Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Lactic acid and H+ evoke muscle reflexes that raise sympathetic nerve activity. Whether these substances are direct afferent stimulants or markers for the acidification of other substances is unknown. Diprotonated phosphate (H2PO4-), a possible mediator of fatigue, increases as the cell acidifies and phosphate is produced. Its role in evoking muscle reflexes is unknown. We used 31P-nuclear magnetic resonance to measure forearm muscle H+ and H2PO4- and microneurography to measure muscle sympathetic nerve activity (MSNA, peroneal nerve) during a handgrip protocol designed to dissociate H+ from H2PO4-. Ischemic handgrip (50% maximal voluntary contraction x 2 min) was followed by a 1-min rest period during which the muscle was freely perfused. This was followed by a second bout of ischemic handgrip and a 5-min recovery. In seven of eight subjects, MSNA correlated with H2PO4-, whereas it correlated with pH in only one subject. To determine whether muscle reflex responses are evoked by H+, lactic acid, monoprotonated phosphate (HPO4(2-), or H2PO4-, we injected H+, lactate, H2PO4- [all 50 mM in 10 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) buffered to pH 6], and HPO4(2-) (50 mM, pH 7.5 in 10 mM HEPES) into the arterial supply of the triceps surae of the cat (n = 9) as we measured mean arterial blood pressure (MAP). H2PO4- increased MAP more than HPO4(2-), H+, or lactate (27.1 +/- 3.7 vs. 5.0 +/- 1.3, 4.6 +/- 3.1, and 7.7 +/- 3.2 rise in mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Role of diprotonated phosphate in evoking muscle reflex responses in cats and humans. 806 33

Eight male patients with heart transplants at least a year after the operation were submitted to a 6-wk endurance training program and explored for their blood lactate kinetics before and after exercise. The tests consisted of a bicycle exercise upgraded by 20 W every 2 min until volitional fatigue. Training induced a significant (P < 0.025) decrease in lactate concentrations from the 40-W to the 120-W exercise step and a significant increase (P < 0.025) in the time into exercise (9.87 +/- 0.87 min vs 7.17 +/- 0.90 min) at which a lactate concentration of 2 mmol.l-1 was reached. Lactate recovery curves were significantly lower (P < 0.036) after training than before training, except at minutes 1, 2, 8, and 60. The fits of a biexponential mathematical model to the lactate recovery curves reveal a significant (P < 0.036) training-induced increase (+71%) in the slow-velocity constant gamma 2v of the model. In view of the functional meaning given to this parameter, namely the ability to remove lactate, it is concluded that training lowers blood lactate concentrations during exercise and recovery in patients with heart transplants at least in part by raising the efficiency with which lactate is removed, and that the ability to remove lactate can be a valuable criterion to evaluate physical fitness.
 ...
PMID:Short endurance training improves lactate removal ability in patients with heart transplants. 883 32

This study was conducted to determine whether bathing in tepid water is effective in facilitating recovery from fatigue after submaximal exercise. Subjects were six young healthy male university students. Following cycle exercise at 80% aerobic power (VO2 max) for 10 min, recovery was observed during and after 10-min bathing. Three conditions were set; (1) water temperature of 38 degrees C, (2) water temperature of 30 degrees C, and (3) no water in the bath tub (control). Measurements were heart rate, blood pressure, skin temperature, rectal temperature, blood lactase and subjective feelings. There were no significant differences in heart rate and blood pressure between the three conditions at any time. Mean skin temperature and rectal temperature decreased more rapidly after the 30 degrees C bathing than the other two conditions (p < 0.05). Lactate removal was largest for the 30 degrees C bathing, with significant difference between the 30 degrees C bathing condition and the no bathing condition (p < 0.05). Recovery from fatigue was best for the 30 degrees C bathing and worst for the control in terms of subjective feeling. In summary, it was shown that immersion in 30 degrees C water after submaximal exercise resulted in a larger removal of lactate than recovery in air.
 ...
PMID:Effects of immersion in tepid bath water on recovery from fatigue after submaximal exercise in man. 885 30

Sarcoplasmic reticulum (SR) Ca(2+)-release channel function is modified by ligands that are generated during about of exercise. We have examined the effects of lactate on Ca(2+)- and caffeine-stimulated Ca2+ release, [3H]ryanodine binding, and single Ca(2+)-release channel activity of SR isolated from rabbit white skeletal muscle. Lactate, at concentrations from 10 to 30 mM, inhibited Ca(2+)- and caffeine-stimulated nodine binding to and inhibited Ca(2+)- and caffeine-stimulated [3H]ryanodine binding to and inhibited Ca(2+)- and caffeine-stimulated Ca2+ release from SR vesicles. Lactate also inhibited caffeine activation of single-channel activity in bilayer reconstitution experiments. These findings suggest that intense muscle activity, which generates high concentrations of lactate, will disrupt excitation-contraction coupling. This may lead to decreases in Ca2+ transients promoting a decline in tension development and contribute to muscle fatigue.
 ...
PMID:Lactate inhibits Ca(2+) -activated Ca(2+)-channel activity from skeletal muscle sarcoplasmic reticulum. 904 23

It has been suggested that during a skeletal muscle contraction the metabolic energy cost at the onset may be greater than the energy cost related to holding steady-state force. The purpose of the present study was to investigate the effect of contraction duration on the metabolic energy cost and fatigue process in fully perfused contracting muscle in situ. Canine gastrocnemius muscle (n = 6) was isolated, and two contractile periods (3 min of isometric, tetanic contractions with 45-min rest between) were conducted by each muscle in a balanced order design. The two contractile periods had stimulation patterns that resulted in a 1:3 contraction-to-rest ratio, with the difference in the two contractile periods being in the duration of each contraction: short duration 0.25-s stimulation/0.75-s rest vs. long duration 1-s stimulation/3-s rest. These stimulation patterns resulted in the same total time of stimulation, number of stimulation pulses, and total time in contraction for each 3-min period. Muscle O2 uptake, the fall in developed force (fatigue), the O2 cost of developed force, and the estimated total energy cost (ATP utilization) of developed force were significantly greater (P < 0.05) with contractions of short duration. Lactate efflux from the working muscle and muscle lactate concentration were significantly greater with contractions of short duration, such that the calculated energy derived from glycolysis was three times greater in this condition. These results demonstrate that contraction duration can significantly affect both the aerobic and anaerobic metabolic energy cost and fatigue in contracting muscle. In addition, it is likely that the greater rate of fatigue with more rapid contractions was a result of elevated glycolytic production of lactic acid.
 ...
PMID:Contraction duration affects metabolic energy cost and fatigue in skeletal muscle. 953 Jan 20

Biopsies (biceps) were examined in 8 bodybuilders across a typical arm-curl training session (80% 1-RM). [PCr] and [glycogen] decreased 62 and 12% after 1 set (n = 4), and 50 and 24% after 3 sets (n = 4). [Lactate] was 91 and 118 mmol &times kg-1, respectively, after 1 and 3 sets. Fatigue was probably partially caused by decreased [PCr] and increased [H+] (first set) and by decreased [H+] in subsequent sets.
 ...
PMID:Muscle substrate utilization and lactate production. 1036 16

Lower metabolic and cardiocirculatory reactions to eccentric compared to concentric exercise are known for large muscle groups. The extent of exercise reaction depends on the muscle mass involved and moreover differs between the various muscle groups, while it is unclear to which extent cardiovascular and metabolic reactions and differences between the types of work exist in the shoulder, also it is not known whether these reactions differ according to training status. Lactate production (LA), heart rate (HR), and blood pressure (BP) were examined following eccentric and concentric shoulder movements in 16 male gymnasts (GN) and 15 male untrained subjects (US). Differentiation was made according to the types of work for peak torque (PT) and local muscle endurance (LME). Following eccentric exercise, the increase of LA and HR was clearly lower than following concentric exercise (p<0.05). No difference was observed between the groups. Diastolic BP showed no changes, whereas systolic BP was higher following concentric exercise. Eccentric PT was higher than concentric PT in GN within a test-retest variability of 15%. LME showed a lower degree of fatigue under eccentric conditions, independent of the group. It is concluded that eccentric exercise of the shoulder leads to lower metabolic and cardiocirculatory reactions than concentric exercise, in spite of higher peak torque and less fatigue. Exercises consisting of a high proportion of eccentric movement may thus be beneficial in the therapy of shoulder complaints, especially in patients with cardiovascular disease.
 ...
PMID:Metabolic and cardiocirculatory reactions after concentric and eccentric exercise of the shoulder. 1060 16

It is unclear whether accumulation of lactate in skeletal muscle fibers during intense activity contributes to muscle fatigue. Using mechanically skinned fibers from rat and toad muscle, we were able to examine the effect of L(+)-lactate on excitation-contraction coupling independently of other metabolic changes. We investigated the effects of lactate on the contractile apparatus, caffeine-induced Ca(2+) release from the sarcoplasmic reticulum, and depolarization-induced Ca(2+) release. Lactate (15 or 30 mM) had only a small inhibitory effect directly on the contractile apparatus and caused appreciable (20-35%) inhibition of caffeine-induced Ca(2+) release, seemingly by a direct effect on the Ca(2+) release channels. However, 15 mM lactate had no detectable effect on Ca(2+) release when it was triggered by the normal voltage sensor mechanism, and 30 mM lactate reduced such release by only <10%. These results indicate that lactate has only a relatively small inhibitory effect on normal excitation-contraction coupling, indicating that lactate accumulation per se is not a major factor in muscle fatigue.
 ...
PMID:Effect of lactate on depolarization-induced Ca(2+) release in mechanically skinned skeletal muscle fibers. 1071 40

Lactate production in skeletal muscle has now been studied for nearly two centuries and still its production and functional role at rest and during muscle contraction is a subject of debate. Historically, skeletal muscle was seen mainly as the site of lactate production during contraction and lactate production associated with a lack of muscle oxygenation and fatigue. Later, it was recognized that skeletal muscle not only plays an important role in lactate production but also in lactate clearance and this in turn has led to a renewed interest in the metabolic fate of lactate in skeletal muscle and also in other tissues. Studies using lactate isotopes have shown that skeletal muscle extracts lactate from the circulation despite a substantial net lactate release, and that skeletal muscle has a large capacity for lactate oxidation; these processes being enhanced with exercise. Lactate dehydrogenase (LDH) controls the formation of lactate and may regulate the turnover of lactate in the muscle cell. Skeletal muscle contains five LDH isoforms (LDH1-5). Of the five LDH isoforms, the heart-specific LDH1, 2 is generally suggested to favour the reaction of lactate to pyruvate whereas the muscle-specific LDH4,5 isoform favours lactate formation. However, in this paper, it is argued that compartmentalization of the muscle cell and LDH association with cell structures may play a more predominant role in whether the LDH reaction proceeds towards lactate or pyruvate formation. The model for skeletal muscle lactate metabolism presented is in essence based on a synthesis of old and more recent studies on skeletal muscle lactate transport, uptake, release, oxidation, and the role of LDH at rest and during exercise.
 ...
PMID:Lactate as a fuel for mitochondrial respiration. 1075 1

Stimulated by recent (13)C and (31)P NMR studies of exercising muscle, we propose a model of the energetics of contraction. Previous studies of energetics have followed energy consumption. However, the rapidity of contraction, in 10-40 msec, requires that energy be delivered rapidly, so that the muscle has power requirements of rapid energy expenditure that are ultimately met by the slower averaged consumption of carbon and oxygen from blood. We propose that energy is supplied in milliseconds by glycogenolysis and that between contractions, glycogenesis refills the pools. The energy for glycogenesis is supplied by oxidative phosphorylation. This mechanism utilizes the rapid conversion of glycogen phosphorylase, the "fight-or-flight" enzyme, to its active form. Lactate is necessarily generated by this pathway to serve as a time buffer between fast and slow energy needs, which resolves the paradoxical generation of lactate in well oxygenated tissue. Consequences of the glycogen shunt are compatible with numerous biochemical and physiological experiments. The model provides a possible mechanism for muscle fatigue, suggesting that at low but nonzero glycogen concentrations, there is not enough glycogen to supply millisecond energy needs.
 ...
PMID:The "glycogen shunt" in exercising muscle: A role for glycogen in muscle energetics and fatigue. 1120 49


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>