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

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

The lateral rectus (LR) muscle of the pigeon was directly stimulated in situ at 41 degrees C. The length tension relationships for active and passive tension were investigated to determine the optimum muscle length (Lo). Isometric responses to single and twin pulses, tetani and sinusoidal stimulation were measured. A linear relationship was found between length and active tension during stimulation. Increase in stimulation frequency produced a corresponding shift in tension with the slope of the curves remaining the same. At Lo (1.21 times resting length) the average contraction time of single twitches was 6.03 ms and the half-relaxation time was 7.77 ms. Stimulation frequencies of 200 Hz and over gave rise to a fused tetanus. Tension increased to a maximum at 200 Hz and rate of tension rise saturated at 600 Hz. The tension response to tetanic stimulation was linear over the range 70-180 Hz. Maximum tetanic tension was around 3.48 N/cm2 and the twitch:tetanus ratio was 0.164. Prolonged activation at fusion frequency showed a high fatigue resistance. Sinusoidal stimulation with pulse trains of 100-180 Hz produced a sinusoidal response over the frequency range 0.6-40 Hz, from which the gain and phase relationships were determined. The muscle response approximates a first order low pass filter, with a characteristic frequency of 11.2 Hz. There is an additional phase lag, equivalent to the response latency, of 2.89 ms. The results are compared to the contractile properties of mammalian eye and avian skeletal muscle. The frequency response of the LR is compared to that of cat soleus and gastrocnemius and to pigeon eye movement dynamics.
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PMID:The contractile properties and movement dynamics of pigeon eye muscle. 318 34

These experiments explore the relationship between patterned impulse activity and contractile properties of skeletal muscles. Soleus (SOL) and extensor digitorum longus (EDL) muscles of adult rats were denervated and stimulated directly from 4 to 15 weeks with the same number of pulse trains at different intratrain pulse frequencies (1-500 Hz), with different numbers of pulse trains (864-4,320,000 pulses/d) at the same intratrain pulse frequencies, or with different combinations of pulse trains at 10 and 100 Hz. Chronic stimulation of the denervated SOL resulted in twitch times-to-peak and half-relaxation times that varied in a graded manner between values longer than those in the normal SOL to values as fast as those in the normal EDL, depending upon the pattern used. Increasing pulse frequencies (constant number) resulted in faster twitches, lower twitch/tetanus ratios, increasing post-tetanic potentiations, and larger tetanic tensions. Increasing pulse numbers (constant frequencies) resulted in slower twitches, lower twitch/tetanus ratios, post-tetanic depressions, and higher fatigue indices. The effect of varying the pulse number on twitch parameters was greater at low frequencies (10-20 Hz) than at high frequencies (100 Hz). SOL muscles receiving pulse trains at both 10 and 100 Hz became much faster than muscles receiving pulse trains at 10 Hz only, even in the experiments where the stimulation pattern contained 9 times as many pulses at 10 as at 100 Hz. Chronic stimulation of both the denervated and the innervated EDL with large numbers of pulses at 10 or 15 Hz resulted in twitches that were only half as slow as those induced in the SOL by the same "slow" patterns. In addition, these patterns led to a marked decrease in maximum tetanic tension and a marked increase in twitch/tetanus ratio. During stimulation with a small number of pulses at 150 Hz, on the other hand, twitch speed, twitch/tetanus ratio, and maximum tetanic tension remained normal or almost normal. We conclude that the isometric twitch and related properties of the rat SOL muscle can be graded within wide "adaptive ranges" by varying either the number or the frequency of pulses. In the EDL, the corresponding adaptive ranges appear much narrower, suggesting that the EDL and the SOL contain intrinsically different muscle fibers.
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PMID:Control of contractile properties within adaptive ranges by patterns of impulse activity in the rat. 319 82

Brief repetitive trains of supramaximal nerve stimulation produce intermittent muscle activation and, in time, a progressive decline in force (i.e., neuromuscular fatigue) and depression of the electromyogram (EMG). These changes may include within-train reductions in EMG due to a failure of neuromuscular propagation. The aim of the present study was to investigate changes in EMG during a 360-second stimulus regimen designed to fatigue soleus and extensor digitorum longus muscles of anesthetized rats by activating the muscle with repetitive trains of 40 Hz stimuli. Measurements included peak force for each tetanus, variation of the within-train EMG (coefficient of variation for area), and magnitude of the first EMG waveform (area) of each train. Fatigue was characterized as the relative decline in force over the course of the test. The responses of the test muscles were categorized, based on an absolute scale of fatigability, into five groups: potentiated, nonfatigable, low fatigability, intermediate fatigability, and high fatigability. Fatigable muscles (low, intermediate, and high fatigability groups) demonstrated a decreased EMG magnitude and an increased EMG-area variation with repetitive activation. This increased variation, however, was nonmonotonically related to fatigability such that the least and most fatigable muscles had the smallest within-train EMG variation. We suggest that these data can be explained by considering the EMG (compound muscle action potential) as a stochastic process that represents a composite of single-fiber events (axonal to sarcolemmal transmission) with variable probabilities.
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PMID:Fatigue-related changes in neuromuscular excitability of rat hindlimb muscles. 322 28

This paper compares the effects of 6 wk of sub-maximal training by electrostimulation (100 Hz) and voluntary contractions on the contractile properties of the adductor pollicis muscle in intact man. The daily training program consisted of ten series of twenty 1-s isotonic contractions (60 to 65% of maximum) separated by 1-s intervals. The observed increase in muscle force, tested in maximal voluntary and electrically evoked contractions, appears to be significantly smaller during electrostimulation than during a training session performed by voluntary contractions. The increase in force recorded during electrostimulation is not associated with changes in the tetanus rates of tension development and tension relaxation (dP0/dt). Conversely, the tetanus time course is found to be significantly accelerated in muscles trained by voluntary contractions. No change of the surface action potential total area was observed during both training procedures. Furthermore, electrostimulation does not improve muscle resistance to fatigue, which is observed to be significantly increased after training by voluntary contractions. This study indicates that electrostimulation augments the muscle force of contraction by changing peripheral processes associated with intra-cellular events, without modifying the nervous command of the contraction. The comparison of the peripheral changes recorded during sub-maximal training by electrostimulation and voluntary contractions suggests that electrostimulation is less efficient, but complementary to voluntary training because the number and the type of trained motor units are different in the two procedures.
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PMID:Training effects of sub-maximal electrostimulation in a human muscle. 334 22

Changes in contractile properties of developing fast-twitch skeletal muscle of the C57/BL6J mouse were studied following neonatal denervation. A sciatic neurectomy was performed at 1 day of age and then denervated and control muscles were examined at 7, 14, and 21 days postdenervation. In addition, normal muscles were studied at 1 day of age. The denervated muscles exhibited prolongation of time-to-peak twitch tension and half-relaxation time, a slowing of the maximum velocity of shortening, and a marked increase in resistance to fatigue compared with controls. Isometric tetanus tension was reduced compared to the control muscle both in absolute terms and when expressed relative to body weight at all ages studied. The absolute isometric twitch tension was reduced at 7 and 14 days, but was reduced only at 21 days when expressed as a fraction of the muscle weight. Post-tetanic twitch potentiation failed to appear in the denervated muscle. It would appear that neonatal denervation results in an uncoupling of the developmental pattern of skeletal muscle.
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PMID:Alterations in contractile properties of extensor digitorum longus muscle from C57BL/6J mice following denervation at 1 day of age. 336 5

Mechanical characteristics and electrical activity were studied in the extraocular muscles of the catfish, Ictalurus punctatus. The contractile properties were determined by stimulation of the individual muscle nerve branches to lateral and medial rectii and the superior and inferior oblique muscles. The speed of contraction was higher than in most other fish muscle, with a twitch contraction time of about 12 ms and a tetanus fusion frequency of 150-170 Hz in all four eye muscles. The fatigue resistance was also high. These properties were the same in fully innervated and partially innervated muscle, largely irrespective of what part of the muscle that was activated. Although different fibre types are known to exist in fish extraocular muscle, it was not possible to obtain functional separation of the mechanical force profile even in the lateral rectus with two distinct motoneuronal innervations. We suggest that polyneuronal innervation of the muscle fibres produces the mechanical responses. Since EMG activity during spontaneous eye movements was similar in the global and the orbital parts of the muscle, all types of fibres in fish extraocular muscle are probably recruited for all types of eye movements.
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PMID:Motoneuronal innervation and mechanical properties of extraocular muscles in the catfish, (Ictalurus punctatus). 342 46

The electrically evoked isometric properties of the triceps surae have been studied in young (22 yr) and elderly (69 yr) men and women. The results show that the triceps surae of elderly subjects had an increased time to peak tension (TPT) of the twitch, a lower specific tension (force/cross section area), and showed a greater relative force loss when subjected to a standard "fatigue" test procedure than young triceps surae. The respective figures for TPT, specific tension, and fatigue index (FI) were 147 +/- 15 ms (male), 143 +/- 8 ms (female), 19.5 N/cm2 and 0.52 +/- 0.16 (male), 0.37 +/- 0.09 (female) in the elderly, compared with 118 +/- 14 ms (male), 132 +/- 11 ms (female), 32.9 N/cm2 and 0.67 +/- 0.11 (male), 0.62 +/- 0.09 (female) in their younger counterparts. The peak rates of rise (delta P50, delta P200) and relaxation (delta PR50, delta PR200) of tetani at 50 Hz and 200 Hz were slower (p less than 0.05) in the elderly group. The delta P50 and delta P200 were inversely associated (r = 0.76 and -0.50 respectively) with TPT, and the half relaxation time (1/2RT) of the maximal twitch was related to delta PR50 (r = 0.53). The decrease of tetanus relaxation rate during the 2 min fatigue test (delta PRF) was greater in the elderly than the young and was positively associated (r = 0.74) with FI. It is concluded that elderly muscle is weaker, more slowly contracting and fatigable than that of the young. However, it is suggested that the reduced specific tension and enhanced fatiguability of the elderly may in part be due respectively to the inadequacies of our estimates of the effective cross-sectional area CSA) of contractile tissue in the lower leg and the influence of blood flow which may be compromised during a 2 min test.
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PMID:Mechanical properties of young and elderly human muscle. 346 6

Carnosine content in muscles functioning under single or tetanic (both direct and indirect) contractions, in the period of active contractility (within the first 10 min of experiment) and in fatigued muscles was determined. In exercising muscle, carnosine content was shown to decrease. The loss of the dipeptide during active contractions was, on the average, 10.5%; that at fatigue--13.8%. At exercise (single contractions), the decrease of carnosine was higher than in the muscles functioning in a short tetanus regime. It was shown that the previously described phenomenon of fatigue elimination by carnosine addition to the Ringer solution washing the muscle is concomitant with the elevation (by 12%) of the intramuscular concentration of exogenous carnosine.
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PMID:[Changes in carnosine levels in muscles working in different regimens of stimulation]. 348 47

Isolated soleus muscle of rat was stimulated electrically (2 Hz) for 7 min under anaerobic conditions. Isometric twitch tension decreased progressively and was 30% of the initial value at the end of stimulation. The decline in relative force was similar to that previously observed in fast twitch muscle and soleus can thus not be termed fatigue-resistant under anaerobic conditions. Phosphocreatine (PCr) decreased from (mean +/- SD) 61.1 +/- 4.4 at rest to 4.0 +/- 1.8 mmol kg-1 dry muscle (d.m.) after 7 min of stimulation, while lactate increased from 3.7 +/- 1.6 to 30 +/- 8 mmol kg-1 d.m. Energy was thus derived from complete utilization of PCr and a low rate of glycolysis resulting in an almost unchanged calculated intracellular pH. It is concluded that tension decline in soleus muscle is not due to decreased intracellular pH but is more related to the capacity to regenerate ATP at a sufficient rate. Contraction and relaxation time of the twitch remained practically constant during the stimulation period. In contrast prolonged activation of fast-twitch muscle results in a slowing of the relaxation of the twitch (Sahlin et al. 1981) and it has been suggested that this is caused by the decrease of intracellular pH. The constancy of both relaxation time and calculated pH in the fatigued soleus muscle is consistent with the hypothesis that there is a connection between these two parameters. In contrast to the twitch, relaxation of tension after a tetanus was prolonged in soleus. Hence, it appears that the rate limiting step for relaxation is different for a twitch than for a tetanus in soleus.
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PMID:Force, relaxation and energy metabolism of rat soleus muscle during anaerobic contraction. 356 37


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