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

The contractile properties, morphology, and the distribution of striated muscle fiber types of the external and sphincter (EAS) were determined using axial force measurements, fiber size cross-sectional area measurements, and histochemistry. Electrical stimulation of motor axons in pudendal nerve at supramaximal intensities (10 V, 0.05 ms duration) elicited twitch contractions of EAS. The time to peak force after a single pulse ranged from 37 to 42 ms. The time for relaxation to half-maximal twitch force ranged from 20 to 29 ms. Repetitive stimulation of motor axons (0.1-3.0 Hz) produced potentiation and fatigue of single twitch contractile force, suggesting that the EAS of the cat is comprised predominantly of fast-twitch muscle fibers. Confirmation of skeletal muscle fiber types was determined by histochemistry. Frozen serial cross sections of EAS were incubated to demonstrate succinic dehydrogenase (SDH) and myosin adenosine triphosphatase after alkaline preincubation (pH 10.4). Based on these reactions, muscle fibers were classified as fast glycolytic (FG) (high ATPase, low SDH), fast oxidative-glycolytic (FOG) (high ATPase, high SDH), and slow oxidative (SO) (low ATPase, high SDH). The mean percentage +/- SE of each histochemical type was the following: FG, 73.5 +/- 3.9; FOG, 22.8 +/- 3.7; and SO, 3.7 +/- 0.6. These results indicate that the predominant fiber type for the EAS is FG. The EAS of the cat is considered a nominally fast-twitch muscle.
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PMID:Physiological, morphological, and histochemical properties of cat external anal sphincter. 320 71

Digoxin could improve diaphragm contractility and fatigability if inhibition of sodium-potassium adenosine triphosphatase enhances calcium influx from extracellular sources, or it could impair contractility and worsen fatigue if it impairs maintenance of the membrane potential. We studied the effects of digoxin on isometric force production, fatigue, and recovery in isolated, directly stimulated, guinea pig and rat diaphragms. Digoxin had no effect on maximal twitch or tetanic tensions compared with control diaphragms in either rat (2 ng/ml to 20 micrograms/ml) or guinea pig (2 ng/ml to 2 micrograms/ml) hemidiaphragms. Digoxin worsened high frequency fatigue and impaired recovery from fatigue in guinea pigs (200 ng/ml to 2 micrograms/ml) but not in rat (2 micrograms/ml) hemidiaphragms. We conclude that digoxin has no effect on diaphragm contractility. Hypopolarization of the membrane potential is the likely cause for the increased fatigability. The difference in responsiveness between species is likely due to insensitivity of rat sodium-potassium adenosine triphosphatase to digoxin.
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PMID:The effect of digoxin on contractility and fatigue of isolated guinea pig and rat hemidiaphragms. 320 78

This work tested whether the membrane electrical properties of cat motoneurons, the contractile properties of their muscle units, and the normal relationships among them would be restored 9 mo after section and resuture of their muscle nerve. Properties of medial gastrocnemius (MG) motor units were examined 9 mo following section and resuture of the MG nerve in adult cats. Motoneuron electrical properties and muscle-unit contractile properties were measured. Motor units were classified on the basis of their contractile properties as type fast twitch, fast fatiguing (FF), fast twitch with intermediate fatigue resistance (FI), fast twitch, fatigue resistant (FR), or slow twitch, fatigue resistant (S) (8, 20). Muscle fibers were classified as type fast glycolytic (FG), fast oxidative glycolytic (FOG), or slow oxidative (SO) on the basis of histochemical staining for myosin adenosine triphosphatase, nicotinamide adenine dinucleotide diaphorase, and alpha-glycerophosphate dehydrogenase (48). Following 9 mo self-reinnervation, the proportions of each motor-unit type were the same as in normal control animals. Motoneuron membrane electrical properties [axonal conduction velocity, afterhyperpolarization (AHP) half-decay time, rheobase, and input resistance] also returned to control levels in those motoneurons that made functional reconnection with the muscle (as determined by ability to elicit measurable tension). The relationships among motoneuron electrical properties were normal in motoneurons making functional reconnection. Approximately 10% of MG motoneurons sampled did not elicit muscle contraction. These cells' membrane electrical properties were different from those that did elicit muscle contraction. Contractile speed and fatigue resistance of reinnervated muscle units had recovered to control levels at 9 mo postoperation. Force generation did not recover fully in type-FF units. The reduced tensions were apparently due to failure of recovery of FG muscle fiber area. Following reinnervation, relationships between motoneuron electrical and muscle-unit contractile properties were similar to controls. This was reflected in a degree of correspondence between motor-unit type and motoneuron type similar to normal units (84 vs. 86%, as defined by Ref. 61). There was a significantly increased proportion of type-SO muscle fibers and a decrease in the fast muscle fibers (especially type FOG) in 9 mo reinnervated MG. Together with the unchanged proportions of motor-unit types, this led to an estimate of average innervation ratios being increased in type-S motor units and decreased in type-FR units.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Properties of self-reinnervated motor units of medial gastrocnemius of cat. I. Long-term reinnervation. 371 73

The extent to which treatment with low doses of the nonfluorinated steroid methylprednisolone affects diaphragm contractility and morphology is unknown. In the present study, we compared the effects of equipotent doses of methylprednisolone and deflazacort, an oxazoline derivate of prednisolone with less systemic side-effects on bone structure and carbohydrate metabolism. Twenty six male adult rats were randomized to receive daily saline (control), methylprednisolone 0.4 mg.kg-1 or deflazacort 0.5 mg.kg-1 i.m. Contractile properties and histopathology were measured after a 6 week treatment period. During treatment, body weight increased in control and methylprednisolone-treated animals, but decreased by 4.2 +/- 1.1% (mean +/- SD) in the deflazacort group. Similarly, diaphragm mass in the deflazacort group was decreased compared to control and methylprednisolone groups. Twitch tension and twitch characteristics of isolated diaphragm bundles were similar in the three groups. Maximal tetanic tension was decreased in the deflazacort group. The force-frequency curve of the deflazacort bundles shifted downwards compared to control. Fatigue occurring during this protocol was greatest in the methylprednisolone- and deflazacort-treated animals. Microscopic examination revealed no gross abnormalities in the three groups. Histochemical analysis after staining for myosin adenosine triphosphatase (ATP-ase) showed that in the deflazacort group cross-sectional area of type I, IIa and IIb fibres were decreased. We conclude that low doses of methylprednisolone caused subtle and negligible changes in rat diaphragm contractile properties without affecting fibre dimensions, while deflazacort at an equipotent dose induced generalized fibre atrophy and changes in diaphragm contractility.
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PMID:Rat diaphragm contractility and histopathology are affected differently by low dose treatment with methylprednisolone and deflazacort. 765 57

1. The goal of this study was to characterize the fatigability, contractile relaxation properties, electrophysiological responses, and histochemical properties of the human paralyzed soleus muscle to determine its relative plasticity. 2. Acute (< 6 wk, n = 3) and chronic (> 1 yr, n = 10) paralyzed individuals had the tibial nerve activated with a 20-Hz square wave delivered for 330 ms every second for 4 min. The soleus muscle peak torque, one-half relaxation time (1/2RT), normalized maximum rate of relaxation (nMRR), and mass muscle action-potential amplitude (M wave) were computed every 30 s. A soleus muscle biopsy was evaluated for myosin adenosine triphosphatase enzyme (ATPase; pH 9.4, 4.6, and 4.2) and nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR). 3. In the chronically paralyzed group the torque was significantly reduced within 30 s of the fatigue protocol. The 1/2RT and nMRR were also significantly changed within 30 s, supporting that muscle relaxation was prolonged. No significant changes were present at comparable times during the same 4-min fatigue protocol applied to the acutely paralyzed soleus muscle. M-wave amplitude was significantly reduced in the chronic group, but only at 3 min of the fatigue protocol. Conversely, no significant changes occurred to the M waves of the acute group. 4. The correlation was high between torque and nMRR (r = 0.88-0.97) and torque and 1/2RT (r = 0.88-0.96) for each chronic subject. A close association was also found between 1/2RT and nMRR (r = 0.88-0.92) for each chronic subject. Because these variables changed minimally in the acutely paralyzed group, a lower correlation was present (r = 0.45-0.52). 5. Torque was weakly correlated to M-wave amplitude (r = 0.55) for the chronically paralyzed group. The greatest change in torque occurred at a time (0-65 s) when the least amount of change occurred in the M-wave amplitude, suggesting that the source of fatigue was within the contractile mechanism and not attributable to neuromuscular transmission compromise. 6. Despite a close association between torque and relaxation properties during fatigue of the chronically paralyzed soleus muscle, there was a significant dissociation after 5 min of recovery. Torque recovered to 60%, whereas the relaxation properties were consistently fully recovered. This suggests that the mechanism causing torque reduction covaried with the mechanism leading to prolonged relaxation during fatigue, but during recovery the two mechanisms no longer covaried. M-wave amplitude was also completely recovered at 5 min despite continued torque depression.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Fatigability, relaxation properties, and electromyographic responses of the human paralyzed soleus muscle. 766 32

This study investigated the histochemical and morphometric properties of fibres in laryngeal, hyoid, tongue and pharyngeal muscles which contribute in maintaining patency of the upper airway. Muscle specimens from adult female goats were stained for nicotinamide adenine dinucleotide dehydrogenase-tetrazolium reductase and myosin adenosine triphosphatase activities, and the composition and size of the fibre types determined. These muscles contained types 1, 2A, 2B and 2C fibres with type 2 fibres predominating and the fibres possessed oxidative enzyme activity suggesting fast contraction speed and yet moderate resistance to fatigue. Abductor laryngeal muscles contained more type 1 fibres than the adductors. Among pharyngeal muscles fibre size and type 1 fibre composition increased progressively from the hyopharyngeus caudally. Upper airway muscles contained relatively small fibres (range of mean diameter: 25.7 to 46.1 microns) with the pharyngeal and lingualis proprius muscles containing the smallest fibres. These properties might influence the response of upper airway muscles to neuromuscular blocking drugs.
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PMID:Histochemical and morphometric properties of muscles of the upper airway of goats. 823 90

This study was undertaken to investigate the mechanisms underlying fatigue of chronically overused motor units (MUs). The force of the tibialis anterior muscle (TA) and the firing properties of single MUs were studied during prolonged maximum voluntary effort in 10 prior polio patients selected such that daily living required all residual TA power. Almost all TA fibers were hypertrophic type I. Activities of intermyofibrillar succinate dehydrogenase (SDH) and calcium-stimulated myofibrillar adenosine triphosphatase (ATPase) were measured in single TA fibers from a representative patient. Neither insufficient motoneuron activation nor peripheral blocking of the electrical impulse played a major role in the loss of force during prolonged contraction or for slow recovery after contraction. The ratio of SDH to calcium-stimulated ATPase, representing the relation between energy resynthesis and energy utilization, was significantly (P < 0.001) lower in prior polio patients (0.230 +/- 0.096) compared to control (0.515 +/- 0.097) type I fibers.
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PMID:Fatigue of chronically overused motor units in prior polio patients. 860 23

Mechanical and histochemical characteristics of the lateral gastrocnemius (LG) muscle of the rat were examined 21 days after capsaicin injection into the LG muscle. The capsaicin caused a decrease in generation rate of twitch and tetanic tension and an increase in fatigue resistance of LG muscle. The histochemical muscle fiber profile evaluated by myosin adenosine triphosphatase and reduced nicotinamide adenine dinucleotide tetrazolium reductase methods showed an increase of type I and IIC fibers and a decrease of the type IIB in whole muscle, and a decrease of the IIA, IIX fibers in the red part accompanied by their increase in the white part. Therefore the capsaicin treatment, which selectively eliminated fibers belonging to the III and IV groups of muscle afferents, induced muscle fiber transformation from fast contracting fatiguing fibers to slowly contracting nonfatiguing ones.
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PMID:Partial transformation from fast to slow muscle fibers induced by deafferentation of capsaicin-sensitive muscle afferents. 934 57

Limitations in energy supply is a classical hypothesis of muscle fatigue. The present paper reviews the evidence available from human studies that energy deficiency is an important factor in fatigue. The maximal rate of energy expenditure determined in skinned fibres is close to the rate of adenosine triphosphate (ATP) utilisation observed in vivo and data suggest that performance during short bursts of exercise (<5 s duration) primarily is limited by other factors than energy supply (e.g. Vmax of myosine adenosine triphosphatase (ATPase), motor unit recruitment, engaged muscle mass). Within 10 s of exercise maximal power output decreases considerably and coincides with depletion of phosphocreatine. During recovery, maximal force and power output is restored with a similar time course as the resynthesis of phosphocreatine. Increases in muscle store of phosphocreatine through dietary supplementation with creatine increases performance during high-intensity exercise. These findings support the hypothesis that energy supply limits performance during high-intensity exercise. It is well documented that pre-exercise muscle glycogen content is related to performance during moderate intensity exercise. Recent data indicates that the interfibre variation in phosphocreatine is large after prolonged exercise to fatigue and that some fibres are depleted to the same extent as after high-intensity exercise. Despite relatively small decreases in ATP, the products of ATP hydrolysis (Pi and free ADP) may increase considerably. Free ADP calculated from the creatine kinase reaction increases 10-fold both after high-intensity exercise and after prolonged exercise to fatigue. It is suggested that local increases in ADP may reach inhibitory levels for the contraction process.
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PMID:Energy supply and muscle fatigue in humans. 957 71

Succinate dehydrogenase (SDH) activities and cross-sectional areas (CSAs) of different types of fibers in the superficial (EDLs) and deep (EDLd) regions of the extensor digitorum longus and soleus (SOL) muscles and the left ventricular muscle of the heart (HEART) of 10-week-old male rats were determined using quantitative histochemistry and a computer-assisted image processing system. The fibers were classified as type I, type IIA, type IIB, or type IIC according to their histochemically assessed adenosine triphosphatase activities. The mean SDH activity was higher and the mean CSA was smaller in type IIA fibers than in type IIB fibers in both the EDLs and EDLd. The mean SDH activity of type IIA fibers in the SOL was higher than that of type I fibers. Fibers in the HEART showed the highest mean SDH activity and the smallest mean CSA among all fiber types in the muscles examined. There was an inverse correlation between CSA and SDH activity for the different fiber types in different muscles. These data suggest that the SDH activity of fibers in muscle is fiber type- and size-specific, and that the highest SDH activity of fibers in the left ventricular muscle of the heart contributes to their functional properties, i.e., high fatigue resistance.
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PMID:Succinate dehydrogenase activities of fibers in the rat extensor digitorum longus, soleus, and cardiac muscles. 1059 50


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