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

Eight horses exercised to fatigue were used to characterize the resulting changes in blood pH, in blood lactate, free fatty acid, bicarbonate, and ammonia concentrations, and in muscle glycogen concentrations. The exercise test was conducted at a speed of 4.5 m/s on a motorized equine treadmill set at a 9% grade. At fatigue, all variables differed significantly (P less than 0.05) from base-line values. Heart rate averaged 191.1 +/- 6.5 beats/min at fatigue, and the plasma lactate concentrations increased from 7.8 +/- 0.95 mg/dl to 94.3 +/- 19.2 mg/dl. Ammonia concentrations increased from 66.7 +/- 6.9 mumol/L before exercise to 136.9 +/- 18.6 mumol/L at fatigue. Bicarbonate concentrations decreased from 31.3 +/- 0.4 mM to 21.1 +/- 1.8 mM, and pH decreased from 7.37 +/- 0.01 to 7.28 +/- 0.04. Free fatty acid concentrations were higher at fatigue and increased throughout the recovery period. Exercise resulted in a 25% decrease of muscle glycogen concentration in gluteus medius specimens.
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PMID:Changes in equine metabolic characteristics due to exercise fatigue. 377 43

Six trained middle-distance runners wer studied under alkalotic (NaHCO3 ingestion), placebo (CaCO3 ingestion), and control conditions to determine the effect of an acute induced metabolic alkalosis on time to run an 800-m race. Pre-exercise, following NaHCO3 ingestion, pH and standard [HCO3-] were significantly higher. In the alkalotic condition, subjects ran faster (2.9 s) and the corresponding post-exercise values for blood [lactate] and extracellular H+ were higher than in the control and placebo conditions, suggesting an increased anaerobic energy contribution. These results support the speculation that the increase in extracellular buffering following NaHCO3 ingestion facilitated H+ efflux from the cells of working muscle, thereby delaying the decrease in intracellular pH and postponing fatigue. It is concluded that the ingestion of NaHCO3 by trained middle-distance runners prior to an 800-m race has an ergogenic benefit.
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PMID:Effect of acute induced metabolic alkalosis on 800-m racing time. 631 44

The relationships between age and cardiorespiratory and metabolic adjustments during cycle ergometer exercise and treadmill walking were investigated at 30%, 60%, 80%, and maximal aerobic power (VO2max). The subjects were 18 females between the ages of 17-40. Tr-admill walking resulted in an 8 percent greater maximal aerobic power than that observed during cycle ergometer exercise. Higher lactate concentrations, respiratory exchange ratios and lower heart rates during the cycle ergometer test supported the possibility of localized fatigue from anaerobic metabolism as a limitation to aerobic power potential. Contrary to previous observations in males, female subjects die not demonstrate a lower stroke volume or higher heart rate during submaximal cycling compared to treadmill walking. At exercise intensities above 30% Vi2max, plasma bicarbonate and pH were consistently lower following exercise on the cycle ergometer. Respiratory compensation as calculated from "excess ventilation," delta VE/delta HCO3-, was approximately 4 1 min-1/mEq 1-1. Compensation was found to be independent of the type of exercise but linearly related (r=0.99) to the resultant metabolic acidosis. It was concluded that cardiovascular responses to equivalent cycle ergometer and treadmill exercise are similar; however, occurrence of a greater metabolic acidosis during cycle ergometer exercise suggests that a smaller muscle mass is used.
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PMID:Cardiovascular, metabolic, and ventilatory responses of women to equivalent cycle ergometer and treadmill exercise. 739 96

Diaphragm strips from young rats (45--60 g) about 0.3 mm thick were fatigued by tetanic stimulation at a train repetition rate of 2 HZ for 3 min. The isometric tension developed was measured during fatigue and recovery in solutions containing 25, 10, or 2 mM bicarbonate at both 37 and 30 degrees C. Tension fell during fatigue to between 20 and 30% of the initial value and this was not significantly influenced by external bicarbonate concentration or temperature over the range considered. Recovery of tension was complete and rapid (t1/2 < 1 min) in 25 mM bicarbonate at both temperatures. In 10 and 2 mM bicarbonate recovery was slowed (t1/2 3.5 and 7 min, respectively, at 30 degrees C, 1.6 and 4.5 min at 37 degrees C) and incomplete (85 and 72% at 30 degrees C, 82 and 61% at 37 degrees C). Muscle creatine phosphate fell during fatigue but was completely restored within 4 min at 30 degrees C in either 2 or 25 mM HCO3. Lactate increased less in muscles fatigued in 2 mM HCO3 and fell at a slower rate during recovery. The results seem to exclude intracellular creatine phosphate concentration as a major determinant in recovery. The evidence suggests that external bicarbonate can affect the recovery of tension following fatigue by altering intracellular acid-base balance.
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PMID:The effect of bicarbonate concentration on fatigue and recovery in isolated rat diaphragm muscle. 742 82

We describe the fabrication and characterization of an optical CO2 sensor based on the change in fluorescence lifetimes due to fluorescence resonance energy transfer from a pH-insensitive donor, sulforhodamine 101, to a pH-sensitive acceptor, either m-cresol purple or thymol blue, entrapped in an ethyl cellulose film. A phase transfer agent allows incorporation of the dyes and water into the film, while providing an initially basic environment for the acceptor. Diffusion of CO2 into the water entrapped in the film produced carbonic acid, causing a pH-dependent decrease in the spectral overlap of the acceptor absorbance with the donor emission, and decreased energy transfer, resulting in increased SR101 donor lifetimes. The lifetime changes were detected as a change in the phase of the emission, relative to the modulated excitation, and were insensitive to excitation intensities and emission signal levels. In addition to an externally modulated 442-nm light source, we excited the sensor with a directly modulated 635-nm laser diode and detected the anti-Stokes emission. The CO2 sensor is not fragile and can provide stable readings for weeks. The use of fluorescence resonance energy transfer, along with the simple entrainment procedure, allows facile change of the CO2 response range through change of the acceptor dye and the use of laser diode excitation sources.
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PMID:A lifetime-based optical CO2 gas sensor with blue or red excitation and stokes or anti-stokes detection. 757 52

Seven Arabian horses performed a standard incremental exercise test on a high-speed treadmill at 6% slope then were randomly assigned to two diets, a control diet of ground hay and concentrates and a similar diet with 10% added fat (by weight). Horses were sprint-trained 4 d/wk, and two additional exercise tests were performed at 5-wk intervals. Heart rates and rectal temperatures were monitored and venous blood samples were collected at rest and at each speed increment. Whole blood was analyzed for glucose, lactate, and hemoglobin concentrations, and plasma was analyzed for pH, pCO2, albumin, total protein, and sodium, potassium, and chloride concentrations. Bicarbonate concentration ([HCO3-]) and strong ion difference ([SID]) were calculated, and total weak acid ([Atot]) was estimated from total protein. During exercise, there were increases in plasma sodium and potassium concentrations (P < .001), whole blood lactate and glucose (P < .001), and hemoglobin concentrations (P < .01). There were decreases in plasma pH, [HCO3-], and chloride concentrations (P < .001). The decrease in plasma pH was associated with changes in [SID] and [Atot] that combined to offset a decrease in pCO2. After sprint training, heart rates at rest and during submaximal exercise were decreased (P < .01), whereas heart rates at the end of exercise were increased (P < .05). Sprint training also increased workrate and estimated oxygen consumption at a heart rate of 200 beats/min (P < .001). Training increased the duration of exercise and the speed attained at the end of exercise (P < .05). Training increased the blood hemoglobin response to exercise and decreased the pCO2 response (P < .01). There were diet x training interactions for pH, pCO2, and [SID] (P < .05). Horses consuming the high-fat diet had higher blood glucose during both standard exercise tests and higher lactate concentrations at fatigue (P < .05) during the last test. Fat adaptation involving sprint training of horses may influence glucolysis at the level of pyruvate during an incremental exercise test.
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PMID:Acid-base variables during incremental exercise in sprint-trained horses fed a high-fat diet. 759 85

The dependence of power on aerobic and anaerobic energy metabolism and on force production was studied in maximal leg exercise. National and international level male rowers (n = 9) performed four modified (legs-only) rowing ergometer exercises: a progressive test, 2-min (T2), 12-min (T12) and 6-min (T6) all-out tests. In T2, significant correlations were observed between power in T2 (PT2) and oxygen debt (r = 0.83, P < 0.05) and between PT2 and average force production (Fav) during the last 30 s (r = 0.85, P < 0.05). These parameters explained 93% of the variation in PT2. The highest correlations between power in T6 (PT6) and physiological parameters were as follows: maximal oxygen uptake (VO2 max: r = 0.87, P < 0.01), blood bicarbonate concentration before the test ([HCO3-before]: r = 0.85, P < 0.05) and blood lactate concentration on anaerobic threshold (BLaAnT: r = -0.82, P < 0.05). Together, these parameters explained 92% of the variation in PT6. In T12, the total power (PT12) correlated with power of anaerobic threshold (PAnT: r = 0.95, P < 0.001) and with the highest VO2 value in this test (VO2 peak: r = 0.92, P < 0.001). These two parameters explained 96% of the variation in PT12. The decrease of at least one of the force parameters during each test was taken as a sign of fatigue. The decline in force was compensated for by an increase in stroke rate at the end of T6 and T12 (P < 0.01, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Interrelations between power, force production and energy metabolism in maximal leg work using a modified rowing ergometer. 833 55

Six weight trained males were studied prior to, during, and in recovery from exhaustive resistance exercise, 105 min after ingesting 300 mg.kg-1 of either a placebo or NaHCO3. The exercise test consisted of four sets of 12 repetitions with a fifth set to volitional fatigue on a Universal leg press machine at a resistance equaling approximately 70% of the subjects 1-repetition maximum. Arterialized venous blood was analyzed for lactate concentration, blood gas, and acid-base parameters. The ingestion of NaHCO3 produced a significant increase in resting pH (7.39 to 7.46), HCO3- (22.9 to 28.3 mEq.l-1), and oxygenated base excess (-1.3 to 4.4 mEq.l-1). With the completion of each exercise set, a progressive decline in the acid-base status of both groups was observed (pH set 1-5: NaHCO3, 7.40 to 7.31; placebo, 7.34 to 7.25; HCO3- set 1-5: NaHCO3, 25.3 to 17.9; placebo, 21.7 to 15.3 mEq.l-1; base excess set 1-5: NaHCO3, 3.7 to -7.1; placebo, -1.4 to -10.7 mEq.l-1); however, the NaHCO3 condition was significantly more alkaline than the placebo condition. Blood lactate concentration [La] progressively increased with the completion of each exercise set ([La] set 1-5: NaHCO3, 1.37 to 11.15; placebo, 1.31 to 9.81 mM); but were not significantly different between treatments. Repetitions performed in the final exercise set were not significantly different between groups (NaHCO3: 19.6 +/- 1.6, placebo: 18.2 +/- 1.1 repetitions).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of sodium bicarbonate ingestion on exhaustive resistance exercise performance. 839 7

A side effect of lithium (Li+) treatment is fatigue. Li+ decreases inositol triphosphate (IP3) accumulation and IP3 may play a role in excitation-contraction (E-C) coupling in skeletal muscle. Li+ carbonate (600 mg b.i.d. x 6 days) was administered in a randomized, double-blind fashion to 12 males to measure the effect upon muscle contractile function: peak twitch torque (PTT), time to PTT, half-relaxation time, maximal voluntary contraction strength (MVC), percent motor unit activation, M-wave characteristics, and tetanic torque (3 min at 15 and 50 Hz). Li+ resulted in a significant decrease in 15- and 50Hz tetanic torque (P<0.00l), MVC, and resting PTT (P<0.05). There were no effects of Li+ upon any of the other measured variables. Li+ had a negative effect upon E-C coupling and did not affect central motor unit recruitment. Elucidation of the role of IP3 in E-C coupling may help to understand fatigue in some neuromuscular disorders.
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PMID:The effects of lithium on muscle contractile function in humans. 860 94

This study was designed to characterise the acid-base and electrolyte effects of shortening the distance required during steeplechase (Phase B) in the face of hot and humid weather conditions during a treadmill-simulated Speed and Endurance test. Eight conditioned Thoroughbred horses underwent 3 randomised permutations of a standardised exercise test on a high speed treadmill. Each test consisted of trotting at 3.7 m/s for 10 min (Phase A); galloping at 11 m/s (Phase B) for 4 (cool laboratory conditions), 3 (hot and humid), or 2 (hot and humid) min; trotting at 3.7 m/s for 30 min (Phase C); and walking at 1.8 m/s for 10 min (Phase X). The treadmill slope was 4% for trotting and galloping and 0% for walking. Cool versus hot and humid conditions were 20 degrees C and 50-60% relative humidity vs. 26-28 degrees C and 80-85% relative humidity, respectively. Pulmonary artery blood samples were obtained at rest prior to exercise (Rest); at the end of Phases A (A10) and B (B2-4); at 10 (C10), 20 (C20) and 30 (C30) min through Phase C; and at 5 min into Phase X (X5). Additional samples for lactate (LA) and glucose (GLC) analysis were obtained 5 min into Phase C (C5) and at the end of Phase X (X10). Samples were analysed for packed cell volume (PCV), haemoglobin (HB), total plasma protein (TP), sodium (Na), potassium (K), chloride (Cl), anion gap (AG), plasma glucose (GLC) and lactate (LA), pH, PCO2, bicarbonate (HCO3) and base excess (BE). Shortening steeplechase distance by 50% under hot and humid conditions (2 min B) resulted in a consistent return to control measurements (4 min B) only for plasma LA. Changes in PCV, HB, TP, K and Cl were related more to the longer galloping distance in the 4 min B trials than to hot vs. cold laboratory conditions. Alternatively, changes in LA, GLC, pH, PCO2 and AG were more related to hot and humid laboratory conditions than they were to galloping distance. These latter variables, when combined with physical measures such as core temperature, bodyweight loss, point of fatigue on Phase C and recovery heart rates may serve as the best monitors of positive responses in future studies of proposed modifications to Phase C, rather than those variables which were more distance than weather-related.
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PMID:Acid-base and electrolyte effects of shortening steeplechase in a three-day-event. 889 54


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