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 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Six male volunteers performed three tests, each comprising a passive heating session to obtain dehydration (loss of 2.6% body mass), followed by exercise on a treadmill until exhaustion (50% of maximal oxygen consumption) in a warm environment (dry bulb temperature 35 degrees C, relative humidity 20%-30%). In one test, the subjects exercised without rehydration (Dh). In the two other tests, 50% of the fluid lost in the dehydration session was replaced by drinking mineral water given either in one amount [913 (SEM 23) ml] before the exercise (Rh1) or divided into four equal portions [228 (SEM 5) ml] before the exercise and on three occasions at 15-min intervals during exercise (Rh4). Rehydration increased exercise duration in Rh1 compared to Dh [112 (SEM 7) min and 82 (SEM 3) min, respectively; P < 0.05]. The difference was not significant with Rh4 [103 (SEM 9) min]. A restoration of the time course of changes in plasma volume, plasma osmolality, heart rate and rectal temperature occurred immediately in Rh1 and as delayed in Rh4 until after 60 min of exercise. Our results demonstrated that the swift replacement of the fluid loss in the dehydrated subjects was beneficial to exercise performance by rapidly correcting the disturbances in body fluid balance.
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PMID:Effect of ingestion pattern on rehydration and exercise performance subsequent to passive dehydration. 805 83

Nine men [24.6 (SEM 1.1) years] carried out isometric contractions (IC) of the right elbow flexors at 50% and 100% of the maximal voluntary contraction (MVC). At 50% MVC they had to maintain IC until the limit time (isotonic IC: IIC50) and beyond for as long as possible (anisotonic IC: AIC50). At 100% MVC, IC was anisotonic since the decrease in force was immediate (AIC100). Measurements of the force, the integrated electromyogram (iEMG) and the heart rate (fc) were made during the entire period of contraction. There was a linear relationship between the iEMG increase and the fc increase for IIC50 and AIC100. This relationship was not found for AIC50. The role played by the peripheral information would seem to have become more important in fc regulation when the isotonic IC preceding the anisotonic IC was sufficiently long (submaximal IIC). It would seem that the idea of muscle exhaustion at the limit time was only relative, and depended greatly on the subject's motivation and his capacity to endure a certain degree of pain.
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PMID:Changes in the heart rate and electromyogram beyond the limit time of an isotonic isometric contraction. 822 31

The effect of L-carnitine on energy metabolism at a high lipolytic flux was studied. Nine healthy male subjects received L-carnitine (CARN) (3 g.d-1) for 7 d, or a placebo (CONT), both with Ca pentothenate. The treatment increased resting nitrogen excretion slightly (+15%, P < 0.02). After an overnight fast, the subjects were submitted successively to 20 min bicycle exercise at 43 +/- 2 (SEM) %VO2max, a glycogen depletion routine involving high intensity bouts to exhaustion, 1-2 h of rest, again 20 min at the initial load, and finally 20 min at 57 +/- 3 %VO2max. After glycogen depletion, blood short-chain acylcarnitine concentrations increased 5 times as much in CARN as in CONT (P < 0.02). Fat oxidation estimated from respiratory gas exchange doubled after glycogen depletion for the same exercise intensity. However, there were no treatment differences in nonprotein RQ, heart rate, perceived fatigue, and blood parameters. It is concluded that during submaximal exercise after glycogen depletion (i.e., at a high lipid flux) substrate metabolism is not influenced by L-carnitine supplementation.
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PMID:Effect of L-carnitine on submaximal exercise metabolism after depletion of muscle glycogen. 832 Nov 12

We investigated the response of plasma and platelet:free catecholamine ([CA]) and sulphated catecholamine ([CA-S]) concentrations after an incremental treadmill test to exhaustion and during recovery. In triathletes (n = 9) plasma and platelet [CA] and [CA-S] were measured before, immediately after and 0.5 and 24 h after exercise. In long-distance runners (n = 9) and in controls (n = 10) plasma [CA] and [CA-S] were determined 2 h instead of 24 h after exercise. Platelet [CA] and [CA-S] remained unchanged throughout the study. Plasma [CA] increased after exercise in all groups (P < 0.05) and returned to pre-exercise values within 0.5 h of recovery. Plasma sulphoconjugated noradrenaline concentration ([NA-S]) was elevated after exercise in the triathletes, long-distance runners and in controls [9.96 (SEM 0.84) nmol.l-1, 11.8 (SEM 1.19) nmol.l-1, 9.53 (SEM 1.10) nmol.l-1, respectively; P < 0.05] compared with resting values [7.13 (SEM 1.04) nmol.l-1, 6.19 (SEM 0.56) nmol.l-1, 6.76 (SEM 0.67) nmol.l-1, respectively] and remained elevated after 0.5 h of recovery [9.94 (SEM 1.14) nmol.l-1, 10.96 (SEM 0.80) nmol.l-1, 8.95 (SEM 0.99) nmol.l-1, respectively; P < 0.05]. In the long-distance runners and controls plasma [NA-S] remained elevated during 2 h of recovery [9.96 (SEM 0.76) nmol.l-1, 9.03 (SEM 0.88) nmol.l-1, respectively]. These results would indicate that plasma [NA-S] increases after sympathetic nervous system activation by an exhausting incremental exercise test and remain elevated up to 2 h after exercise.
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PMID:Sustained noradrenaline sulphate response in long-distance runners and untrained subjects up to 2 h after exhausting exercise. 833 Jun 10

Cerebral blood flow has been reported to increase during dynamic exercise, but whether this occurs in proportion to the intensity remains unsettled. We measured middle cerebral artery blood flow velocity (vm) by transcranial Doppler ultrasound in 14 healthy young adults, at rest and during dynamic exercise performed on a cycle ergometer at a intensity progressively increasing, by 50 W every 4 min until exhaustion. Arterial blood pressure, heart rate, end-tidal, partial pressure of carbon dioxide (PETCO2), oxygen uptake (VO2) and carbon dioxide output were determined at exercise intensity. Mean vM increased from 53 (SEM 2) cm.s-1 at rest to a maximum of 75 (SEM 4) cm.s-1 at 57% of the maximal attained VO2 (VO2max), and thereafter progressively decreased to 59 (SEM 4) cm.s-1 at VO2max. The respiratory exchange ratio (R) was 0.97 (SEM 0.01) at 57% of VO2max and 1.10 (SEM 0.01) at VO2max. The PETCO2 increased from 5.9 (SEM 0.2) kPa at rest to 7.4 (SEM 0.2) kPa at 57% of VO2max, and thereafter decreased to 5.9 (SEM 0.2) kPa at VO2max. Mean arterial pressure increased from 98 (SEM 1) mmHg (13.1 kPa) at rest to 116 (SEM 1) mmHg (15.5 kPa) at 90% of VO2max, and decreased slightly to 108 (SEM 1) mmHg (14.4 kPa) at VO2max. In all the subjects, the maximal value of vm was recorded at the highest attained exercise intensity below the anaerobic threshold (defined by R greater than 1). We concluded that cerebral blood flow as evaluated by middle cerebral artery flow velocity increased during dynamic exercise as a function of exercise intensity below the anaerobic threshold.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Relationship of middle cerebral artery blood flow velocity to intensity during dynamic exercise in normal subjects. 837 62

To determine whether or not muscle endurance training alters exercise-induced sympathetic nerve response, we recorded muscle sympathetic nerve activity (MSNA) microneurographically during forearm exercise and compared MSNA between dominant (D) and non-dominant (ND) forearms of players of racket sports. Three kinds of forearm exercise were conducted on each side; static (SHG) and dynamic (DHG, at a rate of 1 Hz) handgrip exercise at a loading of 25% of maximal voluntary contraction until exhaustion, and 10-min submaximal dynamic handgrip (at a rate of 1 Hz) at an intensity of 0.9 W. Heart rate, ventilation and blood pressure were also monitored at rest and during SHG and DHG exercises. During the last minute of SHG exercise, MSNA burst rate had increased on average by 290 (SEM 46)% in D and 330 (SEM 46)% in ND, while during DHG it increased by 288 (SEM 38)% in D and 344 (SEM 36)% in ND, respectively. There were no significant differences in the MSNA responses between D and ND forearms in either exercise modes. Significant increases in heart rate, ventilation and blood pressure during the last minute of fatiguing SHG and DHG were observed, but there were no significant differences between the two forearms. During submaximal DHG, while MSNA increased significantly above control values in both D and ND, the MSNA response was less in D than that in ND forearm. The results would suggest that exercise-induced MSNA responsiveness is influenced little by muscle endurance training but the intensity of response may be due to the magnitude of metaboreceptor stimulation in the exercising muscle.
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PMID:Comparison of muscle sympathetic nerve activity during exercise in dominant and nondominant forearm. 847 91

Recovery from prolonged exercise involves both rehydration and replenishment of endogenous carbohydrate stores. The present study examined the influence of ingesting a carbohydrate-electrolyte (CE) solution following prolonged running, on exercise capacity 4 hr later. Twelve men and 4 women were divided into two matched groups, which were randomly assigned to either a control (P) or a carbohydrate (CHO) condition. Both groups ran at 70% of maximal oxygen uptake (VO2max) on a level treadmill for 90 min or until volitional fatigue (R1), and they ran at the same % VO2max to exhaustion 4 hr later to assess endurance capacity (R2). The CHO group ingested a 6.9% CE solution providing 1.0 g CHO.kg body weight-1 immediately post-R1 and again 2 hr later. The P group ingested equal volumes of a placebo solution. Run times (mean +/- SEM) for R1 did not differ between the groups (P 86.3 +/- 3.8 min; CHO 87.5 +/- 2.5 min). The CHO group ran 22.2 (+/- 3.5) min longer than the P group during R2 (P 39.8 +/- 6.1 min; CHO 62.0 +/- 6.2 min) (p < .05). Thus, ingesting a 6.9% carbohydrate-electrolyte beverage following prolonged, constant-pace running improves endurance capacity 4 hr later.
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PMID:The influence of ingesting a carbohydrate-electrolyte beverage during 4 hours of recovery on subsequent endurance capacity. 860 16

This study compared fuel substrate kinetics in trained cyclists who ingested a 10% carbohydrate (CHO) drink without prior CHO-loading ([NLC] n=9) with those in cyclists who ingested a water placebo after CHO-loading ([CLP] n=7) during 180 minutes of cycling at 70% maximum oxygen consumption (Vo2 max). Muscle glycogen at the start of exercise was 194 +/- 4 and 124 +/- 8 mmol/kg wet weight (mean +/- SEM) in CLP and NLC subjects, respectively . Total CHO oxidation was similar. Total rate of appearance of glucose from endogenous (Raend) and exogenous (Raexog) origin and plasma glucose oxidation increased significantly (P<.05), with NLC subjects ending significantly higher than CLP subjects (104 +/- 17 v 79 +/- 9 and 115 +/- 16 v 74 +/- 11 micromol/min/kg fat-free mass [FFM], respectively). However, Raend was lower (P<.05) in NLC than in CLP subjects (40 +/- 10 v 79 +/- 9 micromol/min/kg FFM), as was endogenous plasma glucose oxidation (42 +/- 13 v 75 +/- 11 micromol/min kg FFM). Muscle glycogen disappearance was identical in the first hour, but declined thereafter in NLC subjects. Two NLC subjects with the lowest muscle glycogen content were unable to complete the trial despite CHO ingestion. We conclude that with respect to the groups studied (1) CHO loading before exercise reduces the relative contribution of plasma glucose oxidation to total CHO oxidation, but may prolong time to exhaustion as a function of higher muscle glycogen concentration; (2) CHO ingestion has a liver glycogen-sparing effect, causes a reduction in gluconeogenesis, or both, that should delay the onset of hypoglycemia; (3) the progressive increase in plasma glucose oxidation that occurs during prolonged exercise is related to muscle glycogen status and occurs irrespective of whether CHO is ingested: (4) the effects of CHO ingestion and CHO-loading on fuel substrate kinetics are different.
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PMID:Fuel substrate kinetics of carbohydrate loading differs from that of carbohydrate ingestion during prolonged exercise. 860 25

Infrared (IR) thermometers (FirstTemp 2000A, Intelligent Medical Systems, California) were used to monitor tympanic temperature (Tty) in 12 collapsed fun-runners suspected of suffering exertion-induced heat exhaustion (EIHE). Rectal temperature (Tre) was monitored via digital clinical thermometers. Conditions during the fun-run and in the field treatment centre were cool (air temperature 16-18 degrees C, relative humidity 60-65%). On admission, Tty was (mean +/- SEM) 1.2 +/- 0.3 degrees C lower than Tre. For admission plus subsequent monitoring data pooled, although Tty correlated significantly with Tre (r = 0.86, p < 0.001), mean Tty (37.4 +/- 0.2 degrees C) was significantly lower (p < 0.01) than mean Tre (38.4 +/- 0.4 degrees C). Cotton wool ear pads, applied to 10 of the runners on admission to minimise environmental effects on Tty, did not significantly improve the IR monitoring. A Tty > or = 37.1 degrees C predicted a Tre > or = 38 degrees C (an established diagnostic criterion for EIHE) with a sensitivity of 0.93 and a specificity of 0.63. These data indicate that IR tympanic thermometry, when utilised in cool environments, can result in misdiagnosis of heat exhaustion. Although IR thermometry shows some promise as a rapid, non-invasive means of monitoring core temperature, it should not be used in the diagnosis and treatment of heat exhaustion unless further research validates the method.
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PMID:Infrared thermometry in the diagnosis and treatment of heat exhaustion. 877 79

We examined the effects of sodium bicarbonate (BIC) and sodium citrate (CIT) ingestion on distance running performance. Seven male runners [mean VO2max = 61.7 (SEM 1.7) ml.kg-1.min-1] performed three 30-min treadmill runs at the lactate threshold (LT) each followed by a run to exhaustion at 110% of LT. The runs were double-blind and randomly assigned from BIC (0.3 g.kg body mass-1), CIT (0.5 g.kg body mass-1) and placebo (PLC, wheat flour, 0.5 g.kg body mass-1). Venous blood samples were collected at 5, 15 and 25 min during the run and immediately post-exhaustion (POST-EX) and analysed for pH, and the concentrations of lactate ([la-]b) and bicarbonate ([HCO3-]). Performance was measured as running time to exhaustion at 110% of LT (TIME-EX). The pH was significantly higher (P < or = 0.05) for the BIC and CIT trials during exercise, but not POST-EX compared to PLC. The [la-]b was significantly higher (P < or = 0.05) for the CIT trial compared to PLC during exercise, and for both CIT and BIC compared to PLC at POST-EX. Blood [HCO3-] was significantly higher (P < or = 0.05) during exercise for BIC compared to PLC. TIME-EX was not significantly different among treatments: BIC 287 (SEM 47.4)s; CIT 172.8 (SEM 29.7)s; and PLC 222.3 (SEM 39.7)s. Despite the fact that buffer ingestion produced favourable metabolic conditions during 30 min of high intensity steady-state exercise, a significant improvement in the subsequent maximal exercise run to exhaustion did not occur.
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PMID:The effects of buffer ingestion on metabolic factors related to distance running performance. 885 7


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