophosphates can result in exposure to drift and leaf residues for pilots, ground crews, field workers, and residents near sprayed fields. Exposure can be by either the airborne or dermal route, and can produce illness (headaches, fatigue, diarrhea, cramps, respiratory problems) even with low-grade depressions in cholinesterase. Alkyl phosphate metabolites have been shown to be "gold standard" measures of such exposures. Experience in Israel indicates that reduction of health hazards from exposure to drift and leaf residues may be attained by the use of a comprehensive "mix" of preventive measures. These measures include, first and foremost, reduction in total amount of organophosphates used, followed by substitution of less for more toxic organophosphates, reduction in length of spray season, banning the use of flaggers, and greater reliance on tractor spraying. Cotton yield per hectare cultivated has increased despite a reduction in use of pesticides of all kinds and organophosphates in particular. Enclosure and air-conditioning (to prevent heat stress) of cockpits, protective clothing, training and licensing of pilots have been implemented. Education and communication of information, in keeping with the right-to know principle on hazards and how they should be controlled and monitored, is a part of a comprehensive strategy. Aerial or ground spraying should produce no drift in adjacent residential communities. The criterion for achieving this goal is the absence of urine alkyl phosphate metabolites above the threshold of detection.
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PMID:Hazards associated with aerial spraying of organophosphate insecticides in Israel. 184 56

The sublethal biochemical effects of pentachlorophenol (PCP) were investigated in live, intact red abalones (Haliotis rufescens), using a flow-through exposure system, by in vivo 31P NMR spectroscopy. Based on rangefinding tests (6-hr LC50 = 1.6 mg/L; 6-hr no-observable-effect-level (NOEL) = 0.8 mg/L), three abalones were separately exposed to a sublethal concentration (1.2 mg/L) for 5 hr, followed by a 13 hr recovery period. Effects in foot muscle included both a decrease in phosphoarginine and an increase in inorganic monophosphate concentrations ([PA] and [Pi], respectively); both foot muscle concentrations of adenosine triphosphate [ATP] and intracellular pH (pHi) also declined. Parallel in vitro experiments revealed that concentrations of glycerol 3-phosphate, lactate, citrate, succinate, malate, and alanine (Ala) all increased, while those of glyceraldehyde 3-phosphate and glutamine (Gln) remained stable. Also, these effects were not evident until 2 hr into exposure, possibly the time required for PCP to attain an effective concentration in foot muscle. During recovery, while Pi declined to pre-exposure levels, [PA] completely recovered in only one individual. Also, realkalinization of pHi was similar to recovery of [Pi], and ATP returned to near-initial levels, as did glycerol 3-phosphate, lactate, succinate, malate, and Ala; glyceraldehyde 3-phosphate, citrate, and Gln levels declined. Recovery responses corresponded to the time for PCP clearance from foot muscle. The effects of PCP were similar to those of hypoxia, fatigue, hypersalinity, and arginine kinase inhibitors, and so sublethal PCP concentrations may also inhibit electron transport and arginine kinase as well as uncouple mitochondrial oxidative phosphorylation in intact molluscs. Thus, the effects of pollutants on key biochemical processes may now be measured in intact aquatic organisms as they occur, improving our ability to accurately assess the environmental effects of pollutants in the laboratory.
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PMID:Sublethal effects of pentachlorophenol in the abalone (Haliotis rufescens) as measured by in vivo 31P NMR spectroscopy. 188 Jul 88

1. The effects of prolonged exercise on energy metabolism in type I and type II muscle fibres in the vastus lateralis muscle were investigated in six male subjects (20.0 +/- 0.5 years, mean +/- S.E.M.) who performed one-legged cycling at 61% of maximum O2 consumption (VO2,max; determined with one leg) until fatigue or for a maximum of 2 h. 2. Analysis of pools of freeze-dried fibres obtained by needle biopsy and separated into specific types by the myofibrillar ATPase histochemical procedure indicated higher (P less than 0.05) lactate concentrations in type II fibres compared to type I fibres at 15 min (43.9 +/- 9.7 and 51.2 +/- 9.8 mmol (kg dry wt)-1) and at 60 min (18.2 +/- 4.7 and 25.9 +/- 6.5 mmol (kg dry wt)-1). No differences existed in lactate concentration between fibre types for pre-exercise (10.0 +/- 1.6 and 13.3 +/- 2.8 mmol (kg dry wt)-1) or post-exercise. 3. Glycogen degradation was most pronounced in type I fibres. By the end of exercise, glycogen concentration was 82.4 +/- 45 mmol glucosyl units (kg dry wt)-1 in type I fibres and 175 +/- 62 mmol glucosyl units (kg dry wt)-1 in type II fibres. 4. No significant changes in ATP and creatine phosphate (CrP) were found in either fibre type with exercise. 5. It is concluded that, at least for lactate and glycogen, fibre-specific differences are evident in prolonged submaximal exercise. The cause of the difference probably relates both to the unique energy metabolic characteristics of each fibre type and to the manner in which they are utilized during the exercise. 6. The failure to find a reduction in ATP concentration in either fibre type during prolonged exercise in the face of a progressive increase in the number of fibres showing little or no glycogen concentration suggests that protective mechanisms exist that prevent an energy crisis. The nature of these protective mechanisms remains to be elucidated.
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PMID:Energy metabolism in human slow and fast twitch fibres during prolonged cycle exercise. 189 Jun 34

1. The contractile force was compared in isolated soleus muscles from young (2.5-8 months old) and aged (28-31 months old) mice. Force was measured at 25 degrees C during isometric tetanic contractions during isovelocity stretching and shortening contractions. 2. The normalized isometric force was lower by 13.3% in muscles from aged mice. Muscles from young and aged mice produced 0.951 +/- 0.031 N mg-1 (n = 12) and 0.824 +/- 0.048 N mg-1 (n = 9) respectively. The relaxation time, from 90 to 10% of the tetanic force, of muscles from aged mice was 102.1 +/- 3.7 ms (n = 6), which was longer than that for muscles from young mice, 84.4 +/- 3.8 ms (n = 6) (means +/- S.E.M.). 3. The force during shortening was also reduced in muscles from aged animals by the same proportion as the isometric force. Therefore the force during shortening relative to the isometric force was the same in muscles from young and aged mice. 4. During rapid stretching soleus muscles from aged mice produced a similar force to those from young mice. Therefore stretch can remove the weakness in muscles of aged mice. 5. These changes in muscles from aged mice are similar to those produced when inorganic phosphate (Pi) levels are raised, in skinned rabbit psoas fibres, or during fatigue or with low intracellular pH (pHi), in frog muscle. It is possible therefore that the force loss due to ageing may be due to a higher Pi level or a lower pHi.
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PMID:In mice, the muscle weakness due to age is absent during stretching. 189 Jun 52

Fatigue and myalgia are common in patients with acquired immunodeficiency syndrome (AIDS). To determine whether altered muscle metabolism or impaired activation of muscle might account for these symptoms, we utilized three different exercise protocols to produce fatigue in nine AIDS patients who complained of both fatigue and exercise-exacerbated myalgia. Five were taking azidothymidine (AZT), which may cause a mitochondrial myopathy. Simultaneous measures of force, EMG, and muscle metabolites (phosphocreatine, inorganic phosphate, adenosine triphosphate, and intracellular pH) using phosphorus nuclear magnetic resonance spectroscopy were performed during fatigue and recovery. There were no significant differences between patients and controls in terms of fatigability, muscle metabolism, or muscle activation. These results provide no support for the hypothesis that fatigue or myalgia in AIDS patients derives from altered muscle metabolism or that AZT produces mitochondrial myopathy.
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PMID:Fatigue and myalgia in AIDS patients. 192 2


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