UMLS:C0015672 - FACTA Search

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

We compared mdx and C57BL10 anterior tibial muscle force in situ (single pulse, multiple pulse, staircase, posttetanic potentiation, and fatiguing stimulation patterns) to define muscle strength, physiology, and fatigue resistance. The relatively hypertrophied mdx muscle showed: reduced strength (N/cm2), an increased twitch-tetanus ratio, and resistance to post-fatigue twitch slowing. These differences implicate altered mdx calcium regulation, and emphasize the importance of measuring both muscle function and morphology in mdx treatment trials.
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PMID:Twitch and tetanus in mdx mouse muscle. 150 27

The effects of up to 4 months dietary supplementation with 40% galactose on muscle and nerve function were examined in rats. Galactitol, a polyol pathway metabolite, accumulated to high levels in both tissues. This led to changes similar to those found in experimental diabetes, which were largely prevented by treatment with an inhibitor of the first enzyme in the pathway, aldose reductase. For fast twitch extensor digitorum longus muscle there was weight loss, fibre damage, slowing of twitch time to peak, increased twitch tension, and reduced tetanic tension. There were no relaxation deficits. For slow twitch soleus there were no changes in tension production. However, contraction and relaxation for both twitch and tetanus were prolonged. Fatigue resistance was reduced after 1 week. Damage in soleus led to a reduction in mean fibre area after 2 months, which largely recovered by 4 months. There was a selective loss of fast oxidative glycolytic fibres. Histochemical staining for succinic dehydrogenase was normal in galactosaemic soleus, in contrast to the marked reduction seen in diabetes. Sciatic nerve conduction velocity was reduced after 2 months, particularly in normally fast conducting motor and sensory fibres. Resistance to hypoxic conduction block was increased in galactosaemic nerves to diabetic levels. It was concluded that polyol pathway hyperactivity is likely to contribute to the aetiology of diabetic myopathy and neuropathy, and that experimental galactosaemia provides a good model in which to study pathway effects without the complicated hormonal changes found in diabetes.
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PMID:Muscle and nerve dysfunction in rats with experimental galactosaemia. 153 21

To evaluate the regenerative capacity of mdx skeletal muscle, changes in contractile properties of the fast-twitch extensor digitorum longus (EDL) of normal and mdx mice were studied at 7 and 16 weeks of age, following denervation and devascularization (DD) at 4 weeks of age. At 7 weeks, DD EDL of both strains showed significantly decreased isometric twitch and tetanus tensions compared with their non-DD controls. By 16 weeks, normal operated muscle exhibited a recovery of 57% and 58% of absolute tetanus and twitch tensions while the mdx EDL recovered remarkably to 96% and 99% of 7-week values. At 7 weeks, the DD EDL of both strains exhibited significantly slower time-to-peak (TTP) and one-half relaxation time (1/2RT). By 16 weeks, TTP and 1/2RT of the mdx DD EDL no longer differed from non-DD controls, but the normal EDL showed slowed TTP. No differences were found in the maximum velocity of shortening (Vo) or in posttetanic potentiation (PTP). Following DD, there was an increase in resistance to fatigue in both strains at 7 weeks. This resistance persisted at 16 weeks in the normal mouse, but the operated mdx EDL returned to normal. It would appear that following a denervation/devascularization insult, the mdx EDL is able to recover contractile characteristics to a remarkably larger extent than normal EDL.
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PMID:Contractility of mdx skeletal muscle after denervation and devascularization. 155 78

1. Isolated and glycogen-depleted motor units (MUs) have been studied in normal and reinnervated tibialis anterior (TA) muscles of the rat to examine 1) the correspondence between physiological and histochemical classifications, 2) the extent to which unit properties cluster according to type, 3) the relation between unit force and fatigability, and 4) the extent to which reinnervated MUs recover their former properties. 2. MUs were isolated by ventral root dissection and stimulation in reinnervated and normal TA muscles, 3.5-8 mo after common peroneal (CP) nerve section and resuture and in age-matched control rats, respectively. The units were characterized physiologically for classification into four types: slow twitch (S), fast twitch, fatigue resistant (FR), fast twitch fatigue intermediate (FI), and fast twitch fatigue sensitive (FF). Four muscle fiber types were identified histochemically with the use of a modification of the techniques of Brooke and Kaiser, and Guth and Samaha to delineate fiber subtypes on the basis of the pH sensitivity of myofibrillar adenosine triphosphatase (ATPase). 3. Neither the time-to-peak twitch force development nor the profile of unfused tetanus ("sag test") was unambiguous in separating fast from slow MUs. However, all units with a time to peak greater than 22 ms were fatigue resistant, and this time was chosen to delineate fast from slow. The fast unit population was further subdivided on the basis of their fatigability. There is normally a small proportion of S units (6% S) that increased to 20% after reinnervation. Although the fast population was subdivided, there was a continuous distribution of fatigue indexes in normal and reinnervated muscles with the highest number of fast units falling into the FI category. The proportions of fast units were 28% FR, 45% FI, and 21% FF in normal muscles and 29% FR, 38% FI, and 13% FF in reinnervated muscles. 4. In normal muscles, delineation of fast and slow fibers and subdivision of fast fiber types on the basis of acid and alkali stability of myofibrillar ATPase provided a histochemical classification that showed 78% correspondence with physiological classification of the same identified units. In reinnervated muscles the correspondence between physiological and histochemical classifications was reduced to 72%. 5. The normal correlation between MU fatigability and isometric force in TA muscles was not seen in reinnervated muscles that contained more FR MUs. Mean fatigue index from normal units was significantly less at 0.55 +/- 0.03 (mean +/- SE) compared with 0.68 +/- 0.03 from reinnervated units.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Motor-unit categorization based on contractile and histochemical properties: a glycogen depletion analysis of normal and reinnervated rat tibialis anterior muscle. 159 22

Time course of tetanus recorded during 40 Hz stimulation was examined on 70 motor units (MUs) of medial gastrocnemius muscle in 41 rats. Three types of MUs were distinguished: slow(S), fast resistant to fatigue (FR) and fast fatigable (FF). In fast MUs of either type, the stimulation induced unfused tetanus with noticeable sag. It was found that in cases of tetani in FF MUs, the sag developed earlier than in FR MUs. Timing of tetanic peak before the sag appeared correlated with contraction time. Some fast MUs demonstrated a distinct time course of tetanus: the weakly accentuated sag appeared early and it was followed by a relatively significant rise in tetanic tension. However, in slow MUs, 40 Hz stimulation induced fused or fused-like tetani. In these MUs the sag was never observed. The obtained results indicate the relation between the sag time course in tetanus and the extent of tetanus fusing.
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PMID:Motor units of medial gastrocnemius muscle in the rat during the fatigue test. I. Time course of unfused tetanus. 163 78

1. Physiological, enzyme-histochemical, biochemical and morphometrical properties of fast-twitch single motor units were compared between young (3-6 months) and old rats (20-24 months) using the glycogen depletion technique. Monoclonal antibodies (mAbs) were used to identify the myosin heavy chain (MHC) composition in the muscle fibres of the motor unit (motor unit fibres) in order to facilitate correlative physiological, histochemical, biochemical and morphometrical studies. 2. Earlier observations on effects of age on contractile properties of fast-twitch motor units were confirmed and extended. That is, the duration of the isometric twitch, and the twitch and tetanus forces, were increased. Further, motor unit fibres were rearranged, occupying a larger territory and displaying an increased innervation ratio in old age, indicating a denervation-reinnervation process. 3. Motor units with muscle fibres expressing the novel IIX myosin heavy chain (MHC) were observed in both young and old animals, and they constituted the predominant motor unity type identified in the old animals. In contrast to the type IIX MHC motor units in the young animals, the type IIX MHC units in old age often contained muscle fibres which expressed either the type IIA or type IIB MHC, although type IIX MHC fibres were in the majority (so called 'IIX' MHC motor units), but motor units containing all these three fibre types were never observed. There were also single fibres co-expressing IIX and IIB MHCs in old age. 4. In the young animals the IIX MHC motor units had a higher (P less than 0.001) resistance to fatigue (fatigue ratio 0.45 +/- 0.11) than the type IIB MHC units (0.03 +/- 0.05), a succinate dehydrogenase (SDH) activity (0.62 +/- .007) intermediate (P less than 0.001) between those of type IIA muscle fibres classified according to myofibrillar ATPase activity after acid pre-incubation, i.e. type IIA ATPase, (0.84 +/- 0.13) and type IIB MHC motor unit fibres (0.20 +/- 0.04), and cross-sectional fibre areas (1650 +/- 320 microns 2) which were similar to those of type IIA ATPase muscle fibres (1460 +/- 150 microns 2) but smaller (P less than 0.001) than type IIB MHC motor unit fibres (4650 +/- 1180 microns 2).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Effects of age on physiological, immunohistochemical and biochemical properties of fast-twitch single motor units in the rat. 166 38

To distinguish the effects of theophylline on respiratory muscle contractility from alterations in respiratory muscle interaction or blood flow, we examined in vitro contractile properties and fatigue of canine diaphragm in two series of experiments. In the first series, a 40-mg/kg aminophylline infusion was given to dogs, and diaphragm strips were removed for in vitro study when stable tissue fixation of the drug was reached. Compared with control bundles examined before aminophylline infusion, no alterations in twitch tension, tetanic tension, or force-frequency characteristics were observed. Moreover, theophylline-treated strips fatigued faster than control strips, whether subjected to repetitive submaximal or maximal contractions (p less than 0.01). In the second series, diaphragm bundles were equilibrated with high theophylline doses (400 mg/L) in vitro, and inotropic effects compared with the results in the first series. Supratherapeutic theophylline concentrations increased force development at low stimulation frequencies (p less than 0.05 at 10 Hz) and significantly elevated twitch-tetanus ratio (p less than 0.01) but did not protect against development of in vitro muscle fatigue. Poor penetration of theophylline in diaphragm bundles in vitro was excluded, since drug concentrations in the muscle bundle and the muscle bath were virtually equal. We conclude that diaphragmatic tissue concentrations correlate well with therapeutic serum and supratherapeutic bath levels and that only high theophylline concentrations increase canine diaphragmatic contractility in vitro. None of the theophylline concentrations studied could protect diaphragm bundles against the development of low- or high-frequency fatigue in vitro.
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PMID:Effects of theophylline on canine diaphragmatic contractility and fatigue. 174 35

The goal of this study was to characterize how isotonic contractions affect the rate of fatigue development. Muscle bundles dissected from frog sartorius muscles were stimulated with 100-ms long train of pulses (0.5 ms, 6 V, 140 Hz). To measure the effect of the isotonic contractions, isometric tetanus were elicited at regular time intervals during the stimulation to fatigue. In general, isotonic contractions caused a faster decrease in tetanic force than isometric contractions. The difference in tetanic force between an isotonic and isometric fatigue increased gradually over a 20-min period to 7.9 and 13.5% at 0.04 and 0.1 trains/s (TPS), respectively. At 0.2, 0.5, and 1.0 TPS, the decrease in tetanic force was also faster during an isotonic fatigue, which resulted in an initial difference in tetanic force between the two types of fatigue. The difference did not exceed 18.5% and did not persist throughout the stimulation period; i.e., the difference disappeared before the end of the fatigue stimulation. The half-relaxation time was prolonged during fatigue development, and the prolongation was greater during an isotonic fatigue, except at 0.04 TPS. The increases in the half-relaxation time at 0.2, 0.5, and 1.0 TPS were followed by a decrease, and the decreases were especially pronounced during an isotonic fatigue at 0.5 and 1.0 TPS. The results showed for the first time that isotonic contractions cause a faster rate of fatigue development in frog sartorius muscles, and this effect depends on the frequency of stimulation.
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PMID:The effects of isotonic contractions on the rate of fatigue development and the resting membrane potential in the sartorius muscle of the frog, Rana pipiens. 180 19

The studies were performed on medial gastrocnemius motor units of the rat. Changes in amplitude, duration and latency of motor unit action potentials were monitored in the course of fatigue test in the three types of motor unites: FF (fast twitch, fatigable), FR (fast twitch, resistant), and S (slow twitch, resistant) motor unit. In a majority of the motor units the amplitude of action potential decreased. The most pronounced decrease took place in FF units, less pronounced one in FR units, while in S type motor units the decrease was insignificant. However, in a part of investigated motor units the amplitude of their action potential transiently increased at the beginning of the fatigue test and, then decreased or was maintained at the same level till the end of the fatigue test. In a few motor units, particularly the slow ones, no changes in action potential amplitude were observed. In the studied material, a decrease in action potential amplitude was on the average less pronounced than a decrease in tetanus tension in the course of the fatigue test. In a majority of studied motor units the duration of action potential was becoming prolonged, which was most pronounced in FF type motor units and least pronounced in S type ones. In few slow motor units the duration showed no alterations. Changes in action potential duration were much more marked than changes in their amplitude. The changes in action potential in fast motor units were less pronounced than changes in their tetanus tension, while in the slow motor units they resembled each other in intensity. Comparison of motor unit action potential changes with changes in their tetanic tension in the course of fatigue test demonstrated no clear-cut relationship between the two phenomena.
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PMID:Changes in motor unit action potentials during the fatigue test. 182 19

1. Single muscle fibres were dissected from the toe muscles of Xenopus laevis and microinjected with Fura-2 to measure myoplasmic calcium concentration ([Ca2+]i). Injected fibres were illuminated at 340 and 380 nm and the ratio of the resulting fluorescence at 505 nm (the Fura-2 ratio) was taken as a measure of [Ca2+]i. Fibres were fatigued at 21 degrees C by repeated tetani until developed tension had fallen to 50% of control. 2. Tetanic tension declined monotonically during fatiguing stimulation, whereas the tetanic Fura-2 ratio first increased and then declined. At the 10th tetanus, tension was 87% of control whereas the Fura-2 ratio was 106% of control. At the end of fatiguing stimulation, where tension was around 50% of control, the tetanic Fura-2 ratio was reduced to 71%. The rate of decline of both tension and the Fura-2 ratio after a tetanus slowed during fatigue. During recovery, the tension and the tetanic Fura-2 ratio recovered in parallel. 3. The resting Fura-2 ratio increased throughout fatigue reaching 237% of control when tension had declined to 50%. There was a rapid phase of recovery, complete within 1 min, by which time the resting Fura-2 ratio was 198% of control. Subsequent recovery was slower and took 20-30 min to reach a stable level which was 121% of control. 4. The resting Fura-2 ratio towards the end of fatiguing stimulation was greater than the tetanic Fura-2 ratio in the early part of recovery although there was no detectable increase of resting tension during fatiguing stimulation. This observation suggests that the Ca2+ sensitivity of the contractile proteins was reduced at the end of fatiguing stimulation. 5. Plots of the tetanic tension against tetanic Fura-2 ratios throughout fatiguing stimulation and recovery also suggested that Ca2+ sensitivity was reduced during fatiguing stimulation when compared to recovery. 6. The increases in resting [Ca2+]i caused by raised [K+]o (from 2.5 to 10 mM) and/or by application of 15% CO2 were much less than those produced by fatiguing stimulation. Much of the elevated [Ca2+]i in fatigue could be reversed by application of dantrolene (25 microM). 7. The results suggest that both reduced tetanic [Ca2+]i and reduced Ca2+ sensitivity contribute to the decline of tension during fatigue.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Changes in tetanic and resting [Ca2+]i during fatigue and recovery of single muscle fibres from Xenopus laevis. 184 42

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