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

A technique is described for measuring the propagation velocity of a mechanical pulse along a muscle. The pulse is generated and detected by piezoelectric crystals (bimorph benders). Measurement of the time delay for a known crystal separation gives the propagation velocity v (of the order of 100 m s-1) from which the Young's modulus is calculated. Primary results for elastic moduli of frog and toad muscles at 5 degrees C are: 2.6 X 10(6) N m-2 at rest, 3.1 X 10(7) N m-2 in tetanus and 2.1 X 10(7) N m-2 in rigor. Exploratory experiments are also described showing the application of the technique to (i) the development of tetanus, (ii) variation with sarcomere length and (iii) the mechanics of rigor. The pulse technique gives an almost instantaneous measurement of the purely elastic response of a muscle and is thereby of value in basic studies of the mechanism of contraction. It is also a useful non-destructive probe in following the effects of such variables as temperature, fatigue or chemical treatments.
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PMID:Pulse propagation in muscle. 10 92

1. The fatigue in rat anterior tibial (a.t.) motor units was studied and related to microphotometric determinations of succinate dehydrogenase (SDH) activity of the motor unit muscle fibres. 2. Anterior tibial contains fast-twitch type II fibre units with an average contraction time of 11 msec and about 5% slow-twitch type I fibre units with an average contraction time of 20 msec. 3. In type II fibres stained for SDH, absorbance varied continuously from 0.046 to 0.569 and inversely to fibre size, except for the largest fibres. 4. Resistance to fatigue of fast motor units to 100 Hz intermittent stimulation varied continuously within a wide range in near linear relations to absorbance for SDH of unit fibres and inversely to tetanic tension, except for motor units with the largest fibres and the largest tetanic tension. 5. Neither resistance to fatigue nor SDH activity lent itself to any categorization of motor units or fibres into well demarcated functional or histochemical types, since both parameters varied continuously in the unit and fibre population of the muscle. 6. The direct relation between resistance to fatigue of fast-twitch motor units and SDH activity of unit fibres appeared valid for fatigue resistance of: (a) neuromuscular transmission, tested with 100 Hz intermittent stimulation which gave concomitant failure of electrical and mechanical response, (b) excitation--contraction coupling, demonstrated by post-stimulatory depression of twitch tension with preserved maximum tetanus tension and action potential, and (c) contractile mechanism; excitation--contraction coupling?, tested with low frequency stimulation which gave decline of twitch and maximum tetanus tension with preserved action potential. 7. It is suggested that the endurance of each link in the chain of events leading to contraction, including neuromuscular junction and the excitation--contraction coupling system, is under aerobic conditions matched to the contractile capacity of the fibre expressed by its oxidative enzyme activity.
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PMID:Transmission and contraction fatigue of rat motor units in relation to succinate dehydrogenase activity of motor unit fibres. 22 67

At 15 degrees C, direct stimulation of frog single muscle fibers at a frequency of 20 Hz produced a tetanic tension that remained constant for 20 s and then declined. The decline was reversed during 1-s interruptions of the stimulus train in the first 50 s of stimulation, but not with longer stimulation. Posttetanic potentiation (PTP), characterized by prolonged twitch relaxation and contraction times and elevation of twitch height, remained for 10-40 min after a 10-s tetanus and for at least 90 min after a 50- to 150-s tetanus. Posttetanic fatigue appeared only after at least 50s of tetanic stimulation. Fatigue was manifested invariably by a reduction in the height of a 200-ms tetanic contraction and usually by a reduction in twitch height after PTP. Fatigued fibers recovered normal contractile responses in 40-160 min. Hypertonic solutions, which blocked contraction in response to tetanic stimulation, prevented posttetanic fatigue but not PTP. The observations suggest that fatigue is caused by a failure in excitation-contraction coupling, probably in relation to consumption of metabolic substrates. Even 10-s tetani which do not produce fatigue can affect muscle contractile function for up to 40 min.
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PMID:Fatigue and posttetanic potentiation in single muscle fibers of the frog. 30 Sep 90

The mechanical properties of two extraocular muscles (superior oblique and superior rectus muscles) of the frog were studied and compared with those of a frog's skeletal muscle (iliofibularis muscle) which contains the same types of muscle fibres as the oculorotatory muscles. The extraocular muscles are very fast twitching muscles. They exhibit a smaller contraction time, a smaller half-relaxation time, a higher fusion frequency, and a lower twitch-tetanus ratio than the skeletal muscles. The maximum isometric tetanic tension produced per unit cross-sectional area is lower in the extraocular muscles than in skeletal muscles. However, the extraocular muscles show a higher fatigue resistance than the skeletal muscles. With respect to the dynamic properties there are some differences between the various oculorotatory muscles of the frog. The superior rectus muscle exhibits a faster time-course of the contraction, a higher fusion frequency, and a higher fatigability than the superior oblique muscle. An increase of the extracellular K+-concentration evokes sustained contractures not only in the extraocular muscles but also in the iliofibularis muscle; between these muscles there are no striking differences in the mechanical threshold of the whole muscle preparation. The mechanical threshold depends on the Ca++-concentration of the bathing solution and it is found in a range between 12.5 and 17.5 mM K+ in a normal Ringer solution containing 1.8 mM Ca++. The static-mechanical properties of the extraocular muscles of the frog and the dependence of the active developed tension on the muscle extension are very similar to those which are known to exist in the extraocular muscles of other vertebrates. In tetanic activated frog's oculorotatory muscles a linear relationship exists between length and tension. A variation of the stimulation frequency does not change the slope of this curve but causes parallel shifts of the curve. The peculiar properties of the extraocular muscles of the frog are discussed with respect to the muscle fibre types in these muscles and to the diameter of the muscle fibres.
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PMID:The properties of the extraocular muscles of the frog. I. Mechanical properties of the isolated superior oblique and superior rectus muscles. 30 53

Fatigue and recovery from fatigue were related to metabolism in single fibers of the frog semitendinosus muscle. The fibers were held at a sarcomere length of 2.3 microm in oxygenated Ringer solution at 15 degrees C and were stimulated for up to 150 s by a schedule of 10-s, 20-Hz tetanic trains that were interrupted by 1-s rest periods, after which they were rapidly frozen for biochemical analysis. Two kinds of fatigue were produced in relation to stimulus duration. A rapidly reversed fatigue occurred with stimulation for under 40 s and was evidenced by a decline in tetanic tension that could be overcome by 1 s of rest. A prolonged fatigue was caused by stimulation for 100-150 s. It was evidenced during stimulation by a fall in tetanic tension that could not be overcome by 1 s of rest, and after stimulation by a reduction, lasting for up to 82 min, in the peak tension of a 200-ms test tetanus. Fiber phosphocreatine (PCr) fell logarithmically in relation to stimulus duration, from a mean of 121 +/- 8 nmol/mg protein (SEM, n = 12) to 10% of this value after 150 s of stimulation. PCr returned to normal levels after 90-120 min of rest. Stimulation for 150 s did not significantly affect fiber glycogen and reduced fiber ATP by at most 15%. It is suggested that the prolonged fatigue caused by 100-150 s of tetanic stimulation was caused by long-lasting failure of excitation-contraction coupling, as it was not accompanied by depletion of energy stores in the form of ATP. One possibility is that H+ accumulated in fatigued fibers so as to interfere with the action of Ca2+ in the coupling process.
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PMID:Metabolic correlates of fatigue and of recovery from fatigue in single frog muscle fibers. 31 Aug 67

1. Compensatory hypertrophy of the medial gastrocnemius (MG) muscle was produced by denervating or removing its synergists (i.e., the lateral gastrocnemius, soleus, and plantaris muscles) in adult cats. Following survival times of 14-32 wk, intracellular recording and stimulation techniques were used to study the motor-unit population in MG. The data obtained were compared with results from MG motor units in normal unoperated cats of the same body size and weight. 2. Using criteria employed for normal motor units, the units in hypertrophic MG muscles were readily classified into the same groups (types FF, F(int), FR, and S) as in normal MG. There was no detectable difference in the distribution of motor-unit types after hypertrophy. 3. When compared with a normal motor-unit sample, there was a large increase in mean tetanic tension, but no significant change in twitch tension, for each motor-unit type in the hypertrophied muscles. The most marked increase was found among the fatigue-resistant type S and type FR motor units. There was no alteration of twitch contraction times or fatigue resistance in any unit type after hypertrophy. 4. For each motor-unit type, the mean homonymous (MG) group Ia EPSP amplitude was the same in normal and hypertrophic MG populations. There was, however, a significant increase in the average conduction velocity of MG motor axons in the animals with uncomplicated MG synergist removal and maximal MG hypertrophy. 5. On the basis of histochemical staining, muscle fibers from comparable sections of hypertrophic and contralateral (unoperated) MG muscles were presumptively identified as belonging to FF, FR, or S units. There was no significant difference between hypertrophic and contralateral MG muscles in the percentage of each fiber type, although there was some variability in muscle composition from one cat to another. One muscle pair was studied in detail for fiber cross-sectional area. In this cat, with marked hypertrophy by muscle weight, there was a modest increase in the mean fiber areas of histochemical S and FR muscle fibers, but no evident change in FF fibers, on the hypertrophic side. 6. MG motor units were examined in several cats in which synergist removal resulted in scarring and marked limitation of passive ankle mobility, and no evident weight gain in MG. Motor units of all types in these animals showed a decrease in twitch tension and in mean twitch/tetanus ratios, with little alteration in mean tetanic tensions. 7. The main effect of compensatory hypertrophy under the present conditions was a large increase in tetanic tension output from individual motor units due, at least in part, to an increase in fiber cross-sectional area. There was no evidence indicating any "conversion" of motor units or of their muscle fibers from one type to another.
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PMID:Effect of compensatory hypertrophy studied in individual motor units in medial gastrocnemius muscle of the cat. 65 Feb 79

A systematic clinical analysis of skeletal muscle function is presented. Tests range from assessment of muscle weakness with a new hand-held dynamometer (the "Hammersmith Myometer") to studies of the contractile properties of the quadriceps and adductor pollicis muscles described in terms of the force generated at different frequencies of stimulation of the motor nerve, the force-sustaining capability and the time course of relaxation following a brief tetanus. A new measure of the energy-exchanging capacity of muscle is given by the Myothermogram (MTG - so named by analogy with the Electromyogram - EMG). The technique measures metabolic heat production in muscles when maximally activated by voluntary effort or electrical stimulation and the heat changes during sustained contractions. The MTG offers a practical means for assessing in normal and diseased human muscle the metabolic capacity, economy of force maintenance and fatigue mechanisms. Needle biopsy provides safe, rapid and repeatable access to muscle for diagnosis, studies of chemical energy exchange and the correlation of function and metabolism with constituent muscle fibre types. This approach provides a possible basis for recognising the functional disorder and for evaluating the effects of physiotherapy and drug treatments in patients with neuromuscular disorders.
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PMID:Clinical assessment of skeletal muscle function. 66 14

1. Tetanus toxin was injected into gastrocnemius muscles of cats and for 24 h its action on nerve condution of muscle afferents was investigated. 2. During this period stimulus threshold and latency remained constant. No signs of fatigue were observed.
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PMID:Early local tetanus: does tetanus toxin change the stimulus evoked discharge in afferents from the injected muscle? 88 57

The mechanical acitvity of the isolated flexor carpi radialis muscle (FCRM) of the mature male frog (Rana temporaria) was compared to that of the sartorius muscle. Muscles were stimulated directly by massive shocks at 20 degrees C and isometric tension was recorded during single twitch, twitch series, long tetani and long tetanus series. Some groups of muscles were poisoned with IAA-N2 or FDNB. The FCRM showed a high resistance to fatigue during a tetanus series and a "fatigue contracture" during a twitch series. The rate of the tetanic tension rise was smaller by five to six times than in the sartorius muscle (0 to 50% Po) and the twitch/tetanus ratio was always very small. During continuous activity and after the blocking of recovery metabolic pathways, FCRM used its energetic stores two to three times slower than the sartorius muscle. These stores did not seem to be more important. The results indicate that the FCRM is not a "tonic" muscle but, quite possibly, is composed of several types of fibre like many other frog muscles. However, some characteristics of mechanical response cannot be explained by the common classification into two types of fibre.
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PMID:Tonic properties of the Flexor carpi radialis muscle of the male frog (Rana temporaria). 108 Feb 73

The time-course of the isometric tension output, at 20 degrees C, during a long tetanus and after a short period of rest, was investigated in two isolated frog muscles : the sartorius and flexor carpi radialis muscles. To prevent aerobie and glycolytic recovery processes, some muscles were poisoned with 0,4 mM iodoacetic acid (IAA) and nitrogen, for 20 or 40 min. 1. For the unpoisoned sartorius muscle, tetanic tension declined quickly, but after a 0,8 sec period of rest, the muscle was able to develop high tension. Poisoning with IAA-N2 increased fatigue without suppressing the property of a proximate post-tetanic recuperation. 2. In the flexor carpi radialis muscle resistance to fatigue was very large before poisoning and diminished after poisoning. Proximate recuperation was very weak. 3. The results show that the recovery processes are not a primary factor of the development of the short-term fatigue ; they enhance the hypothesis that a failure of the electromechanical coupling can explain the rate of the tension fall in tetanized sartorius muscles.
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PMID:[Tetanic fatigue and proximate post-tetanic recuperation in sartorius and flexor carpi radialis muscles of the male frog. Effects of iodoacetic acid (author's transl)]. 108 32


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