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

1. Maximal calcium-activated force (Fmax) and calcium sensitivity were markedly decreased in detergent-skinned fibres from skeletal and cardiac muscle by solutions that mimicked the total milieu changes associated with fatigue and hypoxia. Further experiments determined the relative contribution of each of the individual changes in milieu. 2. Both Ca2+ sensitivity and Fmax of skeletal and cardiac fibres were decreased with increased [H+] or inorganic phosphate (Pi). These effects were greater in cardiac muscle. 3. Decreasing MgATP over the range observed with fatigue and hypoxia (6.8-4.7 mM) had no effect on Fmax or Ca2+ sensitivity of either muscle type. 4. Decreasing phosphocreatine (PCr: 15-1 mM) increased Fmax but had little effect on Ca2+ sensitivity in both muscle types. In cardiac fibres, the effect on Fmax could be mimicked by inhibition of endogenous creatine kinase. 5. ADP (0.7 mM) increased Fmax and Ca2+ sensitivity, while AMP (0.06 mM) slightly increased Fmax but had no effect on Ca2+ sensitivity of either skeletal or cardiac fibres. 6. Creatine (25 mM) had no significant effect on either Ca2+ sensitivity or Fmax of skeletal and cardiac muscle fibres. At higher levels (50 mM), however, creatine depressed Fmax and slightly altered Ca2+ sensitivity. 7. Thiophosphorylation of myosin P light chains (phosphorylatable light chains of myosin) in rabbit psoas fibres had no effect on Ca2+ sensitivity, yet slightly but significantly increased Fmax under fatigue conditions. 8. Reducing the affinity for ATP hydrolysis (by adding ADP, AMP and creatine) over the range calculated for fatigue/hypoxia (60-45 kJ/mol) produced the enhancement in Fmax expected from added ADP and AMP in cardiac but not skeletal muscle, indicating that changes in affinity influence Fmax of skeletal muscle. Reducing affinity produced little change in Ca2+ sensitivity of skeletal muscle. In contrast, the change produced in cardiac muscle was greater than that expected from addition of ADP and AMP; i.e. decreasing affinity increases calcium sensitivity of the heart. 9. Simple summation of all significant changes expected from each constituent altered by fatigue/hypoxia adequately predicted the observed changes in Fmax and Ca2+ sensitivity in both cardiac and skeletal muscle fibres with but one exception (the change in Ca2+ sensitivity of skeletal muscle at pH 7 was slightly overestimated).
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PMID:Changes of intracellular milieu with fatigue or hypoxia depress contraction of skinned rabbit skeletal and cardiac muscle. 260 Aug 30

Fatigue in patients with mitochondrial cytopathies is associated with decreased basal and postactivity muscle phosphocreatine (PCr). Creatine monohydrate supplementation has been shown to increase muscle PCr and high-intensity power output in healthy subjects. We studied the effects of creatine monohydrate administration (5 g PO b.i.d. x 14 days --> 2 g PO b.i.d. x 7 days) in 7 mitochondrial cytopathy patients using a randomized, crossover design. Measurements included: activities of daily living (visual analog scale); ischemic isometric handgrip strength (1 min); basal and postischemic exercise lactate; evoked and voluntary contraction strength of the dorsiflexors; nonischemic, isometric, dorsiflexion torque (NIDFT, 2 min); and aerobic cycle ergometry with pre- and post-lactate measurements. Creatine treatment resulted in significantly (P < 0.05) increased handgrip strength, NIDFT, and postexercise lactate, with no changes in the other measured variables. We concluded that creatine monohydrate increased the strength of high-intensity anaerobic and aerobic type activities in patients with mitochondrial cytopathies but had no apparent effects upon lower intensity aerobic activities.
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PMID:A randomized, controlled trial of creatine monohydrate in patients with mitochondrial cytopathies. 1045 33

Creatine supplementation has become a common practice among competition athletes participating in different sports over the last few years. The mechanism by which supplementary creatine could have potential ergogenic effects would be an increased muscle creatine and phosphocreatine concentration, leading to a higher rate of ATP resynthesis, a delay in the onset of muscular fatigue and a facilitated recovery during repeated bouts of high-intensity exercise. A critical review of the literature reveals that these ergogenic effects, when found, have been generally shown in untrained subjects performing several exercise bouts under laboratory conditions. The limited body of scientific data available concerning highly trained athletes performing single competition-like exercise tasks indicates that this type of population does not benefit from creatine supplementation. Therefore, the widespread use of creatine ingestion to improve competition performance does not seem to be justified. The potential interest of creatine supplementation for elite athletes could be related to an increased ability to perform repeated high-intensity exercise bouts, either during training or during competition in sports in which repeated efforts are required (e.g. soccer, basketball), but this possibility needs scientific confirmation.
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PMID:Creatine supplementation as an ergogenic aid for sports performance in highly trained athletes: a critical review. 941 70

Fatigue sustained during short-term, high-intensity exercise in humans is associated with the inability of skeletal muscle to maintain a high rate of anaerobic ATP production from phosphocreatine hydrolysis. Ingestion of creatine monohydrate at a rate of 20 g/d for 5-6 d was shown to increase the total creatine concentration of human skeletal muscle by approximately 25 mmol/kg dry mass, some 30% of this in phosphorylated form as phosphocreatine. A positive relation was then shown between muscle creatine uptake and improvements in performance during repeated bouts of maximal exercise. However, there is no evidence that increasing intake > 20-30 g/d for 5-6 d has any potentiating effect on creatine uptake or performance. In individuals in whom the initial total creatine concentration already approached 150 mmol/kg dry mass, neither creatine uptake nor an effect on phosphocreatine resynthesis or performance was found after supplementation. Loss of ATP during heavy anaerobic exercise was found to decline after creatine ingestion, despite an increase in work production. These results suggest that improvements in performance are due to parallel improvements in ATP resynthesis during exercise as a consequence of increased phosphocreatine availability. Creatine uptake is augmented by combining creatine supplementation with exercise and with carbohydrate ingestion.
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PMID:Does dietary creatine supplementation play a role in skeletal muscle metabolism and performance? 1091 67

In a double-blind, placebo, controlled study, we investigated the acute effects of short-term oral creatine supplementation (20 g.day-1 for 6 days) on muscle activation, fatigue and recovery of the m. quadriceps femoris during electrical stimulation, and on maximal performance during sprint cycling. The quadriceps muscles of 23 well-trained rowers were stimulated at different frequencies (10, 20, 50, 100, 150 and 200 Hz). Furthermore, 40 repetitive, electrically stimulated (duration 220 ms, stimulation frequency 150 Hz) concentric contractions were imposed at a constant angular velocity of 180 degrees.s-1 over a range of 50 degrees (from 90 to 140 degrees knee angle), each extension/flexion cycle lasting 1200 ms. To determine recovery, torque was measured at 20, 50, 80, 120, 180 and 300 s after the last contraction. In addition, two maximal 30-s sprints were performed on a cycle ergometer with 4 min rest in between. Following short-term creatine supplementation, body mass [mean (SEM)] increased (P < 0.05) from 85.7 (2.7) kg to 87.3 (2.9) kg. Creatine supplementation had no effect on maximal voluntary isometric torque and muscle activation, or on fatigue and recovery of dynamic exercise. There was also no significant effect on peak power, time to peak power and work to peak power, or total work during both sprints on the cycle ergometer. It was concluded that short-term oral creatine supplementation resulted in increased body mass, but did not enhance muscle performance or maximal output during sprint cycling.
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PMID:No acute effects of short-term creatine supplementation on muscle properties and sprint performance. 1092 16

Creatine monohydrate supplementation has been shown to enhance high-intensity exercise performance in some but not all studies. Part of the controversy surrounding the ergogenic effect(s) of creatine monohydrate supplementation may relate to design issues that result in low statistical power. A further question that remains unresolved in the creatine literature is whether or not males and females respond in a similar manner to supplementation. We studied the effect of creatine supplementation upon high intensity exercise performance in 24 subjects (n = 12 males, n = 12 females). Creatine monohydrate (Cr; 5g, 4x/d 3 4d) and placebo (Pl; glucose polymer 3 4d) were provided using a randomized, double-blind crossover design (7 week washout). Outcome measures included: 2 3 30-s anaerobic cycle test, with plasma lactate pre- and post-test; dorsi-flexor: maximal voluntary contraction (MVC), 2-min fatigue test, and electrically stimulated peak and tetanic torque; isokinetic knee extension torque and 1-min ischemic handgrip strength. Significant main effects of Cr treatment included: increased peak and relative peak anaerobic cycling power ( 3.7%; p <. 05), dorsi-flexion MVC torque ( 6.6%; p <.05), and increased lactate ( 20.8%; p <.05) with no gender specific responses. We concluded that short-term Cr supplementation can increase indices of high-intensity exercise performance for both males and females.
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PMID:Creatine monohydrate supplementation enhances high-intensity exercise performance in males and females. 1109 72

Creatine is a dietary supplement purported to improve exercise performance and increase fat-free mass. Recent research on creatine has demonstrated positive therapeutic results in various clinical applications. The purpose of this review is to focus on the clinical pharmacology and therapeutic application of creatine supplementation. Creatine is a naturally occurring compound obtained in humans from endogenous production and consumption through the diet. When supplemented with exogenous creatine, intramuscular and cerebral stores of creatine and its phosphorylated form, phosphocreatine, become elevated. The increase of these stores can offer therapeutic benefits by preventing ATP depletion, stimulating protein synthesis or reducing protein degradation, and stabilizing biological membranes. Evidence from the exercise literature has shown athletes benefit from supplementation by increasing muscular force and power, reducing fatigue in repeated bout activities, and increasing muscle mass. These benefits have been applied to disease models of Huntington's, Parkinson's, Duchenne muscular dystrophy, and applied clinically in patients with gyrate atrophy, various neuromuscular disorders, McArdle's disease, and congestive heart failure. This review covers the basics of creatine synthesis and transport, proposed mechanisms of action, pharmacokinetics of exogenous creatine administration, creatine use in disease models, side effects associated with use, and issues on product quality.
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PMID:Clinical pharmacology of the dietary supplement creatine monohydrate. 1135 82

People with HIV have a difficult time sustaining muscle mass, which can result in decreased energy and a higher chance of developing AIDS-related illnesses. Creatine, a substance in the body which helps to develop lean muscle mass and strength, is depleted with normal movement and exercise and can be replenished through diet and dietary supplements. Studies have shown that individuals who take creatine monohydrate supplements can experience increased strength and weight and decreased cholesterol and triglyceride levels. Some side effects were evident when creatine monohydrate was taken longer than 3 months. Additional tests are needed to evaluate the specific effects of creatine in a HIV-positive population, however, no reports thus far show it to be unsafe for people with HIV. Individuals should discuss the use of creatine with their physicians, and consider administering it in cycles. Consideration should be given to kidney function, which can be affected by additional creatine intake.
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PMID:Muscle up. 1136 28

Daily creatine supplements (0.258 g kg(-1) ) were administered to adult male Wistar rats (n = 7) in the drinking water. Age matched rats (n = 6) acted as controls. After 5-6 days, contractile properties were examined in soleus and extensor digitorum longus (EDL) muscle strips in vitro at 30 degrees C. In soleus muscles, creatine supplements decreased the half-relaxation time of the isometric twitch from 53.6 +/- 4.3 ms in control muscles to 48.4 +/- 5.5 ms but had no effect on twitch or tetanic tension or on twitch contraction time. In EDL muscles twitch tension, tetanic tension, twitch contraction and half-relaxation times were all unaffected by creatine supplements. Creatine supplements increased the fatigue resistance of the soleus muscles but had no effect on that of the EDL muscles. After a 5 min low-frequency fatigue test, tension (expressed as a percentage of initial tension) was 56 +/- 3 % in control soleus muscles, whereas that in the creatine-supplemented muscles was 78 +/- 6 % (P < 0.01). In the EDL muscles, the corresponding values were 40 +/- 2 % and 41 +/- 9 %, respectively. The force potentiation which occurred in the EDL muscles during the initial 20-30 s of the fatigue test was 170 +/- 10 % of initial tension in the control muscles 24 s after the initial stimulus train but was reduced (P < 0.01) to 130 +/- 20 % in the creatine-supplemented muscles. In conclusion, soleus muscle endurance was increased by creatine supplements. EDL endurance was unaffected but force potentiation during repetitive stimulation was decreased. Experimental Physiology (2001) 86.2, 185-190.
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PMID:The effects of dietary creatine supplements on the contractile properties of rat soleus and extensor digitorum longus muscles. 1142 33

Many athletes and active people have consumed a large variety of supplements in order to get a good shape or a better performance in competitions. Due to this, several studies have been carried out to determine if these supplements are in fact ergogenic aids. Creatine seems to be related to the performance enhance in high intensity intermittent exercises. Carnitine might probably improve the aerobic capacity by stimulating lipid oxidation on muscle cells during long term exercise. Bicarbonate is thought to increase blood pH delaying the onset of peripheral fatigue in high intensity exercises of short duration and strength training. Some other supplements like branched-chain amino acids and chromium are also involved in body composition changes as a gain of fat free mass and loss of fat mass. The effects caused by these supplements during physical activity have not been fully described in literature yet as well as their side effects.
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PMID:[Relation of some nutritional supplements and physical performance]. 1146 29


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