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Query: UMLS:C0392674 (exhaustion)
 13,658 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. In the present study we examined the effect of hyperthermia on the middle cerebral artery mean blood velocity (MCA V(mean)) during prolonged exercise. We predicted that the cerebral circulation would be impaired when hyperthermia is present during exercise and assumed that this could be observed as a reduced MCA V(mean). 2. Eight endurance trained men (maximum oxygen uptake (V(O2,max)) 70 +/- 1 ml min(-1) kg(-1) (mean +/- S.E.M.)) performed two exercise trials at 57 % of V(O2,max) on a cycle ergometer in a hot (40 degrees C; hyperthermic trial) and in a thermoneutral environment (18 degrees C; control trial). In the hyperthermic trial, the oesophageal temperature increased throughout the exercise period reaching a peak value of 40.0 +/- 0.1 degrees C at exhaustion after 53 +/- 4 min of exercise. In the control trial, exercise was maintained for 1 h without any signs of fatigue and with core temperature stabilised at 37.8 +/- 0.1 degrees C after approximately 15 min of exercise. 3. Concomitant with the development of hyperthermia, MCA V(mean) declined by 26 +/- 3 % from 73 +/- 4 cm s(-1) at the beginning of exercise to 54 +/- 4 cm s(-1) at exhaustion (P < 0.001). In contrast, MCA V(mean) remained unchanged at 70-72 cm s(-1) throughout the 1 h control trial. 4. When individually determined regression lines for MCA V(mean) and arterial carbon dioxide pressure (P(a,CO2)) obtained during preliminary exercise tests were used to account for the differences in P(a,CO2) between the hyperthermic and control trial, it appeared that more than half of the reduction in MCA V(mean) (56 +/- 8 %) was related to a hyperventilation-induced drop in P(a,CO2). Declining cardiac output and arterial blood pressure accounted for the remaining part of the hyperthermia-induced reduction in MCA V(mean). 5. The present results demonstrate that the development of hyperthermia during prolonged exercise is associated with a marked reduction in MCA V(mean).
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PMID:Middle cerebral artery blood velocity is reduced with hyperthermia during prolonged exercise in humans. 1143 8

The slope of the expired alveolar partial pressure of carbon dioxide profile increases during exercise. Its relationship to metabolic rate, however, remains to be determined at high exercise intensities. We therefore determined the slope of alveolar partial pressures of carbon dioxide and oxygen (PACO2, PAO2, respectively) during incremental cycle ergometer exercise (an increment of 40 W each minute) to exhaustion in 11 normal subjects. The PACO2 and PAO2 increased as linear functions of carbon dioxide production and oxygen uptake (VO2), respectively, up to the estimated lactate threshold (thetaLa-). At higher intensities PACO2 increased disproportionately but PAO2 continued to increase at the same rate in 7 subjects but increased more rapidly in the remainder. The rate of change in PACO2 per unit rate of change in VO2 averaged 3.15 (SD 1.05) (mmHg.s(-1)). (l.min(-1))-1 while the rate of change in PAO2 per unit rate of change in VO2 averaged -3.53 (SD 0.79) (mmHg.s(-1)) (l.min(-1))-1 over this range. The more rapid increase in PACO2 above thetaLa- was consistent with an accelerated CO2 exchange, whereas the more rapid rate of change in PAO2 in 3 of the subjects may have reflected the development of an increased distribution of the ventilation perfusion ratio in addition to the effects of hyperventilation.
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PMID:Effect of exercise intensity on the changes in alveolar slopes of carbon dioxide and oxygen expiratory profiles in humans. 1151 21

The purpose of this investigation was to observe the effect of hypohydration (-4% body mass) on lactate threshold (LAT) in 14 collegiate athletes (8 men and 6 women; age, 20.9 +/- 0.5 years; height, 171.1 +/- 2.4 cm; weight, 64.8 +/- 2.3 kg; V(O)2 max, 62.8 +/- 1.9 ml x kg(-1) x min(-1); percentage of fat, 11.4 +/- 1.5%). Subjects performed 2 randomized, discontinuous treadmill bouts at a dry bulb temperature (T(db)) of 22 degrees C to volitional exhaustion in 2 states of hydration, euhydrated and hypohydrated. The hypohydrated condition was achieved in a thermally neutral environment (T(db), 22 degrees C; humidity, 45%), with exercise conducted at a moderate intensity as defined by rating of perceived exertion (RPE, approximately 12) 12-16 hours before testing. On average, subjects decreased 3.9% of their body mass before the hypohydration test. Blood lactate, hematocrit, V(O)2, minute ventilation (VE), R value, heart rate (HR), and RPE were measured during each 4-minute stage of testing. In the hypohydrated condition, LAT occurred significantly earlier during exercise and at a lower absolute V(O)2, VE, respiratory exchange ratio, RPE, and blood lactate concentration. Also, the blood lactate concentration was significantly lower in the hypohydrated condition (6.7 +/- 0.8 mmol) compared with the euhydrated condition (10.2 +/- 0.9 mmol) at peak exercise. There were no differences in HR or percentage of maximum HR at LAT nor did plots of V(CO2):V(O)2 reveal differences in bicarbonate buffering during exercise between the 2 conditions. From these results, we speculate that hypohydration did not significantly alter cardiovascular function or buffering capacity but did cause LAT to occur at a lower absolute exercise intensity.
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PMID:Hypohydration adversely affects lactate threshold in endurance athletes. 1183 5

It is not known to what extent the muscles use fats and carbohydrates as substrate for oxidation after intense, anaerobic types of bicycling. Six healthy young men therefore bicycled at constant power for 2 min to exhaustion. Blood was drawn from indwelling catheters in the femoral artery and vein at intervals during the 1-h postexercise recovery. The blood samples were analysed for concentrations of O2 and CO2, and for free fatty acids (FFA), triacylglycerols (TG), and glycerol in plasma. The blood flow was also measured, and the rate of leg uptake of FFA, TG, and O2 and the release of CO2 and glycerol as well as its gas exchange ratio were calculated and integrated over the recovery period. The leg gas exchange ratio integrated over the exercise plus 1-h recovery period was 0.67 +/- 0.06 (mean +/- SEM ), suggesting pure fat oxidation. There was no statistically significant arterial-femoral-venous difference of FFA across the leg. The concentration of TG in plasma fell by 0.18 +/- 0.09 mmol L(-1) (32%) during the first 10 min of the recovery period, and the leg took up 18 +/- 8 micromol TG kg(-1) body mass (bm) during the whole 1-h recovery period. Free glycerol was released from the leg throughout the recovery period in excess of that released from hydrolysis of TG from plasma, suggesting that 30 +/- 10 micromol TG kg (-1) bm was hydrolysed, probably from intra-muscular stores. If fully oxidized, the triacylglycerols hydrolysed can account for 101% of the measured O2 uptake. Thus, muscle seems to use only triacylglycerols as substrate for its oxidative energy release after intense exercise.
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PMID:Leg gas exchange, release of glycerol, and uptake of fats after two minutes bicycling to exhaustion. 1208 40

The unicellular Cyanobacterium Cyanothece sp. ATCC 51142, grown under alternating 12-h light/12-h dark conditions, temporally separated N2 fixation from photosynthesis. The regulation of photosynthesis was studied using fluorescence spectra and kinetics to determine changes in state transitions and photosystem organization. The redox poise of the plastoquinone (PQ) pool appeared to be central to this regulation. Respiration supported N2 fixation by oxidizing carbohydrate granules, but reduced the PQ pool. This induced state 2 photosystem II monomers and lowered the capacity for O2 evolution. State 2 favored photosystem I trimers and cyclic electron transport, which could stimulate N2 fixation; the stimulation suggested an ATP limitation to N2 and CO2 fixation. The exhaustion of carbohydrate granules at around 6 h in the dark resulted in reduced respiratory electron flow, which led to a more oxidized PQ pool and produced a sharp transition from state 2 to state 1. This transient state 1 returned to state 2 in the remaining hours of darkness. In the light phase, photosystem II dimerization correlated with increased phycobilisome coupling to photosystem II (state 1) and increased rates of O2 evolution. However, dark adaptation did not guarantee state 2 and left photosystem I centers in a mostly monomeric state at certain times.
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PMID:Temporal Changes in State Transitions and Photosystem Organization in the Unicellular, Diazotrophic Cyanobacterium Cyanothece sp. ATCC 51142. 1222 55

The carbon and nitrogen mineralisation of a composting mixture of brewing yeast and lemon tree prunings was studied, at different degrees of stabilisation of this matrix, within an incubation experiment in soil. Meanwhile, a growth test in pots with ryegrass (Lolium perenne L.) was carried out using the selected soil and equal amounts of the composting mixture taken at different maturation steps, in order to evaluate the additions of these organic amendments in terms of fertilising value. Samples of the composting mixture, when poorly transformed through the biostabilisation process, showed high CO2-C releases in the soil, due to the microbial attack on easily degradable organic fractions still present in the mixture, with 24.7% mineralisation of the initial total organic carbon (TOC) after a 70 day incubation. On the other hand, mature compost was the most stable matrix, with only 5.4% of TOC mineralised after 70 days. Furthermore, amendments with the initial composting mixture led to negative net N-mineralisation during 56 days of incubation with soil. Only slight negative values of the net N-mineralisation were detected with fully stabilised compost. Nevertheless, pot experiments with ryegrass revealed that mature compost may promote N mineralisation to certain extents. Moreover, mature compost did not produce any phytotoxic effect, behaving as a slow-action organic fertiliser with N made available through a progressive mineralisation. Thus, the results gained through this study are a confirmation that the fertilising quality of a compost destined for agricultural uses is heavily affected by the complete exhaustion of the maturation reactions.
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PMID:Carbon mineralisation and plant growth in soil amended with compost samples at different degrees of maturity. 1273 31

The cardio-pulmonary and biochemical changes observed in a case of McArdle's disease, exercising with increasing work rates to exhaustion in the "second-wind" phase of exercise are reported for the first time. A work rate of 275-325 watts was achieved. Venous blood lactate remained unchanged throughout. The plasma ammonium level reached a plateau of approximately 400 mmol/l at 100 watts. At a work rate of 150-175 watts the ratio of O2 consumption to CO2 production increased, the inverse of an anaerobic threshold. Maximal cardiopulmonary responses were achieved at 200 watts. During the final periods of exercise from 200 to 275/325 watts pulmonary ventilation did not significantly change but there was a decrease in the venous blood H+ concentration, and pO2 and in increase in the pCO2. Creatine supplementation at 25 g/day for five days did not improve exercise performance.
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PMID:Exercise to exhaustion in the second-wind phase of exercise in a case of McArdle's disease with and without creatine supplementation. 1277 95

In the present experiment we have studied the effect of exercise performed before and 24 h after withdrawal of 450 ml of blood on the serum erythropoietin and growth hormone (GH) levels, in humans. Twelve male subjects (x +/- SD) aged 23.2 +/- 2.6 y, with a body mass of 74.8 +/- 7.2 kg, height 178.0 +/- 7.6 cm, BMI 23.6 +/- 2.1 kg x m(-2), VO2 max 2937 +/- 324 ml x min(-1), participated in this study. The subjects performed twice an incremental exercise test until exhaustion, separated by a period of about 7 - 10 days. The second test was performed 24 h after withdrawal of 450 ml of blood (honorary blood donation). In the control study we found no effect of the incremental exercise on the serum erythropoietin concentration, which amounted to 14.24 +/- 7.66 mU x ml(-1) at rest and 14.97 +/- 6.07 mU x ml(-1) at the end of the incremental test. Serum GH level in the control study rose considerably from 0.158 +/- 0.024 nmol x l(-1) at rest to 1.523 +/- 0.336 nmol x l(-1) at the end of exercise and returned to initial value 2 h after the exercise. During the experiment performed 24 h after withdrawal of 450 ml of blood the serum erythropoietin concentration at rest was significantly elevated (p < 0.01) in relation to the control measurement (amounting to 24.85 +/- 13.60 mU x ml(-1)) and at the end of the incremental exercise a tendency towards further elevation (p = 0.09) in erythropoietin concentration up to 28.32 +/- 14.51 mU x m(-1) was observed. Serum GH level during the experiment after blood withdrawal was similar to that in control test and exercise caused a rise in the GH level to 1.056 +/- 0.52 nmol x l(-1), significantly less than in control test, but this increment fell to control value 2 h after exercise. The elevated level of erythropoietin 24 h after blood withdrawal was accompanied by a significant increase (p < 0.015) in blood hydrogen ion concentration [H +] b at rest from 48.2 +/- 2.8 nmol x l(-1) in the control study to 52.9 +/- 4.5 nmol x l(-1) after blood donation. No effect of blood withdrawal on pre-exercise level of plasma lactate concentration, end-tidal O2 and end-tidal CO2 was found. We concluded that withdrawal of 450 ml of blood, within 24 hours significantly increased serum erythropoietin concentration and caused non-lactic acidosis. A single bout of maximal incremental exercise, performed before and 24 hours after blood withdrawal, had no effect on serum erythropoietin concentration in humans but the exercise-induced increase in serum GH concentration performed after blood withdrawal tended to be lower than in the control study.
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PMID:The effect of exercise performed before and 24 hours after blood withdrawal on serum erythropoietin and growth hormone concentrations in humans. 1286 42

We questioned if a non-linear increase in ventilation defining a ventilatory threshold (V(Th)) accompanied the electromyographic (EMG) signs of neuromuscular fatigue. Indeed, the intramuscular accumulation of metabolites may activate the afferent nervous pathways responsible for both the 'muscle wisdom' phenomenon and the respiratory centre activation. During inframaximal (50%) handgrip sustained until exhaustion, minute ventilation (V(E)), V(E)/V(O2) and V(E)/V(CO2) ratios were measured simultaneously with surface EMG of the 'flexor digitorum' muscle. V(Th) was defined as a non-linear V(E) increase and/or an abrupt V(E)/V(O2) increase without any concomitant increase in the V(E)/V(CO2) ratio. Handgrip was repeated during complete arterial blood flow interruption in order to suppress any venous return from the exercising forearm. In both control and blood flow interruption conditions, an abrupt increase in the V(E)/V(O2) ratio was measured in the majority of trials (13 of 15 and 14 of 15, respectively) and the EMG signs of neuromuscular fatigue (a decline in median frequency and/or a non-linear increase in low-frequency EMG energies, E(L)) were concomitant with the V(Th) determination. Thus, V(Th) occurs during sustained static contraction and is concomitant with EMG signs of neuromuscular fatigue. Neurogenic factors seem to be responsible for the two responses which persist despite the absence of any release of metabolites in the circulation.
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PMID:Electromyographic signs of neuromuscular fatigue are concomitant with further increase in ventilation during static handgrip. 1471 45

We studied the changes in urinary bicarbonate, urinary pH and some physical parameters such as minute ventilation (VE), oxygen consumption (VO2), respiratory carbon dioxide (VCO2), heart rate, blood pressure, and blood lactate, before and after the submaximal exercise. Six male subjects aged 28-33 years were involved in the study. They performed the incremental exercise test using a bicycle ergometer until exhaustion. Levels of VE, VO2, VCO2, heart rate, and blood pressure increased continuously with an increase in cycling intensity. These parameters markedly decreased and reached the baseline levels within 5-10 minutes after the termination of exercise. According to an increase in cycling intensity, blood lactate increased continuously during exercise, but after termination of exercise the return of lactate to the baseline level was markedly retarded. Urinary bicarbonate and pH were within the range of those at 0 time (baseline levels) from the beginning until 30 minutes after the exercise. However, they began to increase abruptly about 30 minutes after the exercise, and continued to increase extensively for 2 hours thereafter. Such marked increase in urinary bicarbonate and pH seemed to be correlated with the aerobic metabolism of lactate in the muscles, liver, and kidney, finally producing CO2. It was also suggested that the measurement of urinary bicarbonate and pH may be useful for the estimation of physiological changes in the body after submaximal incremental cycling exercise loading.
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PMID:Significance of post-exercise increment of urinary bicarbonate and pH in subjects loaded with submaximal cycling exercise. 1506 46


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