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

1. Single muscle fibres were dissected from Xenopus lumbrical muscles and microinjected with the photoprotein aequorin in order to measure the myoplasmic free calcium concentration ([Ca2+]i). Fatigue was produced by repeated intermittent tetanic stimulation continued until tension had declined to approximately 50% of the initial level. Fibres were then allowed to recover by giving tetani at less frequent intervals. Aequorin light (a measure of [Ca2+]i) and tension were measured during fatiguing stimulation and recovery. 2. During fatiguing stimulation, tetanic tension declined steadily, but peak aequorin light first increased before declining substantially. The largest light signal was about 155% of initial control while at the end of fatiguing stimulation the tetanic light fell to about 14% of control. 3. Fibres showed a characteristic slowing of relaxation in the fatigued state. This was associated with a slowing of the rate of decline of the aequorin light signal. 4. Intracellular acidosis produced by equilibrating the Ringer solution with either 5 or 15% CO2 caused an increase in the light signal associated with a tetanus. Carbon dioxide also caused a reduction of tension and a slowing of relaxation. 5. In vivo pCa-tension curves were constructed by exposing the fibres to a series of K+ concentrations which produced contractures of different sizes. Light and tension were measured during periods when both were relatively stable and the light signal was subsequently converted to pCa. 6. Exposure of fibres to 5 or 15% CO2 caused the pCa-tension curve to be shifted to the right of the control curve. This indicates a reduced Ca2+ sensitivity of the contractile proteins, which is in agreement with results from skinned fibre studies. 7. The pCa-tension points obtained from tetani during the early part of fatiguing stimulation also deviated to the right of the control pCa-tension curve, suggesting a reduced Ca2+ sensitivity of the contractile proteins. At the end of fatiguing stimulation, however, pCa-tension points did not differ greatly from the control pCa-tension curve, suggesting that Ca2+ sensitivity was approximately normal. Thus the reduced [Ca2+]i during tetani at the end of fatiguing stimulation (when tension was reduced to approximately 50%) could explain all of the reduction in tension. 8. After fatiguing stimulation, tension and light recovered monotonically in some fibres; however, in the majority of fibres, tension and light showed a secondary decline followed by a slower recovery (post-contractile depression). 9. During post-contractile depression, caffeine contractures or tetani in the presence of caffeine gave increased aequorin light signals and the tension developed was close to that produced in an unfatigued tetanus.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Intracellular calcium and tension during fatigue in isolated single muscle fibres from Xenopus laevis. 251 88

1. Physiological properties of motor units in the soleus muscle were studied in anaesthetized rats using ventral root splitting to isolate single units. 2. Motor unit types were classified by the same criteria used to classify cat hindlimb motor units into types FR (fast-twitch, fatigue-resistant) and type S (slow-twitch, fatigue-resistant). Type FR units were estimated to generate 10% of whole-muscle tension and type S 90%. All FR units showed sag in the unfused tetanus at frequencies with interpulse intervals greater than 175% of twitch time to peak, but not at 125% (Burke, Levine, Tsairis & Zajac, 1973). 3. The muscle fibres belonging to twelve single motor units were depleted of glycogen by prolonged stimulation, permitting analysis of their histochemical profiles. Type FR units were found to consist of type IIA muscle fibres and type S units of type I muscle fibres. 4. Direct determinations were made of fibre area, innervation ratio (number of muscle fibres supplied by one motoneurone) and hence specific tension (tetanic tension generated per unit cross-sectional area) of individually identified motor units. Motoneurons were found to innervate between 84 and 178 muscle fibres (mean 110) in type S units and between 126 and 161 fibres in type FR units (mean 142). Fibre areas were larger for type FR units and there was a significant difference in specific tension of the two unit types (type S lower). 5. Indirect estimates of innervation ratio and specific tension were obtained from counts of muscle fibre types, and relative frequencies of motor unit types in the soleus unit pool. Observations agreed well with results of direct measurements. 6. The evidence provided suggests that differences in tension generated by type FR and S units in rat soleus muscle are primarily due to differences in innervation ratio and fibre area, with a small contribution from differences in specific tension.
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PMID:Contractile characteristics and innervation ratio of rat soleus motor units. 260 Aug 27

1. Longitudinal movements of marked segments of single fibres from the anterior tibialis muscle were recorded during tetanus and relaxation under isometric (fixed-end) conditions. 2. During relaxation, shortening and lengthening of different segments occurred simultaneously, starting at about the same time as the end of the linear fall of force (shoulder on the force record). 3. Variations in intracellular pH, measured with pH-sensitive microelectrodes, along the length of fibres were not statistically significant, and are unlikely to be responsible for the non-uniform behaviour of different segments. 4. As expected from earlier studies, both fatigue (produced by increasing tetanus duration or decreasing the time between tetani) and intracellular acidification (produced by raised extracellular CO2), reduced the tetanus force and prolonged the linear phase of force decline in relaxation. Each treatment delayed the start and markedly reduced the amount of segment movement in relaxation. 5. Fatigue and intracellular acidification have a smaller effect on force during stretching than on force produced under isometric conditions. This may contribute to making the segments behave in a more uniform way during relaxation under these conditions. 6. Changes in the Ca2+ uptake mechanisms are also discussed as possible causes for the changes in segment behaviour in relaxation.
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PMID:Effects of fatigue and reduced intracellular pH on segment dynamics in 'isometric' relaxation of frog muscle fibres. 260 Aug 46

1. The effects of pHo (extracellular pH) and lactic acid on pHi (intracellular pH) and tetanic force were examined in frog sartorius muscle. Ion-selective microelectrodes were used to measure pHi. Tetanic force was elicited by field stimulation. Experiments were performed in HEPES-buffered solution equilibrated with 100% O2. 2. Mean pHi values (+/- S.E.M.) of unfatigued frog sartorius muscles were 7.14 +/- 0.02 and 7.05 +/- 0.09 at pHo 7.2 and 6.4, respectively. 3. A stimulation at a rate of one 100 ms tetanic contraction per second for 3 min reduced pHi to 6.21 +/- 0.09 and 6.20 +/- 0.04 at pHo 7.2 and 6.4, respectively. Meanwhile at pHo 7.2, the tetanic force (defined as the maximum force developed during a tetanus) decreased by 82.9 +/- 2.6%, the maximum rate of relaxation decreased by 92.9 +/- 0.9%, and the rate constant of the relaxation decreased by 88.5 +/- 1.6%. At pHo 6.4, the decrease in tetanic force, maximum rate of relaxation and rate constant were 90.6 +/- 1.8%, 93.8 +/- 0.5 and 87.5 +/- 2.7%, respectively. 4. The maximum rates of recovery of pHi following fatigue were 0.068 +/- 0.05 and 0.025 +/- 0.05 pH units min-1 at pHo 7.2 and 6.4, respectively. Recovery of normal tetanic force and relaxation rate was also slower at acidic pHo than at neutral pHo. 5. In the presence of 40 mmol l-1 L-lactic acid at pHo 7.2, the maximum rate of pHi recovery following fatigue was only 0.027 +/- 0.03 pH units min-1 at pHo 7.2. The presence of lactic acid also reduced the recovery of the relaxation phase, but not the recovery of tetanic force. 6. It is suggested that pHi recovery is not a limiting factor for tetanic force recovery and that the extracellular H+ inhibits tetanic force recovery by acting at a site located on the outer surface of the sarcolemma. The recovery of the relaxation phase is believed to be pHi dependent.
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PMID:The effect of lactate on intracellular pH and force recovery of fatigued sartorius muscles of the frog, Rana pipiens. 260 53

From 1969-1985, 106 people contracted tetanus in Finland. The outcome of the disease was good in 78 cases (returned to work), poor in 27 (12 died, 5 institutionalized and 10 retired) and unknown in 1. Poor outcome was the result of a disease requiring respirator treatment. Other clinical factors significantly correlated with poor outcome were blood pressure lability, hyperglycemia, hyperthermia, tachycardia and anticoagulation therapy. Forty people who were representative of the whole series with regard to sex, age and severity of disease attended a follow-up study on average 7 years and 4 months later. Forty age- and sex-matched controls had the same examinations, and compared with them, the 40 patients still had significantly more muscle fatigue and cramps, nervousness, decreased mental capacity and difficulties in balance, speech and memory. They also had more clinical findings, such as peripheral paresis, muscular atrophy, decreased or absent tendon reflexes and decreased mental capacity than the controls.
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PMID:Outcome and neurological sequelae of patients after tetanus. 261 76

Corticosteroids have been shown to produce a myopathy of peripheral skeletal muscle, characterized predominantly by Type II fiber atrophy. To determine if similar histologic and histochemical changes occur in the diaphragm and whether the in vitro contractile properties of this muscle are adversely affected by steroids, we studied two groups of hamsters. The experimental group received triamcinolone while a control group received saline, both given daily for 3 wk as i.m. injections. Soleus (Sol) and extensor digitorum longus (EDL) muscles and costal diaphragm muscle sections were stained for histologic (hematoxylin and eosin, modified Gomori trichrome) and histochemical (myosin ATPase, succinate dehydrogenase [SDH]) analysis. Muscle fiber proportions and cross-sectional areas (CSA) were measured from myosin ATPase sections. In vitro studies of isometric contractions were carried out on small strips of costal diaphragm, measuring maximal isometric twitch (Pt) and tetanus (Po) tensions, time to peak tension (TTP), half relaxation time (1/2 RT), force-frequency relationship, and fatigue characteristics (60 Hz tetani; duty cycle, 0.5). Triamcinolone treatment resulted in no change in muscle fiber proportions. There was no effect on Type I fiber CSA; however, there was Type IIa (Sol, EDL) and Type IIb (diaphragm, EDL) fiber atrophy in triamcinolone-treated animals. Pt and Po (normalized for weight) of diaphragm strips were not different. There was a prolongation in TTP and 1/2 RT, a left shift in the force-frequency curve, and a reduced fatiguability of triamcinolone-treated diaphragm (P less than 0.05). We conclude that a steroid myopathy could be explained by a loss of muscle mass (Type IIb fiber atrophy) rather than an intrinsic impairment in contractile function.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Pathologic changes and contractile properties of the diaphragm in corticosteroid myopathy in hamsters: comparison to peripheral muscle. 262 59

Black widow spider (Latrodectus mactans) envenomation is found throughout both the temperate and tropical latitudes, and is one of the leading causes of death from arthropod envenomations worldwide. The venom is highly neurotoxic, affecting the presynaptic motor endplate to allow massive noradrenaline (norepinephrine) and acetylcholine release into synapses causing excessive stimulation and fatigue of the motor end plate and muscle. Clinically, patients develop a bite site lesion and pain, abdominal pain and tenderness, and lower extremity pain and weakness within minutes to hours of envenomation. Symptoms progress over several hours, then subside over 2 to 3 days. The recommended treatment of 'common' envenomation is calcium gluconate 10% intravenously, titrated to relief of symptoms; antivenin, although effective, may cause hypersensitivity and serum sickness reactions, and should be restricted to life-threatening envenomations only. Brown recluse spider (Loxosceles reclusa) envenomations are seen in the Americas and in Europe, and are endemic to the south and central United States. The venom contains at least 8 enzymes, consisting of various lysins (facilitating venom spread) and sphingomyelinase D, which causes cell membrane injury and lysis, thrombosis, local ischaemia, and chemotaxis. Local envenomations begin as pain and itching that progresses to vesiculation with violaceous necrosis and surrounding erythema, and ultimately ulcer formation. Systemic envenomations may be life threatening, and present with fever, constitutional symptoms, petechial eruptions, thrombocytopenia, and haemolysis with haemoglobinuric renal failure. Treatment of local envenomations is conservative (local wound care, cryotherapy, elevation, tetanus prophylaxis, and close follow-up); systemic envenomation requires supportive care and treatment of arising complications, corticosteroids to stabilise red blood cell membranes, and support of renal function. Dapsone 100mg daily has emerged as a promising therapeutic agent in both animal studies and clinical trials. Over 650 species of scorpions are known to cause envenomation (mostly in children under 10 years); they are endemic mostly in arid and tropical areas. Different venoms and clinical presentations are seen across the different species. Most commonly, an inflammatory local reaction occurs with envenomation, which is treated with wound debridement and cleaning, tetanus prophylaxis, and antihistamines. Occasionally the venom is allergenic, and the resultant allergic reaction is treated in a standard fashion.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Acute arthropod envenomation. Incidence, clinical features and management. 266 28

Active properties of canine vocalis muscle tissue were investigated through a series of experiments conducted in vitro. Samples of the vocalis muscle were dissected from dog larynges excised a few minutes before death and kept in Krebs solution at a temperature of 37 +/- 1 degree C and a pH of 7.4 +/- 0.05. Isometric and isotonic tetanic responses of the vocalis muscle were obtained electronically with a Dual Servo System (ergometer). Isometric tension was recorded at various levels of elongation and stimulation rate. Isotonic shortening was recorded at various levels of force, and shortening velocity was obtained by numerical analysis of recorded data. It was found that fused tetanus occurred at stimulation rates of about 90 Hz, where the isometric tetanic force saturates. Repeated stimulation of the muscle in vitro not only caused nonrecoverable fatigue in the tissue, but also decreased its passive tension. The combined active and passive isometric tension increased with elongation of the muscle. Results of isometric active responses were normalized with respect to average passive response. This normalization allowed for better comparison between tetanic contraction and twitch contraction. It was found that maximum tetanic contraction was 6.4 times greater than maximum twitch contraction obtained in a previous study. A tetanic contraction period was defined and investigated for eight samples of vocalis muscle tissue from different dogs. The tetanic contraction period showed a linear increasing trend with strain.
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PMID:Tetanic contraction in vocal fold muscle. 273 73

The purpose of this study was to document the recovery of isometric contractile function following tourniquet ischemia. Male Wistar rats (N = 27) were subjected to unilateral hindlimb tourniquet ischemia of 0 hr (control, N = 6), 1 hr (N = 5), 2 hr (N = 5), 3 hr (N = 5) and 4 hr (N = 3). Following a 2-week recovery period, isometric force measurements were made from both gastrocnemii of each rat with the contralateral limb acting as the control side. Each muscle was analyzed for maximal twitch (Pt, N/g), maximal rate of rise of twitch tension (DP/dt, N/sec), time to peak tension (TPT, msec), half relaxation time (RT 1/2, msec), maximal tetanus (P0, N/g, at 100 Hz), and fatigue (Burke Fatigue Protocol). Pt, P0, and DP/dt were significantly different from control values (P less than 0.05) for all hours of tourniquet ischemia. A strong negative correlation (P less than 0.001) was found for twitch (R = -0.84), tetanus (R = -0.78), and maximal rate of force development (R = -0.83) with respect to increasing hours of ischemia. The recovery of isometric twitch and tetanic function following tourniquet ischemia is inversely related to the ischemic interval. This study quantified the relationship between muscle ischemia and recovery of function following a 2-week interval and stresses the functional physiological changes which occur in skeletal muscle following tourniquet ischemia.
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PMID:Isometric contractile function recovery following tourniquet ischemia. 277 Feb 93

1. Isometric twitch and tetanic tensions were recorded from whole muscles and single motor units in isolated fourth deep lumbrical muscles from neonatal rats (most at 3-5 days old) and from older rats of various ages. 2. Whole-muscle time to peak contraction reduced from about 120 ms at birth to about 20-25 ms at 20 days and older. 3. The number of motor units in the muscle was constant with age (eleven on average) and there was no significant branching of motor axons below the common peroneal nerve branching point in the thigh. 4. In the 3-5 days age range, mean twitch:tetanus ratio for whole muscles was 0.299 and for single units was 0.177. As a consequence, mean motor unit size (as a percentage of whole-muscle tension) was greater for tetani (29.7%) than for twitches (19.9%). This was not the case in muscles from animals 22 days or older. Evidence is given that the cause of this is low junctional efficacy in some neuromuscular junctions in neonatal muscle. Intracellular recordings supported this view. 5. The relationships of motor-unit size to the contraction time, to the ratio of contraction time:half-relaxation time, and to fatigue index are given. There was no indication of clear segregation of motor units into more than one population, but it is concluded that small motor units are more likely to contain a higher proportion of slowly contracting, fatigue-resistant fibres than large units. 6. The level of overlap by axons in the lateral plantar nerve onto muscle fibres in a single sural nerve motor unit was greater in tetani than in twitches. The results indicate that the distribution of weak and strong inputs was not random, but that there was a tendency for one strong input to accompany a number of weak inputs (on average about two) on each muscle fibre. 7. Intracellular recording indicates that about 12% of fibres at 3-5 days may be electrically coupled.
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PMID:Motor units in a skeletal muscle of neonatal rat: mechanical properties and weak neuromuscular transmission. 282 60


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