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

The purpose of the study is to determine the difference, if any, between the dendritic distributions (field) of slow and fast muscle motoneurons. A cholera toxin subunit conjugated horseradish peroxidase (CTHRPs can label retrogradely the dendrites of motoneurons and was injected into a slow muscle (soleus, SOL) and a fast muscle (extensor digitorum longus, EDL) of the hind limbs of rats. The results show that the dendrites of EDL motoneurons project into Rexed lamina VI, VII, and IX while that of SOL into V, VI, VII, VIII, and IX of the gray matter of lumbosacral spinal cord. SOL motoneurons also have many long dendrites extending into ventrolateral and ventral white matter while such extensions from EDL motoneurons are short and scanty. Thus, the dendritic field of SOL motoneurons is wider than that of EDL motoneurons. It is suggested that this difference may be related to the fact that SOL is a slow, fatigue resistant muscle and is more often used than EDL which is fast, fatigable muscle and less often used in routine muscle activity.
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PMID:Dendritic distributions of motor neurons innervating fast and slow muscles of the hind limb of rats. 235 67

Muscle fatigue is accompanied by a series of biochemical correlations as substrate depletion, lactate accumulation, shifts of pH, increase of phosphate (Pi), arise of free radicals or disturbances of ionic balances. In last time high interest has been directed to the increase of extracellular potassium during extensive muscle activity. It was suggested that high K+ concentration in the interstitium may alter propagation of action potential along the T-tubules or induces membrane depolarization with physiological consequences. In order to elucidate the role of potassium accumulation, experiments were performed on isolated rat muscles. An elevation from 5 to 10 mmol K+ of the bath solution causes a significant decrease of the conduction velocity of the action potential. This effect is more pronounced on fatigue-sensitive fast twitch EDL muscles than on fatigue-resistant slow twitch SOL muscles. Moreover, after tetanic stimulations of these muscles in normal solution, the conduction velocity dropped by the same amount as in high K+ solution but, again, differently in both muscle types. Therefore it is supposed that K+ accumulation during intensive muscle activity contributes to fatigue.
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PMID:[Problems of muscular fatigue--relationship to stimulation conduction velocity and K(+) concentration]. 239 48

Fatigue from high frequency stimulation is associated with EMG signal changes, which are primarily due to a slowing of the sarcolemma conduction velocity. In the present study, in which isolated mouse soleus and extensor digitorum longus muscles have been studied, it is shown that the action potential propagation velocity is (1) decreased by an increased extracellular potassium concentration, (2) independent of extracellular pH, (3) decreased by low intracellular pH, and (4) nearly independent of moderate changes in the sodium gradient. The EDL muscle is more affected than the soleus muscle. The ion effects on propagation velocity are seen within the physiological ranges. The propagation velocity was decreased after 2 min of electrical stimulation and recovered with a time course similar to the pH recovery. The effects of extracellular potassium and internal pH are due to independent mechanisms.
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PMID:Muscle action potential propagation velocity changes during activity. 245 55

We tested the effects of inhibiting the carbonic anhydrase activity of rat soleus and extensor digitorum longus muscles on the isometric contractile properties and the resistance to fatigue. SOL and EDL muscles from female rats were incubated in vitro in the presence of methazolamide, a specific inhibitor of carbonic anhydrase, before determining their contractile properties. Methazolamide had no effects on the contractile properties of the soleus muscle (10(-5) or 10(-3) M) and extensor digitorum longus (10(-3) M), except for the half-relaxation time of the soleus muscle which increased significantly. Values for half-relaxation time were significantly increased with both concentrations of the inhibitor. Muscles were then submitted to a fatigue protocol lasting 30 min. During the fatigue test, no significant difference was observed between control and 10(-5) M methazolamide soleus muscles. In presence of 10(-3) M methazolamide however, the soleus muscle showed a significantly increased resistance to fatigue compared with control preparations. No significant effect was observed with the extensor digitorum longus muscle exposed to 10(-3) M methazolamide. Results are discussed in terms of the presence of two different isoforms of carbonic anhydrase that may be associated with calcium uptake and energy metabolic processes, respectively.
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PMID:Inhibition of carbonic anhydrases in type I muscle fibers influences contractility. 277 80

Chronic administration of an anabolic hormone, nandrolone phenylpropionate, in sedentary female rats for 6 weeks gave a 20% increase in body weight and the same proportional increase in all muscles sampled (heart, diaphragm, soleus, TA, EHP and EDL), such that the muscle/body weight ratio was unchanged. Cardiac muscle was unresponsive to treatment. Acute stimulation of EDL via lateral popliteal nerve gave similar values for contraction time, 1/2 relaxation time and twitch:tetanus ratio in both groups suggesting no slowing of the muscle. Fatigue resistance of EDL was improved with 0.29 +/- 0.029 vs. 0.46 +/- 0.071 of maximum isometric twitch tension being developed after 10 min repetitive stimulation at 4 Hz. This improved endurance was not accompanied by any increase in strength and could not be explained on the basis of cellular hypertrophy, but appears to reflect an increased aerobic capacity of skeletal muscle. The proportion of FOG fibres in EDL increased, 38 +/- 1.1% vs. 46 +/- 1.1%, and this was paralleled in the other skeletal muscles. Specific hypertrophy of FOG and FG fibres could be conclusively demonstrated in soleus and TA, respectively.
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PMID:Effects of an anabolic hormone on striated muscle growth and performance. 296 63

Intracellular potassium ([K+]i), interstitial potassium ([K+]inter), intracellular sodium ([Na+]i), and resting membrane potential (RMP) were measured before and after repetitive stimulation of mouse soleus and EDL (extensor digitorum longus) muscles. At rest, RMP was -69.8 mV for soleus and -74.9 mV for EDL (37 degrees C). [K+]i was 168 mM and 182 mM, respectively. In soleus, free [Na+]i was 12.7 mM. After repetitive stimulation (960 stimuli) RMP had decreased by 11.9 mV for soleus and by 18.2 mV for EDL. [K+]i was reduced by 32 mM and 48 mM, respectively, whereas [K+]inter was doubled. In soleus [Na+]i had increased by 10.6 mM, demonstrating that the [K+]i-decrease is three times higher than the [Na+]i-increase. It is concluded that this difference reflects different activity induced movements of Na and K, and that the difference is not due to the Na/K pumping ratio. The possible involvement of the potassium loss in muscle fatigue is discussed. After stimulation RMP recovered with a time constant of 0.9 min for soleus and 1.5 min for EDL. Within the first minutes after stimulation the intracellular potassium concentration increased by 20.4 mM/min for soleus and 21.7 mM/min for EDL. Free [Na+]i decreased with less than 10 mM/min. The mechanisms underlying the different rate of changes are discussed.
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PMID:Potassium and sodium shifts during in vitro isometric muscle contraction, and the time course of the ion-gradient recovery. 371 46

A study of muscles of the dystrophic mouse has failed to substantiate earlier claims that these muscles were especially resistant to fatigue in vitro or that fast muscles are preferentially damaged. It has been found that the fast muscle selected for previous studies is very often unable to withstand isolation in an organ bath if it is working, and both the difficulty in removing the normal gastrocnemius muscle intact and the need to trim it surgically contribute independently toward its deterioration in vitro. The smaller dystrophic gastrocnemius muscle is less liable to excision damage, is able to satisfy its resting metabolic needs in nutrient solution, and requires no damaging dissection, but is nevertheless unable to recover normally from fatigue. Using EDL and soleus muscles which are small enough to withstand isolation in vitro, no differences are found between fatigue patterns of normal and dystrophic specimens. Responses to rest, KCl, and 2 mM caffeine are also quite similar, and the only distinguishing biomechanical characteristic we have found in dystrophic mouse muscle is a weaker contraction and a longer total twitch time.
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PMID:Observations on the efficiency of dystrophic muscle in vitro. 473 27

1. Extensor digitorum longus IV muscle (EDL IV) of Xenopus laevis was isolated together with its nerve and the 8th and 9th spinal roots. Motor units were functionally isolated and their properties investigated. 2. The motor unit isometric twitch and tetanic tensions, contraction time and axon conduction time and distance were measured. Axon conduction velocity and twitch:tetanus ratio were calculated. 3. The distributions of motor unit properties were continuous and showed no tendency to separate into types. 4. Axon conduction velocity was directly related to unit tetanic tension (expressed as a percentage of whole muscle tetanic tension and to twitch:tetanus ratio and inversely related to contraction time. Unit tetanic tension was directly related to twitch:tetanus ratio and inversely related to contraction time. Contraction time was inversely related to twitch: tetanus ratio. Possible explanations for these relationships are discussed. 5. The units of EDL IV show a greater resistance to fatigue than fast units of other amphibian muscles. There was no separation of units into fatiguable and fatigue resistant types.
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PMID:Properties of motor units in a small foot muscle of Xenopus laevis. 746 59

The study was conducted to determine the effect of persistent fatigue in situ on the inositol phosphate second messenger system proposed to constitute a step in excitation-contraction coupling. Rat EDL, after stimulation in situ for 1 hr (100 Hz for 330 ms, 1/s), showed increased incorporation of myo-[3H]inositol into membrane phosphoinositides during a subsequent 4-h incubation period. The rate of hydrolysis of this pool resulting from 10 sec of tetanic stimulation, as well as the rate of production of inositol phosphates InsP, InsP2, and InsP3, were significantly reduced in fatigued muscles. These results suggest that the metabolic changes that parallel the alteration in contractile response with fatigue reflect a disruption in E-C coupling.
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PMID:Effects of fatigue of rat EDL in situ on metabolism of phosphoinositides. 854 92

The effect on inhibiting the calcium activated neutral protease (CANP) by leupeptin on force output and motor unit size of the partially denervated rat EDL muscle was studied. Partial denervation was performed under anaesthesia by section of the L4 ventral ramus in 3- and 18-day-old Wistar rats. Two days after the operation a silicon strip containing the inhibitor of CANP leupeptin was implanted alongside the partially denervated EDL. Two to 3 months later the animals were anaesthetized and the EDL muscles on both sides prepared for tension recording. The results from these recordings show dramatic reduction in force output and muscle weight in animals operated at 3 days and this reduction was less pronounced in muscles treated with leupeptin. The mean force output of individual motor units increases in the leupeptin-treated partially denervated muscle compared to the untreated muscle. The increased fatigue resistance typical of muscles partially denervated at 3 days [37] is less pronounced in the treated muscle. In animals operated at 18 days the individual motor units actually increased in size and the leupeptin treatment had no effect on the partially denervated EDL muscles. The difference between the response to leupeptin of the 3 day and 18 day operated animals could be due to the different patterns of innervation of the muscles at the time of the application of the inhibitor of CANP.
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PMID:Stabilisation of neuromuscular junctions by leupeptin increases motor unit size in partially denervated rat muscles. 866 65


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